Primary and secondary stresses in pressure vessels | Pressure vessel stress analysis | Pressure vessel design procedure:

The first step in designing a vessel is the purpose of application and specifications that function the container characteristics. The environment and nature of liquid and gases are another important factors.
The parameters involves in the designing:

• The temperature and pressure (maximum safety).
• Factor of safety.
• The capacity to contain the volume.
• Corrosion allowance
• Design temperature.

Spherical vessel:

where,
M = mass, (kg)
P = pressure difference (the gauge pressure), (Pa)
V = volume,
= The density of the vessel material, (kg/m3)
= The maximum working stress that material can tolerate. (Pa)

Cylindrical vessel with hemispherical ends:

where,
R=radius
W=middle cylinder width
overall width=(W+2R)
Stress in thin-walled pressure vessels:

stress in longitudinal axis

p is internal gauge pressure,
r is the sphere’s inner radius,
The thickness of the sphere wall is denoted by t.

Pressure vessel equations for stress | Pressure vessel equations | Pressure vessel formula | longitudinal stress pressure vessel:

sigma = stress in the longitudinal direction, p is internal gauge pressure, and sigma = stress in the longitudinal direction
r is the sphere’s inner radius,
The thickness of the sphere wall is denoted by t.

Mechanical design of pressure vessel | Pressure vessel design | pressure vessel calculations | how to design pressure vessel | pressure vessel dimensions

create outline of the design:
Design and create the requirements of the vessel using the dimensions.
Include dimensions such as shape, diameter, length, pressure, temperature, and construction material.
Find out mechanical strength:
Find out mechanical calculations using the software.
Software gives both 2D or 3D drawings:
pressure vessel design drawing:

Design standards:
The purpose of application of vessel.
Operating pressure and temperature
Materials for fabrication
Vessel head type
Orientation: Horizontal or vertical
Dimensions
Openings and connections
Requirements for heating and cooling
Surface finish
External factors
Design stresses are adjusted using safety factors applied to material properties, including:
Yield strength (design temp)
Ultimate tensile strength (room temperature)
Creep strength (design temp)

Gasket design for pressure vessel:

A gasket is designed in such way that the flanges should be able to create the specific amount of compressive load on the surface of the vessel. It created an seal with no pressure. The gasket should be attached to the flange surfaces and be compressed to reduce the internal voids and spaces.

Design of a noncircular pressure vessel:

Because of the geometry of the cylindrical shape, most pressure vessel and pipe flanges have a circular cross section. However, there are some pressure vessels or pressure ducts where a rectangular or other non-circular shape is required, whether for space or process reasons.

Water pressure vessel design:

Hydrostatic testing uses water for the test.
It is a method that comprises pipeline systems, gas cylinders, boilers, and pressure vessel. These components are tested to check the strength and any kind of leakage from the system.
Hydro tests are quite required for the repair and replacements of the equipment that will operate under the desired conditions.
Hydrostatic test is the type of pressure test that can work by using the water and filling water in the components that removes the air contained within the system. and it pressurizes system with up to 1.5 times the design pressure.

How to calculate static head in pressure vessel:

Pressure vessel end cap design(heads):
Design pressure of vessel includes:
Static head= Pressure resulting from weight of liquid
Acting on internal of the pressure.
Higher liquid height results in higher pressure.
Static fluid pressure is independent of the liquid’s form, total mass, or surface area.
pressure= weight/area=mg/A

Pressure vessel skirt design:

Generally skirt support is provided to the tall columns.
The vertical orientation of the container is supported by the skirt support in pressure vessels. The benefit of using skirt supports is that it reduces the amount of stress at the supports.
Skirt is a cylindrical shell column with a diameter equal to or greater than the vessel’s outside diameter.
The skirt is welded to the vessel’s bottom and sits over the bearing plate.
The bearing plate is located on top of the concrete foundation system.

Pressure vessel skirt support design:

1. The vessel’s dead weight.
2. The vessel’s operating weight.
3. Lateral loads
4. Wind load
5. Seismic load

Skirts are the supports that are used in the vertical pressure vessels. They don’t take load from the pressure of the fluid inside the container.
Weight of the vessel and fluid inside and the environmental loads altogether are considered for the designing of the skirt support.
Skirts gives the less expensive design for the support of the taller pressure vessels.
W+Fw+Ew= Total load.

Design of a jacketed pressure vessel:

A jacketed vessel is a container designed to control the temperature of its contents by encircling the vessel with a cooling or heating “jacket” through which a cooling or heating fluid is circulated.
A jacket is an exterior cavity that provides for a consistent heat exchange between the fluid moving inside it and the vessel’s walls.
Liner-less composite pressure vessels (CPVs), also known as type 5 (type V) tanks in some sectors, are the most efficient composite pressure vessels (burst pressure x volume/weight).

Vacuum pressure vessel design:

vacuum pressure vessel design uses a design pressure which is in accordance with the full vacuum of the vessel state that the internal pressure is vacuum and external pressure becomes 100kpa that is atmospheric pressure.

Pressure vessel fatigue calculations:

Fatigue life of material is determined first. The fatigue of material is determined by testing many samples to check the failure of the material.
At each stress level, the number of cycles should be able to be calculated. Test samples are highly polished round bars that are as close to identical as manufacturing can make them. A test bar is rotated with a load applied so that a fiber at the bar’s surface is in tension and then in compression as the bar rotates, resulting in a complete stress reversal as shown.

There are several stress cycles, each with a different stress magnitude and number of cycles. Fatigue damage from each stress cycle adds up, so the total effect of all stress cycles must be calculated. The rule of Miner:

Pressure vessel shapes:

Although pressure vessels can potentially be any form, the majority are made up of portions of spheres, cylinders, and cones.
A popular design is a cylinder with end caps called as heads. The most frequent head forms are hemispherical or dished.

Design of a vertical pressure vessel support:

They have a better pressure distribution, making them more secure.
They use less energy because gravity allows their contents to flow easily and effortlessly.
They require less ground space for their inhabitation.

Area compensation method in pressure vessel:

Nozzle reinforcement is the method of the area compensation.
This method is used when there is opening in the cut section of the pressure vessel.

An area is removed from the shell and the head. The removed area should be equal to area added and it should reinforce by an equal amount of area near the opening.

composite pressure vessel analysis:

The objective of the analysis of the composite pressure vessel system is that It should increase the storage capacity of the system to the specific level. Hence, using the steel vessel, detailed analysis of the vessel design should be performed according to the multi axial stresses those are resulted from the tank design system in the transition region of cylinder and head.

Minimum wall thickness for pressure vessel:

1/16 inches is the minimum wall thickness is used for the pressure vessels.
pressure vessel volume formula:

where,
V= volume,
r= radius of the internal surface
a= area of the vessel
I= moment of inertia.

Pressure vessel principal stresses:

There are two principal stresses in the pressure vessel.
Hoop stress
longitudinal stress
This shows that the stress along the surface of the vessel should have resultant that balances the internal pressure.

FAQ/short notes:

What is the purpose of a pressure vessel:

Gases and liquids are held at high pressures within pressure vessels.
Pressure vessels are used in boilers, reservoirs, highly pressurized pneumatic cylinders, and industrial uses, among other things.

How do pressure vessels work:

It works at higher pressure or increasing pressures. It reaches the pressure that makes the application function work such that it holds the gases or the liquids in the storage tanks.
It provides the pressure through the valves or through the heat transfer.

What are the types of pressure vessels:

Pressure vessel types depends on the design of the vessels for the functionality of the applications in the industries. Mainly pressure vessels can be divided into the types according to their purpose for the applications. According to above factors mainly pressure vessels have three types:

Storage vessels:

These tanks are mainly useful for the industrial applications. These typically used in horizontal or vertical manner. It stores liquids and gases such as oil, chlorine and natural gases. It can be available in any size ranges. It is available in variable shapes like cylindrical or spherical for their vertical or horizontal manners. The material used in for the manufacture of the the type of product is carbon steel considering the external environment.
Such vessels need careful construction as the internal substances can be bad without proper maintenance.
Process vessels:

Process vessels are designed as per the requirements of the application while construction to reach the required specifications. Various processes can be performed in pressure vessels.
Pressure vessels can be used in conjunction with other products depending on the application. So the manufacturing material required for such vessel components can be of unique material or multiple different materials.
These pressure requires following important factors:
Proper designing
Proper material selection depending on the properties that reaches the applications requirements.
Careful and proper construction as per the specification.

What is the distinction between an autoclave and a pressure vessel:

An autoclave is a type of pressure vessel.
The main difference between the both is that the autoclaves are the type of pressure vessels that uses high pressure and high temperatures, the body should be capable of sustaining such high temperatures and pressures.

Pressure Vessel Design is vast topic, we will continue publishing article on Pressure Vessel. For more articles, click here.

Pressure vessel definition | what is pressure vessel | high pressure vessel | large pressure vessel

A pressure vessel is a container that holds a lot of pressure.
It is a container that is designed to hold gases or liquids at a pressure higher than atmospheric pressure.
It is a closed vessel with the capacity to store high pressure liquids or gases at internal or external pressures, regardless of the pressure vessel’s size, shape, or dimensions.

The liquids/gases are contained in these leak-proof vessels. These containers are designed based on the application’s purpose.
Depending on the pressures, the operating temperatures of the containers change.
The vessel works on the internal preconditioning pressures that are lower or higher than the air pressure.

Pressure vessel stress | Hoop stress pressure vessel

Due to external tensile forces acting on the container’s internal surfaces, the container was able to resist the gas pressure. The thickness of a pressure vessel is proportional to the radius of the tank and inversely related to the maximum allowable normal stress of the material for the container’s internal surface.
The normal tensile stress is related to the vessel’s pressure and radius, but inversely proportional to the vessel’s thickness.

Pressure vessel fabrication | pressure vessel fabrication techniques | pressure vessel fabrication process:

Pressure vessel fabrication is an complicated process.
For the fabrication and assembling of the parts the steps required are follows:
Select the material for the fabrication.

cutting and burning of the material as per the requirement
machining of parts
cooling of weld and sand blasting
Assembling and welding of parts
Fabrication processes basic conditions:
Design conditions.
Procedures for welding to be used
Welding Specifications
Procedures for heat treatment will be used.

Requirements for non-destructive testing

Pressures should be tested.

Pressure vessel inspection | pressure vessel testing requirements | pressure vessel testing standards:

Construction of the container is tested to check the cracks, defects or any other existing failures.
Hydrostatic test:

Hydrostatic test use water for the test. This test is safer method as it releases small amount of energy whenever fracture occurs.
Pneumatic test:

Pneumatic test use air or gas for the test.
mass production often represent samples testing for the destruction in controlled environment.
Testing on pressure vessel is done to make sure the vessel is free from the defects, cracks or any other failures .
Visual Tests (VT):
Visual test is a type of test that provide information and overview regarding the pressure vessel by the observation of the internal and external substances of the tanks.

Liquid Penetrant Testing (LPT) is a form of pressure vessel test that uses thin liquids as a penetrant on the pressure vessel’s surface. The fissures in the vessel’s surface are readily visible. Using a chemical and a penetrant, proper visualization can be observed under UV light.

Magnetic particle testing is performed in conjunction with magnetic current to detect flaws. Whenever there is a defect ,there will be disturbance in the magnetic current.

Radiographic Test (RT):
This type of test is tested using the X-rays to find out the defects on the external or internal surfaces of the vessel.

Ultrasonic Testing (UT):
Ultrasonic testing is the testing that detect the defects using the sound waves.
Whenever there are cracks on the external and internal surfaces of the vessel, the ultrasonic waves experience disturbances.

Reactor pressure vessel:

A reactor pressure vessel is a nuclear power plant that contains nuclear reactor coolant, a shroud, and the reactor core.

The classifications are as follows:
Reactor for light-water –
Reactor with graphite as a medium –

Thermal reactor cooled by gas –

Heavy-water pressurised reactor –

Reactor cooled by liquid metal –

Reactor for molten salt –

Components of the reactor vessel:

Body of the reactor vessel:

The large component containing the fuel assembly, coolant, and fittings to support coolant structures is the reactor body.
A reactor head is attached at the top of vessel.

Assembling the fuel:

The fuel assembly of nuclear fuel, which is typically composed of uranium or uranium–plutonium mixtures.
Typically, it is a rectangular block of gridded fuel rods.Reactor vessel body

Ammonia pressure vessel:

It is a Low pressure vessel.
In this container Ammonia is force fed for the storage by the circulation at low pressure in the vessel.

Pressure vessel material | High temperature pressure vessel material:

Carbon steel (low carbon)
Carbon manganese steel
Steel alloys
Non-ferrous materials

Use of pressure vessel | purpose of pressure vessel

Pressure vessels are primarily used to store gases and liquids at high pressures.
Pressure vessel applications are based on the requirements:

Industry of Oil and Gas: A container is used as a receiver at high temperatures and pressures.
Chemical Industry: It is a pressure vessel in which a process (chemical reaction) needs to take place, culminating in a fundamental change in the container’s content.

Energy (Power Generation) Industry: The energy (power generation) industry emits polluted gases.Therefore pressure vessels are used to store such gases. nuclear power plant uses reactor pressure vessels.

Pressure vessel head types | different types of pressure vessel heads:

There are different types of tank heads and they vary according to the shape according to the advantage to the application:
Ellipsoidal Head:
Most economical.
H=1/4D (Height =H, Diameter =D) has a radius ratio of 2:1 on the major and minor axes, allowing it to withstand greater pressure.
Head with a Hemispherical Shape

This is a more spherical head, with a radius equal to the tank’s cylindrical section.

It aids in the even distribution of pressure across its surface.

The dish and cylinder share a toroidal-shaped transition known as the knuckle.

type 4 pressure vessel:

Type 4 pressure vessel is all carbon fibre pressure vessel containing polyamide or polyethylene plastic.It has low weight and high strength.carbon fibre gives more strength to the vessel that it can sustain high loads.It also increases the corrosion resistance and fatigue resistance of pressure vessels. This type of vessel has maximum volume , Hence it has capacity to store hydrogen at high pressure.

type V pressure vessel:
high-volume pressure container of type v Type V approaches depend on advancements in three major technological fields: materials, design, and tooling.
It uses single material to manufacture a laminate system that gives structural strength at high pressures. It also form barrier layers to persist fluids and gases substances.

Conical head pressure vessel:

Conical Head:

It is also called as tapered tank head. It is used for vessel bottom or cover plates.
It has concentric cone shape.
The conical shaped head contain large and small end cone.

Applications:
Depending on the thickness of the material it can be equipped with around 8000 mm dia. and wall thickness of 20mm.
The conical head forced on the bottom of the pressure vessel to accomodate internal materials and connect two stage vessels of different diameters.

Difference between boiler and pressure vessel:
A pressure vessel is a container which contains the fluids ,gases or combination at high pressures. whereas a boiler is a container that contains the liquid that is water such that it can be boiled by the heat source at higher temperatures.

Pressure vessel dished ends dimensions | pressure vessel end caps:

Dished ends are the caps that are attached to the end of the main body by welding process.
They are manufacured using diffrenet methods so as to reach the application requirements taht depends on the type of dished end.

The type of each dish end gives the characteristics of the end caps.
For plate thicknesses of 25 mm / 1.0 inch or greater.
Plates with a thickness of less than 25 mm / 1.0 inch.
For plate thicknesses of 25 mm / 1.0 inch or greater.

Pressure vessel plumbing:

The pressure vessel is the container having switches that control the opening and closing of the container.
It requires minimal amount of pressure when the tap is opened and it slacks when the tap is closed.
When it reaches to the lowest pressure, the pump stops and the pressure also starts dropping.
The pressure then drop in the pipes to the on switch pump and pump starts again.

Pressure vessel failure modes include ductile rupture, brittle fracture, and abrasion.
abnormal deformation,
insecurity (buckling),

ratcheting (progressive deformation),

fracture due to fatigue,

rupture due to creep,

ratcheting creep,

interaction between creep and fatigue,

buckling creep,

and the impact of the environment on cracking.

Heating pressure vessel | central heating pressure vessel:

An heating pressure vessel is the expansion tank. It is a small tank and protects closed water heating which are not open to ambient temperature.
systems and hot water systems from high pressures.

The container contains air having compressibility cushion shocks caused by hammering and absorbing excessive water pressure caused due to the thermal expansion.
Domestic applications
Automotive applications

Hot water expansion vessel pressure setting | expansion vessel pressure setting:

water pressure should be -60 Psi.
Thermal expansion container contains an pressurized compressed air. It expands and contracts in response to the expanded water from the water heater.
Check the expansion tank’s air pressure.

Pressure vessel with lug support:

Vertical vessels with a height-to-diameter ratio of 2-3 are typically equipped with bracket supports. These are made of plates and attached to the vessel with the shortest possible weld length.

1. It is less expensive.
2. Can be easily attached to the vessel with a short weld.
3. It is simple to level.
4. If a sliding arrangement is provided, it can absorb diametrical expansions.
5. Because of their ability to absorb bending stresses eccentrically of loads, thick wall vessels are best suited for them.

In order to measure the liquid level in a pressure vessel, the gaseous pressure in the vessel’s head must be measured with a second transducer. To obtain the hydrostatic pressure due only to the column of liquid, subtract the head pressure from the overall pressure.

Pressure vessel operation | pressure vessel operation principle:

These vessels operate by reaching a specific level of pressure to meet the application’s requirements. The design is specification of the vessel is the application purpose such as storing ,containing , heat exchange and chemical reaction processing of the products.
Valves, release gauges or heat transfer are used to proper delivery in the vessel.

The pressure level of the the normal atmospheric pressure is approximately 15 psi and it cam increase up to 15000 psi.

Replacement pressure vessels:

Repair of the pressure vessels is done to maintain its operating conditions.
The replacement should be in order to maintain the safe operations and to maintain trouble free service.
The vessel condition repair contains following considerations:
mechanical problems,

Rules for construction of pressure vessels:

The pressure vessel construction requires specific prohibition and non mandatory guidance for the material slections , design of the vessel, design of the components , inspection and testing of the vessel and the parts ,markings and the reports , high pressure protection and certifications of the vessels .

The pressure applied on the internal and external surfaces of the container should be between 10-10000psi ,it may go up to 70000 psi that is the maximum limit.
pressure vessels can be fired or unfired.
The pressure applied can be from external sources or the application of heat transfer.

Vertical pressure vessel:

Vertical vessel is the orientation of the vessel which represents the container in the vertical direction(upright).
It has different supports than the horizontal pressure vessel. It fits with different types of supports foe example skirt and lug that is able to hold the weight of the vessel.
They can perfectly fit into the small spaces.

Water pressure vessel design | hydrostatic pressure vessels | hydrostatic test procedure for pressure vessel:

Hydrostatic testing uses water for the test.
It includes components such as piping systems, gas cylinders, boilers, and pressure vessels.
Theses components are tested to check the strength and any kind of leakage from the system.

Hydro tests are quite required for the repair and replacements pf the equipment that will operate under the desired conditions.
Hydrostatic test is the type of pressure test that can work by using the water and filling water in the components that removes the air contained within the system. and it pressurizes system with up to 1.5 times the design pressure.

What is unfired pressure vessel:

This is type of the vessel that gains the heat from the source either directly or indirectly.
To avoid overheating such containers should observe the caution measurement while handling the system.

Industries that utilize unfired pressure vessel:
petrochemical
power generation
oil and gas
Types:
Thermal oil heaters
Boilers.

Proof testing pressure vessels:

Proof pressure testing is the testing used to verify whether a component can sustain the pressure above the operating pressure without any permanent damage to the system. It is a form of stress that can demonstrate the fitness of the expansion joint under the high pressure conditions.

The test can also prove whether the component can sustain the high pressures. It is a non-destructive testing procedure, as opposed to other methods.

Different types of nozzles in pressure vessels:

Radial Nozzle
Non-Radial Nozzle
Hill Side Nozzle
Tangential Nozzles
Angular Nozzles.

Pressure vessel closures:

The pressure vessel closures provide closure guidance.
These are commonly employed in medium to large pressure containers.
It also has locking mechanisms and attachments for secure use.
Pressure Vessel Closures Have Arrived.

Products are available.

Closures for Pressure Vessels

Aluminum pressure vessel:

Aluminum is being investigated as a replacement for stainless steel, with the major draw being its lower density and the expectation of a significantly lower tare weight.

Pressure vessel with cladding:

A cost-effective solution is to apply a layer of corrosion-resistant material of appropriate thickness to the equipment’s contact surfaces, made of a cost-effective and structurally strong material such as carbon steel.
The technique of integrating two layers of different materials is known as cladding or lining.

While the word Lining is broad and can refer to a variety of materials, the term Cladding is used when the corrosion-resistant layer given is metallic and well-bonded to the surface. As a result, the word Cladding is frequently used to refer to steel-fabricated equipment such as pressure tanks and shell and tube heat exchangers.

Column pressure vessel:

Pressure vessels operate at a pressure greater than atmospheric pressure, whereas columns operate at atmospheric pressure.
Furthermore, pressure vessels are subjected to pressure on all sides of their internal surfaces.

This is in contrast to columns, which only experience pressure in one direction.

Pressure vessels are built to hold liquids and gases at high pressures.
A column’s principal function, on the other hand, is to separate gases from liquids using trays.
In summary, you can select high performance pressure tanks using the information in this guide.

Ultrasonic testing of pressure vessels:

Ultrasonic testing is the testing that detect the defects using the sound waves.
Refers to the thickness of the material’s plate. Whenever there are cracks on the external and internal surfaces of the vessel, the ultrasonic waves experience disturbances.

Difference between pressure vessel and storage tank:

The primary distinction between a pressure vessel and a storage tank is that pressure vessels contain liquids or gases at a pressure greater than atmospheric pressure.
Storage tanks, on the other hand, contain liquids or gases under normal air pressure.
Because pressure vessels can be highly catastrophic, they have more stringent safety requirements.

Storage tank safety design requirements are not as stringent as those of their counterparts.

Different types of pressure vessels:

Pressure vessel types depends on the design of the vessels for the functionality of the applications in the industries. Mainly pressure vessels can be divided into the types according to their purpose for the applications. According to above factors mainly pressure vessels have three types:
Storage vessels:

These tanks are mainly useful for the industrial applications. These typically used in horizontal or vertical manner. It can be available in any size ranges. It is available in variable shapes like cylindrical or spherical for their vertical or horizontal manners. The material used in for the manufacture of the the type of product is carbon steel considering the external environment.
Such vessels need careful construction as the internal substances can be damaged without proper maintenance.

Process vessels:
Process vessels are designed as per the requirements of the application while construction to reach the required specifications. Various processes can be performed in pressure vessels.
Pressure vessels can be used combined with other products as per the application requirements.
So the manufacturing material required for such vessel components can be of unique material or multiple different materials.

Other types include:

High-Pressure Vessels: Autoclaves

• Tanks for Expansion,

• Exchangers of heat,

• Tanks for high-pressure water,

• Tanks for Vacuuming,

• Pressure Vessels ASME,

• Pressure Vessels with thin Walls,

• Boilers are closed pressure vessels that heat fluids, most commonly water.

Jacketed pressure vessel | Pressure vessel jacket | Design of a jacketed pressure vessel:

A jcketed vessel is a container designed to control the temperature of its contents by encircling the vessel with a cooling or heating “jacket” through which a cooling or heating fluid is circulated.
A jacket is an exterior chamber that facilitates consistent heat exchange between the fluid moving in it and the vessel’s walls.

Liner less composite pressure vessels (CPVs) have the highest pressure vessel efficiency (burst pressure x volume/weight) of any composite pressure vessel. They are also known as type 5 (type V) tanks in some sectors.

Pressure vessel for liquid nitrogen:

Cryogenic liquid cylinders are vacuum-jacketed, insulated pressure containers. To prevent the cylinders from pressure buildup, they are outfitted with safety release valves and rupture discs. These containers can withstand pressures of up to 350 psig and hold 80 to 450 litres of liquid.

Pressure vessel cleaning | Pressure vessel cleaning procedure:

Internal polishing.
Internal cleaning and drying is automated.
Cleaning with oxygen.
Flushing with de-ionized water.

Cleaning with steam.

Shotblasting on both the inside and outside of the building.

Rinses with solvents

Baking in the oven to remove contaminants.

Coating both internally and externally

NVR (non-volatile residue) analysis

Particulate matter counts

Surface finish is measured using a profilometer gauge (Ra)

Measurements of coating thickness

Dimensions of the anchor profile

Pressure vessel relief valve:

Pressure vessel relief valve is the device that protect the container by the release of high pressures.
The operation is automatic
Valve can be opened and closed. the valve is opened at certain level and and it closes when the level return back to normal position.

Pressure vessel safety checklist:
External inspection. Cracks, overheating, deformation, leakage.
Structural inspection
Geometric dimension inspection
Surface defect inspection
Wall thickness measurement
Material
Pressure vessel with the coating layer
Welding seam hidden defects inspection

Pressure vessel shear stress:

Cylindrical pressure vessel:
Maximum in-plane shear stress ( τmax(in plane)) =(pgr)/(4t)
Maximum out-plane shear stress (τmax(out plane)) =(pgr)/(2t)

Spherical pressure vessel:
Maximum in-plane shear stress (τmax(in plane))=0
Maximum out-plane shear stress (τmax(out plane))=(pgr)/(4t)

Pressure vessel welding requirements | pressure vessel welding ticket | pressure vessels welding process:

Pressure vessel welding is the joining process that is used to connect the metal plates of vessel using the heat or the pressure. It should be good quality that should sustain loading conditions.
Pressure vessel are used to store the liquids and gases at higher pressure rather than at atmospheric pressure. Welding of the container should be high quality structures and high strength materials as it should sustain the loading conditions.

If the good surface is used, then welding will be easy. There might be occurrence of the errors during the welding process.so it is required to apply some testing test to detect the errors.
Porosity is one of the major factor that can occur during the welding. porosity occurs mostly in any component during the welding process.It creates gas bubbles that look like voids during the testing.To avoid such defects it is advisable to use proper welding methods.

Another important factor is the nitride which is highly adherent contaminant. That can cause edges brittle and create porosity in welding processes.
Inclusions can be mixed with the weld pool and get stuck in the component during the solidification. This can be eliminated by using brush before the solidification.

Thin walled pressure | Thin walled pressure definition | Thin pressure vessel:

Thin walled pressure is the type of vessel that has wall thickness smaller than overall size of vessel.
t wall<r(vessel)
The internal pressure is higher than external pressure.

Thick walled pressure | Definition of Thick Walled Pressure:

This is a vessel with the a wall thickness that is 1/10 or 1/20 more than its radius. The wall encounters more circumferential stress on the interior surface and lessens as it approaches the exterior diameter.
Advantages of composite pressure vessels:
Better performance results.
Fibers carry the load on the composite.
The load on the fibers is distributed by the resin matrix.
The filament winding procedure is used to create a composite pressure vessel.

Air pressure vessel | Air receiver pressure vessel | Air pressure vessel testing:

Air pressure vessels are used to store the fluids, vapors and gases at high pressure.
It is also called as air pressure tanks, tanks storage and containment units.
Pressure testing is used to maintain the integrity of the vessels at high pressure levels.
Non-destructive test.

FAQ/Short Notes

How do you test a pressure vessel:

Testing on pressure vessel is done to make sure the vessel is free from the defects, cracks or any other failures .
Visual Tests (VT):

Visual test is a type of test that provide information and overview regarding the pressure vessel by the observation of the internal and external substances of the tanks.
Liquid Penetrant Testing (LPT):

This is a technique of test in which transparent liquids are used as penetrants on the surface of a pressure vessel.
It shows clearly the cracks on the vessel surface. Under the U.V. light, proper visualization can be observed using fluorescent chemical with the penetrant.
Magnetic Particle Testing (MT):

Magnetic particle testing detects defects by using a magnetic current.
whenever there is a defect ,there will be disturbance in the magnetic current.
Radiographic Test (RT):
This type of test is tested using the X-rays to find out the defects on the external or internal surfaces of the vessel.
Ultrasonic Testing (UT):
Ultrasonic testing is the testing that detect the defects using the sound waves.
Whenever there are cracks on the external and internal surfaces of the vessel, the ultrasonic waves experience disturbances.

What is the distinction between a pressure vessel and a storage tank?

The difference between pressure vessels and storage tank is that the pressure vessels works at higher pressures and storage tanks works at normal atmospheric pressures.
Storage tanks store the fluids.
Pressure vessel hold the fluids at high pressures.
Whenever a vessel reaches a certain pressure, it becomes a pressure vessel.
When pressures reach 15 Mpa or greater.
What is the frequency with which a pressure vessel should be tested:
At least once in every five years.

What are the uses of pressure vessels:

To hold fluids at high pressures.
High reactive chemicals , petroleum products can be stored at high pressures in pressure vessels.
For the heat exchange and removal of excess heat.
For the chemical reactions at certain pressures and temperatures.

Which material is used in manufacturing a pressure vessel:

steel made of carbon
Steels with low alloy content
Steels with a high alloy content
Carbon steel, manganese steel, and so forth.

Why are semispherical end caps used on cylindrical pressure vessels rather than flat ones:

Cylinders are used as they are less expensive than spheres but the spheres are more stronger at the corners. So the spherical or rounded ends are fitted at end caps rather than flat ones .
The following are some of the advantages of a spherical pressure vessel over a cylindrical pressure vessel:
Spherical pressure vessel has smaller surface area per unit than any other pressure vessel shapes. As there is lesser surface area, the amount of the heat transfer from the high temp area will be less than other shapes. So the spherical pressure vessel is more efficient than any other pressure vessels.

Figure 1: Spherical pressure vessel

Figure 2: Cylindrical pressure vessel

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CONTENT

What is parallel flow heat exchanger?

A direct transfer type of heat exchanger in which both hot fluid and cold fluid flow in the same direction to exchange heat energy between them without transfer of any energy from the ambient. 

Parallel flow heat exchanger theory

Heat exchanger is defined as a steady flow adiabatic open system. Flow of both fluids (hot fluid and cold fluid) are in the same direction to exchange heat between. It is a categorized as direct transfer type heat exchanger in which fluids do not have any physical contact between them.  The pressure of both hot and cold fluid remains constant.

The Enthalpy loss of hot fluid is equal to the Enthalpy gain by cold liquid. The variation of temperature between hot fluid and cold fluid in the direction of the flow always decreases.

Where,

T_h,in: Temperature of inlet hot fluid

T_h,out: Temperature of outlet cooled fluid 

T_c,in: Temperature of inlet cold fluid

T_c,out: Temperature of outlet warm fluid

Advantages of parallel flow heat exchanger

Loss of pressure is very low

It is simple in construction and cheap to build.

Parallel flow plate heat exchanger

A cluster of plates are placed in a systematic manner one above the other for the formation of a series of channels for fluid flow to exchange heat energy between them. The increase in surface area by the plates allows more heat transfer between the two fluids.

Parallel flow heat exchanger vs counter flow heat exchanger

The variation of temperature between hot fluid and cold fluid with respect to the flow direction is more pronounced in parallel flow heat exchanger. The entropy of parallel flow type heat exchanger is higher as compared to counter type heat exchanger. Counter flow heat exchanger is more efficient than parallel flow heat exchanger. Hence for the same heat transfer rate required in both cases, counter flow heat exchanger occupies lesser heat transfer area or more compact in size than parallel flow heat exchanger.

What is effectiveness of parallel flow heat exchanger?

‘The effectiveness (ϵ) of a heat exchanger is defined as the ratio of the actual heat transfer to the maximum possible heat transfer.’

Actual heat transfer (Q) = m_h*C_ph*(T_h1 – T_h2) 

= m_c*C_pc*( T_c2 – T_c1)

Maximum possible heat transfer (Q_max) = C_h(T_h1 – T_c1)

Parallel flow and counter flow heat exchanger experiment

Aim: To determine the effectiveness of the heat exchanger in parallel flow and counterflow.

The experiment setup consists of the following component,

• Heater
• Pump
• Hot water inlet and outlet
• Cold water inlet and outlet
• Temperature sensor
• Flow regulator

Procedure:

First, we have to switch ON the testing apparatus, Then switch ON the heater and set the temperature of the water heater. We have to Wait for the temperature of the water to raised upto the set point. Switch ON the pump for both hot and cold water. Set the mass flow rate of both hot and cold water using a flow regulator knob. All the temperature at inlet and exit are recorded. First, set the heat exchanger in a parallel configuration and note the readings.

Specific capacity of hot fluid: _________

Specific capacity of cold fluid: _________

1. Adjusted mass flow rate of hot fluid (m_h) are recorded
2. Adjusted mass flow rate of cold fluid (m_c) are recorded
3. Set Inlet temp. of hot fluid are recorded (T_h1)
4. The Outlet temp. of hot fluid  are recorded (T_h2)
5. Inlet temp. Of cold fluid are recorded (T_c1)
6. Outlet temp. of cold fluid are recorded (T_c2)

Application of Parallel flow heat exchanger

Used for furnace air preheat, which exchange heat between fresh cold air and furnace effluent flue gases.

Shell and tube type of heat exchanger on the ship used parallel flow heat exchanger.

A thin walled double pipe parallel flow heat exchanger

The arrangement in which one fluid flows inside a pipe and the other fluid flows between the outer surface of the first pipe and the inner surface of another pipe that surrounds the first. These pipes are concentric in nature. 

Counter and parallel flow heat exchanger

Both counter and parallel flow heat exchanger are direct transfer type heat exchanger.

The flow direction of the hot and clod fluid in case of counter typer heat exchanger is opposite to each other whereas in case of parallel flow the direction of hot and cold fluids same.

The Log Mean Temperature Difference (LMTD) of  is higher in case of counter flow as compared to the parallel flow heat exchanger and so counter flow heat exchanger are smaller in size for same energy transfer.

Parallel flow heat exchanger calculations

When both hot and cold fluid enters the heat exchanger from the same side, flow in a parallel direction and exit from the same side is known as a parallel flow heat exchanger.

Aim is to calculate the total heat transfer rate (Q) between hot and cold fluids in the parallel flow heat exchanger.

Where,

T_hi is Inlet temperature of hot fluid

T_he is Exit temperature of hot fluid

T_ci is Inlet temperature of cold fluid

T_ce is Exit temperature of cold fluid 

ΔT_i = Inlet temperature difference

     = Thi – Tci

ΔT_e = Exit temperature difference

     = The – Tce

Q = U x A x ΔT_m

Where,

U = Overall heat transfer coefficient

A = Total heat transfer area of heat exchanger

ΔT_m= Log mean temperature difference

Double pipe parallel flow heat exchanger

It has a simple construction in which one pipe is inserted concentrically to the other. Hot fluid and cold fluid enters heat exchanger from the same side and also flow in the same direction to exchange enthalpy between them.

In case of parallel flow heat exchanger what is the value of maximum effectiveness.

‘The effectiveness of a heat exchanger is defined as the ratio between the actual heat transfer rate taking place between hot and cold fluid and the maximum possible heat transfer rate between them.’

The value of maximum effectiveness in a parallel flow can be 50%.

Parallel flow heat exchanger derivation

To derive an equation for Mean Temperature Difference(MTD) and total heat transfer rate (Q)of the parallel flow heat exchanger.

Consider differential heat transfer area ΔA of the heat exchanger of length Δx through which the differential heat transfer rate between hot and cold fluids is dq.

Then, dq = U x ΔT x dA

Where dA = B * dx, and ΔT = T_h – T_c = f(x)

Boundary conditions,

At x = 0 (i.e Inlet) ΔT = ΔTi = Thi – Tci

At x = L (i.e exit) ΔT = ΔTe = The – Tce

Also,

dq = -m_h*c_ph*dt

   = +m_c*c_pc*dt

ΔT = T_h – T_c

d(ΔT) = dT_h – dT_c

d(ΔT) = -dq[(1/m_h*c_ph) + (1/m_c*c_pc)]

dq = U*(dA)*ΔT 

    = U*ΔT*(BdX)

dq = -U*(dA)*ΔT*[(1/m_h*c_ph) + (1/m_c*c_pc)]

Integrating both side by separating variable

Parallel flow heat exchanger diagram

Parallel flow heat exchanger equations

The equation for total heat exchanged

Where,

U = Overall heat transfer coefficient

A = Total heat transfer area of heat exchanger

봗m = Log mean temperature difference

The equation for Log Mean Temp Difference.

Where,

Thi is Inlet temperature of hot fluid

The is Exit temperature of hot fluid

Tci is Inlet temperature of cold fluid

Tce is Exit temperature of cold fluid 

ΔTi = Inlet temperature difference

     = Thi – Tci

ΔTe = Exit temperature difference

     = The – Tce

Parallel flow heat exchanger example

Shell and tube

Double pipe

Plate type

Parallel flow heat exchanger graph

 

Advantages and disadvantages of parallel flow heat exchanger

Advantage:

It is simple in construction and cheap to build.

Quick fetches

Low pressure loss

Disadvantage:

Less effectiveness

Size is bigger for same heat transfer

Identify the characteristics of parallel flow heat exchangers.

The parallel flow heat exchanger is characterized by direct flow type heat exchanger in which direction of flow is same for both hot and cold fluid during energy transfer.

LMTD equation for parallel flow heat exchanger

It is the parameter that takes into account the variation of ΔT (Temperature difference of inlet side and exit side of heat exchanger) with respect to the direction of hot fluid flow by averaging it all along the length of the heat exchanger from inlet to exit.

Log Mean Temperature Difference (LMTD) is the ratio of difference of difference of inlet temperature and difference difference in exit temperature to Log of the ratio of difference of difference of inlet temperature and difference of difference in exit temperature.

Where,

Thi is Inlet temperature of hot fluid

The is Exit temperature of hot fluid

Tci is Inlet temperature of cold fluid

Tce is Exit temperature of cold fluid 

ΔTi = Inlet temperature difference

    = Thi – Tci

ΔTe = Exit temperature difference

    = The – Tce

Optimization of parallel flow heat exchanger

Shell and tube type parallel flow heat exchanger can be optimized by a new type of anti-vibration clamping baffle. The geometric parameter like baffle distance and baffle width also influence its performance. Type of flow is an important parameter to be considered for the optimization of the heat exchanger.

Define temperature gradient in case of Parallel flow heat exchange

The difference of temperature between temperature difference in inlet side and exit side of heat exchanger is known as temperature gradient. In the case of a parallel flow heat exchanger, it is not uniform and gradually decrease in the direction of flow.

In Which Condition we should use parallel flow heat exchanger?

The limit of the exit temperature of cold fluid is exit temperature of hot fluid in case of parallel flow heat exchanger. So, it is mainly used where limiting transfer of heat is recommended.

Numerical question:

Que: Hot water at 46℃ enters the heat exchanger to increase the enthalpy of water that enters at 10℃ and comes out of the heat exchager at 38℃. The mass flow rate of hot fluid is 25 l/s, and the mass flow rate of cold fluid is 19 l/s. If no heat losses take place during heat transfer, What is the temperature of the hot fluid at the exit?

Sol: Given inlet temperature of hot fluid (T1) = 46℃

     Given inlet temperature of cold fluid (T3) = 10℃ 

     Given exit temperature of cold fluid (T4) = 38℃

     To find exit temperature of hot fluid (T2) = X

     Density of water () = 1000 kg/m3

     Mass flow rate of hot fluid (mh)= 25 l/s

     Mass flow rate of cold fluid (mc) = 19 l/s

     Heat capacity of water (c) = 4186 J/kg-K

Heat lost by hot water is the same as the heat gained by the cold fluid.

mh*c*(T1-T2) = mc*c*(T3 – T4)

25 (46 – T2) = 19 (38 – 10)

T2 = 24.72℃

The exit temperature of the hot water is 24.72℃

FAQ/Short Notes

Where does parallel flow heat exchanger used

The parallel flow heat exchanger is mainly used where limited transfer of heat is recommended.The limit of the exit temperature of cold fluid is exit temperature of hot fluid in case of parallel flow heat exchanger.

Crossflow vs parallel flow heat exchanger

For the same heat transfer rate required in both cases, counter flow heat exchanger occupies lesser heat transfer area or more compact in size than parallel flow heat exchanger.

 

When water is heated and oil is cooled in a heat exchanger.  will it follow a counterflow path or parallel flow path?

Both type of heat exchanger can be used, but counter flow type heat exchanger will occupy less space as compared to parallel flow type heat exchanger.

The concept of superheating is crucial in understanding the functioning of steam power plants and boilers. A superheater is a device that increases the temperature of steam above its saturation point, resulting in dry and high-temperature steam. This process enhances the efficiency and performance of the steam power system. Superheaters are typically located in the flue gas path of a boiler and are classified into two types: radiant superheaters and convection superheaters. Radiant superheaters are placed in the furnace area, while convection superheaters are positioned in the convective pass of the boiler. Superheaters play a vital role in preventing condensation, improving heat transfer, and ensuring the reliability of steam turbines.

Key Takeaways

Superheater Type	Location in Boiler
Radiant Superheater	Furnace area
Convection Superheater	Convective pass

Understanding Superheaters

What is a Superheater in a Boiler?

A superheater is an essential component of a boiler that plays a crucial role in steam generation. It is responsible for increasing the temperature of the steam produced by the boiler, resulting in superheated steam. Superheated steam refers to steam that has been heated to a temperature higher than its saturation point at a given pressure. This process of superheating the steam has several significant benefits in terms of boiler efficiency and overall performance.

The Concept of Superheat

To understand the concept of superheat, we need to delve into the basics of steam generation and heat transfer in a boiler. When water is heated in a boiler, it undergoes a phase change from a liquid state to a gaseous state, resulting in the formation of steam. This steam initially exists as saturated steam, which is a mixture of water vapor and liquid water droplets.

The superheater, located in the flue gas path of the boiler, is designed to further heat the saturated steam by absorbing heat from the flue gases. This additional heat transfer raises the temperature of the steam above its saturation point, converting it into superheated steam. The superheater achieves this by utilizing different types of superheaters, such as radiant and convective superheaters, which are strategically placed within the boiler system.

Superheated Steam and its Significance

Superheated steam offers several advantages in various applications, particularly in thermal power plants and industrial processes. The increased temperature of superheated steam allows for more efficient energy conversion and power generation. It enhances the performance of steam turbines by increasing their efficiency and reducing the risk of blade erosion caused by wet steam.

Moreover, superheated steam provides better control over steam temperature, ensuring consistent and precise heat transfer in heat exchangers. This is crucial in industries where temperature control is critical for maintaining product quality and process efficiency.

It is important to note that the design, operation, and maintenance of superheaters are crucial for their optimal performance and longevity. The choice of superheater materials, steam quality, boiler pressure, and temperature control play a significant role in preventing superheater failure and ensuring safe and efficient boiler operation.

In conclusion, superheaters are integral components of boilers that increase the temperature of steam, resulting in superheated steam. This process has numerous benefits, including improved boiler efficiency, enhanced heat transfer, and better control over steam temperature. Understanding the role and significance of superheaters is essential for optimizing the performance of thermal power plants and industrial processes.

Types of Superheaters

Radiant Superheaters

Radiant superheaters are a type of superheater used in steam generation systems. They are designed to increase the temperature of the steam by transferring heat through radiation. This type of superheater is typically located in the hottest part of the boiler’s flue gas path, where it can absorb the maximum amount of heat. Radiant superheaters are commonly used in thermal power plants to improve boiler efficiency and steam temperature control.

Convective Superheaters

Convective superheaters are another type of superheater that increases the temperature of the steam by transferring heat through convection. Unlike radiant superheaters, convective superheaters are located in the cooler part of the flue gas path. They are designed to extract heat from the flue gas and transfer it to the steam. Convective superheaters are commonly used in boilers to increase the steam temperature and improve overall heat transfer efficiency.

Separately Fired Superheater

A separately fired superheater is a type of superheater that is independent of the main boiler. It has its own combustion system and is used to superheat steam separately from the main boiler. This type of superheater is often used in large thermal power plants where the main boiler may not be able to provide sufficient superheating capacity. Separately fired superheaters allow for better control over steam temperature and can be used to increase the overall efficiency of the power plant.

Electric Steam Superheater

Electric steam superheaters are a type of superheater that use electricity to generate heat and superheat the steam. They are commonly used in applications where a clean and reliable source of heat is required. Electric steam superheaters are often used in industries such as food processing, pharmaceuticals, and laboratories. They offer precise temperature control and are easy to install and maintain.

Geothermal Superheater

Geothermal superheaters are a type of superheater that utilize the heat from geothermal sources to superheat steam. Geothermal energy is a renewable and sustainable source of heat that can be harnessed for power generation. Geothermal superheaters are commonly used in geothermal power plants to increase the temperature of the steam produced by the geothermal wells. This type of superheater helps to improve the efficiency of the power plant and maximize the energy conversion from heat to electricity.

In summary, superheaters play a crucial role in steam generation and boiler efficiency. They are designed to increase the temperature of the steam, improve heat transfer, and enhance the overall performance of thermal power plants. The different types of superheaters, such as radiant superheaters, convective superheaters, separately fired superheaters, electric steam superheaters, and geothermal superheaters, offer various advantages and are used in different applications based on their design and operating principles. Proper selection, operation, and maintenance of superheaters are essential for ensuring safe and efficient power generation.

Superheater Design and Components

The superheater is an essential component in steam generation systems, particularly in thermal power plants. Its main function is to increase the temperature of the steam produced by the boiler, improving boiler efficiency and enhancing the overall performance of the power generation process.

Boiler Superheater Coil Material

The choice of material for the boiler superheater coil is crucial to ensure its durability and efficiency. The superheater coil is subjected to high temperatures and pressures, as well as corrosive flue gases. Therefore, it is commonly made from high-quality alloy steels that can withstand these harsh conditions. These materials offer excellent heat transfer properties and resistance to corrosion, ensuring the longevity and reliability of the superheater.

Boiler Superheater Design

The design of the boiler superheater plays a vital role in achieving optimal steam temperature control and maximizing energy conversion. Superheaters are typically positioned in the flue gas path, where they absorb heat from the flue gases and transfer it to the steam. There are two main types of superheaters: radiant superheaters and convective superheaters.

• Radiant superheaters are located in the radiant heat zone of the boiler, where they absorb heat directly from the combustion process. They are typically used in boilers with high steam temperatures and are effective in achieving rapid steam temperature increase.

• Convective superheaters, on the other hand, are positioned in the convective heat zone of the boiler. They absorb heat from the flue gases after they have passed through the radiant heat zone. Convective superheaters are commonly used in boilers with lower steam temperatures and provide a more gradual increase in steam temperature.

Superheater Header

The superheater header is an integral part of the superheater system. It acts as a distribution manifold, collecting the superheated steam from the individual superheater tubes and delivering it to the steam turbine. The design of the superheater header ensures uniform steam distribution and minimizes pressure drop, optimizing the performance of the steam turbine.

Superheater Attemperator

To maintain the desired steam temperature, superheater attemperators are employed. These devices control the temperature of the superheated steam by injecting a controlled amount of water or steam into the superheater outlet. By adjusting the amount of water or steam injected, the attemperator can regulate the steam temperature and prevent overheating. This is particularly important in situations where the load on the boiler fluctuates, ensuring the safe and efficient operation of the superheater.

In conclusion, the design and components of the superheater are crucial for achieving efficient heat transfer, steam temperature control, and overall boiler performance. The selection of appropriate superheater materials, along with the careful design of the superheater coils, headers, and attemperators, contribute to the safe and reliable operation of the thermal power plant and the optimization of power generation.

Superheater Operations

A superheater is an essential component in steam generation and plays a crucial role in enhancing boiler efficiency and power generation in thermal power plants. It is responsible for increasing the temperature of the steam beyond its saturation point, resulting in superheated steam.

Primary Superheater and Secondary Superheater

Superheaters are typically classified into two types: primary superheaters and secondary superheaters. The primary superheater is located in the flue gas path, where it absorbs heat from the flue gases and transfers it to the steam. On the other hand, the secondary superheater is positioned in the convective section of the boiler, where it further increases the steam temperature.

The primary superheater, also known as the radiant superheater, is designed to withstand high temperatures and is constructed using materials that can withstand intense heat. It is responsible for heating the steam to a certain temperature before it enters the secondary superheater.

The secondary superheater, also known as the convective superheater, continues the process of increasing the steam temperature. It utilizes the heat transfer from the flue gases to further superheat the steam. The convective superheater is designed to maximize heat transfer efficiency and ensure the steam reaches the desired temperature.

Superheater Efficiency

The efficiency of a superheater is crucial for optimal steam generation and energy conversion. A well-designed superheater ensures that the steam temperature is precisely controlled, allowing for efficient power generation. It also contributes to the overall boiler efficiency by maximizing heat transfer and minimizing energy losses.

To achieve high superheater efficiency, it is essential to consider factors such as the type of superheater, steam quality, boiler pressure, and the materials used in its construction. Proper maintenance of the superheater is also crucial to prevent any potential failures that could impact its performance and overall boiler safety.

Use of Superheaters

Superheaters are widely used in various industries where high-temperature steam is required. They play a vital role in processes such as power generation, heat exchangers, and steam turbine efficiency. By increasing the steam temperature, superheaters enable more efficient heat transfer and enhance the overall performance of the system.

The use of superheaters allows for better control over the steam temperature, which is essential in applications where precise temperature control is required. Superheated steam also offers advantages such as increased energy transfer, improved turbine efficiency, and reduced condensation in the steam distribution system.

In conclusion, superheaters are integral to the operation of boilers in thermal power plants. They increase the temperature of steam beyond its saturation point, enhancing efficiency and enabling various industrial processes. Proper design, maintenance, and utilization of superheaters contribute to improved heat transfer, energy conversion, and overall system performance.

Comparisons and Distinctions

Difference Between Radiant and Convective Superheaters

In the realm of steam generation and boiler efficiency, the design and operation of superheaters play a crucial role. Superheaters are heat exchangers that increase the temperature of steam, enhancing its energy content and improving the efficiency of thermal power plants. There are two main types of superheaters: radiant superheaters and convective superheaters. Let’s explore the differences between these two types.

Radiant Superheaters:

Radiant superheaters are located in the radiant section of the boiler’s flue gas path. They are exposed to the highest temperatures and heat transfer rates. These superheaters are typically made of high-temperature materials that can withstand the intense heat. Radiant superheaters utilize radiant heat transfer to raise the temperature of steam. They are positioned in the path of the hot flue gases, allowing direct heat transfer from the combustion process to the steam.

The key characteristics of radiant superheaters are:

• They operate at high temperatures, typically above 1000°C.
• They are designed to handle high heat fluxes.
• They are effective in achieving high steam temperatures.
• They are commonly used in boilers with high-pressure and high-temperature conditions.
• They contribute to the overall efficiency of the boiler by increasing the steam temperature.

Convective Superheaters:

Convective superheaters, on the other hand, are located in the convective section of the boiler’s flue gas path. They are exposed to lower temperatures compared to radiant superheaters. Convective superheaters utilize convective heat transfer to raise the temperature of steam. They are positioned in the path of the flue gases after they have passed through the radiant superheaters. This allows for further heat transfer from the flue gases to the steam.

The key characteristics of convective superheaters are:

• They operate at lower temperatures compared to radiant superheaters.
• They are designed to handle lower heat fluxes.
• They are effective in achieving moderate steam temperatures.
• They are commonly used in boilers with medium to low-pressure conditions.
• They contribute to the overall efficiency of the boiler by further increasing the steam temperature.

Difference Between Superheater, Reheater, and Air Preheater

In the context of steam generation and heat transfer, it is important to understand the distinctions between a superheater, reheater, and air preheater. Each of these components serves a specific purpose in the thermal power plant.

Superheater:

A superheater is a heat exchanger that increases the temperature of steam above its saturation point. It is located in the flue gas path of the boiler and utilizes heat transfer to raise the steam temperature. The superheater plays a crucial role in improving the efficiency of the power plant by increasing the energy content of the steam. It ensures that the steam leaving the boiler is superheated, which is essential for various industrial processes and power generation.

Reheater:

A reheater is another heat exchanger that is positioned in the flue gas path after the high-pressure turbine. Its primary function is to reheat the steam that has passed through the high-pressure turbine. By raising the temperature of the steam, the reheater improves the efficiency of the power plant by allowing for additional expansion in the low-pressure turbine. This increases the overall energy conversion and power generation capabilities of the plant.

Air Preheater:

An air preheater is a heat exchanger that is responsible for heating the combustion air before it enters the boiler. It utilizes the heat from the flue gases to raise the temperature of the incoming air. By preheating the combustion air, the air preheater improves the thermal efficiency of the boiler. This results in better fuel combustion and reduced fuel consumption, contributing to the overall efficiency and sustainability of the power plant.

In summary, while the superheater increases the temperature of steam, the reheater reheat the steam after the high-pressure turbine, and the air preheater preheats the combustion air before it enters the boiler. Each of these components plays a vital role in optimizing the efficiency of the thermal power plant and ensuring effective heat transfer throughout the system.

The Science Behind Superheating

Is Superheat Latent Heat?

Superheating is a fascinating phenomenon that occurs in the world of thermodynamics and heat transfer. It involves raising the temperature of a substance, such as steam, above its boiling point without changing its phase from a gas to a liquid. But is superheat considered latent heat? Let’s find out.

In simple terms, latent heat refers to the heat energy required to change the phase of a substance without changing its temperature. For example, when water boils and turns into steam, it absorbs latent heat. However, superheating is different. It involves adding additional heat energy to a substance that is already in the gaseous state, increasing its temperature beyond the boiling point.

Superheating is achieved by passing the steam through a superheater, a component in a boiler system. The superheater is designed to absorb heat from the flue gas path and transfer it to the steam, increasing its temperature. This process allows for precise control of the steam temperature, which is crucial in various applications, such as thermal power plants and steam turbines.

Why is Superheating Desirable?

Superheating offers several advantages in steam generation and boiler efficiency. By increasing the temperature of the steam, the energy conversion efficiency in power generation can be significantly improved. Superheated steam has higher enthalpy, which translates to increased work output in steam turbines.

Moreover, superheating enhances the heat transfer process. The higher temperature of the steam allows for more efficient heat transfer in heat exchangers, resulting in improved overall system performance. It also reduces the risk of condensation and corrosion in the steam distribution system, ensuring the delivery of high-quality steam to various industrial processes.

Superheating and Supercooling Phenomenon

Superheating is not the only phenomenon that occurs in the world of thermodynamics. Supercooling, on the other hand, involves cooling a substance below its freezing point without it solidifying. While superheating is desirable in many applications, supercooling is often an unwanted occurrence.

The superheating and supercooling phenomena are influenced by various factors, including the type of superheater used, the materials used in its construction, and the control of steam pressure and temperature. There are different types of superheaters, such as radiant superheaters and convective superheaters, each with its own advantages and limitations.

To ensure the efficient operation of superheaters, regular maintenance is essential. Proper inspection and cleaning of superheater tubes are necessary to prevent fouling and corrosion, which can lead to reduced heat transfer efficiency and potential superheater failure.

In conclusion, superheating plays a crucial role in various industries, including power generation and heat transfer. By increasing the temperature of steam, superheaters improve boiler efficiency, enhance heat transfer, and ensure the delivery of high-quality steam. Understanding the science behind superheating is vital for optimizing energy conversion and maintaining the safety and performance of boiler systems.

Practical Applications and Considerations

Superheat is a crucial aspect of HVAC systems, boilers, and thermal power plants. It plays a significant role in ensuring efficient heat transfer and steam generation. Let’s explore some practical applications and considerations related to superheat.

Superheat in HVAC Systems

In HVAC systems, superheat refers to the process of increasing the temperature of the refrigerant vapor above its saturation point. This is achieved by removing any remaining liquid content from the vapor. Superheated vapor is then used to cool the air, providing comfortable indoor temperatures.

When HVAC systems utilize superheat, it offers several benefits such as:

1. Improved Efficiency: Superheating the refrigerant vapor allows the system to operate at higher efficiency levels, reducing energy consumption and costs.

2. Better Temperature Control: Superheated vapor provides more precise temperature control, ensuring optimal comfort levels in different areas of a building.

3. Preventing Liquid Refrigerant Damage: By removing any liquid content from the vapor, the risk of liquid refrigerant entering the compressor and causing damage is minimized.

When is Superheat Charging Method Used?

The superheat charging method is commonly used during the installation and maintenance of HVAC systems. It involves adjusting the refrigerant charge to achieve the desired superheat value. This method is typically employed when:

• Troubleshooting: Superheat charging can help diagnose issues related to refrigerant flow, system performance, or component malfunction.

• System Optimization: By fine-tuning the superheat value, the system can be optimized for maximum efficiency and performance.

• Retrofitting: When retrofitting an existing HVAC system, the superheat charging method ensures compatibility and proper functioning of the new components.

Benefits of Superheaters in Boilers

Superheaters are essential components in boilers used in thermal power plants and industrial processes. They increase the temperature of the steam produced, offering several benefits:

1. Enhanced Efficiency: Superheating the steam improves the overall efficiency of the boiler, resulting in better fuel utilization and reduced operating costs.

2. Increased Power Generation: Superheated steam has higher energy content, allowing for increased power generation in steam turbines.

3. Improved Heat Transfer: Superheaters optimize heat transfer by maintaining a uniform and controlled steam temperature throughout the system.

4. Boiler Safety: Superheaters play a crucial role in preventing boiler tube overheating and potential failures, ensuring safe and reliable operation.

Superheaters can be classified into two main types: radiant superheaters and convective superheaters. They are designed using specific materials to withstand high temperatures and pressures.

In conclusion, superheat has practical applications in HVAC systems, where it improves efficiency and temperature control. In boilers, superheaters enhance power generation, heat transfer, and overall system safety. Understanding the considerations and benefits of superheating is essential for optimizing the performance of these systems.

Frequently Asked Questions

Interview Questions and Answers on Superheaters

Superheaters play a crucial role in steam generation and boiler efficiency. They are responsible for increasing the temperature of the steam, ensuring optimal heat transfer and enhancing the overall performance of thermal power plants. Here are some commonly asked questions about superheaters:

Q: What is the purpose of a superheater in a boiler?

A: The main purpose of a superheater is to increase the temperature of the steam produced by the boiler. By raising the steam temperature above its saturation point, the superheater improves the energy conversion process and enhances power generation efficiency.

Q: How does a superheater work?

A: Superheaters are typically located in the flue gas path of a boiler. They consist of tubes through which the steam passes after it has been heated in the boiler. The superheater absorbs heat from the flue gases, increasing the steam temperature before it enters the steam turbine.

Q: What are the different types of superheaters?

A: There are two main types of superheaters: radiant superheaters and convective superheaters. Radiant superheaters are located in the radiant heat zone of the boiler, while convective superheaters are positioned in the convective heat zone. Each type has its own advantages and is used based on the specific requirements of the boiler.

Q: What materials are used in superheater construction?

A: Superheaters are typically made from high-temperature resistant materials such as alloy steels, stainless steels, and nickel alloys. These materials can withstand the high temperatures and pressures encountered in the superheater section of the boiler.

Q: How does a superheater affect steam quality?

A: A well-designed superheater ensures that the steam leaving the boiler is dry and of high quality. By increasing the steam temperature, the superheater reduces the moisture content and improves the steam’s thermal properties, making it more suitable for various industrial processes.

Q: What factors can lead to superheater failure?

A: Superheater failure can occur due to various factors, including high temperatures, thermal stress, corrosion, and mechanical wear. Regular maintenance and monitoring of superheaters are essential to prevent failures and ensure safe and efficient boiler operation.

Q: How does a superheater contribute to boiler safety?

A: Superheaters play a crucial role in maintaining safe boiler operation. By controlling the steam temperature, they prevent the formation of wet steam, which can cause damage to the turbine blades and other components. Proper superheater operation ensures the safe and reliable functioning of the boiler.

Q: What is the impact of superheater design on steam turbine efficiency?

A: The design of the superheater has a direct impact on steam turbine efficiency. A well-designed superheater ensures that the steam supplied to the turbine is at the desired temperature, maximizing the energy conversion process and improving overall turbine performance.

Remember, understanding the role of superheaters in steam generation, boiler efficiency, and heat transfer is crucial for anyone working in the field of thermal power plants and energy conversion.

Conclusion

In conclusion, understanding the important concepts of a superheater is crucial for anyone involved in the field of steam power generation. We have explored the purpose of a superheater, which is to increase the temperature of steam beyond its saturation point, resulting in more efficient energy transfer and improved turbine performance. We have also discussed the different types of superheaters, including radiant, convection, and combination superheaters. Additionally, we have examined the factors that affect superheater performance, such as steam flow rate, temperature, and pressure. By grasping these key concepts, engineers and operators can optimize the operation of superheaters and enhance the overall efficiency of steam power plants.

Frequently Asked Questions

What is the content of a superheater in thermal power plants?

The content of a superheater in thermal power plants primarily includes steam that has been heated above its boiling point to increase its thermal energy and prevent condensation during the process of power generation. The superheater also consists of various components such as tubes for steam flow, headers, and supporting elements.

What is the difference between a radiant superheater and a convective superheater?

The main difference between a radiant superheater and a convective superheater lies in their heat transfer methods. A radiant superheater absorbs heat by radiation from the combustion process, while a convective superheater absorbs heat through the convection of flue gases.

What is the role of an attemperator in a superheater?

An attemperator in a superheater is used to control the steam temperature. It does this by injecting water into the steam to reduce its temperature when it exceeds the desired limit, thereby preventing damage to the downstream equipment.

What is the difference between a superheater and a reheater?

The difference between a superheater and a reheater lies in their function within a boiler system. A superheater heats saturated steam to a superheated state, increasing its thermal energy and preventing condensation. On the other hand, a reheater heats up the partially expanded steam coming from the high-pressure turbine to increase its thermal energy before it enters the low-pressure turbine.

What is the transparency content in a superheater?

The transparency content in a superheater refers to the clarity of the operational and maintenance procedures, safety guidelines, and performance data. This transparency is crucial for efficient operation, maintenance planning, and safety compliance.

What is the difference between a convective superheater and an electric superheater?

A convective superheater absorbs heat through the convection of flue gases, while an electric superheater uses electric coils to heat the steam. The choice between the two depends on factors such as the available power source, operational efficiency, and cost considerations.

What is a geothermal superheater?

A geothermal superheater is a type of superheater used in geothermal power plants. It uses the heat from the earth’s core to superheat the steam, which is then used to turn the turbines and generate electricity.

What is superheat and why is it important in steam generation?

Superheat is the process of heating steam above its boiling point to increase its thermal energy and prevent condensation. This is important in steam generation as it improves the efficiency of the steam turbine and prevents damage to the turbine blades due to condensation.

When is the superheat charging method used in HVAC systems?

The superheat charging method is used in HVAC systems when the system operates with a fixed orifice or capillary tube. It ensures the correct amount of refrigerant charge to maintain the desired level of superheat, thereby optimizing system performance and efficiency.

Why does superheating and supercooling occur in a boiler system?

Superheating occurs in a boiler system to increase the thermal energy of the steam and prevent condensation, which can damage the turbine blades. Supercooling, on the other hand, occurs when the steam or liquid is cooled below its boiling or freezing point without it changing its state, which can help in certain cooling or refrigeration processes.

Explore the essentials of low superheat in HVAC systems, including causes, implications, and adjustment techniques for optimal performance.

DEFINITION OF LOW SUPERHEAT

When there is an excess amount of refrigerant in the coils of the evaporator in comparison to the heat load. This condition is termed as low superheat. The reason for low superheat could be due to insufficient heat load or due to excessive amounts of refrigerant entering the evaporator.

There may be some amount of liquid refrigerant in the suction line which might enter the compressor and cause compressor damage. The reasons for low superheat are explained below:

1. Excess amount of Refrigerant

When there is an excess amount of refrigerant that is flowing through the evaporator coils, enough heat will not be absorbed by the evaporator to vaporize the liquid refrigerant. As a result, we have a low superheat and as the refrigerant can absorb enough heat in the suction line; there is a high possibility that it might enter the compressor and damage that unit.

2. Overfeeding in the metering unit

A metering unit that allows more than the needed amount of refrigerant to the evaporator coils will cause flooding. In case the sensing bulb of the thermal expansion valve is not insulated properly then there is a high possibility of the valve being flooded or overfed. When the device overfeeds, there are high chances for both the suction pressure and the discharge pressure to increase.

3. Reduced airflow through the evaporator

One of the most common reasons for low superheat is due to reduced airflow. With reduced airflow, there isn’t enough warm air to vaporize the refrigerant. As a result, there will be a reduced amount of refrigerant vapor and there is a high possibility for the liquid refrigerant to enter the compressor and cause damage to the unit. In this case, both suction and discharge pressures will be lower than usual levels.

It is recommended to clean dirty filters, coil, and motors to allow more air to enter through the evaporator.

4. Reduced airflow through the condenser

 When the amount of air entering the condenser is low, there is a high possibility for higher pressure and temperature in the condenser and the condenser coils, the refrigerant is available to the metering device at higher pressure.

With an increased pressure drop across the metering device, more refrigerant enters the flow. As more refrigerant enters the flow, the suction and discharge pressure increase; also results in subcooling. The main reason for low airflow through the condenser is due to poor motor bearings or obstructions in the unit.

5. Large Sized Equipment

When the system or equipment is too large, but the load is not enough that is enough heat is not available to vaporize the liquid refrigerant into vapor, then it will result in low superheat. With oversized equipment, the indoor relative humidity is expected higher than usual.

LOW SUPERHEAT LOW SUBCOOLING

When there is an excess amount of refrigerant but a limited amount of heat load that is available in the evaporator, the condition is referred to as low superheat. This could be caused due to low airflow or due to plugged coils in an evaporator. When there is a limited amount of refrigerant entering the condenser, this could be the result of poor compression, an oversized metering device, or overfeeding.

This condition is referred to as low subcooling. When there is limited heat load in the evaporator and limited refrigerant in the condenser, this condition is referred to as low superheat low subcooling. The superheat will help in identifying if the low suction is a result of limited heat entering the evaporator coils.

LOW SUPERHEAT NORMAL SUBCOOLING

Low superheat normal subcooling can indicate that the refrigerant charging is high either due to plugged evaporator coils or due to plugged air filters. The reason for the normal subcooling despite the low superheat is because the refrigeration system is installed with a liquid line receiver. The temperature drop across the liquid line filter or dryer gives a clear indication of the possible cause is due to plugging.

HOW TO RAISE OR LOWER SUPERHEAT?

To raise superheat, there should be more heat load that is available for the evaporator coils to handle. While to lower superheat, more refrigerant should be added so that the heat load can be handled by the coils of the evaporator. It is recommended to add refrigerant to lower superheat and recover refrigerant to increase superheat. It should be noted that additional superheat should not be added if the superheat is found to be 5F already.

LOW DISCHARGE SUPERHEAT ALARM

A low discharge superheat alarm indicates that the compressor is flooding with the refrigerant. This is mostly because the expansion valve is overfeeding to the evaporator or due to a faulty actuator.

A LOW EVAPORATOR SUPERHEAT INDICATES

A low evaporator superheat is a condition wherein the refrigerant hasn’t been capable of carrying enough heat load to the compressor coils. This will limit the refrigerant from vaporizing, because of which liquid refrigerant will enter the compressor which will cause slugging that damages the compressor units and other components of the refrigeration system.

HIGH SUCTION PRESSURE LOW SUPERHEAT

A suction pressure low superheat condition occurs when the capacity regulator is large because of which it feeds in more refrigerant into the coils of the evaporator as the heat load is not enough for the available refrigerant. Another possible reason for this condition could be the high capacity of the thermal expansion valve.

To maintain the total capacity of the system, it is essential to have an appropriate refrigerant charge in the system so that suction pressure and superheat are kept to the right levels that would help in the proper functioning of the refrigeration system.

LOW SUCTION SUPERHEAT CARRIER | LOW SUCTION SUPERHEAT

A low suction superheat carrier is referred to when there isn’t enough air that flows through the evaporator coils. This limits the heat from being carried to the coils of the evaporator which results in low suction superheat. The possible reasons for low suction superheat could be the dirty of plugged evaporator coil that restricts air from flowing through the coils. It is recommended to add refrigerant to lower the suction superheat and add refrigerant to increase the suction superheat.

LOW-TEMPERATURE SUPERHEATER

In a low-temperature superheater, the steam entering the turbine has a high moisture content which increases the rate of erosion. Further, a decrease in the superheat temperature also causes quenching of the metal surfaces of the equipment it passes through.

There is the possibility of stresses on the surface of superheaters, steam pipes, stop valves, and turbine inlets. A severe vibration is reported in case of sudden chilling of the turbine rotor.

LOW SUCTION PRESSURE LOW SUPERHEAT

A low suction pressure low superheat is encountered when there is low heat load which could be because of dirty air filters, an insufficient amount of air flowing through the system, or because of the air being too cold. Other possible causes of low suction pressure low superheat are the non-uniform distribution of the refrigerant and could be the result of oil clogged evaporators.

LOW SUPERHEAT LOW SUBCOOLING TXV

Low superheat indicates that there is an excess amount of refrigerant in the evaporator, or the heat load is not sufficient to vaporize the liquid refrigerant to vapor before it moves to the compressor resulting in compressor damage. Plugging of the evaporator coils can also result in low superheat.

On the other hand, low subcooling indicates that there is an excess amount of refrigerant in the condenser. For refrigeration systems that using a thermostatic expansion valve, it is recommended to be maintained between 100F to 180 F.

Therefore, a low superheat low subcooling TXV is one where the refrigerant is in excess in the evaporator and is limited in the condenser resulting in variations in the subcooling below 10⁰F

0 DEGREE SUPERHEAT ON LOW TEMP REFRIGERATION UNIT

0 Degree superheat or low superheat on a low-temperature refrigeration system could indicate that the refrigerant is not carrying enough heat through the coils of the evaporator to vaporize the refrigerant before entering the compressor coils. Even in a low-temperature refrigeration system, it is essential to collect enough heat that is equivalent to the refrigerant charge in the system.

HEAT PUMP LOW SUPERHEAT

A heat pump that is operating at low superheat does not have enough heat load for the excess amount of refrigerant that is available in the coils of the evaporator resulting in liquid refrigerant entering the compressor valves and causing damage to the compressor and other mechanical components of the refrigeration system.

It is therefore suggested to maintain the superheat of the refrigeration system within certain limits such that the damages to the parts of the refrigeration system are minimized. Further, it is recommended to carrying out timely cleaning of the evaporator coils and the compressor valves to avoid plugging that would reduce the flow of air which could also limit the efficiency of the system.

FAQs

1. What does a low superheat indicate?

It indicates that there isn’t enough heat load for refrigerant that is available in the evaporator coils which could result in flooding of the compressor. The compressor is designed to only work with vapors or gases and the entry of liquid will damage the compressor coils and their other components.

A low superheat could also be the result of plugged evaporator coils which is stopping the entry of the heat load. Limited airflow through the system could also result in low superheat because sufficient airflow is required for carrying the heat to vaporize the refrigerant. A faulty metering device or overfeeding of refrigerant can also result in low superheat.

2. If in recovery boiler feed water temp is low What effect of low temp will be in superheated steam or final steam?

The boiler operates with a layer of heat transfer surface which is hot, and water passes over this surface. As the water passes over the hot surface, steam is produced which enters the steam system. The pressure at the heat transfer surface is higher than at the water system because of the heat of the water.

The steam bubbles leaving the heat transfer surface will either be superheated or cooled to the saturation temperature as it rises through the water. The latter can happen. When water is fed to the boiler, it passes in between the heat transfer surface and the boiling water.

Water that is fed into the boiler is usually preheated but is always cooler than the water in the boiler. As the steam rises from the heat transfer surface to this cold-water layer, the steam bubbles condense resulting in two major issues.

The steam bubbles will have some tiny water droplets in them. As a large amount of feedwater enters, the quality of steam is reduced as the boiler reaches isothermal conditions. Secondly, the addition of cool water reduces steam production.

The issues mentioned above can be reduced by using a continuous steam boiler because, in such a boiler, water will be added at low rates because of which the boiler water will be at the isothermal condition and there will be no clouds or mist that will be formed.

3. How to increase low-pressure superheated steam to high pressure?

It is possible to increase the pressure of air using a vapor compressor, but it is not the same when it comes to the increasing pressure of steam as it contains condensate which can damage the compressor. Further, the increasing temperature cannot guarantee an increase in pressure of the superheat instead, the steam might get more superheated without any increase in pressure.

It is possible to increase low pressure superheat to high pressure superheat by combining a low-pressure steam flow with high-pressure steam. But this will result in the backflow of high-pressure steam into a low-pressure pipe. To prevent this backflow, an ejector needs to be installed.

In an ejector, the higher-pressure steam is used as means of pulling the low-pressure steam whereby the high-pressure steam does not backflow into the low-pressure line. This helps in maintaining the high pressure of the superheated steam in the outlet.

PROBLEM STATEMENT I

 Superheated steam at a temperature of 300⁰C and absolute pressure of 1.013 bar enters a pipe. What is the additional amount of heat that the superheated steam carries in comparison to saturated steam passing the same pipe at the same pressure?

Enthalpy of saturated steam at 1.013 bar is 2676 kJ/kg (retrieved from the steam table)

Enthalpy of superheated steam at 300⁰C and 1.013 bar is 3075 kJ/kg (retrieved from the steam table)

Enthalpy of the superheat = Enthalpy of superheated steam – Enthalpy of saturated steam

3075 kJ/kg – 2676 kJ/kg = 399 kJ/kg

The specific heat capacity of the superheat can be determined by dividing enthalpy in the superheat by the difference between the saturation and superheat temperatures

Specific Heat Capacity = (Enthaply in Superheat)/(Superheat Temperature-Saturation Temperature)
= (399 kJ/kg)/(300-100)
= 1.995 kJ/kg 0C

Cochran boiler was initially bought by Thompson-Cochran group as package boiler technology to South Africa and became an international leader in boiler making after joining with Rolls-Royce group.

It was mainly used in ships to produce steam for a different purpose. It can use oil/coal or heat recovery from the exhaust of diesel engine, to produce steam. These boiler’s were also known as composite boilers.

Cochran boiler definition

It is a vertical drum axis, fire tube boiler which has many horizontal tubes to increase heating surface area. It is categorized as a natural draft, natural circulation, low-pressure boiler.It has better efficiency than the simple vertical boiler. Any type of fuel such as coal or oil can be used with it. 

Cochran Thermax Boiler

It is a vertical drum axis, fire tube boiler which has many horizontal tubes to increase heating surface area. It is categorized as a natural draft, natural circulation, low-pressure boiler. It has better efficiency than the simple vertical boiler. It requires a minimum floor area.  Different kind of fuel such as coal and oil can be used inside this boiler.

Cochran boiler construction and working

A Cochran Boiler consists of the following parts:

1. Shell: 

It is the main body of boiler which in-closes both steam and water.

2. Grate of the boiler

It is part of the boiler where solid fuel is stored and designed for easy airflow through it and simple removal of ashes.

3. Combustion Chamber of the boiler

Part of the boiler where fuel is burnt to produce high – temperature flue gas. The inner surface is lined with fire bricks to avoid overheating of the boiler body.

4. Fire tubes

These are horizontal tubes connected in a bunch whose one end is attached to the furnace and the other to the chimney to increase the contact area of the heating surface.

5. Fire hole

A small hole at the bottom of the combustion chamber is used to position fuel in the boiler.

6. Firebox (Furnace)

The mediator between fire tubes and the combustion chamber is known as fire box.

7. Chimney

It is an exhaust pipe through which flue gases are released to the atmosphere.

8. Man Hole

A manhole is a small opening for maintenance and inspection of the interior part of the boiler.

9. Fire Brick Lining

It is a typical type of insulation made of clay and provided in the interior of Cochran Boiler to reduce convection heat transfer to the outer surface.

10. Ash Pit

Ashes are stored in Ash Pit, which is located below the Grate.

11. Smoke Box Door

It gives access to clean smoke deposit from Smoke Box.

12. Anti Priming Pipe

It is used to prevent water droplets from getting carried away with steam.

13. Crown

It is the place where the burning of fuel inside boiler takes place.

14. Pressure Gauge

It is used to measures steam pressure.

15. Safety Valve of the boiler

 It is a safety accessories mounted on the boiler to release extra steam when pressure inside boiler exceeds safe limit.

16. Water Level Indicator

It is a safety device and uses to inspect the level of water inside the boiler and prevent boiler operation at a low water level.

17. Water Level Gauge

To check the level of water inside the boiler, a glass tube gauge is fitted on the outer surface of the boiler is known as water level gauge.

18. Fusible Plug

A safety mounting on the boiler to prevent any damage due to overheating of boiler. When the temperature of boiler water exceeds the safe zone, the fusible plug will melt and water will flow into boiler’s furnace and extinguish the fire.

19. Stop Valve

It is a safety device mounted on the boiler body to stop the steam flow into the mainline. It is a normally closed valve.

Working of Cochran Boiler

The working principle of Cochran Boiler is similar to that of a vertical fire tube boiler. At the grate, fuel is supplied through the fire hole. Fuel is burnt, and hot gases formed are used to transfer heat to water through fire tube. Water gains thermal energy and gets converted to steam. 

Cochran vertical boiler

A vertical boiler is categorized as a natural draft, natural circulation, low-pressure boiler.

It is a multi-tubular boiler which results in increased surface area of heat transfer.

It is generally used to generate steam for small machinery. These boilers are especially used on ships as auxiliary boilers.

Application of Cochran boiler

The Cochran boiler is used in:

• Paper and pulp industry.
• Chemical processing plant.
• Refining units.
• Various process application industries.

Cochran boiler diagram

Cochran boiler is which type of boiler

It is an upgraded form of simple vertical boiler where heating surface area is increased by the use of multi-tubular fire tubes.

Cochran boiler specification

Following are the specification of the Cochran Boiler 

• Steam Capacity: 3500 kg/hr
• Working Pressure: 6.5 – 7 bar (Rated pressure 15 bar)
• Heating surface area: 120 m2  
• Height: 5.79 m
• Shell diameter: 2.75 m
• Tube diameter: 6 cm
• Efficiency: 70 to 75%

Cochran boiler working

The working principle of Cochran Boiler is similar to that of a fire tube boiler. Different types of fuel such as coal or oil are transferred at the boiler’s grate through the fire hole. Fuel is ignited through the fire hole in boiler, and the natural flow of air takes place into the combustion chamber from the atmosphere.

The high-temperature flue gases formed during the combustion of provided fuel, flow through the bunch of horizontal fire tubes. The heat is convected from the fire tube (inside high temperature flue gas is flowing) to the water. The enthalpy of water is increased steam formation takes place. The exhaust gas is released into the atmosphere.

Cochran fire tube boiler

It is a type of boiler in which flue gas flows inside the fire tube, and water is surrounded to these tubes. Convection heat transfer takes place from hot gas inside the tube to the surrounding water to convert it into steam.

Cochran steam boiler

With high efficiency and reduced fuel required, Cochran economizers are cost-effective and used as waste heat recovery to generate steam.

Accessories attached to the Cochran boiler

Attachments on the Cochran Boiler

1. Water level indicator

It indicates water level inside the boiler which help us to maintain water level between high and low level. 

2. Pressure gauge

The steam pressure inside the boiler is measured with the help of an instrument known as a pressure gauge. 

3. Safety valve

 A quick-release valve, mounted on the boiler’s body to protect the boiler from bursting due to excessive pressure is known as safety valve.

When internal pressure reaches the set value of the safety valve, it automatically gets opened, and the high-pressure steam is released.

4. Stop valve

The main function of a stop valve is to stop the operation of the boiler when required and also control flow within the boiler. 

5. Blow off valve

It is used to remove sediment and scale deposits at the bottom of the boiler’s drum while it is in operation and is also used to empty the boiler for cleaning or inspection.

• Feed check valve mounted on the boiler.

Water flow from feed pimp to boiler is controlled by feed check valve

7. Fusible Plug

It is used to cut-off the fire of boiler in furnace, when the level of water is below the safe zone to avoid damage to the boiler.

Major advantages of the Cochran boiler

Major advantage of Cochran Boiler are listed below

• Lower cost of initial installation.
• Floor area requirement is less.
• Easy to handle and operate.
• Different types of fuel can be used.
• It is portable and handy.

Classification of Cochran boiler

Cochran boiler can be classified on the basis of different criteria as Vertical, Multi-tubes, Fire tube, Internally fired, and Natural circulated boiler.

Cochran boiler advantages and disadvantages

Advantages of Cochran boiler 

• Initial installation cost is less.
• Required less floor area.
• Easy to handle and operate.
• Different types of fuel can be used.

Disadvantages

• Steam generation rate is low.
• Carrying out maintenance and inspection work is difficult.
• Limited pressure range is available.
• Large area is required for installation because of its vertical design.

Cochran boiler capacity

Boiler capacity is defined as steam production rate at full firing condition and usually expressed on a weight basis. Cochran boiler capacity is in the range of 500 kg/s at 16 bar.

 Cochran boiler design

The main cylindrical body of boiler which in-house water and steam is known as shell of a boiler. The top the boiler have hemispherical dome shaped structure to provide space for steam generated.This shape is provided to to have higher area to volume ratio.It has a compact structure and occupies less floor area. It is mostly used for the low capacity requirement. 

Cochran boiler dimensions

• Shell diameter: 2.75 m
• Height of boiler: 5.79 m
• Heat exchanger tube diameter: 6cm
• Heating surface 120 m²

Cochran boiler Economizer

An economizer can be used to reduce fuel consumption by up to 6%. It utilizes waste heat from the main engine of the ship to generate steam.

Cochran boiler horizontal

It is mainly used in locomotives and is a multi-tubular, internally fired, fire tube boiler with natural circulation. It is designed to meet sudden fluctuation demands of steam.

Cochran boiler maintenance

Following are the list of some routine maintenance activities carried out on the boiler:

• Water quality testing and treatment by using chemicals. 
• Chemical cleaning of soot deposit on economizer by using high-pressure air.
• Regular blowdown to reduce scale deposits.
• Maintaining records of testing and inspection log.
• Overall visual inspection.
• Lubrication of components.
• Daily inspection of motor condition.
• Cleaning of filters and inspection of pilot and burner assemblies.
• Regular inspection of gasket condition of the steam line and replacement of damaged gaskets.
• Important to maintaining the required water level inside the boiler’s drum.

Cochran boiler manufacturing process

A numerically controlled plasma cutting machine is used to cut a flat plate. This flat plate is rolled for the required diameter with the help of hydraulic pressure. Longitudinal submerged arc welding is carried out for seamless joining.

Inspection and Quality assurance is carried out throughout the manufacturing process. X-ray technology is used to inspect critical welds. For precise tube-hole alignment, CNC milling is used.

Tubes are manually welded in alignment with tube holes. Furnace, combustion chamber, and front tube shell are fitted to the boiler body.

Pressure testing is done by using a non-destructive method.

Cochran boiler parts

• Shell
• Grate
• Combustion Chamber
• Fire Tubes
• Fire Hole
• Furnace
• Chimney
• Fire Brick Lining
• Manhole
• Flue Pipe

Cochran boiler principle

Convection heat transfer takes place from flue gases to the water by the fire tubes to form steam.

Cochran waste heat boiler

It is a boiler that produces steam by utilizing waste heat from the exhaust gases of the main propulsion unit of a ship or else use fuel at the port. It is also known as a waste heat recovery boiler.

Cochran water tube boiler

It is a water tube boiler in which water is present in the tube and high-temperature flue gas is present in the surroundings of the tube to produce steam.

Difference between Cochran and Babcock boiler

A Cochran boiler is a vertical fire tube boiler in which flue gas flows through the fire tube. Heat energy is transferred mainly in the form of convection from the hot fire tube to the surrounding water to generate steam.

Babcock boiler is a water tube boiler in which water flows inside the tube, surrounded by hot flue gas. Heat energy is transferred mainly in the form of convection from hot gases to the water inside the tube to generate steam. This type of boiler is used to produce high-pressure steam.

Difference between Cochran boiler and Babcock & Wilcox boiler

A Cochran boiler is a vertical fire tube boiler in which flue gas flows through the fire tube. Heat is transferred from the hot fire tube to the water surrounding the tube to generate steam.

Babcock & Wilcox boiler is a water tube boiler in which water flows inside the tube, surrounded by hot flue gas. The heat is convected from tube to water to increase enthalpy of water and convert it to steam. The high-pressure steam is produced by this boiler. It has a longitudinal drum and horizontal, inclined tube for generating high-pressure steam. The angle of inclination of tubes is about 15° or more with horizontal.

Difference between Cochran boiler and Lancashire boiler

Cochran boiler is a vertical fire tube boiler in which flue gas flow through multiple fire tube. It is used to generate low-pressure steam and has an internally located furnace.

Lancashire is defined as a horizontal fire tube type, internally fired boiler. The length of the Lancashire boiler is approximate 7 – 9 meters, and the diameter is in the range of 2 -3 meters.

The definition of Cochran boiler’s efficiency

The efficiency of the Cochran boiler is defined as the ratio of heat actually required to produce steam in certain time span to heat liberated in furnace during the give time period.

Where,

m₁ = is mass of water

hf = specific enthalpy of water at the saturated liquid curve

h1 = specific enthalpy of water in sub-cool region

x = dryness fraction

h_fg = difference of enthalpies between saturated vapour and saturated liquid curve at constant pressure.

C = heat capacity of water

History of Cochran boiler

Cochran boiler was initially bought by Thompson-Cochran group as package boiler technology to South Africa and became an international leader in boiler making after joining with Rolls-Royce group.

It was mainly used in ships to produce steam for a different purpose. It can use oil/coal or heat recovery from the exhaust of diesel engine, to produce steam. These boiler’s were also known as composite boilers.

Following are the Limitations of Cochran boiler

• The steam generation rate is low.
• Pressure handling capacity is limited.
• Not suitable for high steam generation rate.
• Because of its compact size, it is difficult to inspect and maintain.

Problem 1: Feed water supplied per hour 690 kg at 28℃, steam produced 0.97 dry at 8 bar, coal fired per hour 91 kg of calorific value 27,200 kJ/kg, ash and unburnt coal collected from beneath the fire bars 7.5 kg/hour of calorific value 2760 kJ/kg, mass of flue gases per kg of coal burnt 17.3 kg, temperature of flue gases 325℃, room temperature 17℃, and the specific heat of the flue gases 1.026 kJ/kg K.

Find

1. The boiler efficiency

2. The percentage heat carried away by the flue gases

3. The percentage heat loss in ashes

4. The percentage heat loss unaccounted

5. Explain what may have actually happened to the heat included under unaccounted losses.

Solution:

Heat supplied to the boiler per hour= mass of fuel per hour x calorific value of fuel

                                    = 91 x 27,200 kJ/hr

                                    = 24,75,200 kJ/hr

At 8 bar, 

Enthalpy of water at saturated liquid curve (hf) = 721.1 kJ/kg (Data from steam table)

Enthalpy of steam at saturated vapour curve (hg) = 2769.1 kJ/kg

Latent heat of vaporization (hgf) = hg – hf

                                 = 2769.1 – 721.1 kJ/kg

                                 = 2048 kJ/kg

Enthalpy of wet steam = {hf + (X*hfg)}

Where, X = dryness factor

Enthalpy of wet steam = {721.1 + (0.97*2048)}

                                  = 2707.67kJ/kg

Enthalpy of feed water at 28℃ = C x T

Where,

C = heat capacity of water

T = Temperature of water in ℃

Enthalpy of feed water at 28 ℃ = 28 x 4.187

                                  = 117.24 kJ/kg

Heat utilised in steam production per hour

  = mass of steam produced per hour(m) x difference of enthalpy of wet steam and feed water.

  = 690*(2707.67 – 117.24) = 1787396 kJ/kg

1. Boiler efficiency: Ratio of heat utilized in steam formation per hour to heat supplied to the boiler per hour.

= 1787396/2475200

= 0.7221 bar

= 72.21% efficient

2. The percentage heat carried away by the flue gases = mg x Kp (tg – tf)

  Where,

mg = is mass of flue gases = 17.3 kg/kg of coal fired,

Kp = specific heat of flue gases = 1.026 kJ/kg K

tg = temperature of flue gases = 325℃

tf = room temperature = 17℃

Total heat energy carried away by the flue gases

 = 17.3 x 1.026(325 – 17)

 = 5467 kJ/kg of coal.

Percentage heat carried away by the flue gases per kg of coal fired

 = (5467/27200) x 100

 = 20.1%

 3. Percentage heat loss in ashes is the ratio of heating value of ash in kJ/hr to heat supplied to the boiler in kJ/hr.

 = {(7.5 x2760)/2475200} x 100

 = 0.836%

 4. Unaccounted heat loss percentage is calculated by 

 = 100 – (72.21 + 20.1 + 0.836)

 = 6.854%

 5. The heat included under unaccounted losses are those due to radiation, fuel that are not fully burnt, loss of heat with hot ashes etc.

FAQ/SHORT NOTES

Ques.1: Where is Cochran boiler used?

Ans: Cochran boiler is used in following sector:

• Paper industries
• Refining industries
• Chemical industries
• Different process applications

Ques.2: What are the major three different types of boilers?

Ans:Three different type of boiler is Combi Boiler, Heat(regular) Boiler, System boiler.

• The Combi Boiler

The boiler having single unit and used to provide hot water for domestic purpose at home.

• Heat only (regular) boiler

 A hot water cylinder is attached in it.

• System boiler

A system boiler is mostly similar to Combi boiler other than hot water production. A steel hot water cylinder is attached to it.

Ques.3: What is the area of the heating surface of a Cochran boiler

Ans: With the efficiency of around 70 – 75 percent, the Heating Surface area of Cochran boiler is 120 m2. Working of this boiler is 7 bar and rated for 15 bar.

Que 4: What is Units of break specific steam consumption?

       A. kg/kW-hr          B. kJ/kg-K

       C. kJ/kg              D. kg/kW

Ans: A

Que 5: Maximum thermal energy loss in a boiler is due to 

       A. Flue Gas           B. Ash content

       C. Radiation losses   D. Incomplete combustion

Ans: A

Que 6: Which instrument is used to measured temperature of the flue gases most accurately?

       A. Thermometer      B. Thermocouple

       C. Pyrometer         D. Wheat-stone bridge

Ans: C

Que 7: Cochran boiler is a type of

       A. A horizontal fire tube boiler

       B. A vertical fire tube boiler

       C. A horizontal water tube boiler

       D. A vertical water tube boiler

Ans: D

Que 8: Orientation of water tubes in a simple vertical boiler are

       A. Horizontal

       B. Inclined

       C. Vertical

       D. All of the above

Ans: B

Que 9: The ratio of diameter of internal flue tubes of a Lancashire boiler to diameter of its shell is

       A. One-fourth

       B. One-third

       C. Two-fifth

       D. One-half

Ans: C

Que 10: The process of heating dry steam at constant pressure, above saturation temperature is known as

      A. Isentropic

      B. Super heating

      C. Sub cooling

      D. Isothermal

Ans: B

Oldham Coupling:

Invention: John Oldham (1821)-solve paddle steamer design.
Flexible coupling has 3 types. Oldham coupling is one of the type of the flexible coupling.

Oldham coupling definition:

Oldham coupling transmits torque between shaft through mating slots on the center discs mounted on the hub.
Oldham coupling is useful for parallel alignment applications. It can acquire axial and angular misalignments.

Basic applications of couplings:
To transmit power and torque.
To accommodate misalignments (angular, axial, parallel)
To absorb shock loads and vibrations.

Oldham coupling parts:

Oldham Coupling has three discs. All discs are attached to each other using the grooves.
The discs are mounted at the mid-sections of the shafts. The disc is mounted on the input shaft. Another the disc mounted on the output shaft. The three discs are connected to each other.

Central disc: It is the coupling part consisting of two hubs. It contains two shafts on the sides of the discs perpendicular to the hub axis and plugged into the hub axis. The center is used to reduce the backlash. And hence it is press-fitted at the center. It is designed to behave as a mechanical fuse. Mainly Oldham coupling working is based on the parallel misalignment, so the discs sliding motion acquire a large amount of parallel misalignment.

The hubs: Oldham coupling consists of two hubs that are connected at the end of the shafts. It is a round circular type of disc. Hubs are grooved into the center of the discs.

Oldham coupling: Working principle

Oldham coupling has three main parts(three discs).

One input shaft is connected to the disc and the disc is connected to the output shaft.
each one is coupled to input and output shafts, and one is joined to the first two discs with the grooves.
The disc at the center rotates at same speed and same axis as both the shafts.
Its center rotates about the center axis orbit twice per rotation at the midpoint of input and output shafts. Springs are used in the mechanism to reduce the backlash.
The discs are used to connect the driving and the driver shaft in mechanical power transmission assemblies.

Oldham coupling advantages | advantages and disadvantages of Oldham coupling

• It has a low moment of inertia.
• Material used for the center disc is plastic. Hence the electrical isolation between the discs is not possible. All three are aligned to each other.
• If the first disc breaks, the torque limit is exceeded in the center disc so as to prevent the torque transmission.
• It is economical compared to other couplings.
• It has a high torque capacity.
• Easy to dismantle and disassemble.
• Due to the backlash, there is a need for replacement. Hence the replacement is inexpensive compared with other couplings as it is compact in size.
• Accommodate large parallel and radial misalignments.
• It gives protection to the driven components and support bearings.
• It is compact in size, so it is easy installation.
• It has high torsional stiffness.
• Longer service life
• Tighter machining tolerances with one shaft connected to another maintain a consistent performance rate.
• Good surface finish.
• Very low restorative force compared with other coupling designs:
• Low maximum speed=3000 rpm.

Oldham coupling disadvantages | Advantages and Disadvantages of Oldham coupling

• It can accommodate even small angular misalignments.
• It can accommodate very limited angular displacement.
• At the high torque, the axial load which is reactive, can be applied on the support bearings.

Oldham coupling applications:

It can accomodate slightest misalignments.
The driving shafts and the driven shafts generate at a similar speed.
It behaves as an electrical insulator.
It can transmit power and torque.
The material used in the three discs leads to the use of Oldham of coupling in many device applications.

Oldham shaft coupling:

Oldham coupling applications are mainly used to join the two parallel coaxial rotating shafts. It can transmit the torque at the same speed and same rotation mechanism.
An Oldham type coupling is part of the flexible type coupling. It is a better design for the coupling shafts, which has misalignments, and it can transmit torque between the shafts at the same speeds and same direction. The coupling can acquire any slightest amount of misalignment. Oldham coupling has three discs and two hubs, and one center connected by the use of grooves that fit the fins on the midsection, each side, and perpendicular to each other.

Shaft coupling linkages system requirements:

It should be easy to disassemble
It should allow the misalignment between the rotating shafts rotating along any axis.
It should not be any projecting parts.
It should reduce the further misalignments that can occur in the running operations that can increase the power transmission and machine runtime.
It should reach the manufacturer’s target machine train to define non-zero alignment.

Oldham coupling used in:

Robotics and servo applications
Printer and copy machines.

Uses of Oldham coupling:

The purpose of the couplings is to connect two rotating shaft types of equipment, allowing some misalignment.
Careful selection and installation, and maintenance of the couplings at reduced costs.
The coupling provides the connection between the shafts that are even manufactured separately. It also provides disconnections between the repairs and replacements.

Couplings allow misalignments along with lateral, axial, and angular directions.
It provides protection to the support bearings and shaft hubs from overloading.
It can change the vibration characteristics of the rotating shafts.

Oldham coupling design:

It is an old design mechanism with identical slotted elements put together to slide between them. The Oldham designing is used for the machine shafts, which have a parallel misalignment.

Bore diameter= Diameter of coupling bore mounted on the connecting shafts.
Overall length is the length of the coupling end to the end face.
Hub width is the end face to internal face width.
Slider block material
Coupling diameter
Maximum rated torque
Lateral offset – Lateral offset is the parallel misalignment.
Angular offset – Angular misalignment
Axial offset – maximum axial deviation along with the shaft Shaft coupling fastening method

Design calculation of Oldham coupling| Oldham coupling dimensions:

The length L, L=1.75d,
The diameter, D2=2d,
The thickness of the flange, t=0.75d,
Diameter of the disc, D=3L,
Centerline distance, a=D-3d,
The breadth of groove W=D/6,
The groove thickness, h1=W/2,
The disc thickness, h=W/2,
The total pressure on each coupling=F=1/4(p*D*h)
The torque on each side of coupling=T
Ttc=2Fh=p*D*2h/6

Oldham coupling drawing:

Oldham coupling material:

For the Oldham coupling, the material used is different for the parts of the mechanism, Mentioned as follows:
Slider block is manufactured by the polymer material (nylon, acetal, or combination) to reduce the backlash.
The slotted mating halves are manufactured from aluminum to reduce inertia. It can also be manufactured from brass material of smaller sizes.
Materials can be used for mid disc:
Delrin
Materials can be used for side disc(hubs):
stainless steel.
Aluminum alloy.

Oldham coupling mechanism:

An Oldham coupling is the mechanism that is a combination of the rigid connections bodies(kinematic linkages) with definite relative motion. Mechanisms generally have linkages that can move relative to each other—for example, gear and gear train, belt and chain drive, cam and follower.

This also includes the friction devices such as brake and clutches, and structural components, fasteners, bearings, springs, lubricants, etc. And the different types of the machine element parts like spline, pins, and keys.
To perform the mechanical work machine elements mechanism transmits power to the resistance to overcome.
A coupling is a device that is a connection between the two shafts for transmission of the power.

A coupling can allow the misalignment but it does not allow disconnection of shafts during the procedure.
The torque limiting couplings can disconnect or slip due to the torque limit is exceeded.
Oldham coupling is the inversion of the double slider crank mechanism. It is obtained by the connecting links.
It can join the elements having lateral misalignments.

Oldham coupling consists of three discs and two flanges with the slots with two tongues attached to the central floating part perpendicularly to each other. Pins are provided, which pass through the flanges and the floating disc. When the tounge1 are fitted in the slot, it allows relative motion between shafts.

The tounge2 is fitted in the other slot allowing the relative vertical motion between the shafts. The resultant motion of the two components allows motion to accommodate the misalignment of the rotating shafts. The Oldham coupling mechanism is based on the three discs with hubs. The sliding friction develops wear of slider block that creates a backlash in the misaligned systems.

Oldham coupling mechanism applications:

Oldham coupling mechanism is mostly used for the stepper motor-driven positioning stages.
The elements of the coupling absorb the shock loads and the vibrations from the frequent starts and stop of the load reversals.
The Oldham coupling is designed for the motion systems, which are idle half of the time.
The latter is available for mounting the driving and the driven shafts without any disturbance within the shaft alignments.

Misalignments in the Oldham coupling:

• Misalignment is the displaced alignment between the shafts.
• Misalignment can be parallel, angular or axial, or combinations.
• In the Oldham coupling, parallel misalignment is generally observed.
• An angular misalignment in the machine train is that in which the shafts intersect at angles less than 180.
• Tighter alignments have higher energy efficiency.
• The tighter alignments have less wear on the machine parts.

Generalized Oldham Coupling:

Oldham coupling is the inversion of the double slider crank mechanism[citation]
an Oldham coupling is the device used to transmit motion and power between parallel rotating coaxial shafts.
Oldham coupling is the flexible coupling part. It gets its flexibility from the disc materials,

The following shows Oldham coupling types based on the shape:
with circular slots,
with curvilinear slots

The figure shows the generalized Oldham coupling with circular slots (link1),
an input disc mounted at the midsection of the input shafts (link2)
an output disc mounted at the midsection of the output shaft(link4),floating disc(link3).

The radii r1 and r2 are the radii of the centerlines of the slots.
The radii may or may not be equal .It is not necessary that the radii has to be equal.
The radii intersect at the centerline axis of the floating disc.

The primary Oldham coupling type transmits torque at the same speed of both the shafts.
The generalized Oldham coupling has two types of slots. One is circular slots and the another is curvilinear slots.
Using either of the slots. the Oldham coupling can transmit non uniform motion and also It can produce quick return motion.
and It can used in many applications where devices require non-uniform transmission.

FAQ/Short Notes:

How to reduce backslash in Oldham coupling, and what is it?

Backlash is the angular movement in the mating parts of the mechanical parts. It is often possible that backlash occurs in the coupling movement. The excessive backlash can wear out the coupling parts.Backlash is the angular movement in between the mating parts. Coupling inserts inspection needs for the proper precision of the shaft alignment. A backlash has to be less than a 2-degree angular movement.

Control and reduce of the backlash methods:
Replacement of the couplings inserts and defective components.
Reduce the backlash by rotating shafts, and maintain torque at a consistent level.

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CONTENT

DEFINITION OF HIGH SUPERHEAT

In a refrigeration system, high superheat is a condition when the evaporator coil is not provided with enough refrigerant for the heat load that is present. In short, it means that an insufficient amount of refrigerant is reaching the evaporator coil, or the heat load is too much for the evaporator coil to work on.

Image Attribution: “Refrigeration system” (CC BY-SA 2.0) by rfc1036

HIGH SUPERHEAT CAUSES

 The possible reasons for high superheat are as follows:

1. Low Refrigerant in the system

If the amount of refrigerant is lower than what is required; it will evaporate soon after a few passes through the coil. Soon after the refrigerant evaporates, the vapor will continue the cycle by carrying away heat from the load while passing through the evaporator coil.

This heat picked up by the vapor will increase the temperature of the vapor to a higher value i.e., the vapor reaches superheat temperatures. When there exists less amount of refrigerant in the system, the pressure at both suction and discharge ends of the cycle is lower than usual.

2. Restriction in the liquid line

When the liquid line of the system is restricted, there will be an inadequate flow of the refrigerant to the evaporator coil. The pressure at the suction and the discharge ends of the cycle would be lower than normal pressure. The symptoms observed due to restriction in the liquid line are like those noted in a refrigeration system with low refrigerant.

There is an observed decrease in temperature at the location of restriction. There are also chances for the moisture in the system to freeze and cause the restriction.

3. Airflow through the evaporator is too high

When there is an excess flow of air through the evaporator coil, the capability of the system to remove moisture is reduced. The vapor picks up more than usual heat which causes the suction pressure to be higher than normal pressure and has a higher superheat.

4. Excessive heat load

With higher loads, there will more than the usual heat content that is passing over the evaporator coil which will be absorbed by the vapor. This increases its superheat. When the ambient temperature inside a room is higher than usual or when there are too many people in a room, there are higher chances for an increase in the superheat.

5. Faulty Metering Unit

There is a possibility of recording a higher superheat when the metering device is not installed correctly or due to faulty in the unit.

HIGH SUPERHEAT LOW SUBCOOLING

Superheat means the amount of refrigerant that is present in the evaporator. High superheat indicates that the amount of refrigerant in the evaporator is low or not sufficient. Subcooling indicates the amount of refrigerant that is available in the condenser. Low subcooling means that there is an insufficient amount of refrigerant in the condenser.

A refrigeration system is said to be running a high superheat and low subcooling condition when there exist insufficient amounts of refrigerant in the evaporator as well as the condenser.

HIGH SUPERHEAT HIGH SUBCOOLING

Superheat means the amount of refrigerant that is present in the evaporator. High superheat indicates that the amount of refrigerant in the evaporator is low or not sufficient. Subcooling indicates the amount of refrigerant that is available in the condenser. High subcooling means that there is an excessive amount of refrigerant in the condenser.

A refrigeration system is said to be running a high superheat and high subcooling condition when there exist insufficient amounts of refrigerant in the evaporator and excessive amounts of refrigerant in the condenser. The possible reasons for high subcooling are a faulty metering device, underfeeding, fault in the head pressure control system, especially during low ambient conditions.

High subcooling will reduce the performance of the refrigeration system and ultimately damage the compressor valves. Hence it is recommended to troubleshoot this issue at the earliest as possible.

HIGH SUPERHEAT NORMAL SUBCOOLING

When the amount of refrigerant in the evaporator is insufficient for the heat load, then the superheat condition is referred to as high superheat. The state of having an insufficient amount of refrigerant in the evaporator and enough refrigerant in the condenser is termed as High Superheat Normal Subcooling. It is rare for this condition to exist because usually when there is high superheat there should be either low subcooling or high subcooling.

HIGH SUBCOOLING NORMAL SUPERHEAT

As mentioned earlier, when the refrigerant in the condenser is in excess, that condition is referred to as high subcooling. When there is an adequate amount of refrigerant in the evaporator for the heat load, it is referred to as normal superheat. Therefore, a refrigeration system that operates with an adequate amount of refrigerant in the evaporator and with an excess amount of the refrigerant in the condenser is termed as High Subcooling Normal Superheat.

WHAT DOES HIGH SUPERHEAT INDICATE?

High superheat in a refrigeration system occurs when there is a limited amount of refrigerant in the evaporator for the heat load that is present. High superheat indicates that

1. Low levels of refrigerant

2. restriction in the liquid line

3. Airflow through the evaporator is too high

4. Excessive heat load

5. Faulty Metering Unit

HIGH SUPERHEAT HIGH SUCTION PRESSURE

A refrigeration system is expected to have a high suction pressure when there is leakage of refrigerant through the discharge valve. Further, the compressor is not capable of providing the evaporator coil with the required refrigerant to handle the heat load. This condition is termed as High superheat High suction pressure or High head pressure High superheat. The possible reasons for high suction pressure are

1. High heat load

2. Having a high expansion valve capacity

3. Leakage of compressor disc or discs

HIGH DISCHARGE SUPERHEAT

High discharge pressure superheat is a condition whereby there is air present in the system. When the refrigeration system is exposed to this condition, the best solution is to charge the system with refrigerant. Sometimes, even a clogged condenser can cause high discharge pressure. In such cases, it is advised to clean the condenser. In some cases, a closed discharge valve can also cause high discharge pressure and can be reduced by opening the discharge valve.

NO SUPERHEAT HIGH SUBCOOLING

No superheat or low superheat is an indication the refrigerant hasn’t picked up enough heat because of which the liquid will not completely boil into vapor. This liquid refrigerant which will be transferred into the compressor will damage the compressor. Along with this if there exist excess amount of refrigerant in the condenser. This condition is referred to as no super heat high subcooling.

HIGH SUPERHEAT LOW SUCTION PRESSURE

When the refrigerant is low in the system, there are high chances for low suction pressure. When the refrigeration system is running with high superheat and low subcooling, the refrigeration charge is usually low. In such a condition, the system is expected to be at high superheat and low suction pressure. Another possible reason for low suction pressure high superheat is the insufficient amount of heat entering the evaporator which could be because of limited airflow or due to a dirty/plugged evaporator.

ACCUMULATOR HIGH SUPERHEAT

An accumulator is a vessel that stores refrigerant in a saturated state and stops the liquid refrigerant from entering the compressor. It is used as a protection tank. Bigger accumulators are installed to contain larger volumes of liquid to protect the compressor while the increase in capacity of evaporators is not observed. When the amount of refrigerant is limited with an accumulator installed in the system. It is referred to as an accumulator high superheat

CAN LOW AIRFLOW CAUSE HIGH SUPERHEAT?

A dirty or plugged evaporator coil will limit the air flowing through the evaporator thereby reducing the amount of heat that enters the evaporator which results in high superheat. It is also a concern if there an excessive flow of air through the evaporator as the system’s capability to remove moisture is limited.

HEAT PUMP HIGH SUPERHEAT

A heat pump acts as a refrigeration system in the cooling mode. The indoor unit functions as an evaporator and the outdoor system function as a condenser. As the refrigerant charge in the evaporator is low, the heat pump will not be able to handle the heat load and this state is referred to as Heat pump High superheat

HIGH DELTA T AND LOW SUPERHEAT

A high delta T which is above 21⁰F could be a result of limited airflow indoors. If the air movement in the environment around i.e., indoors is limited, the system is not capable to move enough heat from the surroundings to the evaporator of the system. Further, there will a decreased supply air temperature on the system which will, in turn, result in a higher delta T.  Hence this condition is termed as High delta T low superheat.

For systems with low delta T, the compressor of the refrigeration system will be a danger as the saturated liquid refrigerant will enter the compressor.

FAQS

1. Is High superheat bad?

Yes, high superheat is bad as it indicates that there isn’t sufficient refrigerant to handle the heat load from surroundings or environment that needs to be cooled. A high superheat could also indicate a restriction in the liquid line which is the reason for the limited flow of refrigerant into the evaporator coil. Further excessive airflow could also result in high superheat as the air will carry an excessive amount of heat which the evaporator coil is not ready to handle causing a high superheat. An incorrect metering unit or feeding device also results in high superheat which should be rectified.

2. How can I reduce superheat?

The superheat in a refrigeration system can be reduced based on the cause. If the cause is due to the limited refrigerant, then recharging of refrigerant in the condenser is the right step. In case the superheat is due to excessive airflow, then a sir release valve should be installed thereby maintaining the amount of superheat that can be handled by the evaporator. Troubleshooting the metering device is also a method of reducing the superheat.

3. What causes high discharge superheat? 

The possible reason for high discharge superheat could be leakage of refrigerant. Other possible reasons for high discharge superheat are restriction in liquid line or restriction in the filter. Further, a restriction in the actuator feeding to the evaporator could also result in high discharge superheat. There are cases where the system might face high discharge superheat due to restriction of the airflow to the condenser. In this case, it would be recommended to clean the condenser as it is clogged due to dirt.

4. What is a good superheat for 410a?

A good superheat for 410a would be approximately 10F around the evaporator. The suction pressure and suction temperature are measured. The temperature corresponding to the gauge pressure is taken and the difference between the two temperatures should be 10F for a good superheat. The charging and discharging of the refrigeration system will be based on this value.

5. Why do we have suction accumulator installed?

A suction accumulator is installed to avoid the refrigerant in liquid state from flooding the compressor. An accumulator is usually seen in a heat pump or on any device where liquid refrigerant is a concern.

6. What is meant by subcooling? Is subcooling desirable?

Subcooling can be defined as the condition whereby the liquid refrigerant is at a temperature lower than the saturation temperature. Subcooling is the difference between the liquid refrigerant temperature and the saturation temperature of the refrigerant.

It is desirable to have subcooling as it helps it enhancing the efficiency of the refrigeration system as the amount of heat removed per pound of refrigerant is higher. It also ensures that the liquid refrigerant reaches the expansion valve.

7. Is it necessary to know the superheat of a system. If yes, why?

Yes, it is essential to know the superheat of a system as it gives an indication if the level of refrigerant is too less or too much in the evaporator. If the superheat is high, then the amount of refrigerant is limited thereby reducing the efficiency of the system as more energy is required to operate the system. On the other hand, if the superheat is too low, then there are chances for the liquid to enter the compressor resulting in compressor damage.

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Coupling:

Coupling is the device that is used for the connection of shafts to transmit power and torque.

Coupling is the connection of shaft units that are manufactured separately.
Coupling failure occurs due to key and bolts. So it can be covered by flanges to avoid failure.
The shafts may have all-direction axes.
Couplings are used for variable-type applications.
Examples:
Motor and generator
Motor and pump

Flexible Couplings Definition:

Flexible couplings are the coupling device used for the flexible connection.
It is the type of coupling used to join shafts having misalignment in lateral or angular directions.
It has flexible connection allowing the misalignments.
The elements used have the capacity to absorb the shock loads and the vibrations.

Flexible Coupling types:

Bushed pin type Coupling
Universal Coupling
Oldham Coupling

Flexible coupling applications:

Machines,
servomechanisms,
instrumentation,
light machinery,
steel industry,
the petrochemical industry,
utilities, off-road vehicles,
and heavy machinery, etc.

other flexible coupling applications;

Flexible coupling categories:

Elastomeric couplings –

Elastomeric coupling has elastic properties.
It is the part of the flexible coupling which can attain their flexibility from the material’s tension and compression ability.
Material Example: Rubber, plastic, etc.

Advantages:

Material uses: Rubber or plastic leading to low in cost and allows temperature rise.
Resistant to fatigue failure.
It provides longer life at a minimal cost.
Regular maintenance is not required as it doesn’t use any lubrication.
No need to use lubrication, so regular maintenance is not required.

Mechanically flexible couplings –

Mechanically flexible couplings are part of the flexible coupling, and it gets its flexibility from the loose-fitting parts and the rolling and sliding parts.
It requires regular lubrication.
Example: Nylon gear coupling

Gear coupling:

A gear coupling
is the application part of a flexible coupling
It is the type of coupling the shafts with gears mounted on the hubs.
Sleeves (hollow cylinders) have internal gear teeth.

Regular lubrication is required.
lubrication used: grease, oil

Advantages :
It provides good torque characteristics.

Metallic membrane couplings –

Metallic membrane coupling is the application of flexible coupling.
It gets its flexibility from the flexing of the metallic discs (thin).

Miscellaneous couplings –

Miscellaneous coupling is part of the flexible coupling.
This type of coupling gets its flexibility from the combinations of the mechanisms like spring couplings.

Flexible coupling functions:

It Transmits power.
It Transmits torque.
The selection of the flexible coupling
depends on the max rotational speed.
Power loss is due to the friction heat from the sliding and rolling at high speeds.
Loss of efficiency is due to frictional losses.
The flexible coupling has the advantage that it is the coupling that can give efficiency more than 99%.

Flexible coupling drawing:

Advantages of flexible coupling:

It allows small misalignments.
It absorbs shock loads and vibrations.
It can transmit a high amount of torques.
Simple in construction

Disadvantages of flexible coupling:

It has a high cost due to additional parts.
Require more space.

Bush pin type flexible coupling:

It is the type of coupling used to connect shafts with smaller misalignments.

Transmits the torque from the high tensile material to the input shaft.

Material used: Rubber and leather(bush)

The material gives the flexibility to the coupling.

The flanges are keyed to the shafts.

Example: Electric motors.

The permissible bearing pressure value= 0.5 N/mm2

Flexible grooved coupling:

The grooved coupling having the flexible connection is Flexible grooved coupling.
It allows some misalignment in the shaft connection.

Thomas flexible disc coupling:

Some couplings don’t require regular maintenance. It can work properly on its own.
The coupling is all flexible metal parts coupling. The coupling is known as Thomas flexible disc coupling.

Advantages of flexible coupling over rigid coupling:

Flexible coupling can be used with low levels of torque transmission
and small misalignments.
It allows slight misalignment and still can transmit the same amount of torque as rigid coupling.

Difference between rigid and flexible grooved coupling:

As you know that Flexible coupling creates flexible connections between equipment and the components used to assemble the coupling fixed with some amount of loose, that why some amount of misalignment it can absorb. But metallic flexible type has greater torque capability than other flexible couplings, and some torque will be lost during complete operation of equipment.

Flexible shaft coupling:

Flexible shaft coupling is the flexible connection of the coupling shafts
It prevents coupling failure.
It reduces noise, vibrations and protects coupling components.

Flexible spacer type coupling:

It is the type of coupling which has an extra length shaft installed in the shafts.
It provides space to remove the mechanical seal during maintenance.

Flexible coupling alignment tolerance:

Up to 400 mils.

Flexible coupling design:

The flexible coupling is designed to calculate the torque and power transmission, considering the misalignment in any direction.
Due to less misalignment, There is less movement in the parts.
This leading to less axial and bending stresses development in the shafts.
Torque=P/rotational speed,
If the speed of the shaft increases, power increases, and torque decrease. There is the possibility of a loss of torque.

Flexible Coupling alignment:

Limitations

Parallel misalignment=0.005in,for smaller couplings,
Parallel misalignment=0.030in,for larger couplings,
angular misalignment=±3°

Misalignment types:

Parallel offset: This type of offset occurs in the flexible couplings shaft connection where both the shaft axes are parallel to each other and not in the same line.
Angular offset: This type of misalignment occurs in the flexible coupling shafts where the axes of the shafts meet at the center points of the coupling.
Combined parallel and angular offset: This type of misalignment is the flexible coupling offset of the shafts where the axes of the shafts do not intersect and are not parallel to each other.

Flexible coupling material:

Brass.
Aluminum.
Cast Iron.
Stainless Steel.
Carbon Steel.
Rubber etc.

Flexible coupling at high temperature:

At the high temperature, the couplings will transmit thrust between the machines.

A the temperature increases, the couplings will be more flexible and it will give more flexible connection.

At increasing temperatures, The coupling losses it’s torsional stiffness, increasing more pressure.

Flexible chain coupling:

Roller chain coupling, in which sprockets are attached at adjacent ends of the two abutting shafts, then wrapped together by a common roller chain segment that spans both sprockets. Clearance between the chain and the sprockets allows up to degrees of angular shaft-centerline misalignment and up to about 0.010 inches parallel shaft-centerline misalignment. Roller chain couplings are low-cost, high-torque devices but may be noisy. Wear or fretting wear is a potential failure mode.

Flexible coupling encoder:

It is a device used to provide maximum mechanical protection.

It is the protected type flexible coupling device which protects the coupling.

Flexible disc type coupling:

Flexible disk couplings are the disc type coupling that allows smaller angular and parallel misalignment.
Misalignment of about one degree of angular misalignment and an inch of parallel shaft misalignment can be observed.

Flexible grid coupling:

A grid coupling is a system consisting of two shafts, a grid spring(metallic), and a split cover.
This type of coupling is the coupling device that transmits torque between the coupling shafts using a metallic grid spring.
Advantages:
High torque density.
The grid coupling spring elements have the ability to absorb shock loads and peak loads.
It also has the capacity to dampening the vibrations.
flexible type of coupling tend to have ability to allow the misalignment.

Flexible coupling Problems and solutions:

1)The motor power is 50 KW, and the speed given in rpm is 300rpm. The bearing pressure on bush is equal to 0.5MPa. Allowable shear stress is 25MPa, and the bearing stress is 50MPa. The shear yield strength given is 60MPa. Given data: shaft dia. = 50mm,pins diameter(PCD)=140mm.
Determine the dimensions of the rubber bush for flexible coupling.

Solution:

1. Torque transmitted,
   
   
   T=159N-m.
2. shaft diameter
   
   

d=23.8mm
Let, d=25mm,

n= no. of pins,


n=4,
dneck= 8mm shear stress,

yield stress of the pin material.
d=Dpin+2*t(sleeve)
d=20mm
t=6mm
Bush length,
T= 159Nm, p = 0.5MPa,
dbush =0.02m and dc = 0.14m ,L = 56.78 mm.

2)Design a bushed-pin type flexible coupling shaft transmitting 50 Kw at 1000rpm. The bearing pressure in the rubber bush is 0.5MPa and allowable shear stress in the pins is 25Mpa.
The Diameter of shaft is 60 mm.
Given:
P = 50KW;
N = 1000 rpm,
d = 50 mm,

Solution:
T = (p)/ (2πN/60) = (50×1000×60)/ (2π×1000) = 477.46 N-mm.

Design of hub:
D=2d=260=120mm, Length=1.5d=1.560=90mm,

Design of key:
W=20mm,
t=10mm,
L=1.5d=1.560=90mm,

Key in crushing:

Design of flange:
t=0.5d=0.560=30mm,

Design of bolt:


d1=12.24mm.
n=6,

Assume t= 5 mm, (rubber bush)
d2=25+22+25
d2=39mm,
D1=2d+d2+2n D1=171mm, D2=4d=460=240mm, W=Pbd2l, W=0.539l,

l=44.7mm,
W=871.65N.

Due to pure torsion,

Frequently Asked questions:

What are the three types of flexible compression couplings:

Jaw type coupling
Donut type coupling
Pin and bushing type coupling.

Flexible coupling vs. solid coupling:

solid coupling is rigid coupling. a Rigid coupling is the coupling device that is rigid in connection, whereas flexible coupling is the coupling device that is flexible in connection.
Flexible coupling elements have the ability to absorb vibrations and shock loads, whereas rigid coupling is free of vibrations and shock loads.

Shielded coupling vs. flexible coupling:

Shielded coupling is a unique type of coupling.
Shielded coupling is encased in a metal case.
It is used for underground applications.

Flexible coupling types- According to their uses:

General-purpose Flexible coupling
Gear type
Chain type
Grid type coupling
special purpose Flexible coupling
mechanically flexible type, etc.

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Read more about Rigid And Flange Rigid Coupling.