The term “Boiling characteristics” and boiling characteristics related conditions will be prate in this article. Boiling is a very quick vaporization condition for any liquid substance when it reaches to boiling point.
10+ Boiling Characteristics in a mini channel is listed below,
Specific heat can be deriving as; the amount of heat is needed to raise the temperature of one gram of a matter by one Celsius degree. The units of the specific heat are such as calories or joules per gram per Celsius degree.
Specific heat is also known as massic heat capacity. As an example, the specific heat of water is 1 calorie (or 4.186 joules) per gram per Celsius degree.
Formula:-
The formula for the specific heat is,
Where,
Q = Heat energy is absorbed by a substance
m = Mass of a substance
c = Specific heat capacity of a matter which is depend upon the material of the matter
ΔT= Change in temperature
Image – Graph of temperature of phases of water heated from −100 °C to 200 °C – the dashed line example shows that melting and heating 1 kg of ice at −50 °C to water at 40 °C needs 600 kJ; Image Credit – Wikipedia
Cross sectional area:-
The term cross sectional area in geometry is defined as; the shape is carry by the intersection of the surface of a solid substance. The cross sectional area is present in three dimensional shape is a two dimensional shape of the geometry. In other way cross sectional area is that, the shape is can get through cutting rigid parallel to the foundation.
Types of cross sectional area:-
The cross sectional area can be classified in two sections,
Vertical cross sectional area
Horizontal cross sectional area
Image – A graph of z = x2 + xy + y2. For the partial derivative at (1, 1, 3) that leaves y constant, the corresponding tangent line is parallel to the xz-plane; Image Credit – Wikipedia
Temperature:-
For a material temperature represent a physical quantity which helps to understand the state of the matter. Temperature can measure with the help of thermometer. In body temperature and heat both are not same physical parameter.
The physical parameters which are affect temperature such as, thermal conductivity, strength, corrosion, solubility, density vapour pressure and many more.
When the temperature is increases that time the boiling of a matter is also increases and if the temperature is decreases that time the boiling of a matter is also a decrease.
Image – Thermal vibration of a segment of protein alpha helix, with its amplitude increases with temperature; Image Credit – Wikipedia
Volumetric flow rate:-
In the field of engineering and physics volumetric flow rate is widely used. Another form of the volumetric flow rate is fluid flow rate or volume flow rate.
Inside of a pipe or a channel, the volume of the liquid substance is moving through a cross sectional area of the pipe or channel in a particular fixed time period at some standard condition where the temperature and pressure is remains unchanged.
In another word we could express that, the volumetric flow rate is the ratio between the changes of volume with the change in time.
Formula:-
The formula of the volumetric flow rate in piping system is,
Volumetric flow rate = (Flow velocity of the liquid substance) *(Cross sectional area of a pipe or a channel)
The mathematically form of the volumetric flow rate of the piping system is,
Q = vA
Where,
Q = Volumetric flow rate of a liquid substance
V = Velocity of a liquid substance
A = Cross sectional area through which fluid is flow by a open system
Mass flow rate can be defined as the molecules present in the liquid substance are flow through in a given cross sectional area in a fixed time period at standard condition.
Formula:-
The formula of mass flow rate is,
Mass flow rate = (Density of the fluid)* (Velocity of the liquid)* (Cross sectional area)
The mathematical form of the mass flow rate is, ṁ = dm/dt
Where,
ṁ= Rate of the mass flow for the fluid substance
dm = Change in mass
dt = Change in time
Thermal conductivity:-
Thermal conductivity states that the rate at which heat is transferred through a given material is proportional to the negative value of the temperature gradient. And it is also proportional to the area through which the heat flows, but inversely proportional to the distance between the two isothermal planes.
The formula for the thermal conductivity is,
K = Qd/AΔT
Where,
K = Thermal conductivity of a matter and unit is Watt m-1K-1
Q = The net quantity of heat transfer by a material and unit is Watts or Joules/second
d = Distance by the two planes which are isothermal
A = Area of the surface and unit is square meters
ΔT= Temperature difference and unit is Kelvin
Image – Thermal conductivity can be defined in terms of the heat flow across a temperature difference; Image Credit – Wikipedia
Heat transfer coefficient:-
Heat transfer coefficient can be deriving as, the amount of heat can be passes through in a system per unit area in a fixed time period. For this reason the space in added in the equation of heat transfer coefficient which is express the space over which the total amount of heat transfer of heat included.
The overall rate of the heat transfer for mixed modes can be express as in the form of an overall heat transfer coefficient or overall conductance. In this case the rate heat transfer can be express as below expression,
Q̇ = hA(T2-T1)
Where,
Q̇ = Heat transfer rate
h = Heat transfer coefficient and unit is watt per square meter Kelvin
A = Area of the surface through which heat transfer is happened and unit is square meter
T2= Surrounding fluid temperature and unit is Kelvin
T1= Solid surface temperature and unit is Kelvin
Formula:-
The general equation for the heat transfer coefficient is given below,
h = q/ ΔT
Where,
h = Heat transfer coefficient and unit is watt per square meter Kelvin
q = Heat flux and unit is Watt per square meter
Thermal power through unit area express as, q = dQ̇/dA
ΔT= The temperature difference by the surrounding area of the fluid and surface of the solid and unit is Kelvin
Heat flux:-
The term heat flux has both magnitude and direction for this reason heat flux is a scale of vector. The S.I. unit of the heat flux is watts per square metre.
The heat flux or thermal flux can be derive as, the amount of heat flow density, rate of heat flow intensity or heat flux density is a expression of flow of energy of a particular space in a fixed time.
Law of Fourier’s in one dimension:-
The total heat flux can be determined from Fourier’s law. Most of the matter which is stays in solid heat is transfer from one space to another space by convection method.
Formula:-
Mathematical form of law of Fourier’s in one dimension is given below,
φq = -K (dT(x)/dx)
Where,
k = Thermal conductivity
In the equation the negative sign represent that flow of the heat direction is from lower side to higher side.
Image – Diagram depicting heat flux through a thermal insulation material with thermal conductivity, k, and thickness, x. Heat flux can be determined using two surface temperature measurements on either side of the material using temperature sensors if k and x of the material are also known; Image Credit – Wikipedia
Density:-
The density of a matter can be derive as, the mass contain of the matter per unit volume. The symbol is used to express the density for a matter is \\rho.
Formula:-
The formula of the density of the fluid is below,
ρ = m/v
Where,
ρ= Density of a fluid
m = Mass of a fluid
v = Volume of a fluid
From the law of conversion of mass we get a clear concept about the density of fluid. The conversion of mass flow rates states that, the amount of the mass of a particular object cannot not be created or destroyed. The mass of a body is measured by lever balance.
Image – A graduated cylinder containing various non- miscible colored liquids with different densities; Image Credit – Wikipedia
Pressure drop:-
The term pressure drop can be explain as, the dissimilation in net pressure between two points which are carried by a fluid as network. The pressure drop is appear when the frictional force is appear for the reason of resistance to flow, which is act as a fluid that it flow in a motion inside a pipe.
The pressure drop and flow rate of the fluid is dependent to each other. The pressure drop and flow rate of the fluid is directly proportional to each other means when the amount of flow rate of a fluid is increases that time the amount of pressure drop is also increases and the amount of flow rate of a fluid is decreases that time the amount of pressure drop is also decreases.
In this article “Forced convection heat transfer” term and forced convection heat transfer related facts will be prate in a brief manner. Forced convection heat transfer uses in pump, ceiling fan, suction device.
Forced convection heat transfer is a term that is a classification of transport or forced convection heat transfer is a mechanism which helps to produce motion of a flowing fluid by applying force from externally. Almost in everywhere forced convection heat transfer is used such as steam turbine, central heating and many more.
What is forced convection heat transfer?
Alongside thermal conduction, natural convection and thermal convection is are the classification of transferring the heat and also allow to sufficient quantity of heat energy should be transform without any hassle.
Forced convection heat transfer is actually a very special classification of heat transfer. By the help of forced convection heat transfer a fluid is impression to move from one are to another area by applying force from outer side. In this case the amount of heat transfer is an increase for this it’s another term is Heat Rises.
Forced convection heat transfer equation:
When potentially mixed convection is analyze in that case the physical parameter known as Archimedes Number.
In the Archimedes Number two conditions are involves forced convection and free of relative strength. Forced convection heat transfer equation is given below,
Ar = Gr/Re2
Where,
Ar = Archimedes Number
Gr = Grashof Number
Re = Reynolds Number
By the help of Grashof number buoyancy force is express and by the help of Reynolds number inertia force is express. So, from the forced convection heat transfer equation it is clear that Archimedes Number also means ration of Grashof number and square of Reynolds number.
When the value of Ar < < 1 then its represent forced convection heat transfer equation.
The another physical parameter to express forced convection heat transfer is Peclet number. Peclet number is ratio of movement by current means advection and movement from higher to lower concentration means diffusion.
Pe = UL/α
When the value of Pe > > 1 means advection dominates diffusion.
When the value of Pe < < 1 means diffusion dominates advection.
Image – Forced convection by a fan in a snow machine; Image Credit – Wikipedia
Forced convection heat transfer coefficient:
The equation of the forced convection heat transfer coefficient is discuss below,
Forced convection heat transfer coefficient in internal flow and laminar flow:-
Tate and Sieder give a concept of correlation to account for laminar flor in entrance effect.
A forced convection heat transfer coefficient in internal flow and laminar flow can be express as,
NuD = 1.86 (Re . Pr)1/3 (D/L)1/3 (μb/μw})0.14
Where,
D = Internal diameter
μb = Fluid viscosity of bulk mean temperature
μw= Fluid viscosity at the wall temperature of the pipe
When laminar flow is fully developed in that case Nusselt number stays at constant and value of the Nusselt number will be 3.66. In that case the forced convection heat transfer coefficient in internal flow and laminar flow can be express as,
Nu_D = 3.66 + (0.065 x Re x Pr x D/L)/(1 + 0.04 x (Re x Pr x D/L)2/3
Forced convection heat transfer coefficient in internal flow and turbulent flow:-
When in a circular tube fluid is flowing in that case Reynolds number stays at the range between 10,000 to 12,000 and Prandtl number stays at the range between 0.7 to 120. Forced convection heat transfer coefficient in internal flow and turbulent flow can be written as,
hd/k = (0.023 jd/μ)0.8 (μ cp/k)n
Where,
d = Hydraulic diameter
μ = Fluid viscosity
k = Thermal conductivity for the bulk fluid
cp = Isobaric heat capacity for the fluid substance
j = Mass flux
n = 0.4 for hotter wall than the bulk fluid and 0.33 for cooler wall than the bulk fluid
How forced convection does affect heat transfer?
The most advantage of the forced convection heat transfer than the free convection heat transfer is to able increasing more amount of heat transfer.
By the help of forced convection heat transfer the amount of heat transfer can be increases by the help of force exerted by outer side. The relations between the forced convection heat transfer and heat transfers is directly proportional. Increasing the forced convection the heat transfer of the system source also increases.
What affects Convective heat transfer coefficient?
The convective heat transfer coefficient is depending on some factors. They are listed below,
Fluid velocity or flow velocity is a vector field. By the help of fluid velocity motion of a flowing fluid can be determine in the mathematical form. The total amount of length of the fluid velocity is determined as fluid speed. Flow velocity in fluids is the vector field that provides the velocity of fluids at a certain time and position.
The formula of the fluid velocity is given below,
Q = vA
Where,
Q = Volumetric flow rate of the liquid substance
V = Velocity of the liquid substance
A = Cross sectional area of the open system
Density of the fluid:-
From the law of conversion of mass we get a clear concept about the density of fluid. The conversion of mass flow rates states that, the amount of the mass of a particular object cannot not be created or destroyed. The mass of a body is measured by lever balance.
Density of fluid can be defined as the, an object which is containing mass is constant at standard temperature and pressure.
The formula of the density of the fluid is given below,
ρ = m/v
Where,
ρ = Density of the fluid
m = Mass of the fluid
v = Volume of the fluid
The S.I. unit of the density of the fluid is kilogram per cubic meter
Image – A graduated cylinder containing various non – miscible various colored liquids with different densities; Image Credit – Wikipedia
Thermal conductivity:-
Thermal conductivity states that the rate at which heat is transferred through a given material is proportional to the negative value of the temperature gradient. And it is also proportional to the area through which the heat flows, but inversely proportional to the distance between the two isothermal planes.
The formula of the thermal conductivity is given below,
K = Qd/AΔT
Where,
K = Thermal conductivity and unit is
Q = The quantity of heat transfer unit is Joules/second or Watts
d = Distance by the two planes of the isothermal unit is
A = Area of the surface unit is square meters
ΔT = Temperature difference unit is Kelvin
Image – Thermal conductivity can be defined in terms of the heat flow across a temperature difference; Image Credit – Wikipedia
Dynamic viscosity of the fluid:-
Dynamic viscosity of the fluid can be deriving as the ration between the shear stress to the shear strain. The unit of the dynamic viscosity of the fluid is Pascal. By the help of dynamic we can easily understand which product how much thick and how can the fluid can flow in a motion means by the help of viscosity we can recognize the behaviour of the fluid.
The formula of the dynamic viscosity of the fluid is given below,
η = T/γ
Where,
η = Dynamic viscosity of the fluid
T = Shearing stress
γ= Shear rate
Image – A simulation of liquids with different viscosities. The liquid on the left has lower viscosity than the liquid on the right; Image Credit – Wikipedia
Specific heat:-
Specific heat can be deriving as; the amount of heat is needed to raise the temperature of one gram of a matter by one Celsius degree. The units of the specific heat are such as calories or joules per gram per Celsius degree.
Specific heat is also known as massic heat capacity. As an example, the specific heat of water is 1 calorie (or 4.186 joules) per gram per Celsius degree.
The formula of the specific heat of the fluid is given below,
Q = mcΔ T
Where,
Q = Heat energy
m = Mass of the fluid
c = Specific heat capacity
ΔT= Change in temperature
Image – Graph of temperature of phases of water heated from −100 °C to 200 °C – the dashed line example shows that melting and heating 1 kg of ice at −50 °C to water at 40 °C needs 600 kJ; Image Credit – Wikipedia
How to findconvective heat transfer coefficient for air?
Common units which are used to measure the Convective heat transfer coefficient for air is listed below,
1 W/(m2K) = 0.85984 kcal/(h m20 C) = 0.1761 Btu/(ft2 h 0 F)
1 kcal/(h m20 C) = 1.163 W/(m2K) = 0.205 Btu/(ft2 h 0 F)
Btu/hr – ft2 -0 F = 5.678 W/(m2K) = 4.882 kcal/(h m20 C)
Forced convection heat transfer through a pipe:
When in a circular tube fluid is flowing in that case Reynolds number stays at the range between 10,000 to 12,000 and Prandtl number stays at the range between 0.7 to 120.
Forced convection heat transfer coefficient in internal flow and turbulent flow can be written as,
hd/k = 0.023 (jd/μ)0.8 (μ cp/k)n
Where,
d = Hydraulic diameter
μ= Fluid viscosity
k = Thermal conductivity for the bulk fluid
cp = Isobaric heat capacity for the fluid substance
j = Mass flux
n = 0.4 for hotter wall than the bulk fluid and 0.33 for cooler wall than the bulk fluid
The properties of the flowing fluid are need for the application in the method of the equation and can be calculated at bulk temperature for this reason iteration can be avoided.
Application of forced convection heat transfer:
The Application of forced convection heat transfer is listed below,
Heat removal
Heat sink simulation
Thermal optimization
Heat sensitivity studies
Electric fan simulation
Computer case cooling
Cooling system design
Heating system design
Fan cooled central possessing unit
Water cooled central possessing unit
Printed circuit board simulation
Forced convection heat transfer examples:
Examples of the forced convection heat transfer is listed below,
Air conditioning system
Convection oven
Pump
Suction device
Ceiling fan
Hot air balloon
Refrigerator
Car radiators
Difference between free and forced convection heat transfer:
The major difference points between free and forced convection heat transfer is given below,
Parameter
Free convection heat transfer
Forced convection heat transfer
Definition
Free convection heat transfer is appearing for density difference between the higher temperature fluid and lower temperature fluid.
By the help of forced convection heat transfer a fluid is impression to move from one are to another area by applying force from outer side
Application
1. Heat exchanger 2. Gas turbine blades 3. Solar water heater 4. Nuclear reactor design 5. Aircraft cabin insulation
1. Air conditioning system 2. Pump 3. Suction device 4. Ceiling fan
Heat transfer rate
Heat transfer rate for free convection heat transfer low
Heat transfer rate for forced convection heat transfer high
External equipment
Not needed
Needed
Motion of particles
Slow
Move faster
Equipment size
The size of equipment used in the free convection heat transfer is larger.
The size of equipment used in the forced convection heat transfer is smaller.
Flow of molecules
Not controlled
Controlled
Heat transfer coefficient
Less
High
Movement of the molecules
For the reason of temperature and density difference free convection heat transfer work.
For the reason of exerted force apply forced convection heat transfer work.
How does forced convection heat transfer work?
Forced convection heat transfer work when the area of the gaseous substance or liquid substance is facing higher temperature or lower temperature comparative to greater than their neighbouring temperature and causes a difference between the system temperature and neighbouring temperature.
The temperature gap causes the spaces to move as the higher temperature less dense space rise, and the lower temperature more dense space sink.
This article discusses about two phase flow in pipes. The phases represent the state of matter. In a two phase flow the flow contains two states of matter mainly gas and liquid.
In this article we shall study how a two phase flow occurs in pipes. Heat transfer related to a two phase flow. We will also discuss the design of pipes which undergo two phase flow. Let us start our discussion with the definition of two phase flow.
What is a two phase flow?
As the name suggests, a two phase flow is a type of flow in which the contents that are flowing include two states of matter mainly gas and liquid.
The two phase flow can occur in many forms such as transitioning flows from pure liquid to pure gaseous states, separated flows as well as dispersed two phase flows. In dispersed two phase flows on phase is present in the form of bubble, particles, or droplets in carrier form.
In large scale power systems, two phase flows were studied rigorously. Below are the examples or applications where two phase flow plays a very vital role in design process.
Boilers – Pressurized water is passed through heated pipes and this water changes to steam while passing through the boiler. The boiler changes the phase of liquid water. During the phase transformation, the pipe will have a two phase flow that means gas and liquid phases will co exist.
Nuclear reactors – In nuclear reactors, two phase flow is used to remove heat from the reactor core. In reactor core, the fuel is burnt. The fuel used is generally U-235.
Cavitation – In pumps, when the operating pressure is nearly equal to the vapour pressure of the liquid, any increase in pressure will result into local boiling. This phenomenon of local boiling is called as cavitation.
Electrolysis– Electrolysis is a technique which uses Direct Current (DC) to carry out a non spontaneous reaction.
Clouds – We all have seen clouds up in the sky. They are aerosol consisting of a visible mass of liquid, droplets and other frozen particles that are suspended in the atmosphere.
Groundwater flow – Groundwater is the water that flows beneath the surface of Earth. Two phase flow is used to study the movement of air and water in the soil.
Characteristics of a two phase flow
The list below tells us about the characteristics of a two phase flow:
All the dynamical problems are made non linear due to surface tension.
At standard temperature and pressure, the difference between the densities differ by 1000 for air and water.
The speed of sound changes while passing through a phase change. Compressible effects come into play.
The phase changes are not in equilibrium and they do not happen necessarily.
The flow – induced pressure drops can cause further phase change in the system.
Two phase flows can give rise to counter intutive negative resistance type instabilities.
Types of two phase flow
The types of two phase flows depends on the state of matter of the contents participating in the flow. The types of two phase flow are given in the list below-
Liquid- liquid flow – In liquid liquid flow, the contents of the flow include two different types of liquid that are immiscible. The solution is such that one liquid floats on other liquid because of difference in densities and inability to make or break bonds.
Gas-liquid flow – In gas liquid flows, the gas droplets are present on the surface of the liquid. These droplets move faster than the liquid resulting in a slug flow.
Gas-solid flow– Gas solid flow as the name suggests has solid particles suspended in a gas. These solid particles create abrasive action. For examples large sized impurities present in air is an example of gas solid flow.
Solid liquid flow– Solid liquid flow has solid particles suspended in liquid stream. The solid particles do not mix with the liquid. They are immiscible.
Two phase flow in vertical pipes
Two phase flows in vertical pipes refers to interactive flow of two distinct phases in common interfaces. Each of them having their own individual mass and volume.
To calculate the flow rate in vertical pipe, the formula given below shall be used-
Where,
H is the discharge height
Q is the flow rate
K is the coefficient ranging from 0.87-0.97
D is the diameter of pipe
Two phase flow regimes in horizontal pipes
The flow regimes in horizontal pipes can vary dependin upon the temperature and pressure drop inside the pipe. In the next section we shall discuss about the flow regimes and patterns found in the horziontal pipe for a two phase flow.
In two phase flows inside a horizontal pipe, the patterns observed are- bubbly flow, stratified wavy flow, slug flow, intermittent flow, stratified flow, plug flow, annular flow and mist flow. Other types of patterns maybe observed depending on special temperature ranges and pressure ranges.
Two phase flow and heat transfer
Heat transfer does not necessarily take place between two same phase substances. But the heat can be transferred between two different states of matter too.
Generally in heat exchangers, liquid-liquid flow is used to transfer heat. In two phase flows, the temperature of both the constituents are different and we consider the average temperature and pressure of the flow.
Heat transfer in heat exchangers
In heat exchangers, the heat is transferred between two fluids such that the working fluid heats up or absorbs heat from the fluid flowing in the system.
Heat exchangers are used in many applications such as rocket engines, cooling towers, water jackets, geysers etc. The main purpose of heat exchangers is to heat or absorb heat from the fluid flowing in the system. Sometimes it may be required to heat up the fluid and sometimes it may be needed to cool the fluid. Sometimes only latent heat is absorbed meaning the temperature of the fluid in system remains same but only the phase transformation takes place.
This article discusses about slug flow in pipe. Slug flow is a pattern of two phase flow, more specifically a liquid-gas flow. In this pattern, the lighter fluid moves faster continuously which also contains gas bubbles.
A slug flow can cause pressure oscillations inside a pipe flow. Usually the heavier fluid is termed as slug that moves slower. But we can refer the bubbles of lighter fast moving fluid also as slug. In this article we shall study about the slug flow in detail.
What is a slug flow?
A slug flow is a pattern made in a two phase flow where the lighter fluid moves faster pushing along disperse gas bubble.
The term slug refers to heavier fluid that moves slowly. But we can be using this term for lighter fluid also that moves quickly. Slug flow happens inside a two phase flow, specifically a liquid-gas flow. The pressure oscillations in the pipe are caused by this slug flow. Let us study more about this flow in further sections of this article.
Slug load in piping refers to the load applied by slug flow inside the pipe. The slug flow is characterized by intermittent sequence of liquid slugs which are then followed by longer gas bubbles flowing through the pipe.
As discussed in the above section, slug usually refers to heavy liquid that flows very slowly. But here we can refer to lighter fluid that has a swift movement. We can experience pressure oscillations inside pipe due to slug flow taking place.
Slug flow in horizontal pipeline
When the fluid dlow is taking place in a horizontal pipeline, then the resulting slug flow can be referred to as slug flow in horizontal pipeline.
To calculate the load applied by the slug flow in a horizontal pipeline we need to understand that it depends on few factors. These factors are Diameter of the pipe, cross section area of the pipe, resultant force, angle of bend (in case of horizontal pipe the angle is zero) and the length of the pipe. We shall study about the formula for calculating slug loads in next section.
Slug load formula in horizontal pipeline
We have discussed about the slug flow in horizontal pipeline and the factors on which the load depend. In the section below we shall discuss about the formula required to find slug load in horizontal direction.
The formula for slug load in horizontal pipeline is given below-
Where,
D is the diameter of the pipe
A is the cross section area of the pipe
L is the length of the pipe
Theta is the angle of bend
F is the resultant force
Slug flow in vertical pipes
When the pipe in which the slug flow is taking place is vertical, then the resulting flow is called as slug flow in vertical pipes.
The slug load in vertical pipes depends on various factors. These factors are diameter of the pipe, cross section area of the pipe, length of pipe, angle of bend (in case of vertical pipe the angle is ninety degrees), resultant force. In the next section we shall discuss about the formula for calculating slug loads in vertical pipe.
Slug load formula for vertical pipe
The factors on which the slug load depends is discussed in the above section. Now we shall discuss the formula used to calculate the slug load.
The formula for slug load in vertical pipe is discussed in the section given below-
Where,
D is the diameter of the pipe
A is the cross section of the pipe
L is the length of pipe
Theta is the angle of bend
Slug flow in inclined pipes
When the pipe through which the slug flow is taking place then the resulting flow is reffered as slug flow in inclined pipes. We shall see the factors on which the slug load in inclined pipe depends.
The slug load depends on the same factors as that of vertical and horizontal pipes. These factors are diameter of the pipe, cross section area of the pipe, length of the pipe and angle of inclination or bend. In the next section we shall discuss about the formula used for calculating slug load in inclined pipe.
Slug load formula for inclined pipe
The slug load formula depends on some factors and these factors are discussed in the above section already. In this section we shall use these factors and come up with a formula to calculate the slug load in inclined pipe.
The slug load formula is given in the section given below-
Where,
D is the diameter of the pipe
A is the cross section of the pipe
L is the length of pipe
Theta is the angle of bend
How to avoid slug flow in pipes?
Slug flow can create pressure oscillations inside the pipe. Although slug flow can be avoided by taking certain measures. These measures are discussed in the next section.
The following methods can be used to avoid slug flow in pipings-
Usage of low point effluent drain or bypass
Reducing line sizes to the minimum point permitted by the pressure drop
Keeping the arrangement of pipe flow in such a way that it protects against the pipe flow.
Plug flow vs slug flow
The difference between the two is not too big that we equire a table of differentiation for it. Both the flows are actually very similar and hold similar meanings.
The only difference between a plug flow and a slug flow is that in plug flow the bubbles move at a slower rate than the bubbles in slug flow. Also, the size of bubbles are smaller in plug flow as compared to the size of bubbles in slug flow.
Examples of Slug flow
The list below shows the different places where slug flow is used.
To produce hydrocarbons in wells and their transportation through pipelines.
In geothermal power plants, to produce steam and water.
Boiling and condensing of liquid vapour systems of thermal power plants.
To cool core of nuclear reactors in emergency situations.
In chemical reactors, to transfer heat and mass between gas and liquid.
This article answers the question- why does boiler pressure drop? A boiler is a device used to procude steam or heat the working fluid that is used to generate power in further steps.
The fluid used inside the boiler does not necessarily boil. The heated fluid is further used in many applications like generating electricity, cooling and sanitation. In this article we shall study more about boilers and related questions.
Even though the name suggests that the working fluid will boil but is not necessarily true. The working fluid can be used for further applications without reaching its boiling point. In next section we shall see the heat sources from which the boiler gets heat.
Sources of heat
There are many heat sources from which the boiler takes heat. These heat sources provide the necessary heat energy to the working fluid. This absorbed heat energy is then utilised or is converted to another usable form of energy.
The commonly used heat sources are burning of coal, oil, natural gas. Some boilers which are also called as steam generators produce heat with the help of nuclear fission. A nuclear fission is a process in which the atom splits to emit a huge amount of energy. In some applications Carbon Monoxide is also used as a heat source.
The boilers come in variety of materials. They mainly depend on the applications and the working temperature of the boiler. The next section discusses about the materials used for making boilers.
Pressure vessels of a boiler are generally made of steel and wrought iron. Stainless steel is not used in wetter parts of the boiler due to the risk of corrosion. In some steam models, Copper and Brass are used because these materials facilitate easy fabrication in small sized boilers.
Why does boiler pressure drop when heating is on?
When the heating is on the expansion of the steam takes place, due to this the pressure of the steam keeps on increasing.
Due to the increased pressure, the steam starts exerting pressure on the walls of boiler, if there is a leak in the boiler the boiler pressure will keep on decreasing. Another reason for the drop in boiler pressure is due to releasing of air or water to the radiator when bleeding it.
Why does boiler pressure drop overnight?
The main reason for pressure drop inside a boiler is leak. The leaks can take place in many forms. Sometimes it is done on purpose and sometimes it happens unknowingly.
The reasons of pressure drop may include leak in the pressure relief valve, a problem in the expansion vessel, air inside the system or a leak in the pipework itself.
Can a boiler lose pressure without a leak?
In most of the cases, almost 99%, the boiler loses pressure due to leaks only. There may be leaks in pressure relief valve, pipe work or in expansion vessel.
If there is no leak then there can be a fault inside the boiler or the pressure gauge must be faulty. Other than this, when the air or water is bled in the radiator, the pressure inside the boiler will decrease.
Does boiler pressure drop in summer?
The boiler pressure depends on the water content flowing through the pipelines. Generally in summers, the boiler pressure is low.
This happens due to the fact that the water content inside the pipelines is lesser because the boiler is kept idle for a longer time. A lower boiler pressure indicates that the amount of water being circulating in the system is dropped.
Why does boiler pressure drop in winter?
Boilers are subjected to additional pressure after they are kept idle for a long time in summers. When these boilers are put on to use during winters, the pressure on the boilers increase drastically.
Otherwise the boiler will lose pressure when the boiler has leak inside the relief valve or pressure tanks. When the cold water is heated the molecules of water expand in a random manner, if there is a leak the pressure will keep on decreasing from the boiler.
Types of boilers
Many types of boilers can be used to provide the heat to the system. The type of boiler that is to be used depends on the type of application, quantity of heat to be produced and the working fluid.
The different types of boilers are given in the list below-
Boilers come with many accessories and fittings. The list below shows the different accessories used in boilers-
Pressuretrols – It is used to control the pressure inside the boiler. Usually the boilers have three types of pressuretrols- A manual-reset pressuretrol, operating pressuretrol and a modulating pressuretrol.
Safety valves – It is used to relieve excessive pressure. Excessive pressure can lead to explosion. Using of safety valves ensure safety from explosions. As the safety valves release the excess pressure, hence no excess pressure no explosion.
Water level indicators – The name itself suggests us about its functions. The water level indicators tells us about the level of fluid. Other names used are sight glass, water gauge or water column.
Bottom blowdown valves – The blowdown valves provide a means for removing solid particles or sediments that settle at the bottom of boiler. These valves are installed at the bottom of boiler and occasionally used to remove the particulates by using the pressure from the boiler.
Continuous blowdown valve – This valve allows the water to flow out continuously. The main purpose of this valve is to prevent water in the boiler to become saturated salts with dissolved salts.
Trycock – This is used to find the water level inside the water boiler. This is generally used in water boilers.
Flash Tank – The blowdown comes to this vessel with very high pressure. Here the steam can be flashed safely and be used in a low pressure system and can also be vented out to atmosphere.
Hand holes: These are steel plates which allow for inspections of tubes and installation of pipes.
Top feed: This is used to feed water from the top of boiler. This prevents the boiler from fatigue as the thermal stresses acting on the boiler are reduced.
Low water cutoff: It is a safety switch that or an electrode with a safety switch that is used to turn off the burner or switch off the fuel supply to prevent it from running once the water level reduces below a certain limit. If a boiler is “Dry fired” means there is no water content in it then it can lead to catastrophic consequences.
Automatic heat recovery system: This recovery system allows the blowdown only when the makeup water is flowing to the boiler. This results in maximum heat transfer taking place from the blowdown to the makeup water. In this case no flash tank is needed as the temperature of the blowdown discharge is similar to the temperature of makeup water.
The concept of “Heat exchanger efficiency” with heat exchanger efficiency related several facts will be summarize. Depending on the performance of the ideal system heat exchanger efficiency will be determined.
The term of Heat exchanger efficiency can be explain as the relationship between the amount of heat which is transfer in the physical heat exchanger to the amount of heat which is transfer in the ideal heat exchanger. With the help of heat exchanger efficiency we can analysis and design of the heat exchanger.
What is heat exchanger efficiency?
The process of heat exchanger is happened between two fluids which are containing different temperature and the fluids can be classified by any solid wall or the fluids can be touched position to each other.
The term of heat exchanger efficiency explain as, the proportion between the quantity of heat transfer through heat exchanger that is the actual one which one works as a input of the system and the quantity of heat transfer through heat exchanger that is the practical one which one works as a out of the system.
The term heat exchanger efficiency can be written as,
η = Qact/Qideal
Where,
η = Heat exchanger efficiency
Qact = The amount of heat which is transfer in the physical heat exchanger
Qideal = The amount of heat which is transfer in the ideal heat exchanger
Q̇= The amount of heat flow through the heat exchangers and its unit is Watt
U = Heat transfer coefficient and its unit is Watt per meter square degree centigrade
A = The area from where heat is floe and its unit is square meter
ΔT= Temperature difference and its unit is Kelvin.
Image – Partial view into inlet plenum of shell and tube heat exchanger of a refrigerant based chiller for providing air-conditioning to a building; Image Credit – Wikipedia
How to calculate heat exchanger efficiency?
For the system of heat exchanger the efficiency can be calculating by comparing the factors of actual performance with practical performance.
Heat exchanger efficiency = Actual output / Output of the practical system ….eqn (1)
But where the practical heat exchanger is not available for that case eqn (1) is not applicable. In that case we can use the product of heat transfer coefficient and the surface area from where the heat is flowing which is express as UA to express the best rate of the heat transfer that can be easily can get by the given process condition ΔT. So, the equation we are used in that case is given below,
Q = UA(FΔTLM) ….eqn (2)
Where,
Q = The amount of heat flow through the heat exchangers and its unit is Watt
U = Heat transfer coefficient and its unit is Watt per meter square degree centigrade
A = The area from where heat is floe and its unit is square meter
FΔTLM = Log mean temperature difference and its unit is Kelvin
The LMTD approach is applied when input and output temperature is given but the size of the heat exchanger is not selected. The alternative approach for the LMTD the thermal effectiveness method is applied which is calculating the practical world heat transfer amount and the inside of a heat exchanger heat transfer amount. The expression is given below,
E = Q/Qmax ...eqn (3)
Typical heat exchanger efficiency:
The term typical heat exchanger efficiency explain as, the relationship between the amount of heat which is transfer in the physical heat exchanger to the amount of heat which is transfer in the ideal heat exchanger is gives the flow rate near about 90 percentage.
Typical heat exchanger efficiency value is more than the shell and tube, spiral, kettle and tubular heat exchanger.
How to improve heat exchanger efficiency?
Improving the efficiency of heat exchanger is given below,
Online cleaning helps to prevent the scaling and fouling without interrupting the operation of the heat exchanger or without stopping the operation of the heat exchanger. Online cleaning including the basket, brush and ball type system. Online cleaning treat a chemical conjunction arrangement and standalone approach.
Offline:-
The offline cleaning another name is pigging. Offline cleaning is very useful to improve the efficiency of heat exchanger. In this process a equipment which is use looks like a bullet which is placed in every tube of the heat exchanger and pushed down with air high pressure. Chemical cleaning, hydro lancing and hydro blasting are common methods to use offline cleaning.
Periodic cleaning:-
The most useful methods to clean the dirt and debris from the heat exchanger are periodic cleaning. After a certain time lots of unwanted dirt will gather into the system which decreases the working efficiency thus after a time periodic cleaning is very essential.
Maintaining heat exchanger:-
To boost the efficiency of the heat exchanger regular maintenance is very important. The maintaining of heat exchanger helps to prevent blockage, leakage and fouling of the system.
Cleaning of the PHE manually:-
Manual cleaning is important to follow the instruction of the manufacturer’s. When PHE is installed when prefer to clean the plates of the system without isolate them from the frame of the system.
How to calculate plate heat exchanger efficiency?
For the system of heat exchanger the efficiency can be calculating by comparing the factors of actual performance with practical performance.
Heat exchanger efficiency = Actual output / Output of the practical system ….eqn (1)
But where the practical heat exchanger is not available for that case eqn (1) is not applicable. In that case we can use the product of heat transfer coefficient and the surface area from where the heat is flowing which is express as UA to express the best rate of the heat transfer that can be easily can get by the given process condition ΔT. So, the equation we are used in that case is given below,
Q = UA(FΔTLM) ….eqn (2)
Where,
Q = The amount of heat flow through the heat exchangers and its unit is Watt
U = Heat transfer coefficient and its unit is Watt per meter square degree centigrade
A = The area from where heat is floe and its unit is square meter
FΔTLM = Log mean temperature difference and its unit is Kelvin
The LMTD approach is applied when input and output temperature is given but the size of the heat exchanger is not selected. The alternative approach for the LMTD the thermal effectiveness method is applied which is calculating the practical world heat transfer amount and the inside of a heat exchanger heat transfer amount. The expression is given below,
E = Q/Qmax …eqn (3)
How to improve efficiency of plate heat exchanger?
The way the improve efficiency of plate heat exchanger is listed below,
The design of the plate thickness is not depend on the corrosion resistance. The plate design thickness is depending on the pressure bearing capacity. The plate thickness the heat exchanger can be increases by the pressure bearing capacity.
Plate should be choosing:-
Choosing the plate for the heat exchanger plays a very role. The materials which have thermal conductivity such as copper alloy, stainless steel, titanium steel are selected. The thermal conductivity for the stainless steel is about 14.4 watt per meter Kelvin.
Decreasing the thermal resistance:-
The thermal resistance is of heat exchanger of fouling layer is reduce just because of to avoid scaling from the plate. The fouling thickness is when about 1 mm that time the amount of heat transfer coefficient is reduces about 10 percentages. For this reason it is important to control the quantity of water on the both portions of the heat exchanger.
Image – An interchangeable plate heat exchanger directly applied to the system of a swimming pool; Image Credit – Wikipedia
How to calculate shell and tube heat exchanger efficiency?
For the system of heat exchanger the efficiency can be calculating by comparing the factors of actual performance with practical performance.
Heat exchanger efficiency = Actual output / Output of the practical system ….eqn (1)
But where the practical heat exchanger is not available for that case eqn (1) is not applicable.
So, the equation we are used in that case is given below,
Q = UA(FΔTLM) ….eqn (2)
Where,
Q = The amount of heat flow through the heat exchangers and its unit is Watt
U = Heat transfer coefficient and its unit is Watt per meter square degree centigrade
A = The area from where heat is floe and its unit is square meter
FΔTLM = Log mean temperature difference and its unit is Kelvin
The LMTD approach is applied when input and output temperature is given but the size of the heat exchanger is not selected. The alternative approach for the LMTD the thermal effectiveness method is applied which is calculating the practical world heat transfer amount and the inside of a heat exchanger heat transfer amount. The expression is given below,
E = Q/Qmax …eqn (3)
How to increase efficiency of shell and tube heat exchanger?
The process of the increases efficiency of shell and tube heat exchanger is listed below,
Online cleaning
Offline
Periodic cleaning
Reduce the thickness of the plate
Plate should be choose
Decreasing the thermal resistance
Maintaining heat exchanger
Cleaning of the PHE manually
Heat exchanger efficiency vs. effectiveness:
The major difference between heat exchanger efficiency and effectiveness is discuss below,
Parameter
Heat exchanger efficiency
Heat exchanger effectiveness
Definition
Heat exchanger efficiency is the quality or state of being suitable in performance.
Heat exchanger effectiveness is a degree which defines the success story of something which creates desired result.
Focus
Heat exchanger efficiency focuses on the resources and process.
Heat exchanger effectiveness focuses onGoal of the result.
Thinking
Heat exchanger efficiency is only applied for present state.
Heat exchanger effectiveness applied in long term.
Belief’s
To do things correct in process.
To do correct things in process.
Heat exchanger efficiency vs. flow rate:
The major difference between heat exchanger efficiency and flow rate is discuss below,
Parameter
Heat exchanger efficiency
Flow rate
Definition
The relationship between the amount of heat which is transfer in the physical heat exchanger to the amount of heat which is transfer in the ideal heat exchanger
A fluid is flow in a particular time volume of per rate time.
Formula
Q̇= UAΔT
Q = vA
Advantages of Fireplace heat exchanger efficiency:
Advantages of Fireplace heat exchanger efficiency is listed below,
Smoke is not produced
Efficient energy
Economical
Maintenance is low
Long lifespan
Availability
Water to water heat exchanger efficiency:
Water to water heat exchanger efficiency can be explain as, the type of heat exchanger device which carry liquid cooling and which is appropriate process for reduce heat from many classifications of industrial methods.
Air to air heat exchanger efficiency:
In the unit of air to air heat exchanger air runs for long time is greater the device of heat exchanger. The amount of recovery heat is about 80 percentages. The units of air to air heat exchanger are long, rectangular and shallow.
What affects heat exchanger efficiency?
The effect of the heat exchanger efficiency is with the increasing of capacity ratio for the counter flow heat exchanger is also an increase and with the increasing of capacity ratio for the flow heat exchanger is also a decrease.
What is the maximum efficiency for parallel flow heat exchanger?
No matter how large the exchanger is or how high be the flow of overflow at transfer coefficient, the maximum efficiency for parallel flow heat exchanger is 5%.
The term “Total reflux” will be briefly discussed in this article. Reflux is a part of distillation process which is related to vapours condensation and also back to condensate to the source of the system.
Total flux can be explain as, the condition of a method where the two state of a matter liquid and vapor can pass through in the column although product will be not decreases. The law of mass conservation is state that the total reflux is not possible to happen.
Only for the continuous operation total reflux is accepted by the beginning up.
Total reflux ratio:
Reflux is used widely for apparatus setup in the laboratory distillation, continuous distillation columns in industries.
Total reflux ratio can be describe in this way,
Total flux ratio can be explain as, returning all the excess amount of product is again back to the column as the form of flux and the liquid of the system is again back to the reboiler for vaporisation and fed to the column.
So the total flux is,
F = 0, W = 0, D = 0
VN+1 = Ln
In the reflux ratio the total reflux ratio is represent as limiting value.
The method of total reflux is essential to determine the number of plates is needed in the minimum number.
Product withdrawal rate will be zero in the total reflux ratio.
Total flux formula:
Total flux can be derive as, the net amount of electric field lines which are passes through a certain area in a fixed time.
The total flux formula is derive below,
From where the electric field lines are passes the plane is normal then the total flux can be express as,
Now in the case if the plane is lifted with an angle of θ then the projected area will be A cos θ in that case the total flux foe the plane will be express as,
φ= EA cosθ
Where,
E = Magnitude for the electric field
A = Area by which the amount of electric flied will be determine
θ= The angle which is created by the surface of the plane and the direction of the electric field by which the electric field is flow parallel to the axis.
Image – Laboratory apparatus using reflux to supply energy to chemical reactions. An Erlenmeyer flask is used as a receiving flask. Here the distillation head and fractionating column are combined in one piece; Image Credit – Wikipedia
How to calculate total flux?
The relationship between the total flux and the net number of lines of electric field is directly proportional to each other by which the surface area the total flux is flow.
Total flux can be calculated in three ways, they are listed below,
If the field from where the total flux flow is uniform then total flux through a small surface area can be written as,
dφE = E.dS
Where, The Electric field which is express as E is multiplied by area component which is perpendicular to the given field.
Total flux through a surface:-
The total flux through a surface is S, for this reason surface integral can be express as,
Total flux through a closed surface:-
The dimensional formula for the total flux through a closed surface is L3MT-3I-1 and S.I unit of the through a closed surface is kg.m3.s-3.A-1
Total flux through a closed surface is discuss below,
Where,
E = Electric field
S = Any type of closed surface
Q = The total amount of electric charge inside the surface of S
ε0= Electric constant which is also known as Permittivity and value is
Total flux through a closed surface is also identified as, Gauss Law for the electric field in a surface area. The equation stays in integral form and the equation is form of the Maxwell’s equation.
Total reflux condition is possible?
No, total reflux condition is not possible.
The total reflux in general an operating situation in the column where the two states of a matter such as vapor and liquid are passes by each other and in this situation no product is reduced.
Where,
R = L/V = ∞ and D = 0
The slope value in the operating line is, L/V = 1.0
The slope value in the operating line is represent the mass balance for the each plate of y = x.
Total reflux in distillation:
Total reflux is used in a large of industrial fields such as distillation columns, fractionators like chemical plants, petroleum refiners, and natural gas and also in petrochemical processing industries.
Total reflux in distillation is the type of condensed vapor from which distillation method is done and after completing the process the vapor again back to the process. The liquid used in this that is recycled back to column’s top portion which is known as reflux.
Image – The reflux system in a typical industrial distillation column; Image Credit – Wikipedia
What is total luminous flux?
The term total luminous flux, luminous power or photometry derives as the measurement of the light of perceived power. The radiant flux and total luminous flux is not the same factors. The S.I. unit of the total luminous flux is Lumen.
Image – Photopic (black line) and scotopic (green line) luminosity functions. The photopic includes the CIE 1931 standard (solid), the Judd-Vos 1978 modified data (dashed),and the Sharpe, Stockman, Jagla & Jägle 2005 data (dotted).The horizontal axis is wavelength in nm; Image Credit – Wikipedia
What is total heat flux?
Total heat flux has both magnitude and direction for this reason total heat flux is a scale of vector. The S.I. unit of the total heat flux is watts per square metre.
The total heat flux or thermal flux can be derive as, the amount of heat flow density, rate of heat flow intensity or heat flux density is a expression of flow of energy of a particular space in a fixed time.
Image – Diagram depicting heat flux through a thermal insulation material with thermal conductivity, k, and thickness, x. Heat flux can be determined using two surface temperature measurements on either side of the material using temperature sensors if k and x of the material are also known; Image Credit – Wikipedia
Law of Fourier’s in one dimension:-
The total heat flux can be determined from Fourier’s law. Most of the matter which is stays in solid heat is transfer from one space to another space by convection method.
Mathematical form of law of Fourier’s in one dimension is given below,
Where,
k = Thermal conductivity
In the equation the negative sign represent that flow of the heat direction is from lower side to higher side.
What is total ion flux density?
Total ion flux density can be deriving as; the total amount of ion flux is passes by a particular fixed area to the perpendicular direction of the ion flux. The total ion flux density S.I. unit is Teslas or Webers per square meter.
Mathematically the total ion flux density can be written as,
B = μH
Where,
B = Flux density
μ = Ion flux density
H = Ion field
What is total radiation flux?
Total radiation flux can be any classification of radiation such as sound, particles radioactive, electromagnetic.
Total radiation flux is a measurement of physical parameter by which receiving of particle radiation can be determine through a matter from a particular given source.
The mathematical form of total radiation flux is given below,
Where,
L = Total radiation flux
r = The distance from the source of radiation
The units of the total radiation flux is watt per metre squared (W.m-2) and kilograms cubic metres (kg.s-3).
Total flux through a closed surface:
The dimensional formula for the total flux through a closed surface is L3MT-3I-1 and S.I unit of the through a closed surface is kg.m3.s-3.A-1
Total flux through a closed surface is discuss below,
Where,
E = Electric field
S = Any type of closed surface
Q = The total amount of electric charge inside the surface of S
ε0 = Electric constant which is also known as Permittivity and value is
Total flux through a closed surface is also identified as, Gauss Law for the electric field in a surface area. The equation stays in integral form and the equation is form of the Maxwell’s equation.
Frequent Asked Questions:-
Question: – Explain and classified distillation depends on the applications and techniques.
Solution: – Depend on the applications and techniques the distillation can be classified generally in four sections they are,
In the method of simple distillation the matter which is already evaporated is passes by the tube which is made with plastic. This condition is happened when liquid mixture contains higher temperature means stays in heated situation. The process of condensation is completed that time end portion of the plastic tube is by cool chill water to outer wall of the plastic tube. After that the gas in condensed in the wall of the plastic tube and passes the heat to the chill cool water. Taking the heat the chill cool water became hotter and chemical matter is condensed in the end portion of the plastic tube.
Steam distillation:-
Steam distillation is a processby which we can separate heat-sensitive components from a mixture. For this reason steam distillation is used as a purification method for mixture having impurities. The components in the mixture should be volatile in order to do this separation. The principle behind steam distillation process is to separate the components by vaporisation precess them at temperatures below their actual boiling point. Unless otherwise, some compounds may decompose at their boiling points and the separation cannot be done accurately.
Vacuum distillation:-
In the process of the vacuum distillation the heat is not essential. In the method of vacuum distillation pressure stays at the above of the mixture of liquids. The value is decreases than the normal value of vapor pressure and evaporation took place of the most volatile particles.
Fractional distillation:-
Fractional distillation is the process used to separate hydrocarbon components in crude oil. The fractional distillation method includes the separation of important components according to the difference between their boiling points. In other words, it uses distillation for the fractionation of crude oil.
Question: – Explain about magnetic flux.
Solution: –Magnetic flux can be deriving as, the net amount of magnetic field lines which are passes through a certain area in a fixed time.
Image – The magnetic flux through a surface—when the magnetic field is variable—relies on splitting the surface into small surface elements, over which the magnetic field can be considered to be locally constant. The total flux is then a formal summation of these surface elements; Image Credit – Wikipedia
Formula:-
The formula for the magnetic flux is,
φ B = B. A = BA cos θ
Where,
φB = Magnetic flux
B = Magnetic field
A = Area
Theta = The angle which is created by the surface of the plane and the direction of the magnetic field by which the magnetic field is flow parallel to the axis.
In this article we will discuss about fanning friction factor for laminar flow. Laminar flow is the simplest form of flow in which the layers of fluid do not intersect with each other.
The fluid layers flow very smoothly in a laminar flow, there two other types of flows too which we will discuss in detail in this article. We will first discuss about laminar flow, transient flow and turbulent flow. We will also discuss about their properties. Then we shall discuss about a dimensionless number called as Reynold’s number.
What is laminar flow?
A laminar flow is a type of flow in which the fluid moves in a very smooth manner and the layers of fluid do not intersect each other and rather flow in parallel lines.
To check whether a flow is laminar or not we take help of Reynold’s number. This is a dimensionless number which tells us about the type of flow, whether it is turbulent or transition or laminar flow. In later section of this article we shall study about Reynold’s number.
Reynold’s number is a dimensionless number which helps us find the type of flow of fluid The flow maybe laminar, turbulent or transitional. It is very important to know the type of flow while dealing with fluid machinery.
To find the value of Laminar flow, we need the fluid’s kinematic viscosity, density of the fluid and the velocity of the fluid with which it is flowing. The Reynold’s number can also be used to find the frictional losses in the pipe. We shall study more about Laminar flow in this article.
What is Fanning factor?
Like Reynold’s number, Fanning factor is also a dimensionless number that is used while performing calculations in continuum mechanics’ calculations.
It can be defined as the ratio between the local shear stress to the local flow kinetic energy of the fluid. Mathematically, Fanning factor can be given by the following formula-
Where,
f is the Fanning factor
Tau is the local shear stress
u is the bulk flow velocity
Rho is the density of the fluid.
What is Fanning factor for laminar flow?
We have discussed in the above sections about both Fanning factor and Laminar flow. Now let us see what is the formula for Fanning factor for a laminar flow.
For a laminar flow, Fanning factor is given using the formula given below–
f=16/Re
Where,
Re is the Reynold’s number
How do you calculate Fanning’s factor?
In simple terms, a quarter of Darcy’s friction factor gives us Fanning’s friction factor. The formula for Fanning’s friction factor is different for different types of flows.
We shall discuss about the formula used in laminar flow. For a fluid flowing in round tube with laminar flow, the Fanning factor will be given by the following-
f= 16/Re
Where,
Re is the Reynold’s number
Is Friction Factor higher with laminar flow?
Yes. The friction factor is higher with laminar flow. We can prove this by looking at the formula of friction factor. We have already discussed the formula for friction factor in the above section.
From the formula we can see that the friction factor is inversely proportional to Reynold’s number. Reynold’s number is least for a laminar flow hence resulting into higher value of friction factor.
Fanning friction factor use
The name itself suggests that the friction factor is related to friction. And we know how important it is to know the amount of frictional losses taking place in the flowing fluid.
It is also important to know a rough estimate of losses in kinetic energy taking place due to head loss and pressure loss. Fanning friction factor helps us to find the values of these quantities. By knowing these values we can design the pipes accordingly to avoid much loss due to friction.
Friction factor units
We have studied about the formula for finding the friction factor. If we work out the units of all the quantitites that have been used in the formula we will see that everything cancels out and the ratio comes out to be 1.
Hence we can conclude that the Fanning’s friction factor has no units. Just like Reynold’s number it is a dimensionless number. The factor in itself is a ratio between two similar quantities hence the friction factor has to be dimensionless.
Fanning friction factor formula
Fanning friction factor is the ratio between the local shear stress and the kinetic energy density of flow. We have already discussed the formula in the above sections but we shall study about it one more, this time for turbulent flow also.
The section below gives us the Fanning’s friction formula for both laminar and turbulent flow of a fluid flowing in a round pipe-
Laminar
The Fanning friction formula for a fluid flowing in a laminar flow in a round pipe is given below-
f = 16/Re
Turbulent
The Fanning friction factor formula for a fluid flowing in a turbulent flow in a round pipe is given below-
Fanning friction factor pressure drop
Friction is the major reason for pressure drop to take place. The friction will decrease the velocity of the flow of the fluid and also decreases the pressure as the fluid flows in the pipe.
The pressure drop is directly proportional to the Fanning friction factor. Greater the value of Friction factor greater will be the pressure drop against the ends of pipe. Hence we can say that pressure reduces as the fluid flows through the pipe.
Factors affecting Reynold’s number
The formula of the Reynold’s number is given below-
From the above formula we can conclude that the value of the Reynold’s number depends on the density of the fluid flowing, its dynamic viscosity, velocity with which the fluid is flowing and the equivalent diameter of the cross section through which the fluid is flowing.
How are Darcy’s Friction Factor and Fanning’s friction factor related?
Both Darcy’s friction factor and Fanning’s friction factor represent the amount of friction taking place inside the fluid and tells us how much pressure drop is taking place inside the pipe.
Mathematically, Darcy’s friction factor is four times the Fanning’s friction factor. Both of these factors identical and represent the same quantity that is friction and are also used to find the same thing that is pressure drop. The only difference between them being the factor four that is multiplied by Fanning’s friction factor to find the value of Darcy’s factor.
Reasons for pressure drop inside a pipe
There can be many reasons for pressure drop to take place for a fluid flowing inside a pipe. Some of the reasons are given in the list below-
Friction from the walls of pipe will decrease the pressure of the fluid. The pressure of the fluid exiting the pipe will be lesser than the pressure of the fluid entering the pipe.
Bends in or narrowing of a pipe also contribute to the pressure drop inside the pipe.
Obstructions inside a pipe
Sensors attached inside the pipe that also acts as additional obstructions to the flowing stream of fluid.
This article discusses about heat exchanger examples. The name makes it easier for us to understand the meaning of heat exchanger.
The heat exchanger is nothing but an equipment that exchanges heat between two substances in order to bring down or elevate the temperature to desired levels. In this article we shall study about what a heat exchanger is, what are its different types and different examples where heat exchangers are used.
Heat exchanger is an equipment used to transfer heat between the working fluid and the fluid whose temperature is to be brought down or increased.
Heat exchangers uses hollow tubes through which the fluids are passed. The fluids have temperature difference between them due to which heat transfer takes place. The most important thing for heat transfer to take place is temperature difference between the two objects/fluids. In this article we shall discuss about the different types of heat exchangers and their examples.
Types of heat exchangers according to the direction of flow of fluids
According to the direction of flow of fluids relative to each other, we can classify heat exchangers in to three types. These types are given in the list below-
Parallel flow heat exchanger- When the fluids flow in the same direction relative to each other, the heat exchanger will be referred to as parallel flow heat exchanger. The temperature of the hot fluid decreases whereas the temperature of cold fluids increases.
Counter flow heat exchanger- When the fluids flow in opposite direction relative to each other, then the heat exchanger will be referred to as counter flow heat exchanger. We can find the effectiveness of the heat exchanger using the formula discussed in the later sections of this article.
Cross flow heat exchanger- As the name suggests, cross flow heat exchangers are those heat exchangers in which the fluids flow perpendicular to each other. The tubes make ninety degrees to each other.
Types of heat exchangers according to the transfer process
The classification of heat exchangers on the basis of transfer processes are given in the list below-
Indirect contact type- In this type of arrangement, the fluid streams separate and the heat transfer takes place continuously through a dividing wall in and out of the wall in a transient manner. Different types of indirect contact type heat exchangers include storage type heat exchanger, fluidized bed heat exchanger etc.
Direct contact type– In the direct contact type heat exchanger, two fluids exchange heat with each other by coming in direct contact with each other. They exchange heat and then get separated from each other.
Effectiveness of Heat exchanger
The effectiveness of heat exchanger is a ratio between the actual heat transfer taking place to the maximum heat transfer that can take place in the heat exchanger.
The significance of effectiveness is that it allows the designers to predict how a given heat exchanger will perform a new job. The trial and error procedure is eliminated if we know the effectiveness of the heat exchanger.
Heat exchanger examples
The places where heat exchangers are used are given in the list below-
Air pre heaters
The name suggests that the air is being heated prior to sending it to perform any other process. For examples, they can be used in boilers for increasing the thermal efficiency of the power plant. Pre heated air will improve the quality of fuel input into the power plant.
Economizers
It is an alternative to the air conditioning system. Economizers use outside air to cool the building instead of running compressors like those used in air conditioning system. This also saves a huge sum of money as it saves energy.
Evaporators
Evaporators are used to convert any liquid to its gaseous form. The temperature of the liquid remains the same. The phase change process is an isothermal process. The evaporators are used in boilers to change the liquid water to gaseous steam. In evaporators, the temperature of fuel is same as it undergoes phase transformation. On the other hand the temperature of the colder fluid increases that is used as working fluid inside the heat exchanger.
Superheaters
Superheaters are used inside boilers that convert the wet steam to dry steam. The dry steam is that steam in which there is no liquid water content. The dryness fraction of dry steam is 1 or 100%. The superheaters are used for superheating the steam. The quality and enthalpy of superheated steam is greater than the normally used wet steam or saturated steam.
Condensers
Condensers are opposite to what evaporators are. Condensers bring back the liquid from its gaseous state without changing its temperature. The condensers are simple heat exchangers that absorb heat from the steam and convert it back to liquid water. The amount of heat absorbed is equal to the latent heat of vapourisation of water. Similar to the evaporators, the fuel’s temperature remains the same and the temperature of hot fluid that is used as working fluid inside the heat exchanger decreases.
Cooling towers
A cooling tower is a tower used to reject heat from the system to the surroundings. The heat expelled out of the system is waste heat that holds no use in the further process. These towers appears as chimneys through which a cloud of gas is expelled out. This gas cloud is nothing but the gas of working fluid. Heat is being dissipated in the form of steam.
Swimming pool heat exchanger
A swimming pool heat exchanger transfers heat from a hot water stream to the cooler pool water stream without making them come in direct contact to each other.
Hydraulic oil cooler
A hydraulic oil cooler cools the hydraulic oil. These can be used in power packs, power washers and engines, almost anywhere the hydraulic oil is used. The hydraulic oil needs to be cooled because without cooling, the oil may catch fire due to higher temperatures and may be fatal for the operator as well as the machinery.
Boilers
The most common use of heat exchangers is in boilers. The boilers use heat exchangers to heat the liquid water such that it gets converted in to steam. In the entire phase change process, the temperature of the liquid/gas remains the same meaning it is an isothermal process. We have already discussed in the above sections how heat exchangers work inside a boiler.
Water jackets
In water jackets, water is used to cool or heat the exhaust running through the engine. We can see jacketing in rocket engines, the hot exhaust gases heat up the fuel and then the fuel is sent back for combustion. This increases the combustion efficiency of the rocket engine. In automobiles, water jacketing is used to cool the engine and prevent excessive heat loss. The water jacketing brings down the engine temperature.
Other types of heat exchangers
On a broader basis, there are many more types of heat exchangers. They are given in the list below-
Heat exchangers are a pivotal part of many devices and systems that we use daily. They are found in home heating systems, car engines, and industrial processes. But what exactly is a heat exchanger, and how does it work? Let’s delve into the fascinating world of heat exchangers.
Definition of Heat Exchanger
A heat exchanger is a device designed to efficiently transfer (or exchange) heat from one medium to another. These mediums are usually separated by a solid wall to prevent mixing or contamination. The mediums can be gas, liquid, or even solid, and can be the same (e.g., air to air) or different (e.g., air to water).
Main Purpose of Heat Exchanger
The primary purpose of a heat exchanger is to transfer heat between two or more fluids, achieving desired temperatures without letting the substances mix with each other. For instance, in a car engine, a heat exchanger uses air to cool down the hot engine coolant. Similarly, in a home heating system, a heat exchanger transfers heat from the furnace‘s hot air to the cooler air circulating in the building.
Importance of Heat Exchanger
Heat exchangers play a crucial role in many applications. They are vital for thermal efficiency, heat recovery, and temperature control in various systems. Here are some reasons why heat exchangers are so important:
Energy Efficiency: Heat exchangers can recover waste heat from industrial processes, improving overall energy efficiency. This heat recovery process can significantly reduce energy costs and environmental impact.
Temperature Regulation: In systems like car engines or industrial machinery, heat exchangers help maintain optimal operating temperatures, preventing overheating and potential damage.
Comfort and Safety: In buildings, heat exchangers ensure a comfortable indoor temperature and provide hot water. They also play a role in systems like refrigerators and air conditioners.
Industrial Processes: Many industrial processes require precise temperature control. Heat exchangers provide this control, ensuring product quality and safety.
Heat Exchanger Design and Operation
The design of a heat exchanger depends on its intended application. Key factors include the types of fluids involved, the desired temperature change, and the available space. Heat exchanger design also considers the heat transfer coefficient, heat capacity rate, and potential for fouling (build-up of unwanted material on the heat exchanger surfaces).
The operation of a heat exchanger involves fluid flow through tubes or channels. The heat transfer process occurs as one fluid heats up the exchanger’s walls(the “hot” fluid), and another fluid cools it down (the “cold” fluid). The efficiency of this process depends on the materials used, the flow rates, and the temperature difference between the fluids.
Regular inspection and cleaning are essential for maintaining heat exchanger performance. Over time, fouling can reduce the heat transfer efficiency and cause a pressure drop. In severe cases, it can lead to system failure or even a dangerous situation like a crack in the exchanger.
Maintenance tasks include cleaning the heat exchanger tubes and checking for signs of wear or damage. If necessary, repair or replacement of components may be required. Proper heat exchanger maintenance can extend the device’s lifespan, improve its efficiency, and prevent costly breakdowns.
Heat Exchanger Applications
Heat exchangers have a wide range of applications. They are used in heating, ventilation, and air conditioning(HVAC) systems, power generation, waste heat recovery, and many industrial processes. Some specific examples include:
Home Heating Systems: A heat exchanger transfers heat from the furnace to the air circulated throughout the home.
Car Engines: Heat exchangers (or radiators) cool the engine coolant, preventing the engine from overheating.
Power Plants: Heat exchangers transfer heat from the combustion process to produce steam, which drives the turbines.
Refrigeration Systems: Heat exchangers remove heat from the refrigerant, allowing it to cool the inside of the refrigerator or air conditioner.
Understanding the Function of Heat Exchangers
Heat exchangers are crucial components in a wide range of applications, from air conditioning systems in buildings to engines in vehicles. They function by transferring heat from one fluid to another, without the two fluids coming into direct contact. This heat transfer process is fundamental to the operation of many systems and is governed by the heat transfer coefficient.
Heat Transfer Coefficient
The heat transfer coefficient (h) is a measure of the heat transfer rate between the surface of the heat exchanger and the fluid flowing through it. It is influenced by several factors, including the type of fluid, its velocity, and the surface area of the heat exchanger. The higher the heat transfer coefficient, the more efficient the heat exchanger is at transferring heat.
For instance, in a heat exchanger where water is used to cool a system, a higher heat transfer coefficient would mean that the water can absorb more heat from the system, thus cooling it more effectively.
Heat Transfer Functions
Heat transfer in a heat exchanger can occur through three main mechanisms: conduction, convection, and radiation.
Conduction is the process of heat transfer through a solid material. In a heat exchanger, this occurs when heat is transferred from the hot fluid to the heat exchanger material (usually metal), and then to the cold fluid.
Convection is the process of heat transfer through a fluid (liquid or gas) caused by the fluid’s movement. In a heat exchanger, this occurs when the hot and cold fluids flow over the heat exchanger’s surfaces.
Radiation is the process of heat transfer through electromagnetic waves. It plays a minor role in most heat exchangers, but can be significant in high-temperature applications, such as furnaces.
How Heat Exchangers Function
The operation of a heat exchanger is based on the principle of heat transfer. In a typical heat exchanger, two fluids of different temperatures flow through separate channels. The hot fluid loses heat to the heat exchanger material, which then transfers the heat to the cold fluid. This process continues until the temperatures of the two fluids equalize or until the heat exchanger is shut off.
For example, in a car engine, a heat exchanger (or radiator) uses air to cool the engine coolant. The hot coolant flows through tubes in the radiator, transferring heat to the radiator’s metal fins. Air flowing over the fins then absorbs the heat, cooling the coolant.
Heat Transfer Function of Time
The rate of heat transfer in a heat exchanger can change over time due to several factors, including changes in the temperatures and flow rates of the fluids, fouling of the heat exchanger surfaces, and degradation of the heat exchanger materials.
For instance, the buildup of scale or other deposits on the heat exchanger surfaces (a process known as fouling) can reduce the heat transfer coefficient, leading to a decrease in the heat exchanger’s performance over time. Regular cleaning and maintenance of the heat exchanger can help to mitigate this issue.
Heat exchangers are devices that facilitate the transfer of heat from one medium to another. They are widely used in various industries, including HVAC, automotive, and power generation. The heat transfer process in these devices is crucial for their thermal efficiency. Now, let’s delve into the different types of heat exchangers.
Double Pipe Heat Exchanger
The double pipe heat exchanger, also known as a pipe-in-pipe system, is the simplest type of heat exchanger. It consists of one pipe inside another larger pipe. One fluid flows through the inner tube while the other flows through the annular space between the two tubes. The heat transfer occurs through the wall of the inner tube.
The design of this type of heat exchanger is straightforward and easy to install. However, its heat transfer coefficient is relatively low, which means it’s not as efficient as other types. Despite this, it’s commonly used in industries due to its simplicity and low cost. Regular inspection and cleaning are essential for maintaining its performance and preventing fouling.
Baffle Heat Exchanger
The baffle heat exchanger is a type of shell and tube heat exchanger. It features a series of baffles or metal plates that direct the fluid flow across the tube bundle. This design increases the turbulence of the fluid, enhancing the heat transfer process and improving the exchanger’s thermal efficiency.
However, the increased turbulence also results in a higher pressure drop, which can affect the overall efficiency of the system. The baffle design also makes the exchanger more prone to fouling, requiring regular maintenance and cleaning. Despite these challenges, baffle heat exchangers are widely used due to their high heat transfer rates and robustness.
Plate Heat Exchanger
The plate heat exchanger consists of a series of thin, corrugated metal plates stacked together. The plates create channels for the fluids to flow between them. The corrugated design increases the turbulence of the fluids, enhancing the heat transfer process.
Plate heat exchangers are known for their high thermal efficiency, compact size, and low fouling tendency. However, they can be challenging to clean and maintain, and they may not be suitable for high-pressure applications. They are commonly used in HVAC systems, power plants, and food processing industries.
Tube Heat Exchanger
Tube heat exchangers, also known as shell and tube exchangers, are the most common type of heat exchanger. They consist of a shell (a large pressure vessel) with a bundle of tubes inside it. One fluid flows through the tubes, and the other flows outside the tubes but inside the shell.
Tube heat exchangers are known for their robust design, high heat transfer rates, and ability to handle high pressures and temperatures. However, they are relatively large and require more space compared to other types of exchangers. They also require regular inspection and cleaning to prevent fouling and maintain their performance.
Heat exchangers are integral components in a variety of systems and industries, from home heating to large-scale industrial processes. They function by transferring heat from one fluid to another, without the two fluids directly interacting. This heat transfer process is central to their operation and efficiency. Let’s delve into the specifics of how heat exchangers function in various applications.
Heat Exchanger Function in Furnace
In a furnace, the heat exchanger plays a crucial role. It separates the combustion process from the breathable air in your home, ensuring safety and efficiency. The furnace burns fuel (like gas or oil) to produce heat. This heat warms up the metal walls of the heat exchanger. As cool air from your home flows over the warm exchanger, it absorbs the heat and is then redistributed back into your home.
This process is a prime example of a heat exchanger’s ability to transfer heat from one medium (the hot furnace gases) to another (the cool air in your home) without the two ever coming into direct contact. This is crucial not only for thermal efficiency but also for safety, as it prevents harmful combustion gases from entering your home’s air supply.
Heat Exchanger Function in Chilled Water System
In a chilled water system, a heat exchanger is used to cool down water that will be circulated throughout a building for air conditioning purposes. The heat exchanger uses refrigerant to absorb heat from the water, thus cooling it down before it is sent through the building’s air handling units.
The heat absorbed by the refrigerant is then expelled outside the building, ensuring that the interior remains cool. This is a prime example of a heat exchanger’s application in heat recovery and its role in maintaining a building’s thermal comfort.
Heat Exchanger Function in Oil and Gas Industry
In the oil and gas industry, heat exchangers are used in a variety of ways. For instance, they are used in the process of refining crude oil. The crude oil is heated in a furnace, and then it flows into a heat exchanger where it is cooled by water or air.
Heat exchangers are also used in natural gas processing plants to cool and condense the gas. This is a critical step in the process, as it allows for the removal of impurities and the collection of valuable byproducts.
In these applications, heat exchangers must be made from materials that can withstand high temperatures and pressures, such as certain types of metal. Regular inspection and maintenance are also crucial to ensure their performance and longevity.
Heat Exchanger Function in Chiller
In a chiller system, a heat exchanger is used to transfer heat from the liquid being cooled (usually water) to the refrigerant. The refrigerant absorbs the heat from the water, causing it to evaporate. The now cool water is then circulated throughout the building for cooling purposes.
The refrigerant, now in a gaseous state and carrying the absorbed heat, is then compressed and sent to another heat exchanger. Here, it releases the heat it absorbed earlier, condenses back into a liquid, and the cycle begins anew.
Car Heat Exchanger Function
In a car, a heat exchanger, often referred to as a radiator, is used to cool the engine. As the engine runs, it generates a lot of heat. If this heat is not properly managed, it could lead to engine overheating and potential damage.
The car’s heat exchanger uses coolant to absorb heat from the engine. The hot coolant then flows through the radiator where it is cooled by air flow. The cooled coolant is then recirculated back into the engine, and the process repeats.
Components of Heat Exchangers
Heat exchangers are devices designed to transfer heat from one medium to another. They are critical in many industrial processes, including power generation, chemical processing, and HVAC systems. The main components of a heat exchanger include the shell, tubes, tube sheets, baffles, and tie rods. Now, let’s delve into the details of these components and their roles in the heat transfer process.
Shell
The shell is the outer casing of a heat exchanger. It is typically made from a durable material like metal to withstand the pressure and temperature of the heat transfer process. The shell houses the tubes and other internal components, and it also directs the flow of the shell-side fluid.
Tubes
The tubes are the primary heat transfer surface in a heat exchanger. They are usually made from materials with high thermal conductivity, such as copper or stainless steel, to facilitate efficient heat transfer. The fluid flowing inside the tubes is known as the tube-side fluid. The design of the tubes, including their diameter, length, and arrangement, significantly affects the heat exchanger’s performance.
Tube Sheets
Tube sheets are the plates that hold the tubes in place. They are typically made from the same material as the tubes to prevent differential thermal expansion, which could lead to cracking or other damage. The tube sheets also prevent the tube-side and shell-side fluids from mixing.
Baffles
Baffles are components installed inside the shell to direct the flow of the shell-side fluid across the tubes. This increases the fluid’s velocity, enhancing the heat transfer coefficient and improving the heat exchanger’s thermal efficiency. However, baffles also cause a pressure drop, which must be considered in the heat exchanger design.
Tie Rods
Tie rods are used to hold the baffles in place and maintain the structural integrity of the heat exchanger. They are usually made from strong, heat-resistant materials.
Heat Exchanger Types
There are several types of heat exchangers, including shell and tube, plate, and regenerative heat exchangers. Each type has its unique design features, advantages, and applications.
Shell and Tube Heat Exchangers
Shell and tube heat exchangers are the most common type. They consist of a shell housing a bundle of tubes. One fluid flows inside the tubes, while the other flows outside the tubes but inside the shell. This design is versatile and can handle a wide range of temperatures and pressures.
Plate Heat Exchangers
Plate heat exchangers consist of a series of thin, corrugated plates stacked together. The fluids flow in alternate channels between the plates, allowing for efficient heat transfer. Plate heat exchangers are compact and efficient, but they are not suitable for high pressure or temperature applications.
Regenerative Heat Exchangers
Regenerative heat exchangers, also known as heat recovery units, use the same fluid for heating and cooling. The fluid is alternately heated and cooled in a cyclic process, making these units highly efficient.
Heat Exchanger Applications
Heat exchangers are used in a wide range of applications, from heating homes to cooling industrial processes. Here are a few examples:
HVAC Systems: Heat exchangers are used in HVAC systems to transfer heat between the air inside a building and the outside air, or between the air and a coolant fluid.
Power Generation: In power plants, heat exchangers are used to convert the heat energy from burning fuel into electrical energy.
Chemical Processing: Heat exchangers are used in chemical plants to control the temperature of chemical reactions, which can affect the reaction rate and product yield.
Automotive: In cars, heat exchangers are used to cool the engine and the passenger compartment.
Heat Exchanger Maintenance and Operation
Proper maintenance and operation are crucial for the performance and longevity of a heat exchanger. This includes regular cleaning to prevent fouling, inspection for damage or wear, and repair or replacement of worn-out components. The fluid flow rates, temperatures, and pressures should also be monitored and controlled to ensure optimal heat transfer and prevent damage to the heat exchanger.
Heat Exchangers in Different Systems
Heat exchangers are integral components of many systems, facilitating the heat transfer process from one medium to another. They are designed to optimize thermal efficiency, and their applications are diverse, ranging from heating homes to cooling large industrial processes.
Refrigeration System
In a refrigeration system, heat exchangers are used to cool a substance or space. The refrigerant, often a fluid, absorbs heat from the substance or space that needs to be cooled and then flows through the heat exchanger. Here, the refrigerant releasesthe absorbed heat, thereby cooling down before it is recycled back into the system.
The heat exchanger design in a refrigeration system is crucial for its efficiency. The heat exchanger tubes must be made of a material with high thermal conductivity, such as copper or aluminum, to facilitate the heat transfer process. Moreover, the tubes should be kept clean to prevent heat exchanger fouling, which can reduce thermal efficiency and increase the heat exchanger pressure drop.
Chillers are another application of heat exchangers. They use a refrigeration cycle to cool water, which can then be used in air conditioning systems or industrial processes. The chiller’s evaporator acts as a heat exchanger, absorbing heat from the water and transferring it to the refrigerant.
The heat exchangerheat capacity rate, which is the product of the mass flow rate of the fluid and its specific heat capacity, is a key factor in the performance of the chiller. A higher heat capacity rate means that the heat exchanger can absorb more heat, leading to a cooler output water temperature.
Air Conditioning System
In an air conditioning system, heat exchangers are used to cool and dehumidify the air. The system’s evaporator coil acts as a heat exchanger, absorbing heat from the indoor air and transferring it to the refrigerant. This cools the air, which is then circulated back into the building.
The heat exchanger operation in an air conditioning system is influenced by several factors, including the heat exchanger heat transfer coefficient, the heat exchanger heat load, and the fluid flow rate. Regular heat exchanger maintenance, such as cleaning and inspection, is necessary to ensure optimal performance and prevent issues such as heat exchanger fouling or heat exchanger repair needs.
Crude Oil Cooling
Heat exchangers are also used in the petroleum industry for crude oil cooling. The hot crude oil flows through the heat exchanger tubes, transferring its heat to a cooling medium, usually water or air. This cools the crude oil, making it easier to transport and process.
The heat exchanger materials used in this application must be resistant to corrosion and able to withstand high temperatures and pressures. Moreover, the heat exchanger design must ensure a high heat transfer rate to cool the crude oil efficiently.
Frequently Asked Questions about Heat Exchangers
Heat exchangers are integral components in a variety of systems, from home heating systems to industrial processes. They facilitate the transfer of heat from one fluid to another, enhancing thermal efficiency. Let’s delve into some frequently asked questions about heat exchangers.
Heat Exchanger Transfer Function
What is the function of a heat exchanger?
A heat exchanger’s primary function is to transfer heat between two or more fluids without them mixing. This heat transfer process can involve gases or liquids and can be used for both heating and cooling purposes. The fluids can be the same or different; for example, air to air, water to water, or air to water.
How does a heat exchanger work?
A heat exchanger works by allowing a hot fluid to flow past a cold fluid, separated by a solid wall (usually metal) to prevent mixing. The heat from the hot fluid is transferred through the wall and into the cold fluid, which becomes warmer. This process is governed by the heat transfer coefficient, which depends on the materials used, the fluid flow rates, and the surface area available for heat transfer.
What is heat exchanger efficiency?
Heat exchanger efficiency is a measure of how effectively the exchanger transfers heat from the hot fluid to the cold fluid. It is calculated by comparing the actual heat transfer to the maximum possible heat transfer. Factors that can affect efficiency include the heat exchanger design, the materials used, and the presence of any fouling (deposits that can build up on the heat exchanger surfaces and impede heat transfer).
Location of Heat Exchanger in a Furnace
Where is the heat exchanger located in a furnace?
In a furnace, the heat exchanger is typically located between the combustion chamber and the blower. The combustion gases heat up the exchanger, and then the blower pushes air across its surface. The air absorbs the heat and is then distributed throughout the building.
What happens if the heat exchanger in a furnace cracks?
If a heat exchanger cracks, it can allow combustion gases, including carbon monoxide, to leak into the building’s air. This situation is potentially dangerous and requires immediate attention. Regular heat exchanger inspection and maintenance can help prevent such issues.
Heat exchangers are used in a wide range of applications. In homes, they are used in heating systems to transfer heat from a furnace or boiler to the air or water used for heating. In cars, they are used in the radiator to remove heat from the engine coolant. In industrial settings, they can be used for process cooling, heat recovery, and many other applications.
What is a regenerator in the context of heat exchangers?
A regenerator is a type of heat exchanger that temporarily stores heat from a hot fluid and then releases it to a cold fluid. This process is used in some industrial processes and power generation systems to improve thermal efficiency.
What materials are used in heat exchangers?
Heat exchangers can be made from a variety of materials, including metals like steel, copper, and aluminum, which have high thermal conductivity. The choice of material depends on the heat exchanger design, the fluids being used, and the operating conditions.
Frequently Asked Questions
1. What is the importance of a heat exchanger in thermal efficiency?
A heat exchanger plays a crucial role in enhancing thermal efficiency. It allows heat transfer from one medium to another without direct contact, minimizing energy loss and maximizing efficiency. It is used in various industries, including HVAC, oil and gas, and power generation, to improve energy conservation and process efficiency.
2. How does a heat exchanger function in the heat transfer process?
A heat exchanger functions by allowing heat to flow from a hot fluid to a cooler fluid without the two fluids coming into direct contact or mixing. This heat transfer process is facilitated by the exchanger’s material, which is typically metal due to its high thermal conductivity.
3. What is the main purpose of a heat exchanger in a chiller system?
In a chiller system, the heat exchanger’s main purpose is to transfer heat from the liquid being cooled to the refrigerant. This process cools the liquid, which can then be circulated through a system to absorb heat and cool equipment or conditioned spaces.
4. What types of materials are commonly used in a heat exchanger?
Heat exchanger materials must be thermally conductive to facilitate heat transfer. Common materials include various metals such as copper, aluminum, stainless steel, and titanium. The choice of material depends on factors like the type of fluids being used, the expected heat transfer rate, and the operating conditions.
5. How does a baffle heat exchanger function?
A baffle heat exchanger uses baffles, or obstructions, to direct the flow of fluid and increase the turbulence. This increased turbulence enhances the rate of heat transfer and improves the exchanger’s overall performance.
6. What are the key components of a heat exchanger?
The key components of a heat exchanger include the shell (outer casing), tubes (where one fluid flows), tube sheets, baffles, and headers. These components work together to facilitate efficient heat transfer.
7. How does a heat exchanger work in an oil and gas industry application?
In the oil and gas industry, heat exchangers are used to control process temperatures. They can heat crude oil to reduce its viscosity for easier transport, or cool down gases and liquids to safe temperatures before storage and transport.
8. Where is the heat exchanger located on a furnace?
In a furnace, the heat exchanger is typically located between the combustion chamber and the blower. It absorbs heat from the combustion gases and transfers it to the air that is blown through the HVAC system.
9. What is the role of a heat exchanger in a chilled water system?
In a chilled water system, the heat exchanger transfers heat from the chilled water to the refrigerant. This process cools the water, which can then be used to cool buildings or industrial processes.
10. How does the heat transfer function of a plate heat exchanger work?
A plate heat exchanger uses a series of thin, corrugated plates to transfer heat between two fluids. The plates are arranged to create a network of parallel flow channels. One fluid flows through the odd-numbered channels, and the other fluid flows through the even-numbered channels. The corrugations in the plates induce turbulence, which enhances heat transfer and efficiency.
across a temperature difference; 
