Engineering

This article discusses about bending strength of steel. Bending strength is the ability of a material to resist or withstand the bending stress applied.

Strength is ability to withstand or resist a particular amount of stress. A material has a particular amount of strength, only that much stress it can withstand. Any amount of stress which exceeds the strength can lead to material failure. Simply put, the applied stress should be lesser than the strength of the material for minimizing failure.

What is bending strength?

Bending strength or flexural rigidity is the ability of a work piece to withstand bending stress. The flexural strength depends on the failure load, effective length of the work piece and the dimensions of the cross section of the beam.

Mathematically the bending strength is given as-

σ_b = M.y/I

where,

sigma is bending strength or maximum allowable bending stress that can be applied before fracture

M is the bending moment

I is the moment of inertia of the cross section of the work piece

What is bending stiffness?

Bending stiffness and bending strength are not same. As discussed above, bending strength is the ability of the work piece to withstand a given amount of bending stress.

On the other hand, bending stiffness tells the amount of deflection the work piece will undergo under a given amount of bending stress. The bending stiffness depends on moment of inertia of cross section the work piece and the modulus of rigidity of the material of work piece.

Mathematically, bending stiffness can be given as-

Bending stiffness = E x I

Where, E is the Young’s modulus or modulus of rigidity

I is the moment of inertia of the cross section of the work piece

Bending strength of stainless steel

The bending strength not only depends on the material but the dimensions of the work piece too. The table below shows the bending strength of a stainless steel bar.

Base metal	Bending strength (MPa)
700 W	267
700 F	817
900 W	750
900 F	633

Bending strength of steel pipe

Steel pipes are used at a large scale in industries. It is very important to know the physical properties of steel pipe and the behaviour of these pipes under different types of loads.

Bending strength of steel pipe can be found using the formula given below-

σ = 32MD/π(D⁴-d⁴)

where,

D is the outer diameter of pipe

d is the inner diameter of pipe

Pipe is simply a hollow cylinder.

Bending strength of steel plate

Let us assume a steel plate having a depth d and breadth b. The permissible load acting it is P.

The bending strength of this steel plate is given by following-

σ = 3M/bd²

Plate has a rectangular cross section where,

b is the breadth

d is the depth of rectangle

M is the bending moment

Bending strength of steel rod

Steel rods are widely used in construction industry for reinforcement purpose. They are used in aircrafts as well. To avoid construction failure, it is very important to know the mechanical properties of rods being used.

Let us consider a steel rod of diameter d. The bending strength can be given by the following formula-

σ = 32M/πd³

Bending strength of steel bar

Let us assume a circular steel bar of diameter d having permissible force value P. Then the bending strength formula for steel bar will be same as that of steel rod.

The bending strength of steel rod is discussed in above sections.

Bending strength of steel channel

Let us consider a “I” steel channel as shown in the figure below.

To find the moment of inertia of the entire cross section, we add the individual moment of inertia of the parts A, B and C.

The bending strength of this channel can be written from the basic formula. That is,

σ_b =M.y/I

Bending strength of steel square tube

Square tube is simply a hollow square cross section tube. These tubes are used in construction industry and interior designing. It is very important to know the bending strength of square tube before taking into use.

The section modulus of a square tube can be given by-

σ = bd³/3

Hence the bending strength becomes,

σ = 3M/ bd³

How to calculate bending strength of steel

Bending strength can be found using flexural test. Flexural tests can be performed with a single axial load, three point loading set up and four point loading set up.

Let us consider a three point set up. The given data for the set up is given below-

The work piece is a rectangular bar having breadth of 10cm and depth of 10 cm. The length of the bar is 1m and the load at failure is 10kN.

To find the bending strength of in a three point flexural test, following formula is used-

σ = 3FL/ 2bd²

Substituting all the values in above formula we have,

Bending strength= 15 MPa

How to calculate yield strength of steel

Yield strength of any material can be found using a tensile test on universal testing machine. The machine pulls the work piece from its ends and provides us with a stress strain graph from which we can easily make out the tensile strength of the material.

Let us consider the given data-

Load at failure- 5kN

Area of cross section- 1mm^2

The yield strength can be calculated using the formula-

S_yt = P/A

Substituting the values in above equation we get,

Yield strength= 500Mpa

The diagram obtained from this test is commonly called as stress strain diagram.

Stress strain diagram

The graph which shows relationship between stress and strain is called as stress strain diagram.

This graph gives information like yield point, proportional limit, fracture point and ultimate tensile strength of the specimen. This diagram makes it easy to measure the mechanical properties of the specimen.

In this article we will discuss about the “Low discharge superheat” and its related factors.

The Low discharge superheat is when the refrigerant liquid flooding to the compressor or in the screw compressor in the very low oil temperature. The insufficient amount of air flows through the evaporator coils causes low discharge superheat.

With a high ambient temperature the refrigerant liquid go back to the compressor which causes the leakage to the heat exchangers and liquid injection device if it is fitted. This condition also point to an Actuator or Check valve issue. A dirty air filter, evaporator coil or air flow causes discharge measure low. The heat which is carried by the coils is low which result in low discharge superheat.

Process:

The low discharge superheat can be obtaind by the following,

• At first we need to run the refrigeration system minimum for 10 min.
• When the system running for a while we have to attach the pipe clamp thermocouple in one side of the refrigerant line which actually separate the thermal expansion valve and the condenser discharge valve.
• Connect with the refrigerant manifold gauges with discharge service valve.
• Read refrigerant manifold gauge to check the discharge service valve.
• Check the thermocouple temperature using a digital thermometer.
• Measure the pressure chart and temperature for the refrigerant.
• Now need to turn over the condenser pressure reading to a condenser saturation temp.
• Pressure takes from the thermocouple and the temperature of the condenser saturation from it.

Formula:

The low discharge superheat is calculated in the way as any other discharge superheat calculated on a system, by measuring the low discharge superheat and have to subtract the suction superheat and then then leaves with a figure of how much low superheat the compressor has given through compression and mechanical/electrical inefficiencies.

Work:

Prevent damage the machine from worn rings, acid formation and oils breakdowns and make it run more effective.

Example:

Let, the Discharge Temperature = 152, Condensing Sat. Temp. = 91

Then the discharge superheat would be = 61

Exhaustive facts:

In the discharge superheat refrigerant is saturated with oil causes low discharge superheat. Low discharge superheat can causes low temperature to the compressor, if the condition goes more low and low then it could damage the compressor too.

What does a low superheat indicate?

The low discharge of a system means refrigerant liquid floods to the compressor for the load is present through the evaporator coil.

When excess amount of refrigerant is enter into the coil or excessive amount of heat present into coil to vaporize the refrigerant properly,that time this condition appear.

Read more about Low Superheat: Important Terms and 3 FAQs

What causes low discharge superheat?

• Flooding to the compressor with the refrigerant liquid through the evaporator coil. The situation mostly happened when the expansion valve overfeeding to the evaporator or faulty of an actuator.
• Pressure is too high.
• Low evaporator air flow.
• Temperature is low.
• The shape of the system is over sized during discharge of a superheated liquid.
• Reduced airflow through the evaporator.
• Due to low cooling water flow or dirty tubes the refrigerant charge may be excess.
• Over charged of refrigerant liquid or oil.

Low discharge superheat trane chiller:

With the help of the compressor’s discharge temperature the inside condition of the refrigeration or air conditioning system easily can be recognize. In other term the discharge temperature describe as a measurement of the superheated refrigerant’s vapour temperature.

Formula-

Discharge Superheat = Temperature of discharge connection – Saturated temperature of the liquid line.

Purpose:

This is used to point an actuator or check the valve issue. The Trane chillers are used to system for improve the efficiency mechanical or electrical to the compressor,deliver the correct amount of the temperature, humidity. During the flooding of the refrigerant liquid or oil the sound of the system is increases, with the Trane chillers the sound became less which impact is good for the environment .The Trane chillers deliver ventilation for the space and also helps to minimize the operating cost.

York yvaa low discharge superheat:

The low discharge superheat faults due to reason of the quantity of oil in the oil separator causes York Yvaa low discharge superheat. For this reason the oil charge is reduced in these specific circuits to correct the nuisance superheat trips. The change is only applicable to the circuits.

Procedure:

• The first step is to identify the unit and the amount of the oil. The oil should be taken as that much quantity with which it could be removed as per the corresponding compressor.
• As per the correct size the compressors are verified.
• Need to walkout the unit.
• After that need to discharge the unit.
• A container is used which should be have measuring indicators gradually.
• In the next step required oil is removed from the container.
• The oil is separate from the compressor on the oil line.
• In the starting if the refrigerant was removed from the low discharge superheat then make sure to correct the refrigerant level.
• Adding the adjusted refrigerant to the system.
• Apply unit to the system.
• For about one hour the unit should be operate at full load.
• Finally need to note down the oil level from the oil separator.

York low discharge superheat:

Low discharge superheat usually the situation occurs because of overcharge of refrigerant or overcharge of oil. Both condition gives lower discharge temperature. Once the refrigerant is saturated with oil low discharge will continue to occur.

Low discharge superheat sensor:

In the low discharge superheat all chillers will have a certain amount of the oil in the refrigerant, a little amount of oil is good but the system but too much is not good for the entire system. An excess amount of present of oil can cut blade from the impeller and reduce the efficiency of the compressor and also minimize the percentage of the heat transfer. For the recovery from this unwanted situation in the low discharge superheat’s chillers recovery equipment is needed, the recovery equipment is called the low discharge superheat sensor.

The main purpose of the sensor is to sense the oil which is float on the top of the refrigerant. The low discharge superheat condition is happened when the refrigerant liquid flooding into the compressor, or in the case of screw compressor, low cold oil temperature.

Low discharge superheat in chiller :

In the application field after doing the investigation we could find that the performance of the chillers attached with an electronic expansion valve. The chillers mainly work in steady state and transient condition. .The chillers capacity works in both hot and cold starts.

In low pressure the chillers start to work, at this condition the refrigerant enter to the evaporator. In case of low discharge superheat the capacity is very fast. In the cooling condition the chillers leading to low off/on cycling losses. The expansion valve works on the both steady and transient state of the chillers.

The capacity of the chillers is about 25 kW.  The chillers mainly consists four components. The components are compressor, evaporator, expansion unit and condenser. Every chillers system has refrigerant.

What is good discharge superheat?

The temperature of the ideal discharge superheat is about 10K-15K.

Frequently Asked Questions:

Q.What is low discharge superheat?

When a little amount of air could passes to the system for the reason of stopping the head load entry through the evaporator coils,which occur low discharge superheat.

The low discharge indicates that the quantity of refrigerant liquid or oil present in the compressor.

Dive into our comprehensive guide designed to clarify your doubts on ‘How to Calculate Superheat.’ This article provides step-by-step instructions, practical examples, and essential tips to accurately measure superheat in various systems, ensuring a clear understanding of this crucial HVAC concept.

It is calculated by obtaining the difference between two temperatures. The one temperature is the outlet temperature of the evaporator, and the second temperature is converted with pressure.

The temperature measurement is done by using the contact type thermometer.

The superheat level indicates the level of the refrigerant present in the evaporator. If the superheat is higher than the average level, the refrigerant is less than the required level in the evaporator.

The following are the reason for the lower refrigerant in the system,

• The technician has charged low refrigerant than an actual level requirement
• the device resists refrigerants like orifices, thermocouples etc.
• The heat load on the evaporator is higher than the average level

How to calculate target superheat?

The target superheat of the air conditioning system can be obtained by the following.

The target can be calculated with wet bulb temperature near to evaporator inlet and the outside dry bulb temperature.

After obtaining both temperatures, the following formula calculates the target superheat.

Target superheat = (3 * Wet bulb temperature – 80 – Dry bulb temperature)/2

The instrument used for the indoor wet bulb temperature measurement is a digital psychrometer. The instrument used for outside dry bulb temperature measurement is the digital temperature measuring instrument.

The dry bulb temperature remains same in the most case. The target can vary with the change in the wet bulb temperature. At the time of refrigerant charging, the wet bulb temperature is changing.

To obtain proper refrigerant charging, the target superheat is maintained near the actual superheats.

Lets’s understand target superheat with the following calculation,

Suppose, Wet bulb temperature = 64 ° F

Dry bulb temperature = 86 ° F

An equation to calculate target superheat

Target superheat = (3 * Wet bulb temperature – 80 – Dry bulb temperature)/2

Target superheat = (3 * 64 – 80 – 86)/2

Target superheat = (192 – 80 – 86)/2

Target superheat = (26)/2

Target superheat = 13° F

How to calculate superheat in a freezer?

The calculation of the superheat in the freezer is similar to the refrigerator.

The superheat in the freezer is the difference between saturation temperature and freezer outlet temperature.

A pressure-temperature chart obtains the saturation temperature. The evaporator’s outlet temperature is measured with a digital thermocouple. Take the difference between both temperatures.

The answer to the difference is the value of the superheat for the freezer.

How to calculate superheat in a chiller?

The superheat of the chiller can be calculated with the following steps

• Identify the suction line for measurement of pressure.
• To obtain the pressure of the suction line, Fix the pressure gauge near the condenser coil.
• Attach the thermocouple at the outlet of the evaporator coil. The service port is provided for the thermocouple.
• Note the reading of pressure after the system achieves steady flow.
• Note the reading of the temperature at the same time.
• Convert the reading of pressure into the corresponding temperature using a pressure-temperature saturation chart.
• Take the difference between the corresponding temperature and the evaporator’s outlet temperature reading.
• The answer to the difference is the value of the superheat.

This process of calculating the superheat remains the same for refrigeration and another similar system.

How to calculate superheat on a heat pump?

The heat pump is functioning opposite to the refrigerant. The superheat can be calculated with the following steps.

• Identify the suction line in the system as the suction line always has more cross-sectional area than another line
• To measure the suction line pressure in the system, install the pressure gauge neat to the condenser coil.
• Attach the temperature measuring device to the outlet of the evaporator coil. The service port is provided for the measuring device.
• Note the reading of pressure after the system achieves steady flow.
• Note the reading of the temperature at the same time.
• Convert the reading of pressure into the corresponding temperature using a pressure-temperature saturation chart.
• Take the difference between the corresponding temperature and the evaporator’s outlet temperature reading.
• The answer to the difference is the value of the superheat.

This process of calculating the superheat remains the same for refrigeration and another similar system.

For example :

If the low side pressure reading of the gauge is 120 PSIG.

The corresponding conversion of the pressure into temperature with a pressure-temperature chart. The value of temperature is 42 ° F.

The temperature measurement at the outlet of the evaporator is 50 ° F.

Now, take a difference between the corresponding temperature and the saturation temperature at the evaporator.

Superheat = Corresponding temperature at the low side – Temperature measured at the evaporator

Superheat = 50 – 42

Superheat = 8 ° F

So, With these simple steps, we can calculate the superheat of the system. The superheat in this example is 8 ° F.

How to calculate evaporator superheat?

The evaporator superheat calculation remains the same as in the refrigerator.

It is a difference between the measured evaporator outlet temperature and the corresponding saturation temperature.

The vapour line temperature is measured by identifying the large cross-section of the suction line. The temperature measurement is not the same in the refrigeration and the air conditioning.

The temperature and the low side pressure of the system are measured after achieving the steady flow condition. The measurement of the system will change if measured immediately after starting.

How to calculate superheated steam temperature?

The superheated steam is generally generated in the higher pressure boiler.

The degree of superheat is obtained by using either a steam table or Mollier diagram. The energy is required to raise the temperature of the saturated steam.

The temperature of the superheated steam is always greater than 100 ° C at the standard pressure condition.

How to calculate superheat R22?

The superheat in the system with R22 is calculated by the following equation

Total Superheat with R22 = Corresponding temperature at suction pressure – Temperature measured at a suction line or outlet of the evaporator

The superheat is nearby 10 ° F  in most cases. If the superheat is high, then it causes an increase in the heat of compression. This increase in temperature can affect the performance of the compressor. It is required to maintain and monitor the superheat continuously on the system.

How to calculate superheat 404a?

There are two types of superheat in the refrigeration system.

Total Superheat with R404a = Corresponding temperature at suction pressure – Temperature measured at a suction line or outlet of the evaporator

The refrigeration system can be analyzed with evaporator superheat, and the compressor superheat. The evaporator superheat always less than the compressor superheat. The compressor superheat also called the total superheat.

To obtain total superheat for R404, one has to measure temperature at the inlet of temperature with a temperature measuring device. Also, measure the pressure at that location.

The compressor superheat is the sum of the evaporator superheat and vapour line or suction line superheat.

The range of low side pressure for the R404 is nearby 20 psig in the usual case, and the inlet temperature of the compressor is 25° C approx.

For the safe operation of a system with R404 refrigerant, the recommended superheat should be in the range of 20° C to 30° C. If the superheat with R404 is more than the above value, then it can deteriorate the performance of the compressor or system.

The thermal expansion valve is the device used to control the superheat in the refrigeration system. The expansion of TXV can control the evaporator superheat. It can reduce the total superheat at the desired level for efficient working of the system.

How to calculate superheat 410a?

The superheat in the system with R410a is calculated by the following equation

Total Superheat with R410a = Corresponding temperature at suction pressure – Temperature measured at a suction line or outlet of the evaporator

To obtain total superheat for R410a, one must measure temperature at the inlet of temperature with a temperature measuring device. Also, measure the pressure at that location.