Calculating CFM of Air Needed for Cooling

It’s easy to know that EXAIR’s vortex tubes can be used to cool down parts and other items, but did you know that our air knifes can be used to cool down these same things? It’s the same process that we do every day to cool down hot food by blowing on it. Every molecule and atom can carry a set amount of energy which is denoted by physical property called Specific Heat (Cp); this value is the ration of energy usually in Joules divided by the mass multiplied by the temperature (J/g°C). Knowing this value for one can calculate the amount of air required to cool down the object.

Starting out you should note a few standard values for this rough calculation; these values are the specific heat of Air and the specific heat of the material. Using these values and the basic heat equation we can figure out what the amount of energy is required to cool. The specific heat for dry air at sea level is going to be 1.05 J/g*C which is a good starting point for a rough calculation; as for the specific heat of the material will vary depending on the material used and the composition of the material.

Heat Flow Equation
Using the standard heat equation above add in your variables for the item that needs to be cooled down. In the example I will be using a steel bar that is 25 kg in mass rate and cooling it down from 149 °C to 107 °C. We know that the specific heat of steel is 0.466 J/g°C therefore we have everything needed to calculate out the heat load using air temperature of 22 °C.
Calculating Joules/min
Using the heat rate, we can convert the value into watts of energy by multiplying the value by 0.0167 watts/(J/min) which gives us 16,537.18 watts. Furthermore, we can then convert our watts into Btu/hr which is a standard value used for cooling applications. Watts are converted into Btu/hr by multiplying by 3.41 Btu/hr/watt, giving us 56,391.77 Btu/hr.
Converting Joules to Btu/hr
Once you have Btu/hr you can plug the information into a re-arranged Cooling power formula to get the amount of CFM of air required for cooling.
Calculating CFM
As you can see in order to cool down this steel bar you only need to 343 CFM of air at 72°F. This can be done very easily and efficiently by using one of EXAIR’s Air Amplifiers or Air Knife. Sometimes you don’t need to use a vortex tube to cool down an object; sometimes simply blowing on it is good enough and its pretty simple to calculate out which product would fit your application the best.

If you have any questions about compressed air systems or want more information on any EXAIR’s of our products, give us a call, we have a team of Application Engineers ready to answer your questions and recommend a solution for your applications.

Cody Biehle
Application Engineer
EXAIR Corporation
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Offshore Pipe Welding Cooled with Series of EXAIR Super Air Nozzles

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EXAIR model 1122 Flat Super Air Nozzles used to provide cooling blow off.

One of the services we provide to our customers, is assistance in selection of the most suitable product solution for their application.  For most applications we have solutions readily available from stock, though that wasn’t the case in the solution shown above.

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This unique blow off solution cools welds on 450mm (18″) pipes.

This configuration of model 1122 Flat Super Air Nozzles is used to cool pipe welds in an application located off the coast of France.  Pipes with an OD of 450mm (~18”) are welded together, and in order for the welds to be of the highest quality, they must be cooled.  To cool the welds, this customer needed to blow ambient temperature air over the pipes.

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Closeup of nozzles used in this application

Initially, we explored a Super Air Wipe solution.  A Super Air Wipe can provide a full 360° blow off for this pipe, but there was an aspect of the application which led to a better solution through nozzles; an irregularity in position of the pipe.

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Another view of the 1122 Flat Super Air Nozzles

The diameter of the pipes in this application is relatively constant, but there is some fluctuation in position as the pipe is moved.  If using a Super Air Wipe, this could mean contact with a precision machined surface, resulting in a change to the performance of the unit.  But, what if we could find a way to allow the blow off solution to have some “flex”.

swivels
Flat Super Air Nozzles with swivels provide the unique solution needed for this application.

“Flex” in this solution is provided through the use of EXAIR model 9053 swivel fittings, shown above with red circles, each used to mount an 1122 Flat Super Air Nozzle (16 of each).  These allow for proper placement of the nozzles, and also for movement if anything should ever contact the blow off solution.

An additional benefit of the EXAIR 1122 nozzles used in this application, is the ability to exchange shims inside the nozzle to increase or decrease the amount of force delivered from the nozzle.

Understanding the critical requirements of the customer led to this semi-custom solution using EXAIR Super Air Nozzles.  If you‘d like to explore an EXAIR blow off solution for your application, contact an EXAIR Application Engineer.

Lee Evans
Application Engineer
LeeEvans@EXAIR.com
@EXAIR_LE

Calculating Air Flow to Cool Manufacturing Processes

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This application needed a way to cool steel plates from 150C to 70C

I’ve written before about using ambient air to cool an application, calculating the required airflow to maintain a temperature.  And, I was recently contacted by an end user in India in need of a way to cool electromagnets in a similar application.

The need was to reduce the temperature of high manganese steel plates (dimensions of 1800mm x 800mm x 500mm) from 150°C to less than 70°C, using air at 40°C.  These steel plates have a specific heat of 0.5107896 J/g°C, weigh 120kg each, and protect the coil and insulation of the electromagnets in this process.  So, just as was the case in previous applications, we started with the process shown below.

heat load calc process
Heat load calculation process

In doing so, we calculated a heat load of 279,245 BTU/hr., which will require an air volume of 1,805 CFM to cool as needed.  (Click the image below for an expanded view of the calculations)

Electromagnet calculations
Heat load calculations

The recommendation to provide this cooling was the use of (6) 120022 Super Air Amplifiers, operated at 80 PSIG and installed along the length of the plates to distribute airflow.  As we can see in the chart below, each 120022 Super Air Amplifier will move an air volume of 341 CFM at the outlet of the unit, making (6) of these units suitable for this application.  And, if we consider entrainment of additional ambient air at distances away from the outlet of the 120022 Super Air Amplifier, we can consider these units may cool the steel faster than the 1 minute cycle time used for calculation purposes.

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Super Air Amplifier performance chart

This application is a great example of how an engineered compressed air solution can remove process disturbances effectively, and efficiently solve problems.  If you have a similar application or even one that is entirely different, contact an EXAIR Application Engineer.

Lee Evans
Application Engineer
LeeEvans@EXAIR.com
@EXAIR_LE