Tag: steel cooling

Calculating CFM of Air Needed for Cooling

Published on by Russ BowmanLeave a comment

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 other engineered compressed air products can be used to cool down these same things? It’s the same process as cooling down hot food by blowing on it. And we can use the physical properties of any material – whether it’s the massive billets of steel in the photo up top, or the bowl of soup to the right, to calculate the amount of air flow required to change a certain mass of the material from one temperature to another.

For any material, there’s a certain amount of energy required to cause a certain temperature change of a certain mass of the material. This property is called Specific Heat (Cp), and it’s commonly expressed in Joules per gram per degree Celsius (J/g°C), or Btu’s per pound (mass) per degree Fahrenheit. (Btu/lbm°F). The Specific Heat of the material allows us to calculate the amount of heat that has to be removed to cool it from its starting to its desired temperature, using a standard heat transfer equation:

q = mCp ΔT, where:

  • q is the amount of energy it’ll take to cause the temperature change.
  • m is the mass of the material that you want to change the temperature of.
  • Cp is the Specific Heat we talked about above.
  • ΔT is the starting temperature, minus the desired temperature.

Once we know the amount of heat to be removed, we can then apply units of time, and calculate the rate of cooling you’ll need to achieve in order to get the material to the temperature you want, in the time that you want. Let’s work through an example, using a piece of steel weighing 50lbs that needs to be cooled from 300 °F to 200°F:

q = m * Cp * ΔT, where:

  • m = 50lbm
  • Cp = 0.117 Btu/lbm°F
  • ΔT = 300°F – 200°F = 100°F
  • q = 50lbm * 0.117 Btu/lbm°F * 100°F = 585 Btu of energy (heat) to be transferred

Now, let’s say we have two minutes to cool this piece of steel:

585 Btu/2 minutes X 60 minutes/hr = 17,550 Btu/hr

That’s the rate of cooling required for this application. Now, we can use another equation that’s commonly used in the HVAC industry to determine the amount of room temperature (70°F) air flow that’ll remove that amount of heat. It’s called the cooling power formula:

Q̇ = 1.0746 * ΔT * ṁ, where:

  • Q̇ is the rate of heat transfer
  • 1.0746 is a constant
  • ΔT is the difference between the desired temperature and the air temperature
  • ṁ is the flowrate of air in cubic feet per minute

Since “Q̇” is the unknown value, we have to get to use a little algebra and rearrange the equation:

ṁ = Q̇/(1.0746 * ΔT), where:

  • Q̇ = 17,550 Btu/hr
  • 1.0746 = 1.0746 (remember, it’s a constant)
  • ΔT = 100°F – 70°F = 30°F
  • 17,550 Btu/hr/(1.0746 * 30°F) = 544.4 cubic feet per minute

Now, this assumes that equilibrium will be reached (i.e. all of the heat than CAN be transferred to the air flowing past the steel WILL be transferred), but that’s not going to happen. Depending on the geometry of the material to be cooled, there are ways to maximize the contact time between the material and the cooling medium. For example, constructing a tunnel over a section of a conveyor so the airflow can blow in the opposite direction that the material is traveling. Even then, though, it’s unlikely you’ll reach equilibrium, so we’ll apply a service factor, and say our airflow is going to be 30% efficient in cooling the steel (which is really quite high) so we’ll need:

544.4 CFM/0.3 = 1,815 CFM

EXAIR Air Amplifiers are an excellent option for providing this kind of cooling flow. They’re compact, quiet, and efficient. Using the following table, we see that a 3″ Adjustable Air Amplifier supplied at 80psig has a total developed flow rate (Air Volume at Outlet) of 774 SCFM:

So, three of them will generate a total cooling flow of 2,322 SCFM, and that’s not counting the air entrained in the immediate discharge (Air Volume at 6″). That’s even more than we THINK we need…but that can be adjusted and/or regulated.

Another thing I like about the Adjustable Air Amplifiers for an application like this is that they’re, well, adjustable (it’s right there in the name). Turning the exhaust plug in or out will decrease or increase the air flow – this is how you can make gross adjustments to the air flow. A Pressure Regulator in the supply line then allows for precise ‘tweaks’ so you can dial in the performance to the level you need, without using any more compressed air than you have to.

With sixteen distinct models to choose from, EXAIR Air Amplifiers are a quick and easy way to provide a tremendous amount of cooling air flow from a compact, lightweight product.

If you have any questions about using compressed air for cooling, give me a call.

Russ Bowman, CCASS

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

Published on by Lee EvansLeave a comment

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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

Published on by Lee EvansLeave a comment

IMG_7065
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.

air amp chart
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