HVAC High Flow Control with High Pressure and Temperatures

[Blake T]

Hello all,

I am currently building a test bench that can input a high amount of flow, pressure and temperature into an Air Cycle machine.
The inlet to the machine requirements are:
Flow = 71 lbs/min
P = 48 PSIa
T = 235 degree F
Diameter = 3 inches

In order to produce these conditions, I have a 75HP Compressor that produces approximately 335CPM, a 10,000 gallon storage tank and a 200KW Heater.

I am looking for a way to control the amount of flow and pressure but know that controlling 1 will affect the other in some way that will make it difficult to get a precise readout. Some questions I have are:

Should I control pressure or flow first or does it not matter?
What kind of control devices for flow/pressure should I look more into (valves, meters, etc)?
Can I control the flow or pressure after or before the heater?
Is the compressor supplying the storage tank at a different pressure than the inlet pressure going to affect the flow?I am looking for any advice or companies that specialize on control valves or systems that can handle such conditions and greatly appreciate your input.

Blake

 

[berkeman]

Welcome to the PF, Blake.

What is an "air cycle machine", and what is the application?

 

[russ_watters]

I am looking for a way to control the amount of flow and pressure but know that controlling 1 will affect the other in some way...

The short answer is that you can't control both parameters, you can only control one. The device you're feeding the air to will dictate the other based on its internal resistance to the flow.

I'm concerned though about the power requirements of this device and the safety of experimenting with industrial scale equipment.

 

[LURCH]

Is this for testing the environmental conditioning mechanisms in an aircraft ? And the heat, temperature, and flow rate numbers are to simulate the way these units operate in a passenger plane, right? Maybe an aerospace supplier might have what you need.

As for controlling both pressure and flow simultaneously; I haven’t diagrammed it out in detail, but it should theoretically be possible by placing a pressure compensated flow control followed by a pressure control bypass. So long as the pressure in the line after the flow control is greater than the 48 psi you want to send to the machine, the bypass will dump the excess. And the changes in flow resulting from the regulator venting will be immediately compensated for by the flow control.

I wish to second what @russ_watters siad, for goodness’ sake, please be careful. This is more than enough energy to compromise the structural integrity of your containment vessel (your body). Could you post more about what it is you’re testing, and maybe tell us about the safety mechanisms or your rig?

 

[jrmichler]

Please, please tell me that the compressor is rated in CFM, not CPM (whatever that is), and the size of the reservoir in cubic feet. That reservoir had better have an ASME U stamp on it, otherwise it is a very powerful bomb. I have never heard of a pressure vessel size in gallons, only cubic feet (or meters).

The pressure out of the compressor is exactly equal to the pressure in the tank plus line loss. The fact that you do not understand that tells me that you need to consult with somebody that understands pneumatic systems, valves, and controls. The air compressor distributor and/or the valve distributor should be able to recommend somebody.

 

[berkeman]

This is more than enough energy to compromise the structural integrity of your containment vessel (your body).

Well said.

 

[jrmichler]

I was too harsh in my previous post, sorry about that. My experience with compressed air was in a paper mill where the compressed air system had 5 or 6 air compressors, each with a 200 hp motor. If you wish to do this yourself, I suggest the following resources:

Compressed Air and Gas Data, published by Ingersoll-Rand is an excellent resource. Also the operator's manual for your air compressor. Your tank needs a properly sized relief valve, and a condensate drain. It's a very good idea to calculate the worst case condensate flow.

Control valves. Get some control valve catalogs and study their engineering sections. Learn the difference between equal percentage and linear response, and why it is important. I used a lot of control valves from Masoneilan. I liked their Camflex valves because of versatility - the positioner could be switched between linear and equal percentage.

Temperature measurement. Learn why a temperature sensor for air in a pipe does not measure the temperature of the air.

Temperature control. Learn the difference between on/off, proportional, and PID control with respect to air mass flow and heater thermal mass. A good internet resource to get started is www.omega.com. Learn about the effect of lag on control system response. Your temperature sensor has thermal lag from its mass and time delay lag from its location.

You "air cycle machine" has some sort of flow curve, a plot showing the relation between pressure and flow. You feed it pressure, it controls the flow. You need the maximum and minimum flow rates for your design pressure, then you size the valve to deliver that flow rate over the design range of reservoir pressures. Those calculations also tell whether you need a valve with equal percentage or linear response.

Calculate how long you can run your "air cycle machine", starting with the air tank at full pressure, and ending when the control valve is full open and unable to maintain design pressure to the load. Is that long enough to get the data you need?

 

[Asymptotic]

Please, please tell me that the compressor is rated in CFM, not CPM (whatever that is), and the size of the reservoir in cubic feet. That reservoir had better have an ASME U stamp on it, otherwise it is a very powerful bomb. I have never heard of a pressure vessel size in gallons, only cubic feet (or meters).

The pressure out of the compressor is exactly equal to the pressure in the tank plus line loss. The fact that you do not understand that tells me that you need to consult with somebody that understands pneumatic systems, valves, and controls. The air compressor distributor and/or the valve distributor should be able to recommend somebody.

It depends on the manufacturer, but I've seen air receiver pressure vessel volumes expressed in gallons, cubic feet, and sometimes both. For instance, Hanson specifies volume in gallons. https://hansontank.us/airtanks.html