Compressed Air Temperature to use in Pipe Friction Loss Calculations

[PEDARRIN2]

I am trying to wrap my head around what temperature to use for friction loss calculations for a 150 psig compressed air system.

The compressors are sized to produce slightly above what the customer has stated they want for a continuous flow (~1400 scfm). I have a receiver and oversized pipe loop to provide a bit of storage and a flow control valve to manage the compressors - so they are not short cycling.

So I am assuming there will be no time to dissipate heat of compression.

I am assuming ambient conditions of 14.7 psia and 70 F at the intake of the compressor. I am assuming pressure increases to 150 psig within the system, but what is the temperature of the air. I understand the relationship PV/T (in) = PV/T (out) where P and V are changing, but how do I calculate T?

I am wanting this information to determine the weight density of air to use in my friction loss calculations. According to TP 410, air at 150 psi/70 F has a density of 0.840 lb/cf. Air at 150 psi/100 F has a density of 0.795 lb/cf.

This difference can effect pipe sizing.

Am I overanalyzing this?

 

[katmar]

The simplest and best way is to ask the compressor supplier, or dig into the user manual. Using a temperature on the high side will result in a larger and more conservative pipe size. The PV/T relationship is for operations where there is no external work done on the gas. Rather than fiddle with the theory just ask the supplier.

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[bimr]

Sizing compressed air piping can tricky especially without the details of plant operations. You may be overanalyzing a little bit as the piping should be sized for minimal friction loss. I would suggest that you size the piping one to two pipe sizes above the size of the compressor outlet. This is outlined in the attachment. Unless you are running thousands of feet of pipe, the extra cost of the pipe is minimal.

 

[bimr]

Here is link to rules of thumb for compressed air:

http://repository.tamu.edu/bitstream/handle/1969.1/5568/ESL-IE-05-05-10.pdf

Looks like 8-Inch pipe for that capacity.

 

[racookpe1978]

If the pipe is not insulated, it will quickly assume the temperature of the air around the pipe: hottest right near the compressor, then losing heat as the pipe runs to the load. Compressed air won't cool to lose the expansion heat energy won't happen until it expands, right? So it will be environmental losses over the length of the pipe that matter.

Do you really want to use a control valve to even pressure, or a tank rated for 150 psig? Those aren't that expensive, and will give you a place to drain condensate and mount a filter and dehumidifier.

1400 cfm is a substantial flow rate, what length of pipe run are you expecting in what environmental temperatures?

 

[PEDARRIN2]

The project is for a training facility on a military base - so we have to use a receiver, even if we really do not need one. The flow control valve is a recommendation from the air compressor supplier to help control the system.

The flow rate is large (largest I have ever designed for), but it is what the client said was to be the "constant" flow requirement.

I have about 750 feet from the compressors to the most remote use and the environment will be a "hangar" so it will not be too hot.

I contacted the air compressor supplier (which I should have done earlier). they design their compressors to produce air 15 F higher than ambient - so I am going to go with 100 F.

Thanks for the help and links to tips.

 

[chicopee]

Don't forget, it is 1400 scfm free air delivery from the compressor. If it is a reciprocating air compressor, you will need the air receiver also to dampen the pulsation from the compressor. Also, you need to define the pressure, temperature and R.H. values used in the SCFM to calculate the ACFM which as a client I would want to know.

 

[racookpe1978]

750 feet of horizontal uninsulated pipe in after an uninsulated receiver, then open air (no sunlight exposure, but no wind either, not underground) will cool the air near ambient. But, how much additional water will condense back out after the receiver?

 

[PEDARRIN2]

The client only wanted a refrigerated dryer for their application - so we are looking at ~35-38 F pressure dew point. This is a coastal location so a lot of water will likely be pulled out in the inter/after coolers and dryers. I located the dryers upstream of the receiver, because I did not want the extra water collecting in the receiver, although there is an electronic drain there for any incidental condensate. They also require condensate drops in all rooms, so I designed a parallel pipe system in each room, connected the ends, sloped the downstream pipe and directed it to a floor drain. There is a double set of ball valves to collect/discharge condensate. I figured this was a simpler approach than specifying automatic drains everywhere.