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# flow restrictions for compressed air

## flow restrictions for compressed air

(OP)
does anyone have the formula for calculating the maximum flow rate for compressed air through a pipe (say 6" dia)?

### RE: flow restrictions for compressed air

There is a simple answer to that, if you have choked flow the velocity (in Imperial Units) is:

v=(k*g*R(gas)*T)^0.5

Convert that to a volume flow rate, or a mass flow rate using the usual equations.  You have choked flow (which is the maximum flow rate of a compressible fluid) whenever the downstream pressure is less than:

P(max choked) = P(upstream)*(2/(k+1))^(k/(k-1))

In both equations "k" is the ratio of specific heats and all pressures and temperatures must be in absolute terms.

If you are looking for a "maximum commercial" flow rate, then you'll have to restate your question.  That value is very dependent upon maximum allowable velocity which is a function of pressure and temperature.

David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
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(OP)
Ok, thanks.

### RE: flow restrictions for compressed air

For a perfect gas, constant specific heat, the max flow will occur if choking conditions occur.

For adiabatic flow, the Mach No. =1
For isothermal flow the Mach No.  =  sqrt (1/gamma), where gamma is the ration of the specific heats Cp/Cv

Regards

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