How to calculate the flow of any gas through pipe (based on pressure differance)

[Fahad 90]

Hi everyone,

I am really confused as I found tons of equations here and there in regards to the subject matter. Normally, flow rate of "incompressible" fluid can be easily calculated by using Darcy equation which correlates the mass flow rate according to the pressure drop, pipe length and pipe diameter. However, I couldn't find any equation correlates the same for compressible fluid. I understand the concept of the chocked flow and sonic flow, but what I have found in this regard was through nozzle, valve and restriction which is not what I am looking for. I am looking for an equation that can correlates the pressure difference, pipe length and pipe diameter between two location.

your support is highly appreciated in advance.

thanks !

 

[quark]

Check Panhandle's equation

 

[Fahad 90]

thanks for your prompt response. actually, I have checked the both Weymouth and Panhandle equations. however, those equations are limited to long pipes (in miles or Km)and big diameter which will impact the calculations accuracy.

thanks !

 

[quark]

Not necessarily. I recommend Crane TP410 for you. Anyhow check this thread for couple of calculators thread378-242585

 

[katmar]

I second Quark's recommendation of Crane TP410. See more on Crane TP410 below.

For compressible fluids the difficulty in using the Darcy-Weisbach formula is that the density, and therefor the velocity, changes along the length of the pipe. This can be dealt with by assuming some gas law model to link the change in density to the change in pressure, and then by integrating the Darcy-Weisbach formula with the gas law model embedded in it. The most common gas law used is the isothermal model, although for short, high velocity lines such as relief valve vents the adiabatic model can be more relevant.

Crane TP410 presents these two models (although with little detail on the adiabatic model) and discusses how they compare with the Panhandle, Weymouth and Spitzglass formulas. Crane TP410 is a great starting point for anyone tasked with flow and sizing problems for pipes. Just be aware that there are some problems with the way TP410 deals with the pressure drop through pipe fittings for laminar flow.

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"