# Mass Flow through a 1.5 Pipe @ 300kpa

1. Jul 13, 2010

### NateP

Mass Flow through a 1.5" Pipe @ 300kpa

Hi,

I'm having some trouble with finding the "choke" point of a 1.5" diameter pipe.

Conditions:
300 kPa
383 deg K
1.5 in D

I've tried using this little guy, http://www.grc.nasa.gov/WWW/K-12/airplane/mflchk.html, with the Mach = 1, and only get ~1.5lb/min, which can't be correct. Can't figure out what I'm missing?

Thanks
Nate

2. Jul 13, 2010

### stewartcs

Re: Mass Flow through a 1.5" Pipe @ 300kpa

http://www.chem.mtu.edu/~crowl/cm4310/Chapter4b.pdf [Broken]

CS

Last edited by a moderator: May 4, 2017
3. Jul 13, 2010

### NateP

Re: Mass Flow through a 1.5" Pipe @ 300kpa

P1 = P2 in my case, but having trouble understanding if this would fall under Adiabatic or Isothermal, but I take it has something to do with the velocity of the gas?

It looks like I need to start with finding the sonic velocity under the given conditions. Looking at the formula:

a = γ gcRgT /M

Which translates into:
Code (Text):
Sq rt of ( Gamma * Grav constant * Ideal Gas Constant * Temp  / Molecular weight
Do any of these variables change under the given conditions? I can only seem to reference values at 20 deg C and 101 kPa...

4. Jul 13, 2010

### stewartcs

Re: Mass Flow through a 1.5" Pipe @ 300kpa

It's up to you to determine how you want to model the system. If the process is rapid, then the adiabatic assumption is valid. If the temperature of the gas is constant, the isothermal would be best. In reality it's somewhere in between the two.

In compressible flow the density of the gas typically changes by an appreciable amount. However, the 'gamma' term should capture that effect. Obviously the terms labeled 'constant' won't change, hence the name. The molecular weight won't change either. The temp was previously discussed as well as gamma.

CS

5. Jul 13, 2010

### stewartcs

Re: Mass Flow through a 1.5" Pipe @ 300kpa

If P1 = P2 then no flow will occur. There must be a pressure differential in a horizontal pipe for fluid flow.

CS