9 replies to this topic

[atiq124]

Nitrogen pressure is set at 25 psig using a pressure regulator in 2" pipe and the temperature of gas is 25 degree C. The pipe size is then reduced to 1" after 10 meters. How do we calculate the flow rate of Nitrogen in 2" and 1" pipe from this given information ?

Thanks

Attached Files

•  Nitrogen.jpg   17.36KB   11 downloads

[shan]

Is the outlet pressure of 1" pipe 0 psig?

[atiq124]

Hi Shan, the pressure at the outlet of 1" is unknown, there is no pressure gauge on the line, 25psig is known from the gauge on pressure regulator on 2" line which is reduced from 6.4 barg. Thanks

[latexman]

I think either the isothermal compressible flow equation or the adiabatic compressible flow equation would give you about the same answer in your case.  But, without the pressure drop the equations cannot be solved.

Edited by latexman, 11 August 2015 - 06:41 AM.

[samayaraj]

Refer the attached excel calculation. The mass flow rate remains same throughout the pipe. That's the key!

Attached Files

•  14. Nitrogen flow calc.xlsx   20.88KB   98 downloads

[katmar]

As stated by others, you must have the pressure at the end of the 1" line to be able to calculate the flowrate.  But one "trick" worth knowing if you are doing the calculations by hand is how to treat the two different sized pipes in series as one calculation.  The stepped pipe would not be a problem if you know the flow and want to calculate the pressure drop, but the reverse calculation requires trial and error and this gets complicated when you have two different sizes in series

 

I have written up an example that explains this method of modeling the stepped pipe with one equivalent pipe of constant diameter at

http://www.katmarsof...o-example07.htm

[Art Montemayor]

samayaraj:

 

The correct term for sonic gas flow is "CHOKED" flow.  It is NOT chocked flow.  The term choke means to throttle; the term chock means to wedge or block (as from movement).   Sonic flow is being throttled and maintains a constant gas mass flow rate.

 

I don't know why, but a lot of chemical engineers from India keep using the wrong term for sonic flow.  Some Fluid Mechanics professor must have started the fashion of using the wrong term and it has continued to date.

[katmar]

If there is a risk of choked flow occurring, then when using the modeling method I referred to above the smaller diameter pipe of the two should be used to model the line.  Using the larger diameter would of course give the wrong velocity and would not make it clear if there is a risk of getting choked flow.

 

samayaraj - it seems that your spreadsheet is checking for choked flow in the final nozzle only.  Or are you checking for sonic velocity in the piping as well?

[samayaraj]

samayaraj:

The correct term for sonic gas flow is "CHOKED" flow. It is NOT chocked flow. The term choke means to throttle; the term chock means to wedge or block (as from movement). Sonic flow is being throttled and maintains a constant gas mass flow rate.

I don't know why, but a lot of chemical engineers from India keep using the wrong term for sonic flow. Some Fluid Mechanics professor must have started the fashion of using the wrong term and it has continued to date.

Thanks for the correction Mr. Art. It was my mistake and not by my professors. It's a general mistake done by all young engineers and not only Indians. I'll correct it hereafter.

Edited by samayaraj, 11 August 2015 - 11:37 PM.

[samayaraj]

samayaraj - it seems that your spreadsheet is checking for choked flow in the final nozzle only. Or are you checking for sonic velocity in the piping as well?

Dear Mr. Katmar,

Ya this spreadsheet is used to find the choked flow in the nozzle only.