Elevation Difference for Compressible Fluid
Elevation Difference for Compressible Fluid
(OP)
Hello,
I am using Equation 3-20 in the Crane Technical Paper 410 to calculate flow rate of nitrogen out of a pipe which is about 30 ft long with 90 and 180 degree bends. P1= 3 psig (after a pressure reducer) and P2=0 psig. The line size is 4" Schedule 40 S.S. How using equation 3-20, it does not take in account elevation differences (which in this case is about 10 feet). I want to find flow rate of nitrogen. Can I ignore the elevation difference or do I need another calculation method? If another method is needed, is it in Crane Manual or can someone send me a link or explain it in here?
Thank You.
I am using Equation 3-20 in the Crane Technical Paper 410 to calculate flow rate of nitrogen out of a pipe which is about 30 ft long with 90 and 180 degree bends. P1= 3 psig (after a pressure reducer) and P2=0 psig. The line size is 4" Schedule 40 S.S. How using equation 3-20, it does not take in account elevation differences (which in this case is about 10 feet). I want to find flow rate of nitrogen. Can I ignore the elevation difference or do I need another calculation method? If another method is needed, is it in Crane Manual or can someone send me a link or explain it in here?
Thank You.





RE: Elevation Difference for Compressible Fluid
RE: Elevation Difference for Compressible Fluid
RE: Elevation Difference for Compressible Fluid
Regards
StoneCold
RE: Elevation Difference for Compressible Fluid
RE: Elevation Difference for Compressible Fluid
RE: Elevation Difference for Compressible Fluid
I have done one job involving a 100 km pipeline operating at 220 barg->80 barg with a elevation difference from 0 to 2200 m below the sea surface and back to 0. Here it DID matter but that was a first.
Best regards
Morten
RE: Elevation Difference for Compressible Fluid
However, there is another factor which I would like to raise for discussion here. Crane Eq 3-20 includes the factor "K" which represents the total resistance of the line. This would normally include the entrance and exit effects, which are especially important in a short line like this.
As you have an inline pressure reducer you can neglect the entrance effect. The K value for your 30 ft of pipe plus bends will be about 2.6 (assuming 1 each of 90 and 180o bends), and the K value for a free exit is 1.0, giving a total K of 3.6.
If you neglect the exit effect you will overstate the flow by a factor of (3.6/2.6)0.5, or roughly 18%, which is a lot more significant than the static head.
But here comes the bit on which I would like to invite some comment. In this particular case I believe that we could make an argument for neglecting the exit effect as well. The inline pressure reducer will control the static pressure, and will not see the velocity head. As the reason for including an exit effect is to compensate for the velocity head not being recovered, and in this case we did not include the velocity head anyway, it would be wrong to subtract something that was not included to start with. Comments?
regards
Harvey