air pressure differential calculation verfication
air pressure differential calculation verfication
(OP)
hi,
here is a description of what i am trying to accomplish: design a spreadsheet to show air pressure differential from pipe “A” to pipe “B”. pipe “A” is larger diameter than pipe “B”. this is to act as a quick reference for our manufacturing facilities. i am trying to keep this as simple as possible. any input would be greatly appreciated.
i have modeled my spreadsheet as a venturi tube problem using bernoulli’s equation. i am assuming incompressible flow to simplify calculations and because i do not know the flow rate (at the moment, we have no flowmeters in-house and i’m not aware of any at the plants). for the density calculation, i used: rho = P1/(R*T), (assume T = 68F = 528R).
i have the spreadsheet configured so that i can input any pipe dia., inlet pressure, and flow rate and it will output P2 (pressure in pipe “B”). here is an example of my given and calculated values:
given: dia. pipe ”A” = .250 in
dia. Pipe “B” = .215 in
flow rate = 22.5 cfm
inlet pressure (P1) = 100 psi
calculated: outlet pressure (P2) = 44.66 psi
have i oversimplified this problem and made poor assumptions? also, would this same method work if pipe "B" dia. was a nozzle open to atmosphere?
please let me know if more info is necessary. thnx
here is a description of what i am trying to accomplish: design a spreadsheet to show air pressure differential from pipe “A” to pipe “B”. pipe “A” is larger diameter than pipe “B”. this is to act as a quick reference for our manufacturing facilities. i am trying to keep this as simple as possible. any input would be greatly appreciated.
i have modeled my spreadsheet as a venturi tube problem using bernoulli’s equation. i am assuming incompressible flow to simplify calculations and because i do not know the flow rate (at the moment, we have no flowmeters in-house and i’m not aware of any at the plants). for the density calculation, i used: rho = P1/(R*T), (assume T = 68F = 528R).
i have the spreadsheet configured so that i can input any pipe dia., inlet pressure, and flow rate and it will output P2 (pressure in pipe “B”). here is an example of my given and calculated values:
given: dia. pipe ”A” = .250 in
dia. Pipe “B” = .215 in
flow rate = 22.5 cfm
inlet pressure (P1) = 100 psi
calculated: outlet pressure (P2) = 44.66 psi
have i oversimplified this problem and made poor assumptions? also, would this same method work if pipe "B" dia. was a nozzle open to atmosphere?
please let me know if more info is necessary. thnx





RE: air pressure differential calculation verfication
RE: air pressure differential calculation verfication
My work was based on guidelines given in Crane Flow of Fluids tech paper 410. I have also checked my results using compressible flow formulas from "Streeter - Fluid Mechanics"and have achieved results within 10%.
I can't say incompressible flow is quicker to calculate but it is easier for most people to understand. In my company I only know a handful of engineers that can understand compressible flow.
Concluding, in order to be accurate break your pipe into an adequate number of sections to limit the % pressure drop per section.
RE: air pressure differential calculation verfication
RE: air pressure differential calculation verfication
Flow Measurement Engineering Handbook
Miller, Richard W
McGraw-Hill, 1996 (Third Edition)
ISBN 0-07-042366-0
Cut to the chase and don't fool around. I have modeled many cases from Miller and have found most other designers do too, particularly when it comes to software.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
RE: air pressure differential calculation verfication