flow through orifice

[asghar]

Can someone tell me, the gas flow volume through an orifice, calculated from the common formula given by different vendors, is at upstream pressure or downstream pressure?

 

[hacksaw]

either one can be used, but you have to use the correct multiplier in the orifice equation.

 

[asghar]

I came up with the 667 scfm the following formula. I believe this volume is at set pressure of 275 and not at downstream pressure (atmospheric). The constants and factors I used from Anderson Greenwood catalog. Am I right in my assumption that the volume is at set point??

A = Area of Orifice 0.134 Sqr. Inch
F = Factor 6.32
M = Molicular Weight of N. Gas 17.4
T = Temperature, oR, (oF+460) 560
Z = Compressibility Factor 0.97
C = Gas Constant 344
K = Valve Constant 0.878
k = Specific Heat Ratio 1.27
Kb = Back Press. Correction Factor 0.8
Ps = Set Pressure, psig 275
Po = Over Pressure of Set Press. 0.1
Pa = Atmospheric Pressure, psia 14.7
P2 = Back Pressure, psig
P = Pressure absolute 317.2


A = V x MTZ / FCKPKb

V = Flow Rate, SCFM 667

 

[MikeyP]

You are likely to get better responses to your question if you post in a more suitable group, e.g. fluid mechanics.

M

--
Dr Michael F Platten

 

[asghar]

hacksaw and Mikeyp; thanks for your input and I will explore the fluid mechanic forum.

 

[hacksaw]

asghar,

this appears to be a restriction orifice or possibly a relief valve as no d/p is provided, and there are curious mentions of a "valve constant" and a back pressure correction factor.

 

[hacksaw]

on closer study. you are dealing with a relief valve.

case in point, the "pressure absolute" = the set pressure + 10% + 14.7 psia.

just follow the instructions in the AG sizing manual. It is very clear. You will also find excellent engineering support from the factory.