Orifice Meter - Flow Measurement
Orifice Meter - Flow Measurement
(OP)
Can someone explain what is meant by the "the flow measurement was converted to a base pressure of 14.7 psia?" (when the outlet pressure was in fact much higher than 14.7 psia)
Does this mean that if the inlet pressure is 200 psia and the outlet is 50 psia and you covert to base pressure of 14.7 psia it's as if you did the experiment from 200 psia inlet to 14.7 psia outlet.
If so, how easy is that conversion to make, it seems as if all the field equations I see skip straight to the conversion and you never see the derivation of Bernoulli.
Thank you for the help!!!
Does this mean that if the inlet pressure is 200 psia and the outlet is 50 psia and you covert to base pressure of 14.7 psia it's as if you did the experiment from 200 psia inlet to 14.7 psia outlet.
If so, how easy is that conversion to make, it seems as if all the field equations I see skip straight to the conversion and you never see the derivation of Bernoulli.
Thank you for the help!!!





RE: Orifice Meter - Flow Measurement
RE: Orifice Meter - Flow Measurement
RE: Orifice Meter - Flow Measurement
RE: Orifice Meter - Flow Measurement
I am not sure on any of this cause I can't find the answer anywhere, someone jump it and correct me please.
RE: Orifice Meter - Flow Measurement
In short "Standard" conditions are a very effective surrogate for mass flow rate and allow for commerce to take place. It applies to equations that are adapted to volume flow rate at standard conditions (e.g., the AGA 3 measurement equations or the Panhandle A flow equation), but doesn't work at all for equations adapted to actual conditions (e.g., most compressor hp calculations).
One important warning--NEVER use STANDARD volume flow rate to calculate velocity, it is imaginary and does not mean anything at all.
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
"Life is nature's way of preserving meat" The Master on Dr. Who
RE: Orifice Meter - Flow Measurement
So I can just take the final Mcf standard when I see it and x (14.73/ P(flowing actual)) and I will get the volume at the Pactual.
One other question, when I am looking at the orifice equation and I see Pflowing, is that inlet, outlet, at the vena cont...?
Sorry for the dumb question, and thank goodness for people like you that will help with simple things some of us don't know or can't visualize without additional help.
RE: Orifice Meter - Flow Measurement
RE: Orifice Meter - Flow Measurement
To get from standard flow rate to actual flow rate requires more than just the ratio of pressures. I like to calculate density for both the imaginary stream and for the actual stream (which includes temperature and compressibility differences) then:
q(act)=q(std)* [rho(std)/rho(act)]
That way I don't have to remember if I'm dividing actual pressure by std or vice versa. Once you get q(act) then you can calculate bulk average velocity by dividing by area (in consistent units) and getting the time frame right.
AGA 3 has equations for either upstream or downstream pressure taps. A good rule is that P(flowing) for a square-edged orifice station is the pressure at the pressure tap wherever it is (upstream or downstream, never at the vena contracta).
David