Pressure Temperature Compensation of a Gas

I

Thread Starter

Inst eng

I have an orifice flow that is being compensated, And I have a few questions.

The max range of the orifice is calculated at 6110000scfh@ 104psiget dp with flowing density of .21lb/ft3, and base density of .022 lb/ft3. The dcs formula is compensated flow= uncompetitive flow(scfh) *sqrt((p+po/rp)*(rt/t+to)* (rmw/mw).I have an online analyzer which gives sg, a pressure guage, and a temp guage.
The dcs calculates MW=sg*.78*10.73*((t+460)/p+14.7)).

1st
What is the .78 constant?

Since I have an online analyzer would my flow still be correct if the properties change? I am concerned if I calculated the orifice using the wrong density then the flow might be incorrect,but since I have an online analyzer I am thinking it will correct this? I really would like to see the math behind why it does not matter what base density, and flowing density I use in the orifice cal the correction factor still corrects (if this is the case).
 
(1) If your base density is at standard conditions, then
the MW = 8.5 or so given that dry air is 0.0753 lb/ft3
with a nominal sg of 0.29 relative to dry air at standard conditions.

(2) your DCS formula MW=sg*.78*10.73*((t+460)/p+14.7))
appears to be the "real" gas law with a compressibility factor of 0.78.
and calculates the specific volume rather than the molecular weight for a given specific gravity, p, & t.

good luck
 
Top