Partial Volume of Chemical Vapor
Partial Volume of Chemical Vapor
(OP)
Hello friends, I am reviewing a relief valve pressure setting calculation from a consultant and I have a question about partial volume. The equation used is
Vchem = Pvt/Pt
Where
Vchem is the partial volume of the chemical vapor as a ratio
Pvt is the saturated vapor pressure and
Pt is listed as the total pressure, i.e. chemical & air vapor + atmospheric
The chemical vapor pressure (Pvt)is given as 2.48 psia
The chemical + air pressure (Pt) is known based on tank measurement and is 2.5 psig, or, 17.2 psia
It seems that the result should be
Vchem = (2.48 psia)/(17.2 psia) = 0.144 or 14.4%
But the result given is 0.078 or 7.8%
It seems to me that they have doubled up on the atmospheric pressure
Vchem = (2.48 psia) / (17.2 psia + 14.7 psia) = 0.078 or 7.8%
I would appreciate feedback on whether it is correct to add atmospheric to the absolute pressure.
Thanks in advance.
Vchem = Pvt/Pt
Where
Vchem is the partial volume of the chemical vapor as a ratio
Pvt is the saturated vapor pressure and
Pt is listed as the total pressure, i.e. chemical & air vapor + atmospheric
The chemical vapor pressure (Pvt)is given as 2.48 psia
The chemical + air pressure (Pt) is known based on tank measurement and is 2.5 psig, or, 17.2 psia
It seems that the result should be
Vchem = (2.48 psia)/(17.2 psia) = 0.144 or 14.4%
But the result given is 0.078 or 7.8%
It seems to me that they have doubled up on the atmospheric pressure
Vchem = (2.48 psia) / (17.2 psia + 14.7 psia) = 0.078 or 7.8%
I would appreciate feedback on whether it is correct to add atmospheric to the absolute pressure.
Thanks in advance.





RE: Partial Volume of Chemical Vapor
RE: Partial Volume of Chemical Vapor
Thanks for the reply. I looked at some of their other work which uses the same form and had been vetted by a 3rd party reviewer. They had indeed doubled up.
I used to count sand. Now I don't count at all.