Water Vapor
Water Vapor
(OP)
I know my relative humidity, temperature, and pressure, and I am trying to find the specific volume. I do not know the quality. Any help is appreciated.
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RE: Water Vapor
Good luck,
Latexman
RE: Water Vapor
RE: Water Vapor
Good luck,
Latexman
RE: Water Vapor
Specific humidity = 0.622*Pv/(Pa-Pv) kgH2O per kg of dry air
where Pa=atmospheric pressure mbar
Pv=Phi*Pgd/100 mbar
Phi=relative humidity %
Pgd=saturation pressure (mbar from steam tables) at the dry bulb temperature
After this you calculate the molecular weight, the gas constant and then the density from PV=mRT
Regards,
athomas236
RE: Water Vapor
If your pressure is significantly different from the atmospheric pressure the psychrometric chart is based on, that complicates matters. However, if the air pressure you are working with is greater than the chart's base pressure or it can be isothermally compressed to the base pressure of the psychrometric chart without going through the dewpoint (condensation), then you can look up the specific volume at the chart's base pressure and then correct it to the actual pressure using Boyle's law:
P1V1 = P2V2
If the air pressure you are working with is less than the chart's base pressure and an isothermal compression goes through the dewpoint, then follow the post by athomas236 (or get the psychrometric software to work).
Good luck,
Latexman
RE: Water Vapor
RE: Water Vapor
PV=nRT
=mRT/M
This translates to:
Pv=RT/M
where v is the specific volume and R is the universal gas constant. I do not know M or v.
I am given:
P=350 psi
T=160 F
Relative humidity = 40%
How do you calculate molecular weight or the specific volume?
RE: Water Vapor
At 160 F the vapor pressure of water is about 4.75 psia. The partial pressure of water vapor is 1.9 psia. The mole fraction of water vapor = 1.9/(350+14.7). Notice I assumed it was 350 psig. The mole fraction of air = 1-1.9/(350+14.7).
Average molecular weight = 18 x 1.9/(350+14.7) + 29 x [1-1.9/(350+14.7)].
v = RT/MP
Ta Da!
Good luck,
Latexman
RE: Water Vapor
RE: Water Vapor
Are you after the specific volume of the mixture (0.63 ft3/lb) or the partial volume of water vapor?
Good luck,
Latexman
RE: Water Vapor
RE: Water Vapor
Good luck,
Latexman
RE: Water Vapor
RE: Water Vapor
RE: Water Vapor
Good luck,
Latexman
RE: Water Vapor