Vapor Pressure of Water

[A70Duster at aol.com]

<< Does anyone have the formulae for Vapor Pressure?  If I assume RH is 75% 
and can
 measure the Air Temperature inside the intake manifold what is the 
calculation
 for vp? >>


I feel I have a good contribution for this one.

>From steam tables, I calculated a forth order polynomial fitted curve for the 
pressures of saturated water vapor between 40 °F and 100 °F at 14.7 PSI.

Partial Pressure of Water Vapor = 

(0.0672 - 0.0022175 * TEMP
    + 1.1065E-04 * TEMP ^ 2  
    - 8.7841E-07 * TEMP ^ 3 
    + 8.7671E-09 * TEMP ^ 4)


To find the partial pressure (in PSI) of water vapor with known relative 
humidity, put in the temperature (°F) and multiply by the relative humidity 
value.

Vapor pressure of water (below 100 °F) should never be over 1 PSI at STP.

I have an executable program that determines relative humidity and oxygen to 
water ratio.  The user needs to input a dry bulb temperature, wet bulb 
temperature, and atmospheric pressure.  If interested, please email me back.