And, let's keep in mind that the density loss with increasing humidity is very minor.  Raising
relative humidity from 20% to 80% (at 90 degrees F) has about the same effect on density as an
elevation change of 125 feet.  There is a nifty density calculator at:
http://www.nightrider.com/biketech/calc_airdensity.htm
It is designed to help with motorcycle jetting.

Bill

----- Original Message -----
From: "Keith Hughes" <keithahughes@QWEST.NET>

> From this it can clearly be seen that as the water content (truly
> gaseous water) increases, the enthalpy of the resulting mixture
> increases. That is, it contains (or can contain) a greater amount
> of heat. So, *for any given pressure*, the higher the humidity, the
> higher the heat transfer capacity will be. However, as has been
> said, the higher the humidity, the less dense the air. So, there
> are a couple of competing things happening here;
>
> 1. As the humidity increases, the enthalpy, and heat transfer
> efficiency, increases for any given pressure.
>
> 2. As the humidity increases, the density (and hence pressure)
> decreases.