On Sun, 29 Apr 2007 23:24:57 GMT, Lew Hodgett
wrote:


Which container contains the most pounds of water vapor?


An interesting question. The obvious answer is that the second one
would contain 7.67 times as much water vapor. (Assuming 15psi
atmospheric pressure, 115/15 = 7.67). But that ignores state change.

Since I don't have the appropriate property tables memorized, do not
have copies near to hand, and am not inclined to try and find any for
this academic exercise, I will make some assumptions.

The question states that the final temperature is 70F in both cases.
Therefore, the H2O vapor pressure is the same in both cases. But, we
know the partial pressure of the H2O vapor in the first container is
less than the 70F vapor pressure since the air is not saturated, being
at only 50% RH.

Assuming that, since the air in the first container is at 70F and 50%
RH, the partial pressure of the vapor in the first container is 50% of
the H2O 70F vapor pressure. In that case, a 7.67 compression ratio
will increase the partial pressure of the vapor in the second
container to well above the H2O 70F vapor pressure and condensation
will occur as the compressed air cools to the 70F ambient temperature.
Most of the water will condense out leaving the air in the second
container saturated at 100% RH with a H2O partial pressure equal to
the 70F vapor pressure. This is double the assumed partial pressure in
the first container. So, if the assumption above is correct, the
second container will contain twice the mass of water vapor as the
first container with the remainder of the water condensed as liquid.

And, your point about lawyers, debaters, and crap stuck to the walls
is...?