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Re: [Phys-l] thermo question



Not really anything "new" - just a rephrasing. The specific humidity (gm water vapor / kg dry air) and the dew point temperature will be fixed vatues for a closed container - even if the temperature is varied (which is not in this case).

Bob at PC

________________________________

From: phys-l-bounces@carnot.physics.buffalo.edu on behalf of John Denker
Sent: Sat 3/1/2008 11:01 AM
To: Forum for Physics Educators
Subject: Re: [Phys-l] thermo question



On 03/01/2008 07:56 AM, FIZIX29@aol.com wrote:
Consider a fixed amount of gas (moist air) in a container of fixed volume.
The container is in an environment of fixed temperature. When equilibrium is
reached, what quantity or quantities will be constant throughout the volume
of gas?

This question comes from my desire to understand from first principles how
to maintain a constant relative humidity in a fixed amount of gas.

Can we assume the box is not very tall and the gravitational
field is not very huge, so that the gravitational pressure
head is negligible on the scale of things?

This is described as a "gas" problem. Can we assume there is
no liquid water present (and no liquid oxygen or nitrogen)?

Given those assumptions, the question is, what is varying?
We have a fixed amount of gas, a fixed volume, a fixed
temperature, Dalton's law of partial pressures, ideal gas
law ... it seems that there are no remaining variables of
any kind.

What is there to know that we don't already know?

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