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Re: [Phys-l] The Rain it Raineth. - Denouement



As promised the answer, ex cathedra:

For a room to lose RH, it must either warm up, or
condense water vapor, which latter option is a prescription
for 100% RH

The paradox overcame BC, but Bob LaM. gave the approved
response for the room's bulk RH. Still, the local RH in the vicinity
of the waterfall approaches 100% all the same: what one might
call dynamic RH conditions?

Brian W

At 03:35 PM 5/27/2006, bc., you wrote:
At equilibrium, w/ liquid * water available, and temp. thru out
constant (2 deg. C), the result will be 100% humidity. This will be
true no mater the shower's temp. ** I think equilib. reached more
quickly the higher the shower temp.

pc Bob's answer is initial non-equlib. answer.

* true even if shower is emitting snow.
** I haven't thought about unusual condix. e.g. super, cooled or heated
shower.

bc, awaiting crits.

p.s. walls, well insulated so they are at air temp.

Bob LaMontagne wrote:

>2B should be correct.
>
>At 20 degC the saturation vapor pressure is around 22 kPa, so at 50 percent
>RH the actual vapor pressure in the room is 11 kPa.
>
>Water at 2 degC has a saturation vapor pressure of about 3 kPa, so the vapor
>in the room would condense on the cool droplets.
>
>Bob at PC
>
>-----Original Message-----
>From: phys-l-bounces@carnot.physics.buffalo.edu
>[mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Brian
>Whatcott
>Sent: Saturday, May 27, 2006 3:15 PM
>To: phys-l@carnot.physics.buffalo.edu
>Subject: [Phys-l] The Rain it Raineth.
>
>
>I ran across an interesting debate on a newsgroup recently.
>I will put it in the form of a pop quiz for your entertainment.
>
>[Warning: information relayed from newsgroups, like excerpts
>from provincial newspapers, is not guaranteed to be correct]
>
>In an experimental setting an ordinary room of 4000 cubic feet
>was provided with a fan and a shower head over a drain in
>one corner. This air mixed quickly with the room air.
>Air leakage into the room was minimized.
>
>Q1: The room air temperature was 20 degC, humidity 50% RH
>What was the effect on the room's humidity of opening a faucet
> to the shower head and blowing room air through the water fall
> at a rate of 400 cu ft/min?
>1A: The room's humidity increased
>1B: The room's humidity decreased.
>1C: the room's humidity was unchanged.
>1D: Unsure.
>
>Q2: If you answered 1D to Q1, then here is further information -
>the temperature of the water falling from the shower could be switched
>to 2 degC, or 20 deg C or 80degC.
>
>If the fan was started with the water temperature set to 2 degC,
>other conditions as above, which of the following was observed:
>2A: RH increased in the room
>2B: RH decreased
>2C: RH unchanged.
>
>I will relay the received answer in a day or two, if it is not
> generally recognized by that time.


Brian Whatcott Altus OK Eureka!