Re: [Phys-l] Water vapor condensation

[Michael Edmiston <edmiston@bluffton.edu>]

It seems to me you won't be measuring what you think you're measuring unless 
the cold object has a lot of thermal mass and fairly good thermal 
conductivity (such that the surface maintains constant temperature for a 
fairly long time).  If the temperature of the cold object is lower than the 
dew point then water vapor will condense on it fairly rapidly (also 
depending on air movement).  The condensing water will give its very large 
heat of condensation to the object thereby warming it fairly rapidly.  The 
rapid warming continue until the dew point is reached.  At the dew point 
condensation and evaporation both occur nearly in equilibrium, but the 
object slowly absorbs enough heat from the air to get above the dew point, 
and the water evaporates.

If you record the mass during condensation until the mass stops increasing, 
I suspect you would be able to make a rough determination of the heat 
capacity of the object by this method, but I am not sure if you can say much 
about the affect of the surface temperature on the condensation rate... 
unless you can hold the temperature constant, or determine an accurate 
weight gain after a very short time after removal from the freezer.

Other than that, I suspect air movement might be a larger effect than 
surface texture, etc.

Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton University
1 University Drive
Bluffton, OH 45817
419.358.3270
edmiston@bluffton.edu


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From: "Savinainen Antti" <antti.savinainen@kuopio.fi>
Sent: Friday, July 02, 2010 4:58 AM
To: <phys-l@carnot.physics.buffalo.edu>
Subject: [Phys-l] Water vapor condensation

> Hi,
>
> a student of mine is doing a HS project in which she is seeking for a 
> correlation between relative humidity and temperature difference of a 
> surface and air. Her idea is to use a plate that is taken from a freezer 
> and measure the mass of water condensed onto the plate within a certain 
> time frame. Obviously, among other things, the mass depends on the area of 
> the plate.
>
> I was wondering whether of not any other properties of the *surface* 
> besides the area, temperature difference might affect the condensing. 
> Could you suggest a useful reference related to the project topic? AJP and 
> TPT has already been
> looked for.
>
> Regards,
>
> Antti
>
>
>
> Antti Savinainen, Ph.D., B.Ed.
> Adjunct Professor (University of Jyväskylä)
> Senior Lecturer in Physics and Mathematics
> Kuopion Lyseo High School
> Finland
> E-mail: <antti.savinainen@kuopio.fi>
> Website: <http://kotisivu.dnainternet.net/savant/>
>
>
> --
>
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