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Re: cooling water

Date: Sat, 30 May 1998 22:53:49 -0400 (EDT)
Reply-to: phys-l@mailer.uwf.edu
From: LUDWIK KOWALSKI <KOWALSKIL@alpha.montclair.edu>
To: phys-l@atlantis.uwf.edu
Subject: Re: cooling water

The issue of "hot water freezing faster" can be resolved
by an experiment. Put a glass of 50 C water into a freezer
and measure the time it takes Put a glass of 30 C water
into a freezer and measure the time it takes to reach the
temperature of -1 C, for example. Then do the same with 5
C wate, under identical conditions. A CBL thermistor could
be used to monitor the temperature from outside. My
prediction is that it will take longer when the initial
temperature is higher. But I am ready to rething to
rethink this if the experiments show I am wrong.

.....come on Ludwik, nobody wants to put all that hot water
and its vapors into their freezer. What a mess! Besides,
this is not a test where the hot water is likely to win.
The point is that if you set out a small sample of really
hot water in a flat dish--like a Petrie dish--on a very
cold and dry day much of the water will evaporate, BUT this
evaporative cooling will accelerate the cooling of the
remaining water and it may freeze faster. As you can see
all this depends on the temperature of the surroundings,
the relative humidity, and the amount of evaporative
surface the water has.

This is just not a situation that can be handled by a
simple statement. Sometimes hot water may freeze faster
and sometimes cold water may freeze faster. And sometimes
neither may freeze at all. WBN
Barlow Newbolt
Department of Physics and Engineering
Washington and Lee University
Lexington, VA 24450
Telephone and Phone Mail: 540-463-8881
Fax: 540-463-8884
e-mail: NewboltW@madison.acad.wlu.edu

"Prediction is very difficult, especially about the future."

Neils Bohr