Re: [Paddlewise] Taking Water Temps

From: Bill Chitty <gwchitty_at_hotmail.com>
Date: Fri, 5 Jul 2002 15:17:28 -0500
I think you are on the right track with the phenomena of the moving Vs  the
static thermometer.  To be more precise, the static thermometer is working
by conduction only.  The water in contact with the thermometer absorbs the
heat from the thermometer and lowers its temperature to the water
temperature while heating the water imperceptibly.  When you move the
thermometer you add convection to the cooling process and you are speeding
the cooling process of the thermometer.  All this assumes that the water is
at the same temperature everywhere you move it and maybe this should be
called an average temperature.

The process of wind chill is a different mechanism.  To really have wind
chill you need to be moving air over a thermometer that can evaporate water
off its surface continuously.  This would be the "wet bulb" temperature.
The cooling effect is augmented by the evaporation of the water out of the
wet cloth and the temperature measured is actually less than the temperature
of the air.  This also applies to your body, wind chill causes you to cool
by conduction, convection, and evaporation from your pores.

It is hard to say that wind chill affects things that are dry like your car
or your kayak on the roof.  I don't think there is a water chill effect.
Anyway, I'm ranting for no reason.  Towing the thermometer quickly produces
the same effect as holding it still provided all the water is at the same
temperature.  This makes me wonder why the weatherman gives us a "heat
index" in the summer but doesn't deduct for a wind chill factor?

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Received on Fri Jul 05 2002 - 16:52:21 PDT

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