At 4:18 AM +0100 3/4/05, Listar wrote:
>From: "Wayne Culberson" <waynecul@xxxxxxxxxxxxxxx>
>Subject: [OM] Re: OT: Wind chill (was: problem with OM4 & cold weather)
>Date: Thu, 3 Mar 2005 22:41:29 -0400
>
>[snip]
>"Wind chill" is not science, but just a way of expressing how the chilling
>effect of wind and temperature feels in comparison to tempertaure without
>wind. So as an example, -10 with X mph wind speed feels like -25 with no
>wind. Of course it's not exact science and it really doesn't work that
>simply. There is no scientific formula to relate the two. Humidity also
>affects it. It's not exact science.
>Something hotter than the air around it will cool faster with the wind
>blowing by it, whether it be people or things.
There is a standard non-perceptual way to measure wind chill. The US
Army had a full-size statue of a standing man made out of copper
which contains an electric heater and some surface thermocouples.
(The statue may be solid copper, or may be hollow and filled with
moving oil; I don't recall which.) Basically, the amount of
electrical power needed to raise the statue to body temperature (98.6
degrees F) while standing "naked" in the test condition is measured.
For wind chill, the air temperature and windspeed are set to the
desired values, and the amount of power needed to raise the statue
back to body temperature is measured. Then the wind is turned off,
and the temperature is lowered until the same amount of power is
required. This last temperature is the "wind chill" temperature
corresponding to the previous combination of physical temperature and
windspeed.
This statue was invented as a tool to evaluate the effectiveness of
various kinds of cold-weather clothing in protecting the wearer from
exposure.
Joe Gwinn
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