"Wind chill" below absolute zero

[jack]

1. What is wind chill temperature? A human in cold air in a wind feels as cold as a human in colder but still air. We have fitted some approximations to this and come up with an official scale, but it was originally based on subjective judgements, and depends on other conditions as well, eg. humidity, so isn't definitive, but is a useful measure.

2. How a human feels doesn't really have meaning when you get near *that* cold. Instead death feels much like instant death :)

3. However, you should be able to create a standardised measure, right? Have object X at temperature T K in medium Y at temperature 0.x K and pressure Z, flowing at speed v. Establish the rate of heat loss at that moment (which is at least theoretically calculable). Define "wind chill temperature" to be the temperature in still medium at which the rate of heat loss is the same.

4. Could X lose heat faster under some speed than in still near absolute zero medium? I don't see why not. Physics is weird down there, but it can still heat up the surroundings, etc.

5. Does that make a negative Kelvin wind chill? On the one hand, it implies a wind chill colder than absolute zero. On the other hand, it doesn't actually define a wind chill at all because there is no temperature to compare it to. If you have a nice non-asymptotic graph you could extend it, but does that have any meaning?

Comments

Re: Physics Attacks!

[1st-law.livejournal.com]

Negative theta temperature is no more or less "absurd" than a negative temperature due to wind chill even if it is somewhat less likely to be encountered in practice. It is a negative number that drops naturally out of the way we've chosen to define the scale. A population inversion is similarly an artificially defined scale in which you pick only the energy levels of interest. Both the other examples are hardly concerned with thermodynamics though negative temperature in a population inversion is a case of fitting a Boltzmann distribution to something doesn't actually have one (though two points do always make a line).

As an aside you'd presumably have to assume that the air didn't liquefy....or you could have a scale in which it did but I think it's simpler assuming it remains an ideal gas....

I think your point about additive and multiplicative constants is a valid consideration but only if you want to apply the scale to non-humans, which the vast majority of weather forecasters don't.

Wind chill doesn't define something that would cool anything at all. The scale is defined by a constant body temperature. Similarly it's not a measure of heat flux. A normal human can't produce much more than ~100W of thermal energy sustainably. If they find themselves needing to produce more they should put some more clothes on which is the whole point of knowing the wind chill factor.

Why measure heat loss in terms of a temperature? If you were a mountaineer climbing Everest would you rather know the Reynolds number?