"Wind chill" below absolute zero
Oct. 24th, 2006 02:21 am![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
jack1. 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?
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?
Re: Physics Attacks!
Date: 2006-10-24 11:28 am (UTC)This is one of the things I read about, but didn't quite understand. You don't happen to have a link to a clear explanation handy, do you?
It implies the wind is somehow causing a population inversion.
What? I agree, if wind actually cooled something to below 0k, that would require [weird entropy stuff], but I have no idea if that's remotely plausible, and certainly didn't postulate in my example anything at or below absolute .
Maybe you could have a negative solar windchill if you tried hard enough.
Oh?
Re: Physics Attacks!
Date: 2006-10-24 01:04 pm (UTC)No, not really if you don't understand Wikipedia's. The basic idea is that normally energy states fill up from the bottom (low-E) end - occupation of a state being proportional to exp (-1/kT) or something close thereto depending on exactly what it is that is filling the state up. Obviously if T is negative they would start filling up from the top (high-E) instead. This is good if you want to make a laser.
Re: Physics Attacks!
Date: 2006-10-24 02:41 pm (UTC)