As I understand it, in a wind you feel colder than in stationary air at the same temperature because you lose heat faster. There are various formulae for approximating the equivalent actual temp in terms of temp and wind speed.
These formulae can give a value below 0K, which at first glance is a reasonable extrapolation, but is actually fairly meaningless partly because there isn’t an actual temperature for it to be equivalent to but mainly because the formulae are approximations and thus only valid in the range they were tested, which probably is way above even 100K, because if you chill in that you’re probably dead.
OTOH, if you define the chill in terms of heat lost per second or something, it could be meaningfully defined below 0K, I think; though I’m not sure, possibly these calculations are also unextrapolatable approximations.
Actually, assuming you had some substance actually moving about you at absolute zero (sort of a contradiction there), it would probably be * adding * energy into the system via molecular collisions, and there'd be an inverse windchill effect, albeit one that could only be measured with sensitive instruments.
Micco is wind chill really caused by forced convection currents? I was always under the impression it was caused by an increased rate of evapouration (though admittedly I’ve never studied wind chill).
Wind chill is a very real phenomenon. You feel colder because you are colder.
And it’s not just humans that experience “wind chill”; many inanimate objects are also affected. After shutting off your car, the engine will cool off faster if it’s windy[sup]1[/sup]. And your home heating bill will be higher during a windy month[sup]1[/sup].
[sup]1[/sup][sub]Compared to the same temperature with no wind.[/sub]
Wind chill in humans is caused by two factors; loss of heat through evaporation of surface moisture and the fact that heat will more readily be transferred to new, cool air than it will to a layer of relatively static air that has already absorbed some body heat. Either or both of these factors can affect non-human objects too.
In most cases where wind chill is an issue, forced convection is the dominant mechanism. None of these mechanisms act in isolation, so at any given time you may or may not have conduction, natural convection, forced convection, radiation, and evaporative cooling. Almost all of these will be affected by wind velocity to some extent. If you want to rigorously calculate the heat transfer, you have to consider all mechanisms and how they inter-relate. But in most cases, one of them will dominate at least to a first-order approximation.
Wind chill doesn’t just affect exposed skin. It’s still an issue when you’re wearing a heavy coat. The coat insulates your body, which means there is a temperature gradient from the inside of the coat to the outside, but you’re still losing heat through it. This means the outside of the coat is warmer than the ambient temperature and wind chill causes it to lose heat faster than it would if there were no wind. Evaporative cooling is probably pretty negligible here unless you’re moving significant amounts of vapor through your Gore-Tex. I haven’t studied that particular case so I can’t say for sure, but I suspect the evaporative cooling would be minimal compared to the forced convection in most cases where we think wind chill is important.
Evapouration would most defintely be the major factor given some conditions. Thinking about it though it seems to me at temps less than ~5C you would expect forced convection currents to dominate.
Are the effects of evapouration included in the defintion of ‘wind chill’? If they were it would be possible for wind chill to cool something below the ambient temp.