How does cool temperatures get rid of sweat faster than higher temperatures? Isnt the rate of evaporation higher at higher temperatures?
In: Physics
From a human perspective “warm” and “cool” consists of a relatively narrow temperature range. The relative humidity affects the rate of evaporation far more than the small differences in temperature.
You are right, cold air decreases evaporation rate. However cold air is often dry, whereas hot air is often humid, this makes it harder for you to evaporate the sweat in hot humid environments.
There is also the fact the body doesn’t sweat in the cold, whereas you are adding to the amount of sweat in the heat.
I think there is probably a perception problem, which is caused by humidity.
When it is humid, there is a vicious double whammy in your *perception* of the effectiveness of evaporation at higher temperatures. Humidity reduces the evaporation rate (for any given temperature), and evaporation of sweat is of course a key means for your body to lose heat.
This means that when it’s hot and humid sweating is less effective due to humidity so it is harder to get rid of heat which means that:
* because you are hotter you sweat more, so the evaporation of sweat that does occur is harder to notice because sweat is replaced as fast as it evaporates; and
* on top of that, you perceive it to be hotter than it is, for the foregoing reason.
But actually evaporation is occurring rapidly. I live in the sub-tropics. On a hot very humid day I can drink large amounts of water, *feel* like sweating is doing nothing, and yet not need to pee. That water is going somewhere.
When it is hot and not humid, evaporation rates are sky high.
Rate of evaporation depends on temperature *and* relative humidity. The fastest way to evaporate water is to pass dry, hot air over it. However, being exposed to hot temperatures will also make you sweat more. So, cool temperatures *can* get rid of sweat faster simply because you’re not sweating as much. Also, cool air with low relative humidity might allow for faster evaporation than warm air with high relative humidity, but that all depends on exactly how warm and how humid the air is.
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