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I thought that if you're wet, a breeze will feel cold because the water moisture is evaporating and whisking away heat along with it. With a towel at room temperature (same temperature as a breeze), the heat will be whisked away even faster, all in a moment in fact. So shouldn't that feel really cold?

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Evaporation cools you down, not water getting whisked away from your body!

Temperature has to do with the average energy states of all the particles in a substance. Only the high energy (think $212^o$ or higher) particles will escape via evaporation. If you take away all the high energy particles, what happens to the average? (hint it goes down).

On the other hand, with a towel, you're taking away any water molecules that touch the towel, so it doesn't change the average energy of the water on your skin and therefore it doesn't lower your skin temperature.

For a crude simulation, consider the distribution of temp. of water molecules on your skin (disclaimer: it's somewhat meaningless for an individual molecule to have a temperature, but the general idea works here):

enter image description here

The black line indicates the average temperature. Notice what happens to the average when you get rid of everything above 212:

enter image description here

And contrast with just taking away a bunch of water molecules at random with a towel:

enter image description here

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  • $\begingroup$ +1 thanks for that answer, I seriously appreciate it. Next time I will actually read the question. Regards $\endgroup$ – user154420 Jul 4 '17 at 17:14
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    $\begingroup$ I agree with this answer except for your mention of temperature when it comes to evaporation. Yes, only the "high energy" particles evaporate (because they can escape the bond); but they are not at 212°. Evaporation can occur at lower temperatures depending on the pressure and humidity; temperature of the water itself doesn't have to be at the boiling point. The "whisking away" helps to lower the partial vapour pressure right above the area where you just evaporated vapour into; keeping the energy barrier to evaporation low (and adding convective heat transfer). $\endgroup$ – JMac Jul 4 '17 at 17:20
  • $\begingroup$ @JMac I knew someone was gonna chime in with that. I'm trying to give a simple answer to a conceptual question. Appealing to the 212 temperature is the most intuitive when thinking about the water molecules changing phase. I mean an individual molecule can't even have a well defined temperature, I'm glossing over some stat mech for them. $\endgroup$ – Señor O Jul 4 '17 at 17:26
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    $\begingroup$ @SeñorO I think omitting to mention a specific temperature is doing a far bigger favour than including it in the hopes it will be glossed over in the appropriate way. It's those kind of statements that confuse people when they go to learn more complex variations on a topic. "But I was told that it actually does get to 212°" is something I can imagine a student saying; and oversimplifications like that are how you get there. $\endgroup$ – JMac Jul 4 '17 at 17:45
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The main flawed assumption here is that the towel carries away heat faster than evaporative cooling of the water. In reality, a dry or even slightly damp towel is a thermal insulator, meaning that rubbing yourself dry with it doesn't really transfer all that much heat from you to the towel. In the process, though, you're removing a very effective source of heat transfer (namely, evaporative cooling), so you get a net warming effect.

Supporting this line of thinking is the fact that rubbing a soaking wet towel on you is extremely unpleasant in its coldness, since you're not removing any of the water that's on you; you may in fact be prolonging the cooling by replenishing the water that evaporates.

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  • $\begingroup$ I think more importantly to the "warm" feeling of a towel is not that it removes the water; but the fact that it is a thermal insulator and people are relatively warm. That means the towel helps to hold your heat in (and rubbing a towel adds friction). Note that none of this changes the answer or directly relates to the question; just more of how you feel. $\endgroup$ – JMac Jul 4 '17 at 18:08
  • $\begingroup$ i don't see how a towel being an insulator will do anything simply because its not going to be on your body long enough to insulate your heat. Also, i don't typically rub myself dry, I just mat myself down. $\endgroup$ – Goldname Jul 4 '17 at 22:35
  • $\begingroup$ i don't see how a towel being an insulator will do anything simply because its not going to be on your body long enough to insulate your heat. Also, i don't typically rub myself dry, I just mat myself down. $\endgroup$ – Goldname Jul 4 '17 at 22:35

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