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How does a fan cool your skin, exactly?

  1. Sep 17, 2010 #1
    Is the only reason air moving over your body caused by a fan or breeze feels cool because of increased evaporation of moisture from your skin? Or does it blow air being warmed by your skin away from your body to be replaced with relatively cooler air?

    Also, does air movement also produce some amount of heat, albeit very small? I wonder this because it seems like the air movement would increase the kinetic energy of air against your body and maybe also raise the air pressure as well. Is heat produced as well as mitigated by a fan?
     
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  3. Sep 17, 2010 #2

    OmCheeto

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    Yes. Yes. Yes. Yes.

    In that order.
     
  4. Sep 17, 2010 #3
    Gee, I was hoping I was thinking some of it wrong and I would learn something from posting it as a question.
     
  5. Sep 17, 2010 #4
    Cannot be said any better without equations.

    Moving air would produce heat if it were directed to air that was colder. Perhaps if you blew a strong enough fan on snow, a small part of it might melt. In usual settings though, hot still air contains more energy than the incoming fan air.
     
  6. Sep 17, 2010 #5

    Danger

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    Well, you were wrong in that assumption. Jeez, what a dummy! :biggrin:
    Even in the absence of evaporative cooling (sweat), the body still transfers heat to its surroundings by conduction and radiation. Replacing that surrounding air with a fresh batch of lower temperature will be felt as cooling. If the incoming air was hotter, you would feel that as well, but not in a pleasant way (unless it's winter, which it pretty much always is where I live; it's supposed to snow again tonight, and I'm not happy about it).
     
  7. Sep 17, 2010 #6
    If the in-coming air was hotter, would evaporation-cooling still increase due to the air-movement and would this outweigh the effect of the incoming heat?

    This makes me think of those guys stuck in the collapsed mine shaft. I believe I heard the temperature in the mine is in the upper 30s (celsius) and it doesn't cool down at night. At least they seem to have plenty of room to walk around.
     
  8. Sep 17, 2010 #7

    Danger

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    I believe that it would depend upon both the temperature and the speed of the airstream. The blast wave from a nuke might be travelling at 2,000 km/h when it hits, but at 1,000° C it's still gonna burn you. (Alright, that's an extreme example that overlooks the obvious, but it's just a "for instance".)
     
  9. Sep 17, 2010 #8

    PhanthomJay

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    I remember some years ago atop the 6000 ft summit of Mount Washington in New Hampshire (USA) when the air temp was 35 below zero( degrees F) and the wind was blowing at hurricane strength. The Wind Chill factor (a measure of what it feels like, compared to a near calm wind at that air temperature, due to heat loss), was something like 80 degrees (F) below zero! Skin would freeze in a matter of seconds under those conditions.
     
  10. Sep 18, 2010 #9

    Danger

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    Welcome to winter in Alberta.
     
  11. Sep 19, 2010 #10
    Because of friction?
    I would have thought that moving air lowers the pressure and thus the temperature too.
     
  12. Sep 19, 2010 #11

    PhanthomJay

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    Brrrrrr...how cold does it get there? How windy?
     
  13. Sep 19, 2010 #12

    Drakkith

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    The moving air itself has a pressure. Assuming a normal everyday fan, the differences in pressure between the static air and the moving air isnt noticeable to those who are enjoying the cool refreshing breeze.
     
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