How does a fan cool your skin, exactly?

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Discussion Overview

The discussion centers around the mechanisms by which a fan cools the skin, exploring concepts such as evaporative cooling, heat transfer, and the effects of air movement on temperature perception. Participants consider both theoretical and practical implications of these phenomena.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that the cooling effect of a fan is primarily due to increased evaporation of moisture from the skin, while others suggest that it also involves the removal of warmer air and replacement with cooler air.
  • There is a question about whether air movement generates heat due to increased kinetic energy and pressure, with some participants affirming this idea.
  • One participant mentions that even without evaporative cooling, the body transfers heat to the surrounding air through conduction and radiation, which can be enhanced by the movement of cooler air.
  • Another participant raises a hypothetical scenario regarding the effects of hotter incoming air on evaporation and whether it could outweigh the cooling effect.
  • The concept of wind chill is introduced, with a participant sharing a personal experience of extreme cold and its effects on skin temperature.
  • There is a discussion about the relationship between moving air, pressure, and temperature, with some participants questioning the effects of friction and pressure changes.

Areas of Agreement / Disagreement

Participants express a range of views on the mechanisms of cooling by fans, with no clear consensus reached. Some agree on certain aspects, such as the role of evaporative cooling, while others challenge or refine these ideas, indicating ongoing debate.

Contextual Notes

Participants reference various conditions and scenarios, such as extreme temperatures and air movement, which may influence their claims. There are also unresolved questions regarding the interplay of heat generation and cooling effects in different contexts.

Who May Find This Useful

This discussion may be of interest to those studying thermodynamics, heat transfer, or anyone curious about the practical effects of air movement on temperature perception and comfort.

brainstorm
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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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brainstorm said:
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?

Yes. Yes. Yes. Yes.

In that order.
 
OmCheeto said:
Yes. Yes. Yes. Yes.

In that order.

Gee, I was hoping I was thinking some of it wrong and I would learn something from posting it as a question.
 
brainstorm said:
... Or does it blow air being warmed by your skin away from your body to be replaced with relatively cooler air?...

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.
 
brainstorm said:
Gee, I was hoping I was thinking some of it wrong and I would learn something from posting it as a question.

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).
 
Danger said:
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).

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.
 
brainstorm said:
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?

I believe that it would depend upon both the temperature and the speed of the airstream. The blast wave from a nuke might be traveling at 2,000 km/h when it hits, but at 1,000° C it's still going to burn you. (Alright, that's an extreme example that overlooks the obvious, but it's just a "for instance".)
 
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.
 
PhanthomJay said:
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.

Welcome to winter in Alberta.
 
  • #10
Dr Lots-o'watts said:
Moving air would produce heat if it were directed to air that was colder.

Because of friction?
I would have thought that moving air lowers the pressure and thus the temperature too.
 
  • #11
Danger said:
Welcome to winter in Alberta.
Brrrrrr...how cold does it get there? How windy?
 
  • #12
Sakha said:
Because of friction?
I would have thought that moving air lowers the pressure and thus the temperature too.

The moving air itself has a pressure. Assuming a normal everyday fan, the differences in pressure between the static air and the moving air isn't noticeable to those who are enjoying the cool refreshing breeze.
 

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