General Question

OperativeQ's avatar

Why do fans or wind feel cool?

Asked by OperativeQ (1222points) March 12th, 2010

This question popped into my head yesterday. Fans blow air, which then hits you and makes you feel cool (as you all know), buy why does it work that way?

I always thought that when something is moved faster, it heats up because of friction with the air. Am I wrong? Am I also wrong in thinking that air has friction with itself?

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9 Answers

noyesa's avatar

Moving air carries heat away.

elenuial's avatar

Your body is always radiating heat (which is why those infrared thingies work), and tries to achieve a stable temperature at all times (this is called homeostasis). A fan or a breeze moves away the air particles which contain some of the heat you’re radiating, so you feel cooler because there is literally less heat around you. Of course, your body will keep generating heat, and the fan will keep moving it, so you always feel “cooler” because you’re constantly being cooled.

Snarp's avatar

In addition to the above, you also sweat imperceptibly, and the moving air increases the evaporation of the sweat. Evaporation pulls heat away from your body.

Zajvhal's avatar

I think @Snarp has the right answer. It’s the evaporation. It’s physics, evaporation is cooling. That’s why in drier climates the heat doesn’t feel as “hot,” because when it’s drier, it’s easier for the sweat to evaporate which is a cooling process for your body. When the air is too saturated, the sweat won’t evaporate, so your body keeps producing more, hoping to cool itself.

elenuial's avatar

It’s a combination of the two. That’s why you get a slight cooling effect from a fan even on a muggy day—you’re still pushing heat around. The evaporation is a big part of it, though, and is definitely responsible for the muggy day phenomenon in general, though.

PrancingUrchin's avatar

It’s called convection which is one of the three primary modes of heat transfer along with conduction and radiation. Convection is the movement of heat through particle movement in a fluid.

lilikoi's avatar

Heat loss from your body stems from convection, conduction, and radiation. Sweat and the evaporation of it is the most efficient way for our body to transfer heat, and I believe involves all three modes (conduction and radiation transfer heat to sweat, convection helps evaporate water). Some of your sweat may just roll off your body before completely evaporating. Doesn’t matter – once the heat is transferred to the water, it goes away as long as the water goes away. When air moves across your skin, convection would play the major role in heat transfer. If you are standing still and there is no air movement and you are not sweating, your body is still losing heat to the environment due to radiation and conduction.

When something moves faster through air, say a person, there is some heat produced due to air friction (skin friction), but it is negligible compared to the heat your body produces via other processes and the amount of heat your body will lose to the air. Air is a bunch of molecules so on a molecular level, the molecules can rub against each other and create molecular friction.

Ivan's avatar

It’s the same reason why you blow on hot food. You blow the hot air surrounding the food so that the temperature gradient between the food and the surrounding air becomes steeper, allowing more heat to flow out of the food.

Jabe73's avatar

Same reason you feel colder on a 0 degree morning with a 40 mph wind than on a 0 degree morning without the wind, wind chill factor. Moving air blows away generated radiant heat faster, if your wet even faster yet, because liquids absorb heat.

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