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Glasnerven t1_j5rhfa4 wrote

Reply to comment by VulfSki in Why does hot air cool? by AspGuy25

> Just because air is flowing, doesn't mean it's cooling down the metal. Flow doesn't equal cooler.

Roughly speaking, flow equals better heat transfer. We're used to thinking that flowing air = cooler because we--our bodies--are usually warmer than the air around us. Even if it's hot enough outside that the air is warmer than we are, then we're probably sweating, so we have evaporative cooling going on--and flowing air makes that happen faster.

So, in our personal experiences, we almost always find that it feels cooler when air flows over us. It's really easy to over-generalize that and assume that it's a universal law.

You can easily test it at home, though. Get two little cups of ice, make sure there's the same amount of ice in each one, and then put a fan on one and let the other sit in still air. You should notice that the ice with the fan melts faster--the flowing air is heating it faster than the still air is heating the other ice.

You might also already have a device built around this effect: a convection oven or air fryer.

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VulfSki t1_j5rqk0a wrote

Yes, I understand how all that functions. Humans get cooked down from perspiration, which is because the energy to evaporate sweat is partially comes form the heat on our body, and air flow helps with that.

But airflow itself doesn't equal cooking in the general sense, because it only works if you are removing heat by taking it to something that is at a lower temperature, can't violate newton's law of cooling.

You did provide a great explanation, even though I was already aware of all that.

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