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bikerlegs t1_j5q9frf wrote

Everyone has already mentioned the flaws with the temperature gun so I won't delve into that. Instead I'll explain "wind chill". Temperatures feel colder when there is wind for 2 main reasons.

One of them being evaporation on a wet surface. This is why licking your finger and holding it to the wind helps you tell the wind direction by which side the cold part of your finger is facing. Wind accelerates evaporation which is an endothermic process (absorbs heat).

The second reason is that heat transfered through conduction happens when two molecules bump into each other and exchange their individual kinetic energy. Much like two balls in billiards hitting each other. When a while material is subjected to this the kinetic energy of each molecule is represented as heat. So wind allows more molecules to bump into each other and thus more heat transfer.

Now, it is incredibly important to note that this process of heat transfer through conduction works in a specific way to AVERAGE the temperatures between two materials. So cold air cools and hot hair heats up. Don't believe me? Hold your hand in front of a hair dryer. 😆 Given your material isn't wet evaporation can be dismissed and temperatures will only average. So that means your hot oven is definitely heating any material you throw in it that is at a lesser temperature until they reach a state of equilibrium and the convection (wind) accelerates this process.

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a_cute_epic_axis t1_j5qnz9n wrote

Wind chill can never reduce the temperature of an object below the dry bulb temperature of the air, unless that object is wet. In that case evaporation can occur and will result in cooler-than-dry-bulb temps until the water evaporates or until the air reaches 100% humidity.

The only time wind chill has any other effect is if the item in question is producing heat...e.g. a person or a house with the heat on inside. In this case the object will experience greater heat loss as the windspeed goes up. If the object doesn't have an internal heater, then the wind chill will speed cooling until the object reaches the dry bulb temp, and then have no impact.

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TommyTuttle t1_j5qa6nf wrote

But I’m confused about one thing: wind chill does not reduce actual temperatures. If water is in a chamber at one degree above freezing with a wind chill of 20 below, that water will not freeze. Because the temperature is still above freezing. The only freezing you’d get is due to evaporative cooling, ie an actual drop in the real local temperature of the water.

Metal is not subject to evaporative cooling. So I’m confused as to how wind chill might lower temperatures in a hot chamber. You’d think the wind would bring everything rapidly to the air temperature.

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jawshoeaw t1_j5qcc6n wrote

That's correct. Windchill annoys me. It's often misused and confusing. There are Reddit posts saying things like "Here I am in Michigan in a T shirt, it's -60F today". but it's actually 0F with windchill of -60F. And yes, wind does not cool things below ambient unless they are wet (or unless the wind itself is bringing in colder air)

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jawshoeaw t1_j5qd1il wrote

Windchill is a human experience and does not apply to physical objects like a computer. No matter how fast the wind is blowing over your dry computer, it cannot reduce the temperature below the temperature of the air making up the "wind". What it can do is reach an equilibrium temperature faster. At least in my experience (and wikipedia) this phenomenon is called "air cooling your computer" and not wind chill.

edit for clarity: wind definitely cools things off faster than no wind :)

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bikerlegs t1_j5qdk4w wrote

This isn't true. I also just looked on Wikipedia and it explains the same thing I explained. Wind chill is the additional cooling effect that wind brings. Not necessarily from evaporation, it still included conduction. So you're dry computer is still experiencing wind chill by definition.

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jawshoeaw t1_j5qdu0v wrote

From the very beginning of the article on Wikipedia:

"Wind chill or windchill (popularly wind chill factor) is the lowering of body temperature due to the passing-flow of lower-temperature air.

It's a non-scientific term with no agreed exact formula and has nothing to do with inanimate objects.

Edit: Of course wind cools things - didn't mean to be nit-picking, I just don't like "windchill" because it's poorly defined. I mean there could be moisture on inanimate objects, that could be removed by dry air and cool further.. but there are good terms for those phenomenon such as evaporative cooling, convective, etc.

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a_cute_epic_axis t1_j5qoaif wrote

> Windchill is a human experience and does not apply to physical objects like a computer.

It does if the computer is on and is exposed to wind. It has nothing to do with being human or alive, and everything to do with having an internal source of heat. Even in things that have no source of heat, wind chill will accelerate cooling until the object reaches the dry bulb temp (assuming there's no evaporation), as you mention... which rather obviously means it is not limited to "human experience".

You can argue that the term windchill refers to something typically used to describe human/animal outdoor comfort, but the concept is in no way limited to that.

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