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.

Ignoring the effect from length scaling and drag from walls, it gets more complicated. Liquids have viscosity, and do in fact behave differently at different scales. We use the Reynolds number to describe the different behaviors - laminar or turbulent flow. At small enough scales, your vortices will dissipate very quickly, and at large enough scales, you can ignore viscosity.

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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>The larger volume's energy would dissipate slower.

Why though? Why is volume relevant here

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Moving air does actually cool better without evaporation. The air just has to be colder than the thing. That’s why your computer has fans.

Even if the linear velocity of the pool is the same, that is a lot more mass moving at that same velocity. It would have much more momentum and take longer to slow.

Yeah, but that's usually what people are actually thinking of when they say "moving air cools better". It's not really the air moving, it's the evaporation, but the average person doesn't necessarily know that.

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> Usually these thermometers accept emissivity as a setting

That little nugget said more than most of the in-depth answers above. Thank you, you done good.

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That’s not an exception, it’s a different thing from convective heat transfer

Note that this author seems to think that "depression" is more primary than brain physiology. Depression is a basket term for symptoms, not an underlying physical illness diagnosis. On a brain scan you can find things like inflammation, which is not mentioned in teh DSM at all, but you can fix mental health problems by addressing inflammation.

A "laser thermometer" as commonly sold is just a small FoV infrared thermometer with a laser pointer strapped on top. (The exception is very advanced thermometers which use calibrated lasers and optical ranging to measure reflectivity.)

Usually these thermometers accept emissivity as a setting. They don't measure it.

Yes. Mostly because of momentum and friction.

Your small cup has a much higher friction at the edges in proportion to the momentum of the circling liquid.

You could of course balance this by stirring the swimming pool at a slower rate - but that wasn't part of your question...

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Answer: Your question is a bit of a misnomer in itself and your coworker doesn't seem to understand thermodynamics - The real question is why the center of the oven is warmer than the outsides of the oven, which yes, is partially due to convection (the movement of the fluid in the oven circulating away heat as it travels) and the design of the oven (where latent 'pools' of fluid allow heat to build up), but is mostly due to the fact that the fluid being circulated is AIR which is an insulator due to the nature of the gas composition and it being in gaseous form. Air insulates regardless of its velocity, but as father Bernoulli taught us, the faster it moves under constant pressure, the less entropy is able to pool into measurable heat. For this oven, it makes sense that the outsides would be cooler than the insides, since the whole point of an oven is to concentrate high heat within a container that won't combust. There are other issues at play such as the difference conductivity and radiation constants of different elements, but that's another reason why oven's are constructed with materials that melt far above the safety limits, such as sand/acrylics. You can measure this yourself by going into a temperature controlled environment (read: "in-doors") and touch a wooden surface, then touch a metal surface, noting that the metal surface will always seem cooler to the touch because metal is a poor insulator and will emit heat calories to entropy at a much greater rate than wood, which is carbon-based and has evolved to literally be pockets of air at the molecular level.