Cooling things: Difference between revisions
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It doesn't cool quite as quickly, but that's generally not an issue. | It doesn't cool quite as quickly, but that's generally not an issue. | ||
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===Is a flipped AC a heater?=== | |||
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In various countries, ACs are designed that way. | |||
When they are not, you could still mount them in reverse, but it's not going to be nearly as efficient like that (real question is whether its CoP is still >1 like this) | |||
and there may be reasons it will not work like that, or isn't the safest thing to do. | |||
For various reasons. | |||
Function: Most ACs them will stop moving heat if the cold side is below 15C or so. | |||
Efficiency: An 'hot outside, cool inside' AC is generally not going to push for more than 15 C of difference. | |||
" When it's freezing outside, you need more than that. | |||
Efficiency/safety: This also carries into the size of the condenser and evaporator. | |||
: Would this lead to pressure issues? | |||
Efficiency: Various designs deal with cold-side condensation by vaporizing it. That doesn't make much sense when that's outside. | |||
These and other potential issues are designed out of heat pump systems. | |||
Revision as of 22:27, 9 August 2023
Physical mechanics of cooling
Passive cooling
Passive cooling tends to mean 'what happens with no moving parts'.
...so whatever amount of conduction, radiation, or convection would happen anyway.
Sometimes includes adding a fan.
You're stirring the air better than just convection would, so heat transfer goes a little faster than if warm air just sits around - but the difference is rarely much (if you're in gravity, convection will happen).
And you could argue that's technically active cooling (because you're adding work, so using energy), but intuitively it feels like it hardly qualifies.
On the technical side
This tends to mean
- conduction - a good conductor spreading heat throughout
- if any cooling happens, conduction's spreading brings the whole down
- radiation - thermal radiation means movement of charges in materials (anything above 0 K) is radiated as EM at the surface
- (black-body radiation can be seen as a "thermal radiation's real-world math becomes easier if we make some assumptions like that it's not really interacting in other ways")
- convection - fluid flow, in this context often
- air,
- flow caused by heat changing temperatures and densities
- that flow assisting better heat interchange with that fluid, because warmer air moving up tends to draws in colder air from the sides (which technically is an effect that needs gravity)
In practice there's more than one of these happening, but often one that counts for most exchange.