Cooling things: Difference between revisions
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===Windows and windcatchers=== | ===Convection in houses; Windows and windcatchers=== | ||
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Isolation lessens the absorption, though not so much other concentration. | Isolation lessens the absorption, though not so much other concentration. | ||
Which means that throughout the day, the walls in general, and the air in some rooms, will be warmer than the outside air. | |||
Particularly when evening air gets colder in the day. | |||
In fact, desert areas see some specific designs ''exactly'' because the day/night temperature difference is larger, | |||
and you may have a little more space to work with too. | |||
When opening a window on two sides of the house, combined with a little wind, | |||
creates enough draft that you are replacing the air throughout the day, | |||
then you are moving out the concetrated heat, | |||
and replacing it with whatever the outside air is. | |||
Ideally, houses don't trap heat like that, | |||
but where they do, this can matter a few degrees for free. | |||
Windcatchers refers to one of two or three things, | |||
which all amount to designing for some draft without active machinery. | |||
Few are hugely efficient, but it's passive so it's free. | |||
You can lessen local buildup of heat above ambient, but also that you never go below ambient | You can lessen local buildup of heat above ambient, but also that you never go below ambient | ||
One is using already-present wind to create a draft, as just mentioned. | |||
If you can't count on wind, then putting the windows to the north and south helps a little, | |||
because one heats more than the other, and you get some natural convection. | |||
You can also make what amounts to a chimney, that is directly heated by the sun (so on a sun-facing wall), which heats the air inside that chimney so that it slowly moves upwards (and is never in the home), and that air movement draws in air from whatever other ventilation the house has, usually just outside air through windows and such. | |||
In some circumstances you can do even fancier things. | |||
If you are very lucky and have an underground canal near you, | |||
this is likely to be somewhat colder. | |||
If you also have the space for large towers, you can catch wind, | |||
and blow them over that canal. This is basically larger-scale evaporative cooling, | |||
and in theory you can can cool down air to the temperature of that water. | |||
https://en.wikipedia.org/wiki/Windcatcher | https://en.wikipedia.org/wiki/Windcatcher | ||
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===Spray bottle, misting system, etc.=== | ===Spray bottle, misting system, etc.=== | ||
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More efficient, heat-wise? No. | More efficient, heat-wise? No. | ||
They will probably last longer than e.g. water in a PET bottle, though, | |||
because glycol lessens the expansion{{verify}} and thereby the willingness of water to break whatever it is in, particularly in larger containers. | |||
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'''One-time instant ice packs''' | '''One-time instant ice packs''' | ||
The things that go cold when squeezed, | |||
e.g. used in first aid kits, sports, particularly where keeping ice is not practical. | |||
Often contains | Often contains | ||
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It's not advisable to use them as ice packs afterwards, due to the toxicity{{verify}} | It's not advisable to use them as ice packs afterwards, due to the toxicity{{verify}} | ||
https://www.sciencebuddies.org/science-fair-projects/project-ideas/Chem_p081/chemistry/how-do-cold-packs-work | https://www.sciencebuddies.org/science-fair-projects/project-ideas/Chem_p081/chemistry/how-do-cold-packs-work | ||
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'''What is the first-aid purpose of those ice packs?''' | |||
'''What is the first-aid purpose of ice packs?''' | |||
This restricts blood circulation, which can numb pain, and limit the amount of bruising. | This restricts blood circulation, which can numb pain, and limit the amount of bruising. | ||
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====In defrosting a fridge, where does the water go?==== | ====In defrosting a fridge, where does the water go?==== | ||
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The same place that the small but fairly continually generated condensation water goes: out the hole in the bottom, onto a pan over the compressor, which due to being slightly warm will be | The same place that the small but fairly continually generated condensation water goes: out the hole in the bottom, and classically onto a pan over the compressor, which due to being slightly warm will be evaporated somewhat soon. | ||
In theory, | In theory, defrosting large amounts of frost can make that overflow. | ||
Due to positioning this should nor be an electrical risk, | |||
but during manual defrosts you may still care to catch water (use towels), | |||
to not have a pool of water everywhere, including there where you can't see it. | |||
Note that this hole is small, and sometimes clogs with food. Declog is with anything pokey (there's nothing much you can damage here), though there often is a plastic doohickey for it (that you may have thrown away not knowing what it is). | Note that this hole is small, and sometimes clogs with food. Declog is with anything pokey (there's nothing much you can damage here), though there often is a plastic doohickey for it (that you may have thrown away not knowing what it is). | ||
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Latest revision as of 15:04, 30 June 2024
Physical mechanics of cooling
Passive cooling
Passive cooling tends to mean 'what happens with no moving parts'.
...so whatever amount of conduction, radiation, and/or convection would happen anyway.
Sometimes includes adding a fan, to add to the convection.
You're stirring the air better than just convection would, so heat transfer goes a faster than if warm air just sits around - but the difference is rarely much -- convection always does this at least a little when there is temperature difference (if you're in gravity; this is about density differences).
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.