Cooling things: Difference between revisions
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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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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.