Cooling things

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Physical mechanics of cooling

Passive cooling

Passive cooling tends to mean 'what happens with no moving parts'. 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
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.

Evaporative cooling

Refrigeration cycle


Heat pumps

Free cooling

Dessicant based systems

Peltier effect and related effects


Peltier device behaviour and uses


On efficiency

Using the effects - practice and products

When passive cooling works

Windows and windcatchers

Convection in houses

Device cooling

Passive device cooling


Heat pipes and vapor chambers

Personal cooling

Fans / Why wind helps even when you're not sweating

Spray bottle, misting system, etc.

Some small tricks

Wrapped towel


Swamp coolers

Mini dehumidifier

"Personal ACs"

Air conditioning

One-hose and two-hose portable air conditioners

Car AC

Is a flipped AC a heater?

"Eco coolers"

Passive effects


Parts of designs

Heat exchanger


Cold and hot drinks

Ice packs



Adding some more considerations: SCOP, EER2, SEER, SEER2, CEER

More on fridges and freezers


On frost

Does a lot of ice make a fridge/freezer less efficient?

My freezer causes freezer burn on food, what do I do?

In defrosting a fridge, where does the water go?