Cooling passive material

[lolherp]

Are there any materials that are able to dissipate heat? I know how computers can run different chemicals, water, and other stuff to cool it but is there a passive material that can decrease heat?

[John Cuthber]

No, there can't be.

At least not for any length of time.

You could use something like a wax that melts and absorbs heat, but you would have to keep supplying it with solid wax to keep it cool.

[lolherp]

How about for relatively "low" temperatures?
Like temperatures up to 140 degrees Farenheit?

[Fuzzwood]

The heat has to go somewhere, the energy cannot simply vanish.

[lolherp]

Of course but I meant something that is very good at absorbing heat and keeping it there and then later when it's cooler, is able to dissipate the heat quickly and at not-low temperatures.

[swansont]

For there to be spontaneous heat transfer with a there must be a temperature difference, with the heat flowing from hot to cold. A substance that retaining absorbed energy (i.e. it has a high specific heat capacity) would also tend to lose that energy slowly.

[Bill Angel]

The mixing of ammonium nitrate and water is an endothermic reaction that is used in cold packs to absorb heat. It is also reversible.

[John Cuthber]

I have a bottle with some ammonium nitrate solution in it.
How long do I need to watch it before the dissolution reverses?

[Bill Angel]

The ammonium nitrate doesn't react with water, it is just hydrated by it. That means the water molecule is left intact and is just electrostatically bonded to the ammonium nitrate molecule. The water being absorbed by the ammonium nitrate is an endothermic process and is reversible. You can heat up the ammonium nitrate and drive the water off the compound.

[swansont]

IOW it's not a spontaneous/passive system, as specified in the OP.

[John Cuthber]

It would be simpler to just use evaporating water as the coolant.

[Enthalpy]

Said water or easily vaporized liquid could be in a closed circuit, eliminating the need to replenish it. Then the heat sink could be farther away from the heat source, hence bigger and more easily blown with fresh air.

 

An especially interesting shape of closed circuit is a tube whose inner faces are corrugated, possibly sintered, so the liquid wets them well. This would enable vapour to flow at the middle of the tube and liquid to flow back at the wall, even in seemingly less favourable orientations.

 

The tube being hermetically closed, the pressure could adapt to the operating temperature.

 

We're on the verge of inventing the heat pipe.

[CaptainPanic]

If you are looking for something without a flow (no water, wax, air), and no energy input (no electricity required, so no Peltier element), then you are looking at a radiator.

 

Here's a random website which shows some passive cooling units (note: these still require the air to circulate). Scroll down to "Passive Air Cooling".

 

Finally, even in space, radiators work. The ISS has radiators too, but I can't find a good picture now. Still, these only work if the radiators are relatively hot in comparison to whatever they are radiating at.