What's the best kind of a stone slab to place under electronic devices to keep them cool?

Question

What's the best slab of stone to place under electronic devices to keep them cool?
Each stone has its own thermal profile which includes its thermal diffusivity, thermal conductivity, and thermal inertia. But I don't know which combination of thermal properties a stone should have to be a good candidate for placing under a laptop, for example, to keep it cool.

Bob D · Accepted Answer

The thermal inertia $I$ of a material can be thought of as the materials tendency to absorb thermal energy. It is a combination of the thermal conductivity $k$ of the material and its volumetric heat capacity $ρc$
$$I=sqrt{kρc}$$
Where $k$ = thermal conductivity
$ρ$= density
$c$= specific heat.
$ρc$= volumetric heat capacity
So to compare slabs of the same dimensions, particularly thickness, those slabs comprised of materials having the highest thermal inertia should should theoretically have the greater tendency to absorb heat.
I haven't found any tables for thermal inertia of stone materials, but here is a site that provides information on their thermal conductivity.
https://www.naturalstoneinstitute.org/stoneprofessionals/technical-bulletins/rvalue/
BTW if it were me I would use a granite counter top. Many folks have them. I use mine to help defrost things like frozen hamburger patties. Works great.
Hope this helps.

niels nielsen · Answer

for optimum heat transfer out of your computer and into the surrounding environment, in the interests of keeping the computer cool, a stone slab would be a poor choice because it does a very slow and inefficient job of conducting heat.
The standard measure of "goodness" for getting rid of heat is a substance's thermal diffusivity, which is its thermal conductivity divided by its density and its specific heat capacity. The diffusivity of sandstone is about 1 and that of aluminum is about 100 which is why heat sinks are made out of aluminum and not stone. Silver comes in at 165, but is a lot more expensive than aluminum, which is why heat sinks aren't made out of silver.

What's the best kind of a stone slab to place under electronic devices to keep them cool?

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