Everything in Keltari's answer is right, I just want to expand it with
some other important info:
When you want to "transfer" heat, you need to deal with 2 major values:
Thermal conductivity and heat capacity. First is how easily get/give
heat from/to other material, like get the heat from hot surface and
give the heat to cold surface. The second is how much energy can it
store.
Thermal conductivity of liquid metals are very low compared to solid ones.
Pure, solid, aluminium has a thermal conductivity of about 200 W/(m K), pure copper is about 390 W/(m K). Mercury, on the other hand, has a value about 8.5 W/(m K) and the value for water is about 0.6 W/(m K). So liquid metals
are better than water for heat transfer, but much worse than solid metals.
The heat capacity is another part. A 1 K change in temperature (i.e. 1 °C or 2 °F change) for liquid water requires 4.187 kJ/kg, while the same change for mercury is 0.125 kJ/kg, this means same heat from the CPU surface incurs a 32 times larger temperature change in mercury!
If we think simply, 14 times better conductivity and 32 times worse
heat capacity is about 50% worse sum related to water cooling, and
still not taking into account other dangerous factors, like toxicity or
the short circuit factors. (This calculation is not proper, because
there's many other parameters which these values depend on, such as current
temperature, pressure, and there is side dissipation on transfer, etc.)
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– Journeyman Geek – 2018-03-02T06:09:38.090How many metals are liquid at room temperature? All of the other metals would need to be heated to a high temperature, which would heat up—rather than cool down—your system. – Infiltrator – 2018-03-02T06:24:59.197