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Originally Posted by wijdeveld
I've done some calculations for a phase-change setup (Vapochill PE) with different evaporator materials.<snip>
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Density and "warmth" are irrelevant in a system at equilibrium.
The thermal conductivity is all that is important when it comes to a base-plate material.
An evaporator head is a significantly different scenario to a waterblock. An evaporator requires a fairly long "residence" time (in comparison to water) for the coolant to evaporate to give its full effect. Depending on the design the actual area over which the coolant evaporates will be fairly large. This then necessitates a fairly thick base-plate thickness to minimise the spreading resistance for the heat of the CPU to the full area of cooling effect that is provided by the evaporating coolant. Due to the thickness of the bp material, the difference between copper and silver can be fairly significant.
In a waterblock where there is no evaporation and the effect of the cooling is not time/location dependent as per the flow rate of coolant, thus the point of cooling may be much more concentrated. This enables the very thin base-plates that Cascade SS and the S-TDX are using, being well under 1mm on average (excluding the wall sections), as there is less of a need to minimise the spreading resistance of the bp material.
Calculate the spreading resistance difference between silver and copper over that sort of thickness, and apply that as a ratio of the total thermal resistance of the entire "TIM, bp, convectional" heat-flux pathway, and the net C/W difference works out to around 0.003 or so for the die-size that Phaestus is using. Given his predicted heat-load, that's about a 0.2C difference, or something which can easily be "hidden" through even minor variations in lapping quality.