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Originally Posted by Althornin
...Look at JD's numbers for example. .6 and 390 - what good are they? Without the units, thermal conducitivity number mean nothing.
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OK, he doesn't give units, I'll give them to you, standard, almost always used in a metric world, the unit is W/m*°C. Watts per metre for one degree celsius. Even if it was given without a unit the proportion is enough to tell you what you want to know, Copper is ~650 times better than water. Heat transfer is directly proportional to k. Irrelevant for a comparison when we have no idea of the convection coefficient.
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Originally Posted by Althornin
Because thermal conductivity changes based on temp delta and surface area of contact...
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Bullshit. Thermal conductivity changes based on absolute temperature (google Wiedemann-Franz Law). It has nothing to do with surface area and delta T is only relevant insomuch as k is varying slightly throughout the heat path. Slightly.
What I think you mean is that heat transfered, heat flux or watts changes based on temp delta and surface area of contact. Rearrange this to our scenario, temp delta is directly proportional to heat flux 'Q'. Surface area 'A' is a constant, heat path length 'L' is a constant and thermal conductivity 'k' is a constant.
EDIT: Thermal conductance, defined as the inverse of thermal resistance, is perhaps your intended meaning?
The formula, Fouriers Law is Q=k*A*dT/L or for us dT=Q*L/k*A. This applies to a waterblock, it is half the story. It is not applicable to direct die. (except within the die itself, this is the same for DD or conventional WB)
Direct die is almost purely governed by Newtons law of cooling. Water blocks are dominated by it as well, how much so depends on the design philosophy. It is similar. Q=h*A*dt. 'h' is the convection coefficient, units W/m^2*°C. It is a function of water flowrate, thermal conductivity, density, viscosity, specific heat capacity, thermal diffusivity and the main problem, surface geometry and localised water velocity...
We do not know it. Thats the problem.