Originally posted by: Evadman
that seems like too high of an increase. I can't believe that the grease is inhibiting that much heat transfer. I need to learn more about thermodynamics.
Q=UAdT, where dT is the log mean temperature difference between the two sides, A is the area through which heat is conducted, and U is the conductance....basically a constant k over the thickness dx.
You have to dissipate a constant amount of heat, equal to the CPU's output...so in the neighborhood of 100W. Being able to do this across a low delta-T requires the conductance to be very high. Assuming that the heatsink temperature at the point of contact is ~30 degrees in both cases, and the thickness of the paste is constant, that means that the diamond paste has to be 3 times as conductive as the AS. Is we assume the heatsink is at ~20 degrees, that goes to 1.9 times as conductive to achieve the stated performance (54->38).
That's well within the stated difference in conductivity between silver and diamond, where of course the grease that holds the stuff in suspension will decrease the performance of both.