Originally Posted by

**Aeschylus;13107461**
Heat transfer is often modeled as circuits, believe it or not, and I think this visualization method is the most straightforward one for describing it. A resistor of value 12 ohms puts up less resistance than a resistor of 50 ohms.

Material 1 (CPU): 50 ohms (COMPLETELY arbitrary, just for sake of argument.)

Material 2 (grease): 20 ohms (ditto)

Material 3 (HSF): 30 ohms (ditto)

The energy flowing through the composite material has an easier time going through the grease than through the HSF or the CPU. You get the idea.

Now, this surely isn't the full story, but I hope this helps describe that one needs to examine the heat transfer through each individual media to understand what kind of energy is being transferred to the adjacent media. Each Material X is going to be a set of equations all its own. Once you solve one layer, you can move on to the next.

Heat transfer was arguably the most difficult and wide-spectra course in the mechanical engineering department at my university, so a sufficiently able person could go into hours worth of explanation on this one simple example.

The gist of it is: overall conductivity can't really be coalesced into a single value - at least not without some rudimentary analysis, i.e., it isn't as simple as treating the lowest value as your k-value.

There are formulas, but if I showed them to you, you might vomit. Perhaps a more able mind on here can show you an easy way of looking at them, but my professor did his best to keep it on the brain-melting level. Thus I'm pretty awful at being able to explain things like this.

This is an excellent resource if one of your buddies has one on hand.

Hope this helps.

Edit: I forgot to mention a higher k-value allows for more heat transfer. It's kind of an "I knew that" sort of thing, but just to clear up any ambiguities. More Watts/(kelvin*surface area.) The idea behind thermal grease is to maximize surface area between the CPU and HSF without restricting heat flow, since at the microscopic level they're not actually flat. Hence, lapping.

/lecture