Thermal conductivity are often used for surfaces between the computer chip and the heat sink to increase heat transfer and they want high thermal conductivity to decrease the thermal resistance. By $$\Delta T=RQ$$ and $Q$ is constant by the chip. When we decrease R, and keep Q constant from the chip, we decrease $\Delta T$ between the chip and the heat sink.

This is where I get confused because I assumed we would want the temperature difference between the chip and heat sink to be as high as possible. If the two temperatures are close to each other then wouldn't that make the chip heat up and exceed the operating temperature? I thought we would want the heat sink to be much colder than the chip so the chip will cool.

Can someone clarify?


1 Answer 1


Not quite - you want the cold sink to be as cold as possible. The cold sink is the cold air (or water or coolant) flowing over the heatsink.

The heatsink is designed to efficiently connect the chip to the cold sink, so it needs to be as low resistance as possible.

In thermodynamic calculations consider the chip==heatsink and the airflow to be the cold side.

  • $\begingroup$ Lets say the chip needs to operate at $T_H$ and it dissipates constant 2 W. If we have a low total resistance, then doesnt that make the coolant temperature very close to $T_H$? But you just said you want it as low as possible. This is why I am getting confused $\endgroup$ Apr 18, 2014 at 19:54
  • $\begingroup$ @Greg, you normally assume the cold sink temperature doesn't change, either because it's constantly being refreshed (fresh air or coolant flowing over the heatsink) or because it has a very very large thermal mass. The chip is heating up above the cold sink temperature. You want to have as little temperature difference as possible, because that means the chip is heating up less. $\endgroup$
    – The Photon
    Apr 18, 2014 at 20:14
  • $\begingroup$ @ThePhoton It all makes sense now that I remember the coolant is being constantly replenished and I assume it's a constant temperature. Thanks guys $\endgroup$ Apr 18, 2014 at 20:19
  • $\begingroup$ @GregHarrington, you said something VERY wrong in: "Lets say the chip needs to operate at $T_H$". The chip temperature is not a given here, it's the result of $T_{SINK} + \Delta T$. That's your conceptual problem right here. $\endgroup$ May 19, 2014 at 0:53

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