Heat removal from a CPU

prajput · July 2020

I was playing around with my PC today 🧐, and I noticed a big block of metal (having slots) between the CPU fan and the processor. I have a feeling it has something to do with heat removal but I am not quite sure 😥. Can anyone explain what it is and why it is placed there?

kkanade · July 2020

That's a heat sink and it helps to transfer the heat generated by an electronic (or a mechanical device) to a fluid medium. In the case of a cpu its the air that moves with the help of the fan. The slots that you noticed are actually fins. Fins are extended surface which enhance heat transfer by conduction and convection. This increase in heat transfer is primarily due to lowering of thermal resistance. Thermal resistance of a fin can be lowered by increasing the thermal conductivity and the overall area of convection. An increase in thermal conductivity increases heat transfer by conduction. An increase in overall area of convection increases convective.

prajput · July 2020

Now that I have your attention, how do we design such a cool thing? Are there any parameters that we have to keep in mind when we design a fin?

kkanade · July 2020

As mentioned the main objective is to lower the thermal resistance which can be lowered by increasing the thermal conductivity of the fin and the overall area of convection. Fin performance can be described using either fin effectiveness or fin efficiency. Fin effectiveness is defined as ratio of fin heat transfer rate to the heat transfer rate of the object without a fin. Fin efficiency is defined as ratio of fin heat transfer rate to the heat transfer rate of the fin if the fin temperature were equal to its base temperature. The value is always less than 1. Generally, there is a temperature distribution over the fin (base of the fin is hotter than its tip).