Modeling Air-Cooled Heat Sinks as Heat Exchangers

Heat sink performance is generally described by quoting its thermal resistance, R_th, in degrees C per Watt. When R_th is based on data, it can be relied on. When it is predicted, there may be problems. R_th=1/hA_eff, the ´convective resistance model´, can over-predict the heat transfer by more than 100%. Adding a ´fluid resistance´ can get to the right result, but the most reliable approach is to use heat exchanger theory, which many workers have done. The intent of this paper is to point out why heat exchanger theory is the most appropriate approach for predicting the thermal resistance of a heat sink, and to illustrate some of the benefits of that approach, including some new possibilities for compact models. There is no claim to originality: many others have used, and are still using, heat exchanger theory in this way.