A thermal characteristic study of extruded-type heat sinks in considering air flow bypass phenomenon

An experimental investigation carried out to study the forced air cooling heat sinks used in electronic packaging is discussed. The parameters include clearance between the heat sink and adjacent PCB (printed circuit board), lateral space between heat sinks, and height and width of heat sink. A fin efficiency model is used to calculate the convective coefficient and fin efficiency. The results show that the air flow bypass effect on thermal performance, due to top clearance or lateral space, is significant, more than 20%. Thermal performance can be improved by either increasing height or decreasing width of the heat sinks. The convective coefficient, however, may not increase monotonically with thermal performance. The results indicate that, generally the Nusselt number can be expressed as an exponential form of the Reynolds number and the exponent is about 0.6