An experimental study on the performance of miniature heat sinks for forced convection air cooling

In recent years the design of portable electronic devices must incorporate thermal analyses to ensure the device can be adequately cooled to acceptable temperatures. Consumer demand for smaller, more powerful devices has lead to an increase in the heat required to be dissipated and a reduction in the surface area both of which result in an increased heat flux. In this paper, an experimental study is performed on one of the smallest commercially available miniature fans, suitable for cooling portable electronic devices, used in conjunction with both finned and finless heat sinks. Previous analysis has shown that due to fan exit angle, flow does not enter the heat sinks parallel to the fins or bounding walls. This results in a non uniform flow rate within the channels of the finned and finless heat sink along with impingement of the flow at the entrance giving rise to large entrance pressure losses. In this paper straightening diffusers were attached at the exit of the fan which resulted in aligning the flow entering the heat sinks with the fins and channel walls. In designing the finned heat sink current optimization criterion for finned heat exchangers has been applied to ensure maximum heat transfer rates; the finless heat sink was designed to the same specifications. The maximum overall footprint area of the cooling solution is 534mm2 with a profile height of 5mm. The thermal performance of each cooling solution was investigated by quantifying its thermal resistance over a range of fan speeds and comparing the results to cases without diffusers. In order to investigate the flow field, detailed velocity measurements were obtained using Particle Image Velocimetry, which provided a further insight into the physics of the flow in such miniature geometries and in designing the straightening diffusers. The thermal analysis results indicate that the cooling power of the solution is increased by up to 20% through the introduction of a diffuser. Hence, demonstrating the need for integrated fan and heat sink design of low profile applications.