Blockage effect of axial-flow fans applied on heat sink assembly

Heat sink assembly has become a standard module on CPU for handling the PC thermal management because of its effective heat emission and low manufacturing cost. From earlier experience, it is well known that heat-dissipating effect varies significantly for different PC layouts, which diminishes fan performance by blocking its flow path. Thus, there is a substantial demand existed for thermal engineers to realize this blockage effect systematically. As a consequence, this experimental study investigated the blockage effect on the performance and noise characteristics of axial-flow fans applied on heat sink assembly. To simulate the blockage effect, a flat plate is placed at a certain distance on the top of the axial-flow fan to partially block its flow path. The fan performance is determined in an AMCA 210-99 test chamber while the noise measurements are carried out in a semi-anechoic chamber. Several commonly used fan sizes and blockage distances are investigated in this study. The experimental results indicate that the decrease in flow-rate is insignificant while the static-pressure loss is dramatic. Also, blockage effect mainly contributes to the increase in broad-band noise while its contribution to the narrow-band noise is negligible. Regarding the heat management, the blockage plate has nearly no effect for a large blockage distance; however, a steep decrease of thermal resistance is found for a small blockage distance.