強制對流平板散熱器於電子熱傳之研究

Abstract

As cost-effective and manufacturing advantages, plane plate heat sink has been widely used for electronic-cooling industry. However, it is not an easy task to develop a proper heat sink perfectly fitting into electronic system. Not only rating problem, but also sizing problem is an essential part of system packaging, and definitely worth to be addressed within integration of multi-disciplines. Analyses have been performed to predict pressure drop and heat transfer behaviors in plane plate heat sink. It takes into account of many design variables, including heat sink geometry, material property, heat source size and location, environment condition, and coolant pumping constraint…etc. The utilization of existing correlations for friction factor and Nusselt number was investigated. The study indicated that novel all-in-one asymptotic solutions provided by present author can predict pressure drop and heat transfer performance of fin array within acceptable accuracy over laminar, transition and turbulent flow, saying Re<5000. The model assumes heat source in contact with heat sink base that cooled by equivalent convective heat transfer coefficient specified over opposite side, and adiabatic for the rest surfaces. Method of separation of variables was used to obtain exact solution in form of infinite series. Compared to experimental data, pressure drop predicted by present model is within -14% to +9%. Prediction discrepancy of overall thermal resistance between present model and Flotherm model is within -3% to 5%. By the aid of self-development numerical program, the influences of design variables and performance limitation of heat sink have been systematically examined. The results illustrated that specifying operation point of heat sink for pressure drop and airflow rate is an essential part of optimization for heat sink performance. The minimal achievable overall thermal resistance is limited by given pressure drop and airflow rate while heat sink is subjected to specified frontal area, heat source size/location, environmental conditions and variation range of design variables. There exists critical pressure drop and airflow rate to achieve target heat transfer performance. It is bare possible to achieve design goal if either specified pressure drop or airflow rate is less than those critical value. Compensation factor has been defined for quantitatively evaluating the location effect of heat source with variations in base thickness, effective heat transfer coefficient and heat source size. The study of compensation factor indicated that, increasing heat transfer coefficient and reducing heat source size alleviates the location effect of heat source, or obtains a lower compensation factor. On the other hand, as increase of base thickness, compensation curve rise up when base is thin, then fall down and reach a valley when dimensionless thickness is over than 0.6~0.7.