Thermal Performance of an Elliptical Pin Fin Heat Sink

Christopher L. Chapman, and Seri Lee Aavid Engineering, Inc. Laconia, New Hampshire 03247 Bill L. Schmidt Silicon Graphics Computer Systems Mountainview, California 94039 Comparative thermal tests have been carried out using aluminum heat sinks made with extruded fin, cross-cut rectangular pins, and elliptical shaped pins in low air flow environments. The elliptical pin heat sink was designed to minimize the pressure loss across the heat sink by reducing the vortex effects and to enhance the thermal performance by maintaining large exposed surface area available for heat transfer. The performance of the elliptical pin heat sink was compared with those of extruded straight and crosscut fin heat sinks, all designed for an ASIC chip. The results of the straight fin were also compared with those obtained by using Sauna , a commercially available heat sink modeling program developed based on empirical expressions. In addition to the thermal measurements, the effect of air flow bypass characteristics in open duct configuration was investigated. As expected, the straight fin experienced the lowest amount of flow bypass over the heat sink. For this particular application, where the heat source is localized at the center of the heat sink base plate, the overall thermal resistance of the straight fin was lower than L m ;f N u P r Q Qconu Qrati R Rbase Rj % Re t Ta~b Tan T. T. characteristic length, m fin parameter defined in Eq. (6), m-l ma9s flow rate, kg/8 number of fins Nusselt number Prandtl number rate of total heat transfer, W rate of convective heat transfer, W rate of radiative heat transfer, W oyerall thermal resistance, ‘c/w conductive resistance of base, 0 C’/ W fin thermal resistance, “c/w convective resistance of base, 0 C’/ W Reynolds number fin thickness, m ambient temperature, K inlet air temperature, K bulk mean air temperature, K wall temperature, K bulk mean flow velocity, m/s the other two designs mainly due to the combined effect of Greek Symbols enhanced lateral conduction along the fins and the lower flow bypass characteristics.