Numerical Simulation of the Thermal Performance of a Microchannel Heat Sink with Variable-Height Fins in Counter-Flow Mode

In this paper, a novel heat sink with variable-height fins under a counter-flow configuration was proposed and its thermal performance was systematically investigated by three-dimensional numerical simulation. The primary objective was to optimize the thermal performance of microchannel heat sinks through the modification of flow arrangements and fin structural design. The results reveal that the counter-flow arrangement can significantly reduce the maximum base temperature, form a centrally symmetric temperature field, and enhance the uniformity of the base surface temperature. Among all proposed variable-height fin schemes, the linearly rising–descending-height fin (LRDHF) model can effectively reduce the peak temperature and enhance the temperature uniformity of the base surface. Under the conditions of a heat flux of qw = 2.5 × 106 W/m2 and Re = 200, the minimum base temperature and the absolute average temperature difference can be reduced to 339.9 K and 0.65 K, respectively. Parametric analysis indicates that at a fixed heat transfer area, increasing the channel width while decreasing the channel height deteriorates the thermal performance of microchannel heat sinks. In addition, high-accuracy empirical correlations for flow and heat transfer applicable to the LRDHF model considered in this work are established, with the average errors of the friction factor and Nusselt number correlations not exceeding 10% and 8%, respectively. This study verifies the synergistic benefits of integrating a streamwise variable-height fin structure with a counter-flow arrangement, offering an effective optimization strategy for the design of high-performance microchannel heat sinks.