Microchannel heat sinks have provided an efficient solution in the thermal management of high-power density devices. In general, however, they cannot exhibit high thermal performance and lower pressure drop simultaneously. In this work, an improved design of microchannel heat sinks possessing a combination of high thermal performance and low pressure drop is proposed, where the superiority of double-layered concept and the advantage of porous-ribs design are taken into account. In the improved design, two layers of rectangular channels are stacked one atop another with porous ribs utilized in the upper layer while solid ribs employed in the lower layer. The thermal performance and the flow characteristics of the improved design are numerically studied using a three-dimensional solid-fluid conjugate model. Four other heat sinks with different structure (solid-ribs single-layered, porous-ribs single-layered, solid-ribs double-layered, and porous-ribs double-layered) are designed for performance comparison. The results demonstrate that the improved design yields the lowest thermal resistance and the best temperature uniformity on the bottom wall among all the five designs whether at an identical Reynolds number or at a fixed pumping power. The appropriate combination of better thermal conductivity of solid ribs and lower pressure drop of porous ribs in a double-layered heat sink is responsible for the performance improvement.
