Heat transfer and flow characteristics in symmetric and parallel wavy microchannel heat sinks with porous ribs

Based on the synergistic design concept, double-layered microchannel heat sinks with parallel and symmetric wavy porous fins are developed with the desire to simultaneously attain pressure drop reduction, heat transfer enhancement, and cooling uniformity improvement. Using a 3D fluid-solid conjugate model, the hydrodynamic and thermal details are numerically studied to compare two wavy configurations with the solid-and porous-fin designs. The results demonstrate that for wavy microchannel heat sinks, the porous-fin design can significantly enhance heat transfer performance and reduce pressure drop. The symmetric configuration yields a higher pressure drop reduction, whereas the parallel one provides a higher increment in thermal performance. As a result, using the porous design, two wavy configurations have nearly the same level of pressure drop penalty, but the parallel configuration contributes to higher thermal performance. The decreased flow rate of the channel due to the permeation of coolant fluids into porous ribs and the slip effect on the channel wall contribute to the pressure drop reduction. The permeation effect of coolant greatly restrains secondary flow characteristics induced by wavy walls which are responsible for the enhanced coolant mixing in conventional heat sinks. Consequently, the increased inlet flow velocity at a constant pumping power contributes to the improved thermal performance, namely the reduced thermal resistance and the increased Nusselt number. With a stronger coolant permeation owing to the jet-like impingement flow, the parallel configuration yields a slightly lower thermal performance compared to the symmetric configuration in the new design. Finally, the parametric analysis at a fixed pumping power is further carried out for optimizing the proposed design.