A new design of double-layered microchannel heat sinks with wavy microchannels and porous-ribs

A new design of double-layered microchannel heat sinks, which combines wavy microchannels with porous vertical ribs, is proposed in this work. The flow and heat transfer behaviors of the new design are investigated via a three-dimensional solid-fluid conjugate heat sink model. The superiority of the new design is highlighted by comparing the new design with three existing double-layered designs under constant pumping power constraints. The three existing designs include a design with straight microchannels and solid-ribs, a design with straight microchannels and porous-ribs, and a design with wavy microchannels and solid-ribs. The results show that porous-ribs reduce the pressure drop across heat sinks, whereas wavy microchannels induce Dean vortices and enhance coolant mixing. In a low pumping power region of 0.005 to 0.01 W, the coolant inlet velocity is found to be the most dominant factor to determine the cooling capacity of heat sinks, whereas in a high pumping power region of 0.1 to 0.2 W, the coolant mixing becomes the dominant one. The new design has both wavy microchannels and porous-ribs, thus providing the best cooling capacity among the four double-layered heat sinks in the whole pumping power range of 0.005 to 0.2 W. The new design is further optimized by single-parameter analyses. It is found that with a fixed pumping power of 0.05 W as constraint, there is an optimal wavelength or an optimal amplitude of wavy units to achieve the lowest thermal resistance; however, the thermal resistance monotonously reduces with the increase in porous permeability or the decrease in quadratic drag factor.