Performance comparison of wavy microchannel heat sinks with wavy bottom rib and side rib designs

Employing wavy microchannels has been proven to enhance the heat transfer performance of microchannel heat sinks as compared to employing straight microchannels, and the heat transfer enhancement is much larger than the pressure drop penalty. The wavy microchannels have been adopted on the side walls of microchannels or top and bottom walls; however, it is still a pending issue that which scheme should be adopted in practical applications. In this work, a three-dimensional fluid-solid conjugate model is developed to investigate the heat transfer performance of the left-right and up-down wavy microchannel heat sinks. With the same pumping power and channel cross-section area, the global thermal resistance and the maximum bottom wall temperature variation of the two wavy designs are compared for various wavy amplitudes, wavelengths, channel aspect ratios, and width ratios of channel to pitch. The simulations show that the both wavy designs induce a symmetric pair of counter rotating Dean vortices in the plane of the channel cross-section, which enhances the coolant mixing and thus improves the heat sink performance. The Dean vortices induced by the up-down wavy design are located near the side walls of channels, whereas they are generated near the top and bottom walls of channels for the left-right wavy design. Regardless of amplitude, channel aspect ratio, and width ratio of channel to pitch, the up-down wavy design exhibits a better heat transfer performance than the left-right one when small wavelengths are adopted; however, at large wavelengths, the two designs show almost the same performance. The above results can be attributed to the different Dean vortices induced by the two designs. The Dean vortices generated in the up-down wavy design mix the flow between the hot bottom portion and the cool top portion of channels, whereas the Dean vortices generated in the left-right wavy design are confined to near either the hot bottom or the cool top. Thus, the up-down wavy design should perform better in general. The results obtained here can provide a useful guidance for the optimal design of wavy microchannel heat sinks.