Heat transfer enhancement for microchannel heat sink by strengthening fluids mixing with backward right-angled trapezoidal grooves in channel sidewalls

To strengthen the fluids mixing in channels for enhancing heat transfer, a new design of microchannel heat sink with periodic gradual-expansion and sudden-constriction cross-sections was proposed by arranging backward right-angled trapezoidal grooves in channel sidewalls. The flow and heat transfer characteristics in the new design was numerically investigated and compared with those in two comparative microchannels, which have the same channel volume and the same or almost the same convective heat transfer area as the new design. The pressure and viscous resistances of channel walls were innovatively analyzed for explaining why grooves can maintain a lower pressure drop for microchannels. The results indicate that the new microchannel shows a significant improvement of heat transfer enhancement and overall performance although its pressure resistance and viscous resistance are much higher than those of other ones. The pressure drop and Nusselt number of the new microchannel are 1.02–1.45 and 1.31–2.14 times higher than those of the smooth straight microchannel, respectively. After an optimum process of the forward angle (θ) of grooves, the relative Nusselt number of the new microchannel can be achieved up to 2.23 at θ = 15°and Re = 737 while the overall heat transfer factor can be achieved up to 1.89 at θ = 18°and Re = 442.