Microchannel heat sink is one of the most promising cooling solutions for electronics with high heat flux. In order to further enhance the heat transfer performance of microchannel heat sink, a novel microchannel with rectangular grooves on the wall is designed, and the heat transfer and flow characteristics of Al2O3/water nanofluid in microchannels are numerically studied. The mixture model is used involving the slip velocity between nanoparticles and base fluid. By comparing with the conventional smooth channel, it's found that grooves are helpful to destroy and redevelop the thermal boundary layer. The disturbance by grooves also leads to much higher pressure drop through the channel than smooth one. This work will be helpful for the design of highperformance microchannel heat sink.

Erythritol as a phase change material has a main disadvantage: low thermal conductivity. In this paper, we proposed a novel erythritol/graphene composite phase change material and its thermal properties were predicted by molecular dynamics method. The effects of graphene mass fraction, size and number of layers on thermal conductivity were analyzed. The mechanism of graphene on thermal conductivity was revealed from the microscopic point of view. The results show that graphene can efficiently improve the thermal conductivity of the composites, thus improving the thermal properties of erythritol. The thermal conductivity of the composites increases with the increase of graphene amount, size and number of layers. When the mass fraction of graphene increased to 8 wt%, the thermal conductivity is doubled. This study can provide guidance for the design and application of erythritol-based composite phase change materials.