Multi-objective optimisation of thermal and hydraulic performance with various concentrations of hybrid Fe3O4/graphene nanofluids in a microchannel heat sink

Abstract

An accurate thermal resistance network and an objective function of pressure drop were established for a microchannel heat sink (MCHS) to evaluate the heat transfer and hydraulic performance of hybrid Fe3O4/graphene nanofluids with different concentrations in the MCHS. An optimised geometry of the MCHS with nanofluids at 40 °C under mass concentrations of 0.1, 0.3, and 0.5 wt% was obtained through multi-objective particle swarm optimisation (MOPSO). By using the K-means clustering method, a Pareto front of an optimised solution set was divided into three clustering zones with the optimal heat transfer performance, balanced performance, and optimal hydraulic performance. Combined with a comprehensive enhanced heat transfer factor, suggestions for trade-off in these three zones were proposed. The results indicate that the hybrid Fe3O4/graphene nanofluids is an attractive heat transfer medium in the MCHS and the optimised dimensions obtained by the MOPSO can simultaneously reduce the thermal resistance and pressure drop across the MCHS. Nanofluids with higher concentrations can amplify the effects of reducing the thermal resistance without increasing the loss of pumping power when the working temperature of the MCHS increases. The increase in the concentration of nanofluids can constantly decrease the dimensions of the MCHS in the Pareto front. Therefore, ensuring the stability of nanofluids can prevent the resulting pseudo-high concentration from influencing the accuracy of optimisation data.

Keywords

• Microchannel heat sink
• Fe3O4/Graphene nanofluid
• Thermal and hydraulic performance
• Multi-objective optimisation