Heat transfer of nanofluids in converging and diverging microchannels by mixture model

Today, the use of nanofluids in microchannels is widely used for cooling microelectronic components. In this study, the flow and heat transfer of nanofluid in a converging and diverging microchannel has been investigated. The governing equations are solved by finite element method and two-phase mixture model in Comsol Multiphysics software. The results of this simulation were obtained for Reynolds numbers (100-700) and different concentrations of nanoparticles (0-0.02) for diverging and converging microchannels with different slopes (0-0.05). Also, the effect of two different nanofluids water-copper and ethylene-glycol-copper has been considered in the simulations. Nanoparticles diameter is 50 nm and the average height of the microchannels is 50 microns. The results include Nusselt number and performance coefficient for different situations. For water-copper nanofluid with a volume fraction of 1% in a converging microchannel with a slope of 3% and Reynolds 100, it increases by about 1.6 times for a converging microchannel and 1.1 times for a diverging microchannel compared to a flat microchannel. In this case, the performance coefficient for convergent and divergent microchannel is 1.37 and 1.74, respectively. In the same conditions, for ethylene glycol-copper nanofluid, the Nusselt number for converging microchannel becomes 1.22 times compared to flat microchannel and 1.13 times for divergent microchannel. In this case, the performance coefficient for convergent and divergent microchannel is 1.17 and 1.4 respectively.