Numerical investigation of the effect of a porous block and flow injection using non-Newtonian nanofluid on heat transfer and entropy generation in a microchannel with hydrophobic walls

The microchannel cooling technology is an efficient procedure for dissipating heat from high-power devices. In this research, forced convective and entropy generation of a non-Newtonian fluid (water) with 1% and 3% volume fraction of nanoadditives (Al2O3) are investigated in a two-dimensional microchannel. Three configurations for microchannel are considered in this examination to investigate the effect of different Reynolds numbers of injection (25, 37.5, and 50), Darcy numbers (0.01, 0.005, and 0.001), and velocity boundary conditions (hydrophobic and superhydrophobic) on dimensionless velocity, dimensionless temperature, Nusselt number, and entropy generation. Microchannel in case A equipped with an injection in case B and both injection and the porous block in case C. The results show more relative Reynolds number and nanoparticle concentrations and less the Darcy number cause higher dimensionless velocity around the hot wall and the Nusselt number, which is beneficial. The same changes in velocity and temperature can be seen by applying superhydrophobic boundary conditions instead of hydrophobic due to less impact of the solid walls on the flow. The Nusselt number can be increased up to 128.86% in case C. Frictional entropy generation raises by the considerable amount of 461.62% in the presence of porous media. In comparison, this amount is just 133.47% for thermal entropy generation. However, entropy generation analysis shows thermal entropy generation is considerably more than frictional entropy generation; thus, it has a dominant role in calculating total entropy generation.