Nanofluids flow in microchannels in presence of heat source/sink and asymmetric heating

The effect of thermal asymmetry on forced convection of alumina/water nanofluid in a parallel-plate microchannel in the presence of heat source/sink is theoretically investigated.Walls are subjected to different heat fluxes, q′′_wt for the top wall and q′′_wb for the bottom wall, and nanoparticles are assumed to have a slip velocity relative to the base fluids induced by Brownian motion and thermophoresis. Because of low-dimensional structures in microchannels, a linear slip condition is considered at the surfaces, which appropriately represents the nonequilibrium region near the interface. Considering hydrodynamically and thermally fully developed flow, the basic partial differential equations including the continuity, momentum, energy, and nanoparticle fraction have been reduced to two-point ordinary boundary value differential equations before they have been solved numerically. It is shown that nanoparticles eject themselves from the heated walls, construct a depleted region, and accumulate in the core region, but they are more likely to accumulate near the wall with the lower heat flux. In addition, the imposed thermal asymmetry would change the direction of nanoparticle migration, and it distorts the symmetry of the velocity, temperature and nanoparticle concentration profiles. Moreover, one-sided heating leads to a best heat transfer rate for larger nanoparticles but with a penalty of a very high-pressure drop. In contrast, for the smaller nanoparticles, asymmetric heating leads to a better heat transfer rate and a reasonable increase in the pressure drop. Also, the performance of the system is increased in the presence of heat absorption, since it enhances the heat transfer rate with no significant change in the pressure drop.