Two-component heterogeneous mixed convection of alumina/water nanofluid in microchannels with heat source/sink

•Nanoparticle migration effects on flow and thermal fields.•Effects of nanoparticle migration on heat transfer enhancement of nanofluids.•Imposing asymmetric heating to find different modes of nanoparticle migration.•Strong influence of thermal boundary condition on nanoparticle migration.•The best performance is achieved under one-sided heating.

The nanoparticle migration effects on mixed convection of alumina/water nanofluid in a vertical microchannel in the presence of heat source/sink with asymmetric heating wall are theoretically investigated. The modified two-component heterogeneous model of Buongiorno is employed for the nanofluid which considers Brownian diffusion and thermophoresis, the significant base of nanoparticle migration. Because of low dimensional structures and surface roughness of microchannels, a slip condition is considered at the surfaces to appropriately examine the non-equilibrium region at the fluid–solid interface. After the fluid flow is assumed as fully developed, the governing equations including continuity, momentum, energy, and nanoparticle volume fraction are simplified to ordinary differential equations and solved numerically. With the scale analysis of governing equations, it is revealed that the temperature-dependent buoyancy effects are negligible; however, the concentration-dependent buoyancy effects have significant impacts on flow and heat transfer characteristics. It is also shown that the imposed thermal asymmetry distorts the symmetry of velocity, temperature and nanoparticle volume fraction profiles and changes the direction of nanoparticle migration. In addition, the best performance is achieved under one-sided heating and a higher slip velocity at the surfaces.

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