Effects of nanoparticle migration and asymmetric heating on magnetohydrodynamic forced convection of alumina/water nanofluid in microchannels

•Magnetohydrodynamic forced convection of alumina/water nanofluid in microchannels.•Nanoparticles migration effects on rheological and thermophysical characteristics.•Brownian motion and thermophoresis effects on nanoparticles migration.•Effects of asymmetric heating on the heat transfer enhancement.•Describing the anomalous heat transfer enhancement in nanofluids.

The present paper is a theoretical investigation on effects of nanoparticle migration and asymmetric heating on forced convective heat transfer of alumina/water nanofluid in microchannels in presence of a uniform magnetic field. Walls are subjected to different heat fluxes; qt″ for top wall and qb″ for bottom wall, and because of non-adherence of the fluid–solid interface due to the microscopic roughness in microchannels, Navier’s slip boundary condition is considered at the surfaces. A two-component ​heterogeneous mixture model is used for nanofluid with the hypothesis that Brownian motion and thermophoretic diffusivities are the only significant slip mechanisms between solid and liquid phases. Assuming a fully developed flow and heat transfer, the basic partial differential equations including continuity, momentum, and energy equations have been reduced to two-point ordinary boundary value differential equations and solved numerically. It is revealed that nanoparticles eject themselves from heated walls, construct a depleted region, and accumulate in the core region, but more likely to accumulate near the wall with lower heat flux. Also, the non-uniform distribution of nanoparticles causes velocities to move toward the wall with a higher heat flux and enhances heat transfer rate there. In addition, inclusion of nanoparticles in a very strong magnetic field and slip velocity at the walls has a negative effect on performance.

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