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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