Fully developed forced convection of alumina/water nanofluid inside microchannels with asymmetric heating

• Forced convection of alumina/water nanofluid inside microchannels
• Nanoparticle migration effects on rheological and thermophysical characteristics
• Brownian motion and thermophoresis effects on nanoparticle migration
• Effects of asymmetric heating on the heat transfer enhancement

The effects of nanoparticle migration and asymmetric heating on the forced convective heat transfer of alumina/water nanofluid in microchannels have been investigated theoretically. Walls are subjected to different heat fluxes; qt″ for the top wall and qb″ for the bottom wall to form the asymmetric heating. Because of the microscopic roughness in microchannels, Navier's slip boundary condition is considered at the fluid–solid interface. A two-component mixture model is used for nanofluids 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, energy, and nanoparticle distribution equations) have been reduced to two-point ordinary boundary value differential equations and solved numerically. It is revealed 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 toward the wall with the lower heat flux. In addition, the non-uniform nanoparticle distribution makes the velocities move toward the wall with the higher heat flux and enhances the heat transfer rate there. Moreover, the advantage of nanofluids is increased in the presence of a slip velocity at the walls.

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