Effect of magnetic fields on heat convection inside a concentric annulus filled with Al2O3–water nanofluid

• Convective heat transfer of nanofluids inside annuli in the presence of a uniform magnetic field.
• The effects of a uniform magnetic field on nanoparticle migration and heat transfer rate.
• Nanoparticles migration effects on fluid flow and heat transfer rate.
• Slip effects on thermal performance of the system.

In the current study, forced convective heat transfer of an MHD fully developed laminar nanofluid between two concentric horizontal cylinders is investigated in the presence of a radial magnetic field. In contrast to a conventional no-slip condition at the surfaces, the Navier’s slip condition is considered at the surface to represent the non-equilibrium region near the surfaces. Employing the modified Buongiorno model, the conservative partial differential equations have been collapsed to two-point ordinary boundary value differential equations before being numerically solved. To consider the effects of thermal boundary condition on nanoparticle migration, two distinctive cases including constant heat flux at the outer wall and adiabatic inner wall (Case A) and constant heat flux at the inner wall with adiabatic outer wall (Case B) have been considered. Our results indicate that due to thermophoresis force, the distribution of nanoparticles was denser at the adiabatic wall for the case A which affects the local and the universal fluid flow and heat transfer characteristics. Moreover, inducing a radial magnetic field on the system, heat transfer rate was increased for the case A which had a decreasing effect on the case B. Finally, slip velocity at the walls enhances heat transfer rate for both cases.

The effects of uniform magnetic field and slip velocity at the walls on concentration of nanoparticles and heat transfer characteristics of the fluid have been investigated.Figure optionsDownload as PowerPoint slide