Mixed convection of non-Newtonian ferrofluid inside a concentric horizontal annulus is studied numerically under the influence of a non-uniform magnetic field. In the present study, the effects of ferrohydrodynamics (FHD) and magnetohydrodynamics (MHD) are taken into account simultaneously. It is assumed that the non-Newtonian fluid obeys the power-law model. Furthermore, the inner cylinder is considered to be rotating in order to create the forced convection effects. The effect of various parameters on the mixed convection performance have been examined, namely, the Richardson number (0.1-10), power-law index (0.8-1.2), Magnetic number arising due to the FHD principles (0-5) and the Hartmann number as a result of MHD effects (0-5). Results reveal that increase of the Richardson number causes an increase in the average Nusselt number for the pseudoplastic and Newtonian fluids, while this trend is nearly negligible for the dilatant fluid. In addition, regardless of the value of all considered parameters, it is observed that the average Nusselt number is a decreasing function of the power-law index. Considering the FHD effects, it is noticed that for pseudoplastic fluid the Nusselt number increases as magnetic number enhances but the opposite manner occurs for dilatant fluid. Also, application of magnetic field causes both enhancement and deterioration effects on the heat transfer of Newtonian ferrofluids depending on the Richardson numbers. At MHD conditions, increasing the Hartmann number results in decrease of the Nusselt number for pseudoplastic fluid, whereas this effect is not considerable for Newtonian and dilatant ferrofluids.
