This study has used the two-phase Euler-Lagrange method to evaluate the hydrothermal characteristics for a laminar flow of water-Mn0.6Zn0.4Fe2O4 magnetic nanofluid in a circular pipe under the effect of magnetic field with both positive and negative gradients. Brownian and thermophoretic forces were considered in the simulation. Concentration distribution was found to be non-uniform at the cross section of the pipe, the value of which is greater in center of the pipe than near wall. Nonuniformity in the concentration distribution will change the velocity profile under the application of magnetic field. Applying magnetic field with negative gradient increases the convective heat transfer coefficient, while decreases it in the case of positive gradient. Increasing the magnitude of magnetic field gradient causes a more considerable change in the convective heat transfer coefficient. In the presence of the magnetic field, the convective heat transfer coefficient also increases with increasing Reynolds number, concentration and particle size which the effects of magnetic field on heat transfer is less significant at higher Reynolds numbers. Moreover, the pressure drop increases in the case of applying magnetic field with negative gradient while applying the positive one would act as a pump and sucks the fluid from upstream.
