مهدی بحیرائی

Hydrothermal characteristics of water–MnZnFe2O4 magnetic nanofluid between two parallel plates are evaluated under effect of localized magnetic field. The Eulerian–Lagrangian approach is employed considering the effects of Brownian, thermophoretic, magnetic, lift and drag forces. Convective heat transfer enhances by increasing each of the parameters of nanoparticle size, concentration and magnetic field strength. The rate of enhancement for convective heat transfer is lower at higher magnetic field strengths due to the magnetic saturation phenomenon. Concentration is non-uniform in transverse direction, and nanoparticles migrate to central regions. In the sections with positive magnetic field gradient, the magnetic force is exerted on the particles in the flow direction and consequently, velocity increases in the central regions while decreases near the walls. Conversely, in the sections where the magnetic field gradient is negative, the velocity decreases in the central regions while increases near the walls. This causes local changes in convective heat transfer. Moreover, the pressure increases along the channel in the sections with positive magnetic field gradient, whereas in the sections with negative magnetic field gradient, the pressure drops with a greater slope compared with the case without magnetic field. Additionally, the wall temperature decreases with increasing the magnetic field gradient.