Modelling and Simulation of Flow and Heat Transfer of Ferrofluid under Magnetic Field of Neodymium Block Magnet

Abstract Neodymium magnets are the strongest type of permanent magnet commercially available. This investigation aims to numerically study the behavior of ferrofluids in the presence of block neodymium magnets which could be used in a wide range of applications. The problem formulation is derived using the principles of ferrohydrodynamics (FHD) and magnetohydrodynamics (MHD), and the finite volume method is employed for solving the equations. The flow of water-Fe3O4 magnetic nanofluid at 250≤Re≤2300 in a three-dimensional channel under heat flux exposed to a block neodymium magnet is considered. The results indicate that the magnet can significantly affect the flow field and heat transfer while FHD effects are completely dominant and MHD effects are ignorable. In the presence of the magnet, a secondary flow is created, which is more considerable in the low Reynolds numbers. Applying the magnetic field increases the heat transfer so that at Re=250, where the heat transfer is low, it can increase the Nusselt number by a factor of 2. Moreover, the magnetic field remarkably increases the wall skin frictions. Considering both the increments of heat transfer and friction, the Reynolds number of 1500 has the maximum thermal performance factor. By increasing the Reynolds number or the distance between the magnet and channel, the magnetic effect decreases. It is found that the thermal performance factor is increased by reducing the distance of the magnet and channel. In addition, by decreasing the height of the magnet by half (from 1 cm to 0.5 cm), the thermal performance factor improves by 6%.