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 neodymium block magnets which could be used in a wide range of applications. The prob- lem formulation is derived using the principles of ferrohydrodynamics (FHD) and magne- tohydrodynamics (MHD), and the finite volume method is employed for solving the equa- tions. The flow of water-Fe 3 O 4 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 com pletely dominant and MHD effects are ignorable. In the presence of the magnet, a secondary flow is created, which is more significant for 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 mag- netic field substantially increases the wall skin friction. Considering both the increments of heat transfer and friction, the Reynolds number of 1500 has the maximum thermal per- formance factor. With increasing Reynolds number or 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, if the height of the magnet is decreased by half (from 1 cm to 0.5 cm), the thermal performance factor improves by 6%.
