The paramagnetic fluid has the positive magnetic susceptibility which depends on the temperature. This suggests that the heat and fluid flow of air can be controlled by a magnetic field. This phenomenon is called magnetothermal convection. In this study, the effect of the magnetothermal force is numerically investigated on the natural convection between vertical heated parallel plates under the gravity field. The heat and fluid flow is simultaneously solved by the lattice Boltzmann method (LBM). For the evaluation of the external force on LBM, the validation is firstly carried out for the natural convection in a square cavity. It is confirmed that employed scheme has a comparable validity to the reference data. In the computation for the natural convection between the parallel plates, it is found that, because the hotter fluid receives weaker magnetic force, the magnetothermal force is expressed as a repelling force. This force is directed to perpendicular to the flow direction, thus the hotter fluid is taken away to the bulk region, and the colder fluid is attracted toward the magnet. Therefore, the thermal boundary layer at the magnet location is affected by the magnetothermal force. The local heat transfer enhancement is also discussed with the different wall heat flux and magnet location.
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