Control of thermal convection in water by strong gradient magnetic fields

Heat transfer in water was visually observed using a liquid-crystal sheet with thermochromism under strong gradient magnetic fields. Upward thermal convection was significantly suppressed by the magnetic force, however, it remained to a small extent even under magnetic levitation conditions with a gradient field of B(dB/az) = 1360 T²·m^-1. A thermal conduction state without convection was realized under a stronger gradient field of B(dB/dz) = 2880 T²·m^-1 at 35-40°C, and surprisingly the downward magnetic convection was observed under the same field at 40-45°C. The temperature dependence of the magnetic susceptibility of water is responsible for the convection behavior in the gradient fields.