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/dz)=1360 T2m-1. A thermal conduction state without convection was realized under a stronger gradient field of B(dB/dz)=2880 T2m-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.