Effect of a magnetic field on the convection of paramagnetic fluid in unstable and stable thermosyphon-like configurations

Convection of a paramagnetic fluid inside a vertical cylinder placed in the bore of a superconducting magnet was studied. The bore and the cylinder were placed coaxially. The side wall of a top cylinder was electrically heated, while the side wall of a lower cylinder was cooled by running water through a constant temperature bath. Two configurations were investigated: unstable (the lower side wall heated and the upper one cooled) and stable (the lower wall cooled and the upper wall heated). A mixture of water and glycerol was used as a working fluid, and its magnetic susceptibility was increased by adding Gd(NO3)3 · 6H2O. Between the upper and lower side walls a Plexiglas thin cylinder plate was placed. This middle cross-section was illuminated with LED light to visualize the fluid temperature with dispersed liquid crystal slurry. For the unstable configuration, multiple spokes were observed with further increase in the number of spokes with a magnetic field. The magnetic field enhanced the convective flow and also induced flow from a quasi conduction state. The corresponding heat transfer rates were measured with and without a magnetic field. The differences between the stable and unstable configurations of the experimental setup were discussed.