Visualization of magnetoconvection

The opacity of liquid metals represents a seemingly insurmountable barrier for visualizing flows of electrically conducting fluids under the influence of a magnetic field. We demonstrate that this fundamental limitation of experimental magnetohydrodynamics (MHD) can be overcome by using (transparent) electrolytes in place of (opaque) liquid metals if a superconducting magnet with field strength of the order of 10 Tesla is used instead of traditional electromagnets. We study the Rayleigh–Bénard convection as a prototype problem under a horizontal magnetic field using a shadowgraph method and tracer particles. It is shown that recent observations of Burr and Müller [J. Fluid Mech. 453, 345 (2002)] of an increased heat transfer in magnetoconvection can be attributed to the two-dimensionality and a smaller length scale of motion due to the magnetic field. The present approach provides a rational framework for the application of modern optical flow measurement techniques like laser Doppler velocimetry and particle image velocimetry to MHD problems.