Investigation of convective flows in model systems of directional solidification configurations

Convective flows in water in a vertical cylindrical test cell heated from below were studied. A sequence of different stable flow configurations is found. The time dependent convection is characterized by well defined frequencies. Water results were compared with results of the directional solidification of InSb by the vertical Bridgman technique. A clear correlation of material inhomogeneities and unsteady thermal convection is possible using theoretical results of the critical Rayleigh number (Ra). The first flow configuration which occurs at slightly supercritical Ra is a steady unicellular antisymmetric roll. At higher Ra staggering of rolls occurs only in vertical direction. The shape and aspect ratio of the container can influence the flow transitions.