CHANNEL CONVECTION IN PARTLY SOLIDIFIED SYSTEMS

Channel plume flow arising from thermosolutal convection has been examined in metallic, aqueous and organic systems, covering a range of Prandtl numbers over three orders of magnitude. Observations were made directly in the transparent aqueous and organic systems and after the event in fully solidified metallic alloys. Plume dimensions and those of the concomitant channels are remarkably similar in all three materials, as are the composition differences between plumes or channels and the matrices. Detailed measurements and observations of these dimensions and of flow rates in the transparent materials are described and discussed. Analysis of plume flow rates in the transparent systems, if extrapolated to metals, would predict convective flow rates between 0.1 ms(-1) and 0.2 ms(-1). The validity of this extrapolation is qualified by the way in which posthumous solute channels develop in the fully solidified metallic samples.