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The growth of compositionally stratified solid above a horizontal boundary

Published online by Cambridge University Press:  26 April 2006

Andrew W. Woods  and
Herbert E. Huppert
Andrew W. Woods
Affiliation:
Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Silver Street, Cambridge, CB3 9EW, UK
Herbert E. Huppert
Affiliation:
Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Silver Street, Cambridge, CB3 9EW, UK
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Abstract

The compositional stratification in solid formed by cooling a binary alloy from below is investigated theoretically and experimentally. It is shown that in order to grow composite solid the boundary temperature needs to be below the eutetic temperature. Two separate cases are considered. In the first, heavy fluid is released on solidification. The solid growth is then governed by the diffusive transport of heat and composition. The resultant solid is shown to have a fixed composition until the far-field conditions change. In the second case, light fluid is released on solidification. This generates turbulent compositional convection in the melt which significantly increases the transport of heat and composition across the solid/melt interface. As a result, the fraction of heavy component in the solid initially increases, but subsequently decreases to conserve mass. A simple theoretical model, using the approximation of a flat solid/melt interface is developed; this predicts differences in the thermal flux in saturated and undersaturated melts. Laboratory experiments involving aqueous solutions of sodium carbonate cooled from below which released light fluid displayed compositional convection and stratification of the solid as predicted.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 199 , February 1989 , pp. 29 - 53
Copyright
© 1989 Cambridge University Press

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