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Experimental study of directional solidification of aqueous ammonium chloride solution

Published online by Cambridge University Press:  26 April 2006

C. F. Chen  and
Falin Chen
C. F. Chen
Affiliation:
Department of Aerospace and Mechanical Engineering, University of Arizona, Tucson, AZ 85721, USA
Falin Chen
Affiliation:
Department of Aerospace and Mechanical Engineering, University of Arizona, Tucson, AZ 85721, USA Present address: The Institute of Applied Mechanics, National Taiwan University, Taipei, Taiwan, 10764 ROC.
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Abstract

Directional solidification experiments have been carried out using the analogue casting system of NH4Cl-H2O solution by cooling it from below with a constant-temperature surface ranging from - 31.5°C to + 11.9 °C. The NH4Cl concentration was 26% in all solutions, with a liquidus temperature of 15 °C. It was found that finger convection occurred in the fluid region just above the mushy layer in all experiments. Plume convection with associated chimneys in the mush occurred in experiments with bottom temperatures as high as + 11.0 °C. However, when the bottom temperature was raised to + 11.9 °C, no plume convection was observed, although finger convection continued as usual. A method has been devised to determine the porosity of the mush by computed tomography. Using the mean value of the porosity across the mush layer and the permeability calculated by the Kozeny-Carman relationship, the critical solute Rayleigh number across the mush layer for onset of plume convection was estimated to be between 200 and 250.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 227 , June 1991 , pp. 567 - 586
Copyright
© 1991 Cambridge University Press

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