Experimental study of directional solidification of aqueous ammonium chloride solution
Journal
Journal of Fluid Mechanics
Journal Volume
227
Pages
567-586
Date Issued
1991
Author(s)
Abstract
Directional solidification experiments have been carried out using the analogue casting system of NH 4 Cl-H 2 O solution by cooling it from below with a constant-temperature surface ranging from - 31.5°C to + 11.9 °C. The NH 4 Cl 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.
SDGs
Type
journal article