Abstract
Progressive freeze-concentration of dilute sodium chloride solution was carried out to analyze the effects of the operating conditions of the ice crystal growth rate -(u)- and the stirring rate -(N)- at the ice-liquid interface on the apparent partition coefficient of solute between ice and liquid phase -(K)-. K increased with an increase in the combined operation parameter u/N0.2. Under the similar operating conditions, the ice crystal structure was analyzed with pure water as a sample in progressive freezing. By using polarized light analysis, dendrite ice-crystal structure, which grew in the reversed direction of heat flow, was clearly observed. This ice-crystal structure was not observed under the ordinary light. The mean diameter of the dendrite ice-crystal structure showed a clear negative correlation with the combined operation parameter u/N0.2. These results suggest that the mechanism of the solute incorporation into ice phase in progressive freeze-concentration is its incorporation in the space between the dendrite ice-crystal structure.
