Natural convection suppression and crystal growth during unidirectional solidification of a binary system

Abstract

We studied experimentally the interaction between natural convection and dendritic growth in the mushy layer during unidirectional solidification of aqueous ammonium chloride solutions cooled from below. Small amounts of hydroxyethylcellulose were added to the solution to increase its viscosity, leading to the suppression of convection. Natural convection consists of salt fingers in the liquid phase and plumes in the mushy layer for a low-viscosity solution, but the onset of plumes is suppressed for a high-viscosity solution. The mushy layer becomes sparsely packed, and the primary and secondary arms of the dendrites grow to noticeable sizes with increasing its viscosity, which yields a low solid fraction, such as 1% on average in the mushy layer for a viscosity ratio of 25.5. This demonstrates that natural convection strongly affects the morphology of dendrites. © 2000 Scripta Technica, Heat Trans Asian Res, 29(2): 120–131, 2000