Onset of compositional convection during solidification of a two-component melt from a bottom boundary

• Published in: Journal of crystal growth Vol. 267; no. 3; pp. 714 - 723
• Main Authors: Hwang, I.G., Choi, C.K.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.07.2004; Elsevier
• Subjects: A1. Convective instability; A1. Solidification; B1. Ammonium chloride solution; B1. Boundary layer; B1. Mush; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Solidification; A1. Solidification; B1. Ammonium chloride solution; B1. Boundary layer; B1. Mush; A1. Convective instability; Inorganic compounds; Superheating; Al. Solidification; Ternary compounds; Theoretical study; Rayleigh number; Ammonium chlorides; Al. Convective instability; Convection; Solidification; Thickness; Time dependence; Disturbances; Instability; Boundary layers
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2004.04.003

When a two-component melt is solidifying from a bottom boundary, convection may be induced in an unstable compositional boundary layer. In this study, the onset of compositional convection during time-dependent solidification is investigated by using similarly transformed disturbance equations. The critical Darcy–Rayleigh numbers based on the mushy-layer thickness are found numerically for various Lewis numbers, superheats, and Darcy numbers. In aqueous ammonium chloride solution, the critical conditions at the onset of mushy-layer-mode convection are consistent with existing theoretical and experimental results. For small superheats and Darcy numbers, the present predictions for boundary-layer-mode instabilities approach the results of convective instability during steady solidification.