Modeling of solid phase sedimentation during directional solidification in a side cooled cavity

Abstract

Purpose: The purpose of this paper is to present a new numerical approach for modeling the multi-phase flow during an alloy solidification process. In many solidification processes, advection of solid may have a dramatic effect on bulk convection field as well as on the solid front growth and hence on the macro-segregation pattern. In the present work, a numerical model is developed to simulate directional solidification in presence of melt convection as well as solid advection in the form of sedimentation. A 2D cavity filled with hyper-eutectic aqueous ammonium chloride solution (25?wt.% of ammonium chloride) being chilled from one of the side walls has been chosen as the model problem for the numerical simulation. Design/methodology/approach: A fixed grid volume averaging technique has been used for solving mass, momentum, energy, and species equation while taking into account the solid phase advection and local re-melting. Two different criteria have been identified for the solid particles in the mushy zone to be mobile. These two criteria are represented by a critical solid fraction, and a critical velocity. Based on these two criteria, the mushy zone has been subdivided into two different regions namely, an immobile coherent zone consisting of packed equiaxed crystals and a mobile non-coherent zone where the solid crystals are able to move. Findings: The numerical results are compared with corresponding experimental observations. Originality/value: The solid advection velocity and source terms dealing with solid velocity have been calculated using an explicit scheme, whereas the main conservation equations are solved using an implicit scheme.