The primary focus of the present work is the development of macro-models for numerical simulation of multi-phase transport phenomena occurring during the solidification of multi-component alloy systems. As a first step, a generalised algorithm is developed for macroscopic modelling of heat, mass and solute transport in multicomponent alloy solidification processes. Microscopic features pertaining to complex thermo-solutal transport mechanisms are incorporated through a novel formulation of latent enthalpy evolution, consistent with the phase change morphology of general multi-component alloy systems. An algorithm is developed for the prescription of the coupling between temperature and the melt-fraction. The model is essentially based on a fixed-grid enthalpy-based finite volume method, with fluid flow modelling achieved by the SIMPLER algorithm of pressure-velocity linking. As a demonstration of the numerical model developed in this study, simulations are performed for two different ternary steel alloys of apparently contrasting thermo-solutal transport characteristics. The resulting convective flow phenomena and macrosegregation patterns for such a system is analyzed in details, with a quantitative estimation of predictive capabilities in dealing with constituent species that may widely differ in their respective thermodynamic properties. The mathematical model is tested by comparing the present numerical results with the benchmark analytical solutions and experimental data reported in the literature, and very good agreements can be observed in this regard.
Thesis submitted by Suvankar Ganguly, Guide: Dr. Suman Chakraborty, Year 2007