FINITE ELEMENT STUDY OF DOUBLE DIFFUSIVE CONVECTION AND SOLIDIFICATION UNDER THE COMBINED INFLUENCE OF MICROGRAVITY AND MAGNETIC FIELDS

摘要

A finite element model is presented for the g-jitter induced double diffusive convection and solidification phenomena with and without the presence of magnetic fields in a Sn-doped Bi single crystal growth system planned for space experiments in space vehicles and the International Space Station. The model is developed based on the deforming finite element formulation with the penalty formulation for pressure approximation and an isothermal front tracking algorithm is used to predict the solid-liquid interface. Extensive numerical simulations are carried out and studied parameters include the effects of solutal striation on the solidification front location and interface morphology under both steady state and g-jitter (or time varying gravity perturbations) conditions with and without the presence of a magnetic field. Both synthesized g-jitter and real g-jitter taken from space flights are used, with the former intended to provide a fundamental understanding of system performance and later to obtain quantitative information in real flight environments. Computed results show that the concentration effects on interface morphology must be considered for an accurate prediction of solidification interface morphology. Also, an applied magnetic field can be very useful means to suppress the deleterious g-jitter induced convection and solutal striation and their effects on solidification.