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Purpose -The quality of crystals grown in space can be diversely affected by the melt flows induced by g-jitter associated with a space vehicle. This paper presents a full three-dimensional (3D) transient finite element analysis of the complex fluid flow and heat and mass transfer phenomena in a simplified Bridgman crystal growth configuration under the influence of g-jitter perturbations and magnetic fields. Design/methodology/approach -The model development is based on the Galerkin finite element solution of the magnetohydrodynamic governing equations describing the thermal convection and heat and mass transfer in the melt. A physics-based re-numbering algorithm is used to make the formidable 3D simulations computationally feasible. Simulations are made using steady microgravity, synthetic and real g-jitter data taken during a space flight. Findings -Numerical results show that g-jitter drives a complex, 3D, time dependent thermal convection and that velocity spikes in response to real g-jitter disturbances in space flights, resulting in irregular solute concentration distributions. An applied magnetic field provides an effective means to suppress the deleterious convection effects caused by g-jitter. Based on the simulations with applied magnetic fields of various strengths and orientations, the magnetic field aligned with the thermal gradient provides an optimal damping effect, and the stronger magnetic field is more effective in suppressing the g-jitter induced convection. While the convective flows and solute transport are complex and truly 3D, those in the symmetry plane parallel to the direction of g-jitter are essentially two-dimensional (2D), which may be approximated well by the widely used 2D models. Originality/value -The physics-based re-numbering algorithm has made possible the large scale finite element computations for 3D g-jitter flows in a magnetic field. The results indicate that an applied magnetic field can be effective in suppressing the g-jitter driven flows and thus enhance the quality of crystals grown in space. Paper type Research paper

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Results show that a combined action derived from magnetic damping and microgravity can be an effective means to control the melt flow and solutal transport in space single crystal growth systems.

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.