AHP SETUP FOR LOW LAMINAR MELT FLOW STUDY IN CRYSTAL GROWTH

Summary For verification of numeric methods and development of experimental benchmarks for 2D and 3D models of heat and mass transfer in crystal growth, the experimental AHP setup based on a novel AHP crystal growth method is designed to conduct experiments with NaNO3 and ice. It is equipped with PIV and PVT visualizations systems to provide finding of field of flow velocity and temperature distribution in the fluid. Preliminary investigations have proved the possibility to suppress natural convection and to create low melt flow similar to micro gravity conditions and shown good coincidence of calculated data on mass transfer with those observed in the experiment. INTRODUCTION Solid-liquid phase-change phenomena are present in a large number of industrial applications and natural processes. Numerical modelling of such strongly non-linear, moving boundary, thermal and fluid flow problems is not a trivial task. In the case of solidification, the planar interface appears to be unstable depending on environment conditions, creating different structures, such as cells or dendrites. These local mechanisms have drastic consequences at a larger scale and convective motion in the interdendritic melt is a primary cause for a macrosegregation that is the variation in composition of a solidified alloy for instance. In the microgravity environment, despite the absence of natural convection, problems arising from the effects of Marangoni convection or g-jitter effects seriously damped initial enthusiasm on using space labs for crystal growth. Computer simulation has a major relevance as a tool of analysis of the experimental studies or for the design of engineering hardware. In order to assess a satisfactory level of confidence of the simulation tools, both the model and the procedure have to be tested through properly designed validation experiments, reproducing the basic features of the simulated phenomena. Therefore, experimental benchmarks for code validation have gained a special attention in the recent years. In the prevailing growth methods, when a strong forced or thermocapillary convection takes place, a complex flow unstable by its nature is formed. Under such conditions, it is extremely difficult to realize quantitative correlation between experimental and calculated data. In this connection, special interest presents solidification from a thin melt layer (1,2) when low laminar flows are initiated. Employing modern visualization tools, which provide a way for thermometric and velocimetry measurements, and expanding a number of model liquids, it is possible to carry out researches in heat and mass transfer during solidification within a wide range of determining parameters.