Modeling of solidification processes under consideration of particle transport in the melt under terrestrial and microgravity conditions

In this work the interaction of solid particles with the moving water-ice solidification front under terrestrial and microgravity conditions is studied by numerical simulations as well as by experiments. A global, three-dimensional, time-dependent model is used to simulate the solidification processes taking into account buoyant convection and the injection of the particles, their transport through the fluid and their interaction with the moving interface. In basic parameter studies without considering any particle transport and interaction, the thermal conditions of the solidification processes in the module were systematically varied and their influence on the position and shape of the solidification front investigated. It was found that there is only a minor influence on the pure solidification process whether the experiments are carried out under terrestrial or microgravity conditions. Also, the orientation of gravity relative to the solidification direction plays only a minor role. For the simulation of the TEXUS 56 sounding rocket experiment, the injection of the particles, their transport through the fluid and their interaction with the interface were considered in the simulations. The simulation results of the TEXUS 56 experiment agree reasonably to the experimental data. In both cases, a transition from a convex to a concave solidification front is observed. The calculated and measured growth rates are also in the same range and finally it was confirmed by the model that the injection of the particles causes a forced flow, which disturbs the solidification process for a short time period. Once the injection process is stopped, the forced flow decays quickly. The resulting particle distribution is comparable in experiment and simulation and no significant particle movement in the fluid is observed.