Interaction of solid particles with a moving solidification front under microgravity conditions during the TEXUS56 and TEXUS58 sounding rocket missions – an experimental and theoretical study

We studied the interaction of solid particles with the moving water–ice solidification front under microgravity conditions onboard the TEXUS56 and TEXUS58 sounding rocket missions. In addition, a global, three-dimensional, time-dependent model is used to simulate the solidification processes including the particle transport and their interaction with the moving interface. The results obtained by the numerical simulations show a good correlation with the data from the sounding rocket experiments. This applies to the temporal development of the position and shape of the solidification front, the injection and transport of the particles in the fluid as well as their incorporation into the moving solidification front. The injection procedure causes a forced flow resulting in a disturbance of the solidification process for a short time period. After that no significant particle movement was observed. Most particles are immediately captured by the moving solidification front. The capture of the particles was expected from theoretical considerations as the critical capture velocity of the particles is smaller and partially much smaller than the actual solidification velocity for the given conditions. The action of the particles on the interface morphology was also investigated. Unexpectedly, no tip of the interface below a particle was observed in the high-resolution video images recorded during the TEXUS experiments as it would be predicted from theory as a result of the different thermal conductivities of particle and liquid. It is supposed that for the given conditions the latent heat release might lead to a flattening of the solidification front and is thus the cause of the experimental observations found here.