A STUDY OF FREEZING AND MELTING WITH EUTECTIC INTERACTIONS

The phenomenon of freezing and melting following sudden contact between a pool of binary, eutectic-forming, solution and an underlying solid layer of the lighter pool component was investigated. Experiments were conducted using various salt (KI, NaCl, MgCl(,2), or CaCl(,2)) solutions as the pool and air-bubble-free ice as the solid. Both the melting regime and the selective freezing regime, were studied. Experimentally, the temperature transients and the phase-change rates were measured and the interface morphology as well as the micro-physical process near the phase-change front were observed. Within the temperature and the density ratio ranges explored, the ice melting rate was found to be very sensitive to the ratio of solution to ice melt density but independent of solution and ice temperature difference. By varying the density ratio, two different convection patterns in the pool and two different morphologies of the solid-liquid interface were observed. For low-density ratios, the interface was less wavy and the average wavelength was much larger than observed for high-density-ratios. In both convection regimes, melt streamers were observed emanating from the crests of the wavy interface into the pool. The measured wavelengths (spacing) between the streamers for four different pairs of materials were correlated with density ratio and agree favorably with Taylor instability theory predictions. In the selective freezing study, the growth of a solid-liquid two phase region over a subcooled ice slab was investigated. The morphology of the two-phase region for NaCl-H(,2)O pool were observed. The two-phase, liquid front motion was recorded through a telescopic device together with measured transient temperature distribution. Assuming that each infinitesimal element of the two-phase region is in local thermodynamic equilibrium with the solid and that the solid is semi-infinite in extent, a similarity model was developed to predict the dependence of the freezing rate and temperature distribution on the parameters of the system. For a thick ice slab, the analytical and the experimental results agree quite well. The effects of a thin ice slab on the growth of the two-phase region was also examined. *Work performed under the auspices of the U.S. Department of Energy