RADIATION INDUCED MELTING OF A SEMITRANSPARENT PHASE-CHANGE MATERIAL

The purpose of this study is to obtain an improved understanding of the physical processes which occur during solid-to-liquid phase transformation for the special case when such phase change is effected by the internal absorption of thermal radiation from a source external to the material. To meet this end, theoretical and experimental studies were conducted. An analytical model was developed for predicting radiative and thermal conditions during radiation induced phase change, as well as liquid/solid interface displacement with time. Energy equations are written separately for the two phases and required to meet simultaneous temperature and energy balance considerations at a common boundary, the liquid/solid interface. Parametric calculations are undertaken to determine the extent to which some fourteen identifiable dimensionless controlling parameters of the phase change process influence the temperature distribution, liquid/solid interface motion, and expansion of the overall thickness of the material. Experimental simulations were conducted in the laboratory by using a high intensity tungsten filament lamp to melt both horizontal and vertical slabs of a low fusion temperature material (n-octadecane) contained within a test cell especially designed for this purpose. In both situations the temperature profile was obtained by a thermocouple rake implanted within the slab. The liquid/solid interface displacement was measured with a vernier cathetometer during the horizontal melting and by photography during the vertical melting. Comparisons between data and model predictions for the horizontal melting show good agreement. The vertical melting experiments show strong evidence of natural convection effects on the phase-change process