The discharging process (melting). Figure 6 shows photographs of a test sphere at time
points during the melting process from t=0 to 131 min when the ice had melted completely. The
temperature of the HTF used in this was 7.28C and the radius of the glass sphere was 3.5 cm. At
the start of the melting process, the solid fraction was observed to melt uniformly. Since its
density is lower than its surrounding liquid, after an interval of time, the solid fraction was seen
to float at the surface of the melt water and to contact the inside surface of the sphere. The solid
fraction remained in contact with the inner wall of the test sphere for most of the melting
process. However, at the end of the melting process the solid fraction was seen to float at the free
surface of the melted water. Figure 6 shows that the spherical shape of the solid fraction was
retained for most of the melting process except towards the end when it was seen to lose its
spherical shape and become flattened or elongated until melting was completed.