Abstract
Melting and solidification of phase change material (PCM) in a capsule is of practical importance in the latent heat thermal energy storage (LHTES) systems which are considered to be very promising for e. g. peak cut of electricity demand in the summer season. The melting process in both cylindrical and spherical capsules including melt flow in the liquid layer under inner wall temperature variation has attracted less attention until very recently. According to the experiment on the capsule bed LHTES system, the peripheral wall temperature distribution could be a key factor in close-contact melting heat transfer. In the past investigations heat conduction has been regarded as a dominant mode in the liquid film layer when the Stefan number is relatively small. And the effects of the fluid flow in the liquid film layer have not been considered. This paper presents the approximate solutions for close-contact melting with inner wall temperature variation in both horizontal cylindrical and spherical capsules. And the effects of distribution of the inner wall temperature and molten mass fraction were investigated analytically. A comparison between constant temperature and variable temperature cases was made and it was concluded that consideration of wall temperature variation is important.
