Analysis of close-contact melting with inner wall temperature variation in a horizontal cylindrical capsule

Melting and solidification of a phase change material (PCM) in a capsule is of practical importance in latent heat thermal energy storage (LHTES) systems which are considered to be very promising to reduce a peak demand of electricity in the summer season. Two melting modes are involved in melting in capsules. One is close-contact melting between the solid bulk and the capsule wall, and another is natural convection melting in the liquid region. Close-contact melting processes for a single enclosure have been solved using several numerical methods (e.g. Saitoh and Kato (1994)). However, there is no theoretical solution considering the inner wall temperature variation within cylindrical or spherical capsules. In this report close-contact melting heat transfer characteristics including melt flow in the liquid film under inner wall temperature distribution were analysed and simple approximate equations are presented, which facilitates designing of the practical capsule bed LHTES systems. The effects of the Stefan number and variable temperature profile etc., were clarified in detail. The melting velocity of the solid bulk under various conditions was also studied theoretically. In addition the effects of variable inner wall temperature on molten mass fraction were investigated