EXPERIMENT ON MELTING IN HEAT-STORAGE CAPSULE WITH CLOSE CONTACT AND NATURAL-CONVECTION

Close-contact melting heat transfer characteristics, including natural convection in the liquid region in a horizontal cylindrical capsule, were studied experimentally. Elucidation of the heat transfer mechanism in such a case is of special importance in designing cost-effective ice storage and heat storage systems employing the latent heat of fusion thermal energy storage (TES) concept. Experimental results are presented on melting heat transfer in horizontal cylindrical capsules. This phenomenon includes both close-contact heat transfer in a narrow layer between the solid and the capsule wall and natural convection in the liquid melt. Hitherto, attention has been focused mainly on close-contact melting, and the contribution of natural convective heat transfer in the liquid phase has been neglected. The contribution of natural convection in a cylindrical capsule was clarified when Rayleigh and Stefan numbers were varied over a wide range of values. In most previous studies, these parameters were kept within a relatively narrow range, and the effect of varying parameters was not discussed. It is shown in the present paper that the contribution of close-contact heat transfer is reduced as the Stefan number increases and therefore the contribution of natural convection in the melt region becomes significant. Experimental results are compared with numerical results in which both close-contact and natural convection effects are included. The results facilitate the design of practical latent heat TES systems using various capsules.