Melting in an enclosure heated at constant

This paper describes a two-part study of the time-dependent melting of an enclosed phase- change material heated at a constant rate from the side. The first part describes experimental measurements with n-octadeoane conducted in a 74 cm tall enclosure. The heat flux Rayleigh numbers of these experiments are of the order of lo, and the liquid flow pattern is weakly turbulent. The second part of the study describes the liquid-superheat effect analytically, by means of a 'matched boundary layers' solution for the convection regime of the heat transfer and melting process. The predicted overall Nusselt number relation- ship agrees very well with the empirical correlation based on experiments. THIS PAPER describes a two-part study of the process of melting in the presence of natural convection in an enclosure that is being heated at a constant rate. The general subject of natural convection melting in enclosures has received considerable attention, because of its applicability in areas such as thermal energy storage, metallurgy, manufacturing and geo- physics. The existing work, however, is primarily based on the model in which the heating effect is provided by an isothermal side wall the temperature of which remains fixed in time (see, e.g. the two reviews by Viskanta (l, 21). The constant-rate heating mode deserves to be studied because it can serve as a good model for the operation of latent-heat storage devices for solar energy. The first part of the paper (Section 2) describes a series of laboratory experiments conducted in a con- siderably taller enclosure than in the existing exper- imental studies, that is, at high Rayleigh numbers where the flow shows signs of turbulence. The second part of the study consists of a compact boundary layer analysis of the convection-dominated regime. Therefore, in addition to the new focus on the con- stant-rate heating mode, two additional objectives of this study are to extend the high Rayleigh number domain experimentally (Section 2), and to document analytically the effect of liquid superheat in the con- vection regime (Section 3).