This paper describes a two-part study of the time-dependent melting of an enclosed phasechange material heated at a constant rate from the side. The first part describes experimental measurements with n-octadecane conducted in a 74 cm tall enclosure. The heat flux Rayleigh numbers of these experiments are of the order of 1013, 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 relationship agrees very well with the empirical correlation based on experiments. © 1989.