Application of solid/liquid phase change material (PCM) for passive cooling of electronic modules is on the increase. A simplified method of predicting the thermal performance of passive cooling systems is needed for efficient design of thermal storage systems. This paper presents an experimental and approximate analytical method for quick estimation of the rate of thermal transport in solid/liquid PCM during and after the melting process. However, the emphasis of this paper is on the transport phenomena after the melting process is completed. This research is motivated in part by the need for a simplified analytical method of predicting the rate of heat transfer in buoyancy-driven fluids within a partitioned enclosure, and the need for a fundamental understanding of the rate of heat transfer in liquid melt after the phase change phenomena. These needs are of practical importance for efficient design of a thermal energy storage system. The approximate analytical model serves as a quick method of studying the performance of a thermosyphon system.