Prediction of melting characteristics of encapsulated phase change material energy storage systems

Abstract This paper presents a numerical study of encapsulated phase change material (PCM) energy storage systems consisting of a single capsule or multiple capsules with different arrangements. A numerical model is developed for predicting the melting characteristics of encapsulated PCM with circular geometry, subjected to the flow of heat transfer fluid (HTF) over the capsules. The model also incorporates the effect of natural convection inside the PCM capsules. The single capsule system is analyzed to capture the effect of different parameters such as capsule size, fluid temperature, fluid velocity, and direction of flow. The model is applied to investigate multiple capsule systems to enhance the melting rate by the effective distribution of PCM capsules. Straight and alternate arrangements are compared for a varying number of capsules by maintaining the same latent energy storage capacity. Parametric studies are also performed for multiple capsule systems. Subsequently, a novel design of graded systems is proposed for improving the multi-capsule system by reducing the total duration of melting. The capsules are arranged with a percentage reduction in size along the flow direction, keeping the overall energy storage capacity constant. Simulation results show that there exists an optimum value of the reduction percentage for which the melting time is lowest.