Phase change energy storage system: An analysis of cyclic melting and freezing

Abstract

The thermal performance of a storage system using paraffin wax, myristic acid and a mixture of 50% wax a?? 50% myristic acid, as phase change materials (PCM), is investigated using a heat exchanger consisting of vertically placed, concentric copper tubes. The temperature of the heat transfer medium was from 65-85 A?C during the melting experiments and 25-35 A?C for the freezing experiments. The flow rate for air was varied between 160 a?? 180 l/min. Cyclic melting and freezing experiments were performed on the three PCMs, subjecting the PCMs to different melting and freezing periods. The efficiency, defined as the ratio of the energy withdrawn to the energy stored, was evaluated. Myristic acid has the highest efficiency of 79.5%, followed by wax and the mixture of wax and myristic acid. Numerical studies were performed using FLUENT version 6.0. From the visualization results, the melt front is almost uniform and melt layer stable during the initial period of the phase change process. Plots of heat flux at different heights verify a higher melting rate near the top of the heat exchanger.