Solar thermal energy storage using phase change materials

Abstract

A latent heat thermal energy storage (LHTES) system is designed and constructed to find a good alternative for the hot water storage tank used in solar domestic hot water (SDHW) system. The system is a shell and tube heat exchanger with a special design combined with phase change material (PCM) as the storage media. The PCM used in this study is paraffin wax. Paraffin wax is safe, inexpensive and has a phase change temperature suitable for SDHW systems. The experimental study focuses on the effect of the volume flow rate of the heat transfer fluid (HTF) and the initial PCM temperature on the solidification time and the heat transfer characteristics of the LHTES system, during the energy discharging process. Paraffin wax proved to be suitable PCM for LHTES systems for SDHW applications, as it has suitable transition temperature range (58 – 62℃ ) and has relatively high latent heat of 201.8 J/g. The experimental results show that the HTF discharge flow rate and the initial temperature of the phase change material have a significant effect in the total solidification time. Increasing the discharging rate results in shorter solidification times. For example, increasing the HTF flow rate from 1 LPM to 2 LPM shortened the PCM total melting time by a 19% and a 15% for 70℃ and 80℃, respectively. Increasing the initial temperature results in shorter solidification times. For example, increasing PCM initial temperature from 70℃ to 80℃ shortened the total solidification time by 20%. However, it should be noticed that the initial temperature is limited to what the available source of energy suggests