Application of phase-change material in an active-type solar water heater: Effect of void fraction

Phase-change material (PCM) is a latent type material that can be integrated with water as thermal energy storage in a solar water heater (SWH). The encapsulation method is usually applied to store PCM in the SWH tank. This method contributes to adding the heat transfer surface area for PCM. Previous research provides information that PCM encapsulation can increase the thermal performance of the SWH system. However, no study has revealed the thermal behavior of horizontal-type SWH tanks related to the number of capsules. The void fraction is a parameter in the tank associated with the number of PCM capsules. This study aims to experimentally investigate the effect of the tank void fraction on the thermal performance of an active-type SWH. The cylindrical capsule of a copper tube was filled with paraffin wax as PCM. Several capsules were put into the tank with various void fractions. Experiments were carried out during the charging process with the solar simulator as a heat source for SWH. Water and PCM temperature were recorded for all variations of void fraction. The temperature data was used to evaluate the thermal performance, then compared each variation. The cumulative heat stored for the void fraction 87.33%, 83.95%, and 79.73% were 13.24 MJ, 16.16 MJ, and16.76 MJ, respectively. The lower the void fraction, the higher the cumulative heat stored in the SWH tank. The mass of PCM determines the thermal energy storage in the SWH system.