Abstract
Solar energy has been considered as one of the most promising energy source because of its inexhaustible feature. The techniques to generate electrical power from solar energy can be divided into two categories nowadays, solar photovoltaic (PV) and solar thermal. Compared to solar photovoltaic systems, solar thermal systems have much higher energy conversion efficiency reach up to 50%. In order to increase the heat storage ability of working fluid used in solar thermal systems, the addition of phase change materials (PCMs) into working fluid have been demonstrated to be an effective method. However, during the operation of PCMs, an unfavorable phenomenon called supercooling is widely observed. In this study, Zn microparticles have been chose to be PCM and coated with TiO2 and Al2O3 as shell layer. The as-synthesized materials are analyzed by SEM, XRD, EDS, and DSC. The difference in surface morphologies was examined by SEM. Elemental analysis was performed by XRD and EDS. And the DSC measurement was used to investigate the phase change behavior of Zn with different oxide coatings. The results show that both of the Zn particles coated with TiO2 and Al2O3 possessed high durability and the performance remained stable under 40 cycles thermal test. However, due to the difference in thermal conductivity and shell thickness, various extent of supercooling will be induced. Al2O3 shell with higher thermal conductivity was able to make the final encapsulated Zn particles possess lower degree of supercooling, and the shell thickness can be controlled easily. In summary, this study provides a guideline for material selection. By choosing the material with high thermal conductivity as shell layer and controlling the appropriate shell thickness, the supercooling raised by shell structure can be less.