Structure optimization of a phase change material integrated solar air collector/storage unit based upon phase change analysis

Abstract A phase change material (PCM) integrated solar air collector/storage unit (SACSU) for mid-temperature applications was proposed in the study. The composite PCM with expanded graphite (EG) in mass fraction of 3% was prepared to enhance the thermal conductivity. Firstly, an experiment was performed to investigate the thermal performance of the PCM integrated SACSU in the charging and discharging process. Secondly, a numerical model based on the enthalpy – porosity and melting – solidification models was developed and experimentally validated; and then, the heat transfer performances and phase change characteristics were numerically analyzed. Finally, the parameters of the diameter and height of the PCM filling tube were optimized. The results indicated the SACSU could prolong the utilization of solar energy for nearly two hours compared with traditional evacuated solar pipes. Additionally, the structure optimization showed that the duration of discharging process could be extended with the increase of aluminum pipe diameter and the optimized performance could be achieved with the PCM filling length of 1400 mm in the study.