Effect of steady-state and unstable-state inlet boundary on the thermal performance of packed-bed latent heat storage system integrated with concentrating solar collectors

Abstract The real-time change of solar radiation intensity leads to the instability of the outlet temperature of the collector, which has an important influence on the thermal performance of the thermal energy storage system. Therefore, the dynamic thermal performance of a packed-bed latent heat storage system integrated with a solar parabolic trough collector is studied in this paper. Moreover, the effects of different mass flow rates on the total charging capacity, total exergy input, total exergy storage and exergy efficiency of the system are investigated. The result indicates that the steady-state and unstable-state inlet boundary conditions show significant differences in thermal performance. Under the unstable-state boundary conditions, when the mass flow rate increases from 0.1 to 0.2 kg/s and 0.1–0.4 kg/s, the maximum temperature difference between the PCM capsules and the air decreases to 24.11% and 47.39%, respectively. The larger the mass flow rates, the smaller the temperature difference, which is the opposite of the steady-state situation. Under steady-state inlet temperature conditions, the exergy efficiency gradually decreases with the increase of mass flow rate. Under unstable-state inlet temperature conditions, the mass flow rate has little effect on the exergy efficiency, and which is about 41.00%.