Transient Thermal Behavior and Thermal Buffering of a Novel PCM-Integrated Cavity Solar Receiver

Parabolic trough solar collectors are promising technologies for supplying thermal energy; however, their performance is strongly dependent on the continuity of solar irradiation. Solar interruptions can cause rapid reductions in heat transfer fluid (HTF) temperatures and reduce thermal stability and performance. This study numerically investigates the thermal behavior of a novel phase-change material (PCM)-integrated cavity receiver, patented under Turkish Patent No. 2021/013862, developed to reduce temperature fluctuations during solar interruptions. The receiver combines a cavity configuration with a PCM-based latent heat storage layer. A three-dimensional transient CFD model using the enthalpy–porosity approach was used to simulate melting and solidification. High-density polyethylene (HDPE) was employed as the PCM, while water was used as the HTF. Under the investigated solar irradiation condition, the novel solar receiver absorbed 2458 W. The water outlet temperature reached 437.52 K when the HDPE completely melted at approximately 31 min. During charging, the HDPE stored 2021.4 kJ of thermal energy, comprising both sensible and latent heat. Sensible heat accounted for 55.8% of the total energy stored in the HDPE, while latent heat accounted for 44.2%. Following solar interruption, solidification was completed at approximately 21 min. During solidification, the water outlet temperature decrease was 17.5 K for the PCM-integrated receiver, compared with 58 K for the non-PCM receiver, representing a 69.8% reduction in temperature decrease. The water outlet temperature decrease in the PCM-integrated receiver corresponded to only 4.3% during the solidification period when direct radiation was interrupted. The results demonstrate that the proposed receiver provides effective thermal buffering and improves thermal stability under short-term solar interruption.