Efficiency enhancement in direct thermal energy storage systems using dual phase change materials and nanoparticle additives

The study aims to enhance the reliability of direct thermal energy storage (TES) using phase change materials (PCMs) and nanoparticles, ensuring sustained heat supply even during periods of low or intermittent solar radiation. The study specifically investigates a TES system comprising a double -cylindrical shell container with two distinct PCM types: petroleum jelly or petrolatum with 1 % Al 2 O 3 nanoparticles by volume in the outer shell and wax in the inner shell. Additionally, a redesigned heat exchanger is employed to improve heating efficiency. The study examines two configurations: an open system and a closed system with a storage water tank. The deliberate strategy of augmenting PCM volume is aimed at enhancing heat transfer during both the charging and discharging phases. The performance of closed and open system configurations is compared, with a focus on highlighting the temperature profiles during the charging and discharging processes. The incorporation of 1 % Al 2 O 3 nanoparticles in the PCMs led to a significant enhancement in efficiency, with the two-phase materials case achieving the highest efficiency of 73 %. Furthermore, the utilization of nanoparticles resulted in an improvement in efficiency of approximately 5 %. These findings demonstrate the potential of using dual PCM layers with NPs additives in direct TES systems.