Passive combined heat transfer enhancement techniques for performance improvement of shell tube latent heat thermal energy storage

Abstract

Latent heat thermal energy storage (LHTES) in heat exchangers, utilizing phase change materials (PCMs), is a key for managing power demand. The poor heat transfer characteristics of PCM are a challenge, therefore, improvements are continuously researched to increasing LHTES performance. This paper presents a 2D numerical study aiming to improve the latent storage system using a combination of techniques including dual PCMs and shape of pipe carrying the heat transfer fluid. Optimal PCM position is first determined to achieve fast storage process. Furthermore, two inner tubes with circular and elliptical shapes and their orientation and their impact on the charging process are investigated. Moreover, to further improve the thermal efficiency and accelerate the charging time, Al₂O₃ nanoparticles are incorporated into the PCM placed at top of the heat exchanger to enhance heat transfer characteristics where lower melting rate is observed. Outcomes indicate that dual PCM technique with placing PCM of lower melting point at the bottom accelerates the storage process by 37.06 %. Additionally, using a double elliptical inner tube in the vertical position boosts the melting rate and gives better performance than using one or two circular tubes. Finally, adding nanoparticles to the top PCM leads to the fastest charging time, reducing hence the charging time by 83.3 %. These outcomes contribute to energy efficiency enhancement of latent heat storage systems.