Enhancement of PCMs performance using nano-particles in horizontal triple-series shell-and-tube heat exchangers: A numerical study

Integrating Phase Change Materials (PCMs) as a storage system into a parabolic trough collector (PTC) setup can enhance energy security. However, PCMs have a drawback in terms of their low conductivity. To improve reliability, a cascaded array is used for the storage system. The thermal performance of three series shell and tube heat exchangers filled with PCM1 (64-68 degrees C), PCM2 (57-60 degrees C) and PCM3 (46-48 degrees C) during the charging process is evaluated. A 2D simulation model is developed, and 11 computational cases are considered. Firstly, results of utilizing two different designs of heat exchangers are analyzed. The effective geometry is chosen to validate previous experimental findings, and the range of percentage variation is 1.7 to 10.97 %. To optimize the thermal performance of the storage system for residential applications, two distinct nanoparticles of Al2O3 and GNPs are employed with maximum volume fractions of 10 and 3 %, respectively. Findings reveal that the immersion of 10 % Al2O3 accelerates the melting time of PCMs 1, 2, and 3 by 38, 31.6, and 31.6 %, respectively. Also, dispersion of 3 vol% of GNPs shortens the melting time up to 78.1 %. Meanwhile, the PCM's effective average temperature rises the most at this volume fraction, reaching 93.4 degrees C. On the other hand, it is observed that a higher concentration of Al2O3 (10 vol%) declines the energy and exergy storage of the system by 40.6 and 39.8 %, respectively. Conversely, increasing GNP volume fraction to 2.5 % enhances the system's energy and exergy by 21.1 and 62.9 %, respectively. These advancements enhance the storage system's thermal performance, broadening its potential applications.