Effect of volume fractions of phase change materials on the dynamic performance of two- and three-stage cascaded latent heat thermal energy storage systems

This paper investigates the effect of volume fractions of phase change materials (PCMs) on the dynamic characteristics and performance of two- and three-stage cascaded latent heat thermal energy storage systems (LHTESS) in terms of melting time, charging capacity, and dynamic effectiveness. Water is used as a heat transfer fluid (HTF) with one, two, and three PCMs composed of PCM40, PCM50, and PCM60 for melting temperatures of 40, 50, and 60 °C, respectively. Axial cascaded systems using two-stage PCM40/60 and three-stage PCM40/50/60 are investigated at seven different volume fractions to achieve better-cascaded systems, which have lower stratification and melting time with higher effectiveness and charging capacity. A transient, three-dimensional, computational fluid dynamics simulation using ANSYS Fluent 2019 R3 software is developed. The simulation results are validated with numerical and experimental results published in the literature. The results indicated that volume fractions of 80/20 % for PCM40/60 and 49/41/10 % for PCM40/50/60 attained lower melting time (by 6.0 % and 20.9 %) and higher charging capacity (by 16.0 % and 40.0 %) and average effectiveness (by 11.8 % and 12.6 %) than the best single case (PCM40). Additionally, the results show that PCM40 has a lower melting time by 53.0 % and 156.0 %, higher rate of charging by 42.62 % and 106.58 %, and higher average effectiveness by 9.68 % and 15.25 % than PCM50 and PCM60, respectively.