Numerical study on the melting performance of a diverging-converging shell and tube latent heat storage system

A shell and tube latent heat thermal energy storage (ST-LHTES) system is being considered for integration into a concentrated solar power plant. In this regard, the geometry of the shell surface significantly influences the thermal performance of such systems. While cylindrical, conical, and eccentric configurations have been widely studied, the effect of diverging–converging shells has not been systematically explored. The present study proposes a novel diverging–converging ST-LHTES system and investigates the charging performance through a three-dimensional enthalpy–porosity model. The H/w (height-to-sectional length) ratio in the proposed vertical configurations varies from 3 to 6 while maintaining a constant convergence angle (θ). The results indicate that an H/w ratio of 4 delivers the best thermal performance. Specifically, the PCM charging time for an H/w ratio of 4 is reduced by 5.56 %, 11.12 %, and 13.89 % compared to H/w ratios of 3, 5, and 6, respectively. Additionally, the best-performing design configuration (H/w = 4) is evaluated under different inclination angles (φ), eccentricities (ε), and Reynolds numbers (Re). The horizontal system (0°) decreases melting time by 3.12 %, 9.37 %, and 12.50 % compared to the 30°, 60°, and 90° configurations. The eccentricity analysis of the horizontal configuration indicates that increasing eccentricity enhances the melting rate by enlarging the upper region of the shell, thereby promoting natural convection. Furthermore, higher Reynolds numbers improve heat transfer, resulting in a faster melting rate.