Numerical evaluation of the latent heat thermal energy storage performance enhancement by installing longitudinal fins

Abstract

Abstract Charging and discharging processes inside the shell-and-tube type latent heat thermal energy storage, which uses technical grade RT 25 paraffin as the phase change material and water as the heat transfer fluid, have been numerically investigated in order to evaluate the enhancement of the latent storage thermal performance when longitudinal fins are installed onto the tubes in comparison to the plain tube configuration. The study of latent storage tank performance enhancement using low thermal conductivity material, such as paraffin, is necessary to increase the efficiency of solar energy systems and reduce the operating cost of the system. Transient problem of three-dimensional fluid flow and heat transfer has been described with the defined mathematical model, in which simulation of phase change heat transfer is incorporated through the enthalpy formulation. Governing equations, with appropriate initial and boundary conditions, have been solved iteratively using the finite volume method in the ANSYS Fluent numerical solver using an upgraded numerical procedure. In order to validate the numerical procedure, numerical results have been compared with experimental measurements, obtained from experimental investigations carried out on the constructed shell-and-tube latent storage with longitudinal fins, and good agreement between numerical and experimental results is observed. The comparison of the two studied configurations shows a significant improvement in the overall heat transfer with the installation of fins in both the charging and discharging cycles, with a 52% reduction in the total melting time and a 43% reduction in the total solidification time compared to the plain tube configuration. Relative accumulated/released energy, defined as the ratio of accumulated/discharged energy and maximum storage capacity for the plain tube configuration, represents comprehensive latent storage efficiency and has been introduced as a performance enhancement metric. Finned tube latent storage is fully charged at relative accumulated energy value of 0.949, since maximum value of 1 can never be reached because of the decreased phase change material s mass due to fins. The same value is achieved 3\xa0h later in the plain tube configuration. Similarly, finned tube latent storage is fully discharged at relative released energy value of 0.948, and the same value in plain tube configuration is reached 12\xa0h later. Clearly, reduction in phase change material mass and obstruction of natural convection in the liquid phase due to installation of fins are negligible on the overall latent storage thermal performance during both charging and discharging. Results obtained by this investigation will be used as guidelines for further analyses focused on defining the optimal fin configuration and geometry parameters of shell-and-tube latent storage tanks.