Numerical investigation into selecting the most suitable shell-to-tube diameter ratio for horizontal latent heat thermal energy storage

Abstract

To control greenhouse gas emissions and improve the sustainability of renewable energy technologies, thermal energy storage systems are receiving significant attention in recent years. Extensive research has been conducted on shell-and-tube Latent Heat Thermal Energy Storage (LHTES) systems to match energy supply and demand. The selection of the tube and shell diameter in the heat exchanger is a crucial aspect in the design of LHTES systems. This research intends to deliver the most suitable shell-to-tube diameter ratio for the complete operation of horizontal thermal energy storage. Different shell-to-tube diameter ratios were studied using two schemes: (i) varying the shell diameter on a fixed-sized inner tube, and (ii) varying the inner tube diameter within a fixed shell diameter. The outer shell was constructed of acrylic, while the inner tube was made from copper, and paraffin RT50 was used as the phase change material. Numerical simulations were performed using the enthalpy-porosity method and verified with data from the literature. Performance indicators, such as average liquid fraction, temperature, average storage/retrieval rate, Fourier number and storage/retrieval density were utilized to evaluate the system's performance. Results indicated that the thermodynamic characteristics were similar in both schemes. The maximum energy density was found to be around 268 kJ/kg and remained constant until a diameter ratio of 5 and 4 for the charging and discharging processes, respectively, before decreasing. During charging, the Fourier number decreased initially and then stabilized at 0.4 after the diameter ratio of 5, while it stabilized at 1.2 during discharging. The best diameter ratio was found between 4 and 5 for the charging process, and between 3 and 4 for the discharging process. Ultimately, the most suitable diameter ratio was recommended as 4 for the complete cycle.