Enhancement of Melting Process Inside Toroidal Tube Heat Exchanger With Different Cross-Sectional Geometries

Utilizing phase change material (PCM) in concentric tube and shell-and-tube latent heat exchangers known as latent heat thermal energy storage (LHTES) have been extensively studied due to the high ability and density in storing energy during the melting (charging) process. Inadequate melting in these systems reduces the thermal performance of LHTES systems. To facilitate and accelerate the melting process, the innovative design of such systems is a key. The present study proposes novel designs of toroidal tubes embedded in the LHTES system as a latent heat exchanger. The effect of the cross-sectional geometry of the tube on the thermal performance of the system is investigated through simulation and comparison of different cross-sectional geometric shapes. A mathematical model based on the enthalpy-porosity approach is developed and numerically solved by the finite volume method to simulate the energy transport processes inside the system. Several transient heat transfer characteristics, e.g., thermal filed, melt fraction, Nusselt number, and energy storage during phase change, are determined and compared for all cases to evaluate their thermal performance and find the optimal geometry. The results indicate that downward triangular geometry for the cross-sectional shape of the tube shows the best performance as it significantly enhances the melting process, resulting in a faster energy storage rate during the charging process. Compared with the circular toroidal tube as the base geometry, the downward triangular shape design for the toroidal tube can improve the charging power of the system by 21%.