Numerical investigation of thermal energy storage characteristics of dual phase change material in double elliptic pipe

Latent heat storage offers high thermal energy density. However, the low storage rate is a challenge to address. This study aims to evaluate the effects of cascading dual-phase change material (dual-PCM) within a double elliptic pipe on thermal performance and storage rates. The melting process of dual-PCM in the enclosure is numerically analyzed. The numerical model is validated by comparison with experimental data of the literature. Nine design configurations are examined, focusing on the orientation (vertical and horizontal) and the inclination of the elliptic enclosure in order to find out the most effective storage unit. The thermal and flow fields are analyzed alongside the evolution of the melt fraction, charging times, and stored energy. Results indicate that the cascading dual-PCM inside an outer horizontal elliptic enclosure with an inner vertical heating elliptic pipe reduce thermal energy storage time by up to 49 %, demonstrating the most efficient melting process. Furthermore, the study indicates that vertical elliptical pipes reduce thermal energy storage time by 24.7 % compared to horizontal ones, and that lower inclination angles provided a faster and more uniform melting process. Dual-PCM configurations in horizontal orientations significantly enhance energy storage efficiency.