Enhanced thermal performance of a multi-module latent heat storage heat exchanger with mesh-like flow channels

Abstract

Latent heat thermal energy storage (LHTES) systems effectively address renewable energy supply-demand mismatches. However, most high-density LHTES heat exchangers suffer from low heat transfer efficiency. To address this challenge, a novel high-efficiency LHTES device integrating multiple heat transfer enhancement strategies is proposed. The device comprises multiple phase change material (PCM) modules with mesh-like flow passages. A two-dimensional mathematical model is developed and validated. The thermal performance during melting and solidification is investigated and benchmarked against a state-of-the-art triple-tube design under identical PCM mass and shell dimensions. The effects of PCM module volume ratio, spatial arrangement, and heat transfer fluid (HTF) temperature on thermal performance are analyzed. The laminar flow assumption for PCM natural convection is validated. A Grashof number formulation with dynamic characteristic length is proposed. Results demonstrate that the Gr formulation with dynamic characteristic length accurately captures PCM natural convection. The proposed design achieves higher Nusselt numbers than the triple-tube configuration, with improvements of 80.2 % in the maximum and 26.7 % in the minimum values. The horizontal arrangement of PCM modules reduces melting time by 18.01 % compared to the vertical layout, while solidification time remains nearly unchanged. The optimal melting and solidification structures reduce melting and solidification times by 53.50 % and 47.96 %, respectively, with average energy storage and release rates 2.04 times and 1.82 times those of the triple-tube design. The thermal performance advantages of the proposed structure over the triple-tube design are more pronounced at lower HTF temperatures. This study provides new insights for advancing high-performance LHTES systems.