Design method and parameters optimization of finned-tube latent thermal energy storage for heat pump applications

Abstract

This study employs a finned-tube heat exchanger as the heat-exchange core and modified Sodium acetate trihydrate (SAT) as the storage medium to design a 6.0 kWh finned-tube latent thermal energy storage (FT-LTES) unit and investigate performance enhancement via geometric optimization. The modified SAT was subjected to 2000 thermal cycles. Compared with the initial state, the latent heat decreased by 7.0%, while the degree of supercooling increased by 9.2 °C. A 3D transient computational model, integrating shell conduction theory with phase change dynamics, was developed to systematically evaluate five geometric parameters: fin thickness, fin spacing, tube diameter, horizontal tube spacing and vertical tube spacing. The discharging performance was evaluated based on the key metrics: effective discharging time, average discharging power and effective water supply volume. The results reveal that, within the studied parameter range, the effective discharging capacity of the FT-LTES module increases with greater fin thickness, smaller fin spacing, and reduced tube spacing, while exhibiting a non-monotonic relationship with tube diameter, initially increasing and then decreasing. An optimized structure for the FT-LTES unit was identified, with fin thickness, fin spacing, horizontal tube spacing, vertical tube spacing, and tube diameter of 0.2 mm, 1.9 mm, 12.0 mm 16.0 mm and 25.4 mm, respectively. Multi-cycle thermal storage and release tests on the optimized structure demonstrated 128.0% improvement in effective water supply volume compared to the original LTES unit.