Analysis of Heat Transfer Characteristics in a Latent Heat Storage Module Using Circular-Finned Tubes

This study investigates the heat transfer characteristics of a latent heat storage module equipped with circular-finned tubes to enhance thermal energy storage performance. The module incorporates circular fins to effectively increase heat transfer area, thereby enhancing the heat exchange efficiency between the heat transfer fluid (HTF) and phase change material (PCM). For this research, Barium Hydroxide Octahydrate (BHO), an inorganic PCM with a phase change temperature of approximately 78°C, was selected for its suitable thermal properties. To assess the module’s performance comprehensively, we constructed a dedicated experimental apparatus that enabled quantitative analysis of both heat charging and discharging characteristics under controlled conditions. The experimental results showed an average heat discharge of 1.027 kWh and thermal utilization efficiency of 79.25%. The overall heat transfer coefficient varied significantly with PCM phase states, showing the highest values in liquid state (0.257∼0.863 kW/m²⋅K), followed by latent phase (0.025∼0.072 kW/m²⋅K), and solid state (0.015∼ 0.044 kW/m²⋅K). The outside heat transfer coefficient was calculated as 0.033∼0.162 kW/m²⋅K in the latent phase and 0.018∼0.064 kW/m²⋅K in the solid phase. Statistical analysis revealed that HTF flow rate significantly influences the overall heat transfer coefficient across all PCM states, while the effect of HTF inlet temperature was found to be minimal. Through this study, essential heat transfer data required for latent heat thermal storage module design were obtained, and it is determined that the design of latent heat thermal storage modules should consider the phase-dependent heat transfer characteristics of PCM.