Numerical analysis on phase change material melting process of a conical spiral tube energy storage tank

Spiral tube heat exchangers have been widely used in phase change energy storage due to the compact structure and large heat transfer area. Therefore, this study numerically analyzes the effects of spiral tube diameter, number of rotations, and unsteady heat source on the melting process in conical spiral tube energy storage tanks using Fluent software. The results indicate that when the tube diameter is increased from 8 to 11 mm and the number of rotations is increased from 5 to 8, the melting time is extended by 15.74% and 17.83%, respectively. The energy storage capacity increases by 0.64% and 1.83%, respectively. The average energy storage rate decreases by 13.05% and 13.58%, respectively. Furthermore, the sinusoidal wave heat source with small heat source periods has little effect on the melting process, while large heat source periods can significantly accelerate the melting. And the influence of amplitudes on the thermal storage performance under large heat source periods is more obvious. When the heat source period is increased from 2 to 160 min and the amplitude is increased from 5 to 20 K, the melting time is reduced by 24.50% and 17.20%, respectively. The total energy storage capacity decreases by 6.36% and increases by 1.62%, respectively. The average energy storage rate increases by 24.03% and 22.74%, respectively. The study provides guidance for the performance optimization of spiral tube phase change systems.