Performance assessment of single-sided operation in a high-temperature latent heat storage system under fault conditions during charging and discharging

Abstract

As the high-temperature latent heat storage (LHS) market continues to expand, ensuring its safe and stable operation is paramount for facilitating its rapid development. In specific operational scenarios and instances of failures, large-scale integrated LHS systems may operate with either single or partial sets of heat exchange tubes. However, a notable research gap exists in the comprehensive exploration of the impact of partial operational conditions on the thermal performance of LHS systems. Consequently, this study conducted experiments involving both- and single-sided charging and discharging using a cylindrical high-temperature LHS system equipped with two sets of heat exchange tubes. To comprehend the ramifications of single-sided operation on temperature distribution across both active and inactive sides, as well as its influence on charging/discharging power and accumulated stored/released energy on the active side. The analysis of phase change material (PCM) temperature distribution revealed that single-sided charging significantly influenced the inactive side, while single-sided discharging exhibited a comparatively minor impact on the inactive side. As PCM melted during charging, temperature disparities diminished due to natural convection, while non-uniform temperature persisted in unmelted PCM. Examination of the PCM liquidus indicated that the metal heat exchange tube enhanced heat transfer on the inactive side, resulting in substantial PCM melting during charging. However, the heat transfer effect of metal heat exchange tubes during discharging was insignificant, leading to a considerable amount of liquid PCM on the inactive side after discharging. The total heat storage for both-sided charging was 1002.71 MJ, whereas, for single-sided charging using two tubes, it was 1074.42 MJ and 1000.60 MJ, respectively. Correspondingly, during discharging, the average powers were 682.74 MJ, 543.62 MJ, and 538.11 MJ, respectively. The cycle efficiency for the both-sided operation was 68.09 %, while those for single-sided operations of two tubes were 50.6 % and 53.78 %, respectively. The reduced cycle efficiencies of single-sided operations were attributed to prolonged charging and discharging durations and the presence of more liquid PCM on the inactive side after discharging.