Configurational explorations and optimizations of a phase change material based thermal energy storage with tube bundle

Compared to the extensive attentions paid to latent heat thermal energy storage (LHTES) with single tube in shell, the configurations of multiple serpentine tubes as bundles are less explored. Maldistributions of heat transfer and temperature along the heat transfer fluid (HTF) tube and charging process are barely discussed and improved. In this study, a numerical model is developed and validated. Targeting to charging process, effects of configurational parameters are revealed in detail with a focus on the maldistributions. Results show that a smaller tube pitch and a larger tube branch number benefit the charging time and charging power, while the dominant influence factor could switch from Reynolds number to heat transfer area. Moreover, the phase change material (PCM) temperature maldistribution exists for more than 50% of the charging time. Moreover, a chart with five classified zones to evaluate the charging time is proposed. Cases with unevenly allocated HTF tubes are further investigated. It is found that as the HTF inlet mass flow rate is 0.167 kg/s, the melting time of the two region case and three-region case could be reduced by 11.1% and 14.1%, respectively. There exists a pseudo minimum charging time when the HTF inlet mass flow rate is 1.667 kg/s.