Effect of shell shape on the charging and discharging performance of a vertical latent heat thermal energy storage unit: An experimental study

Abstract

In this paper, the effect of shell shape on vertical latent heat thermal energy storage (LHTES) unit is experimentally investigated to alleviate the heat transfer lagging region and enhance its charging and discharging performance. A cylindrical (CYL) and two conical (CON-I and CON-II) LHTES units are designed and fabricated, and they have the same heat transfer area and internal volume. Paraffin with a narrow range of phase change temperature and high enthalpy was selected as phase change material (PCM), and water is used as heat transfer fluid (HTF). The thermal behaviors of CYL, CON-I and CON-II such as evaluation of melting and solidification fronts, temperature response characteristics, heat transfer characteristics and energy and exergy conversion are comparatively studied. A correlation is developed to predict the entire melting and solidification time of different LHTES units under different HTF flow rates and temperatures. The results demonstrate that CON-I and CON-II can provide a better temperature field uniformity and enhance the heat transfer rate between HTF and PCM. When compared with CYL, the entire melting/solidification time is reduced by 16.95 %/8.07 % and 29.94 %/23.22 % for CON-I and CON-II, and the time-averaged heat transfer rate is increased by 20.69 %/23.61 % and 35.87 %/41.24 % for CON-I and CON-II during the melting/solidification processes. In addition, the developed correlation is able to well predict the entire melting and solidification time of PCM in the LHTES unit with a relative error of ±5 %.