The latent heat thermal energy storage (LHTES) unit with shell and tube type is widely considered to be one of the most competitive technologies to store and use solar energy thanks to its high thermal storage density, low cost and little temperature fluctuation. The phase change material (PCM) is filled in the annular space between the inner shell and outer tube, while the heat transfer fluid (HTF) flowing through the inner tube. However, the heat transfer process during the melting and solidification processes of PCM is complicated involving heat conduction, natural convection and solid-liquid phase change, which is closely related to the geometric parameters of LHTES unit. Thus, the main purpose of the current study is to explore the effect of geometric parameters on the charging and discharging performances of the LHTES unit. Firstly, a visual experiment was carried out to observe the evolution of the solid-liquid interface and monitor the temperature variation of PCM during the melting and solidification processes. Then, a two-dimensional numerical model was established and validated by the experimental data to investigate the effect of geometric parameters on the charging and discharging performances. Four kinds of geometric parameters with different shell heights were designed and studied under the same volume and heat transfer area of PCM. Results demonstrated that during the melting process, the complete melting time increases with an increase of the shell height, vice versa for the solidification process. When the height of shell increases from 100 mm to 400 mm under the same HTF inlet temperature and flow rate, the complete melting time can be increased by 20.14% and the complete solidification time is saved by 22.87%. This means that the geometric parameters of LHTES unit should be designed carefully to comprehensively consider the weightings of the charging and discharging processes in practical applications.
Keywords Latent heat thermal energy storage, Phase change material, Shell and tube, Charging and discharging performance, Geometric parameter