Experimental Validation of a CFD and a ε-NTU Model for Coils in a Large PCM Tank
Abstract
An experimental validation for a computational fluid dynamics (CFD) and effectiveness-number of transfer unit (ε-NTU) model for tubes in a large phase change material (PCM) tank has been conducted. In previous work, experimental validation of a CFD and ε-NTU model was carried out on latent heat thermal storage systems having one, two and four coils of polyvinyl chloride tubes coiled inside a 290 mm diameter by 330 mm high cylindrical tank filled with PCM. The heat transfer fluid (HTF) passes through the tube during the charging and discharging processes. Salt hydrate PCM with phase change temperature of -27 °C was used for all the three tube configurations while water was used in the four tubes tank experiment. Further experimental validations of a CFD and ε-NTU model were carried out on a large PCM tank, having eight coils of copper tubes inside a 550 mm diameter by 830 mm high cylindrical tank filled with PCM. The inlet and outlet HTF temperatures as well as twelve temperature locations in the PCM tank were compared with the CFD results. The average effectiveness of the phase change process of each experimental point was also compared with results from the CFD as well as the ε-NTU technique. From this study, it was concluded that the CFD model and the ε-NTU technique developed can accurately predict the behaviour of the thermal storage system during the freezing process. There are however, discrepancies in the melting process due to the exclusion of the effect of natural convection in the models developed. The paper will give details of the CFD model of the phase change thermal storage system. Results from the CFD model, experiments and εNTU technique will also be presented.