Numerical simulations and experimental verification of the thermal performance of phase change materials in a tube-bundle latent heat thermal energy storage system

Theoretical simulation and experimental validation of a new design tube-bundle latent-heat thermal storage (LHTS) working under solar-thermal application conditions was performed. A laboratory-scale experimental test rig was designed and tested for charging and discharging processes by using lauric acid and water as a phase-change material (PCM) and heat-transfer fluid (HTF), respectively. Six equal size tubes with 2 cm diameter and 45 cm length were clamped together with a central diameter tube for carrying the HTF. The temperature of the PCM during charging and discharging in the tubes in the bundle was measured radially. A 3D numerical model using ANSYS FLUENT was developed to simulate the time-dependent liquid fraction, temperature, and stored power of the PCM. The simulation was conducted after the successful validation with the experimental results at different HTF inlet temperatures (70 °C, 75 °C, and 80 °C) and (10 °C, 15 °C, and 20 °C) for charging and discharging processes, respectively, as well as with different Reynolds numbers (750, 1250, and 1750) for both processes. Although the design of the proposed LHTS was very simple, the results revealed that it has a superior thermal performance and fast charging and discharging period when compared to a double-pipe LHTS. Accordingly, the time was shortened by about 85.3% and 82.5% for charging and discharging processes, respectively.