Abstract
Thermal energy storage using Phase Change Materials (PCM) with low thermal conductivity presents one of the barriers to ensuring the storage and release of large heat quantities in a short time suitable for solar applications. One of the best techniques to overcome this obstacle is the inclusion of nanoparticles into the PCMs. Furthermore, the use of finned storage units can significantly boost thermal performance. In this paper, A comprehensive 3D numerical study is presented to investigate the performance of a vertically-configured-cylindrical copper LHTES using Nano-Enhanced PCM (NEPCM) with both outer and inner longitudinal fins. Based on the enthalpy-porosity technique, the numerical model is established taking into account the natural convection effect and transient variations in the thermo-physical properties of NEPCM. An experimental setup is built to analyze the thermal behavior of LHTES with CuO and Al2O3 based NEPCM, and to validate the numerical model. Once validated, the numerical model is employed to investigate the combining effect of using fins and NEPCM based on CNT 1% and Al2O3 2% nanoparticles. Transient numerical simulations are conducted for both charging and discharging cycles for six scenarios corresponding to several NEPCM and configurations (with and without longitudinal fins). Both experimental and numerical investigation show that the NEPCM ensures a great improvement, resulting in large time savings during both charging and discharging phases compared to pure PCM. Moreover, the results show that placing six outer and inner longitudinal fins in the wall of LHTES shortens discharge and charging times by 71% and 62%, respectively, as compared to the reference case (pure PCM without fins). Furthermore, using NEPCM with 1% CNT nanoparticles by weight dispersed in PCM combined with six outer and inner longitudinal fins reduces discharge and charging times by 89% and 84%, respectively. Although CNT is very effective by highly enhancing the PCM thermal characteristics, it is very expensive compared to metal oxide nanoparticles. However, it was discovered that using 2% Al2O3 for finned LHTES can achieve nearly the same results as using 1% CNT.