Natural convection flow of a suspension containing nano-encapsulated phase change particles in a circular enclosure with a pair of heated and cooled cylinders

This study investigates the thermal characteristics and efficiency of an insulated circular enclosure containing two cylindrical tubes, one acting as a heater and the other as a cooler. The enclosure uses nano-encapsulated phase change material (NEPCM), which combine the advantageous properties of PCM and nanofluids. The primary goal is to analyze heat transfer mechanisms, phase change phenomena, and the overall thermal performance of the system. The governing equations for the NEPCM mixture are reformulated in a dimensionless framework and solved using a penalty finite element method. Key parameters investigated include the tilt angle of the cavity, the gap between the horizontal cylinders, the cylinder diameter, the nanoparticle concentration, the melting temperature, the heating intensity, and the Stefan number to understand their influence on the thermal performance. In particular, reducing the gap between the hot and cold cylinders improves heat transfer by minimizing thermal boundary layers. In addition, introducing a 5% volume fraction of NEPCM particles results in a significant 313% increase in the average Nusselt number compared to a 1% volume fraction system. These results demonstrate the potential of NEPCM to significantly improve thermal efficiency, providing a novel improvement over previous efforts in the literature.