Entropy generation and natural convection flow of a suspension containing nano-encapsulated phase change particles in a semi-annular cavity

The natural phase change convection of a new type of hybrid nanofluids, suspensions of Nano-Encapsulated Phase Change Materials (NEPCM), was addressed in a semi-annular inclined enclosure. The nanoparticles consist of a polymer shell and a nonadecane shell, in which the nonadecane core can change phase at its melting temperature and absorb/release a significant quantity of latent heat. The NEPCM-suspension circulates in the enclosure due to the natural convection, and the NEPCM particles contribute to heat transfer by phase change. The equations governing the movement and heat transfer of the suspension and nanoparticles were inserted in the form of partial differential equations. The finite element method was used to numerically solve the equations. Then, the entropy generation of NEPCM suspension in the attendance of the phase change was examined. The influence of the fusion temperature and volume fraction of nanoparticles, Stefan number, Rayleigh number, and inclination angle of enclosure on the thermal behavior and entropy generation of the suspension was explored. The results showed that the contribution of phase change core of nanoparticles was significant, and the heat transfer was enhanced by the presence of NEPCM particles. The fusion temperature of particles controls the Bejan number (entropy generation) behavior of the NEPCM suspension. There is an optimum phase change temperature for nanoparticles, which results in maximum heat transfer. For a horizontal enclosure, the optimum fusion temperature is the average temperature of the active walls. This optimum phase change temperature is a function of the tilting angle of the enclosure.