Lattice Boltzmann simulation of effects of realistic boundary conditions on volumetric radiation-conduction melting of a novel cylindrical enclosure filled with phase change materials

In this research, a novel solar latent heat thermal energy storage (LHTES) system, including the cylindrical enclosures filled with a phase change material (PCM), is proposed, which can be installed on the building windows to alleviate the drawbacks of traditional PCM-filled double-glazed windows, such as daylight hindrance and leakage. The lattice Boltzmann method (LBM) is used to simulate the volumetric radiation-conduction melting of the PCM within a single cylinder of the proposed LHTES system with considering more realistic conditions such as convective boundary condition, shadow effect, and variable solar radiation angle compared with the available works in the literature. As such, several boundary conditions are assessed, and parameters such as cylinder diameter, extinction coefficient, scattering albedo, solar angle, shadow effect, and natural convection heat transfer coefficient are studied on the time history of the melting fraction and charging time. The results revealed that considering the applied conditions, such as convection heat loss to the environment and shadow, significantly affects the charging time of the system. It is shown that the charging time for convective boundary condition with $h=4$, $8$, and $12W{m}^{-2}{K}^{-1}$ increases, respectively, by 11%, 30%, and 50% relative to a case with the insulated boundary condition without the shadow effect and 38%, 91%, and 175% compared with the insulated case with a 90° shadow.