Cooling a cavity equipped with a hot electrical element using nano-encapsulated phase change material /water: Study of mixed convection and natural convection

Abstract

According to phase change materials (PCMs) operate at their phase change temperature, they can store a lot of latent heat energy without changing the temperature, so these materials are widely used in thermal storage tanks. The direct use of PCMs is not possible in all systems, therefore encapsulation of PCMs has been suggested by researchers. In the present work, the thermal performance of the natural and mixed convection flow inside a nested cylinder with a hot electrical element is investigated. Nano-encapsulated phase change material (PCMs) are mixed with the water-based fluid. Also, the effects of forced convection due to inner cylinder rotation along with natural convection are studied. Fluid flow, temperature distribution, melting zone of PCM nanocapsules, Nusselt numbers, and thermal performance are simulated using computational fluid dynamics by developing OpenFOAM solvers using C++ code. The governing PDE equations are solved in the FVM method and solved using the SIMPLE algorithm. The simulations are modeled for different Ra numbers (102−104), Reynolds numbers (0–20), and θf values. θf values correspond to the dimensionless melting temperature of the core of nanocapsules. This number depends on the temperature of the cold and hot sources and the phase change temperature of the core of NEPCMs. Based on the results, it is showed that there is an optimal number for θf, which is in the range of 0.3–0.5 in the lower Ra numbers (102), and θf=0.5 at upper Ra numbers (104). In the case of dominant conduction heat transfer mechanism, the presence of nanocapsules did not affect heat transfer. However, at a high Ra number, it was able to enhance Nusselt number by up to 13%. Also, at high Ra numbers (104), the rotation of the inner cylinder does not help to improve heat transfer.