Hydrothermal and entropy generation analyses of natural convection of nano-encapsulated phase change materials suspension in a cavity subjected to the localized heating

Abstract

Being heated electronic components significantly reduces their efficiency, and thus requiring high-efficient cooling strategies to keep such devices operating at an optimal temperature level. The present study is devoted to investigating the cooling performance of water-based nano-encapsulated phase change materials (NePCMs) suspension in the presence of a heat source with uniform temperature. The nano-sized PCM capsules are constructed by n-nonadecane as the core and polyurethane for the protective shell. The n-nonadecane is capable of absorbing/releasing a significant quantity of latent heat in the process of its phase transition, which is actually beneficial for improving the heat transfer performance. The home developed FORTRAN program based on the finite volume method (FVM) combined with the artificial compressibility algorithm is employed to solve the nonlinear coupled equations for fluid flow and heat transfer. The influences of the Rayleigh number (103≤Ra≤105), the Stefan number (0.1≤Ste≤0.9), the volume fraction of the nano-capsules (0≤ϕ≤0.04), and the heating position (0.25≤a≤0.75) on the hydrothermal behavior and entropy generation are explored. The findings reveal that there exists a capsule loading interval wherein the heat transfer enhancement can be achieved, but beyond that range, the deterioration of cooling performance may occur. Moreover, the contribution of suspending NePCMs to the heat transfer improvement is greatly more noticeable at low Rayleigh number, and particularly for the arrangement of upper heating. The average Nusselt number decreases with the increment of the Stefan number, and the variation approximately follows an exponential change for all considered Rayleigh numbers and heating positions. Concerning the entropy generation, it is essentially contributed by the heat transfer irreversibility, and the region with high irreversibility is always located around the intersection of the heated surface and the insulated vertical wall. This research can provide theoretical guidance for cooling the electronic components by utilizing the NePCMs suspension.