Free convection of a suspension containing nano-encapsulated phase change material in a porous cavity; local thermal non-equilibrium model

Abstract

Due to the instinctive temperature-dependent heat capacity of the Nano-Encapsulated Phase Change Material (NEPCM), there is a growing interest in the potential applications of such materials in heat transfer. As such, steady-state natural convection in a porous enclosure saturated with nanofluid using NEPCMs has been investigated in this study. The cavity is assumed to have constant hot and cold temperatures at the left and right vertical boundaries, respectively, and fully insulated from the bottom and top walls. Considering the Local Thermal Nonequilibrium (LTNE) approach for the porous structure, the governing equations are first non-dimensionalized and then solved by employing the finite element Galerkin method. The impact of different parameters, such as porous thermal conductivity (k s ), solid-fluid interface heat transfer (10 H 10 5 ), Stefan number (0.2 Ste 1), and volume fraction of nanoparticles (0.0 φ 0.05) on the patterns of the fluid and solid isotherms, streamlines and the contours of the heat capacity ratio, fusion temperature (0.05 θ f 1), local and average Nusselt numbers, and overall heat transfer ratio has been studied. It is shown that improving the porous thermal conductivity not only leads to an increase in the rate of heat transfer but also augments the fluid flow inside the cavity. For low values of the Ste, the rate of heat, transferred in the porous enclosure, is intensified. However, regardless of the amount of the Stefan number, the maximum rate of heat transfer is achievable when the non-dimensional fusion temperature is approximately 0.5. Employing NEPCMs in a highly conductive porous structure is more efficacious only when the phases are in the state of local thermal equilibrium. Nonetheless, the rate of heat transfer is higher when the Local thermal non-equilibrium is validated between the phases. Besides, for poor thermal conductivity of the porous medium like glass balls (LTE condition), adding 5% of the nano-encapsulated phase change materials to pure water can boost the rate of heat transfer up to 47% (for Ste ¼ 0.2 and θ f ¼ 0.5). This thermal investigation of NEPCMs shows in detail how advantageous are these nanoparticles in heat transfer and opens up an avenue for further application-based studies.

Exploration of the entropy due to the nano–encapsulated phase change materials (NEPCMs) within oblique prismatic containers

“…In equation (A2), r c is estimated as the average density of the liquid and the solid phase of PCM, Ghalambaz et al [6].…”

“…Here, to present a formula of the overall heat capacity of the NEPCM particles, the latent heat of the change phase should be considered. Three formulas can be introduced of the latent heat of phase change, namely, rectangular, triangular or sine profiles as presented in [6] as: In equation (A5), T Mr is the small temperature interval where the fusion temperature T f occurs in its middle.…”

“…A liquid suspension of nanoencapsulated phase change materials (NEPCMs) was considered as a working fluid. The main findings revealed that at = Ra 10 , 6 the middle range of the fusion temperature (q = 0.5 f ) reduces the entropy generation. Ghalambaz et al [3] used the structured non-uniform mesh finite element method to investigate the timedependent free convection within porous containers filled with a suspension comprising nano-encapsulated phase change materials (NEPCMs).…”

“…They noted that at the high Rayleigh number and in case of the inclination angle greater than / p 2, the melting process of NanoPCM is fast. The heat transfer at a heated section in an inclined partially heated and porous enclosure is examined by Ghalambaz et al [6]. The worked mixture was NEPCMs and various values of the fusion temperature were assumed.…”

Magnetic micropolar nanofluids flow in double lid‐driven enclosures using two‐energy equation model

“…They concluded that the solid wall has significant influences on the overall heat transfer. The thermal nonequilibrium state within various engineering systems and valuable outcomes are found in the studies reported by References [22‐25].…”