Abstract
A Nano-Encapsulated Phase-Change Material (NEPCM) suspension is made of nanoparticles containing a Phase Change Material in their core and dispersed in a fluid. These particles can contribute to thermal energy storage and heat transfer by their latent heat of phase change as moving with the host fluid. Thus, such novel nanoliquids are promising for applications in waste heat recovery and thermal energy storage systems. In the present research, the mixed convection of NEPCM suspensions was addressed in a wavy wall cavity containing a rotating solid cylinder. As the nanoparticles move with the liquid, they undergo a phase change and transfer the latent heat. The phase change of nanoparticles was considered as temperature-dependent heat capacity. The governing equations of mass, momentum, and energy conservation were presented as partial differential equations. Then, the governing equations were converted to a non-dimensional form to generalize the solution, and solved by the finite element method. The influence of control parameters such as volume concentration of nanoparticles, fusion temperature of nanoparticles, Stefan number, wall undulations number, and as well as the cylinder size, angular rotation, and thermal conductivities was addressed on the heat transfer in the enclosure. The wall undulation number induces a remarkable change in the Nusselt number. There are optimum fusion temperatures for nanoparticles, which could maximize the heat transfer rate. The increase of the latent heat of nanoparticles (a decline of Stefan number) boosts the heat transfer advantage of employing the phase change particles.
Highlights
Enhancing convective heat transfer has become a key element in various industrial applications
The numerical simulations are conducted for the following parameters: geometrical aspect ratio 0.1 ≤ R ≤ 0.2, dimensionless rotational velocity −1000 ≤ ω ≤ 1000, heat capacity ratios 1 ≤ Rc ≤ 100, thermal conductivity ratios 1 ≤ Rk ≤ 100, the Nano-Encapsulated Phase-Change Material (NEPCM)
This can be attributed to the fact that changing the heat capacity or the thermal conductivity of the inner cylinder induce only local effects limited to the region near the cylinder, which are very limited compared to the flow intensity in the whole cavity and to the convective heat transfer occurring between the hot wall near the wavy wall and the cold fluid near the left wall
Summary
Enhancing convective heat transfer has become a key element in various industrial applications. Sheikholeslami et al [4] analyzed the free convection of magnetizable hybrid nanofluid free convection in a circular enclosure with two circular heaters These studies showed that the inclusion of nanoparticles with in the host fluid enhances the heat transfer. Ding [14] studied the laminar convective heat transfer of nanofluids, composed of γ-Al2 O3 nanoparticles and de-ionized water, flowing throughout a copper tube. Zhao et al [26] investigated free convection in open-celled metal foams These studies were limited to single-phase heat transfer problems. The use of Nano Encapsulated Phase Change Materials (NEPCM) suspensions, as a new type of nanofluids, is promising to enhance heat transfer in natural and forced convection flows. The current research focuses on studying the phase change behavior and heat transfer enhancement of nano-encapsulated suspensions in a wavy wall cavity for the first time
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