Convective Heat And Mass Transfer In A Complex Cavity Partially Filled With Porous Medium

Fluid flow, heat and mass transfer phenomenon in porous media extends all over the natural world and the areas of industrial and agricultural production, in which, the composite regional issues combined with porous media and fluid have a broad application background, such as drying process and solidification process, high-performance thermal insulation construction, heat pipes, solar collectors, geothermal engineering, nuclear energy using and crude oil extraction and so on. Although nearly half a century, the fluid flow and heat and mass transfer phenomenon in both porous medium cavity and pure fluid chamber have been taken in-depth disscussion by scholars both of home and abroad, there is relatively little research about the composite cavity partially filled with porous media. In engineering practice, there are many problems involving the composite cavity, therefore, more attentions are needed to the fluid flow, heat and mass transfer in the composite cavity, so as to provide appropriate guidance to engineering practice.Temperature, concentration and the porous layer in the composite cavity partially filled with porous media have significant effects to the fluid flow and heat and mass transfer in the cavity, while the majority of previous studies are limited to only one factor. In this paper, we took the combination of theoretical analysis, numerical simulation and experimental study as the solution methods, discussed the influence of the stress slip condition at the fluid/porous interface and mainly discussed the rule of fluid flow and heat and mass transfer in the composite cavity with coexisting temperature gradient and concentration gradient. Based on multi-buoyancy, porous media layer and the stress slip condition at the fluid/porous interface, we established a two domain model of the double-diffusive natural convection in the composite cavity, adopted the finite element theory supported by the weak constraint condition at the interface on the dimensionless equations for discrete and solution.In the case of the co-existence of temperature field and concentration field, took simulation and analysis under different working conditions, got the basic rule of the double-diffusive natural convection in the complex cavity, showed the changing situation of the flow field, temperature field and concentration field with characteristic parameters such as the thickness of porous media d, Rayleigh number Ra, the buoyancy ratio N, Lewis number Le, Darcy number Da, the interface stress slip factorβ1 andβ2 and so on, and discussed the effect law of these characteristic parameters on the wall heat and mass transfer coefficient.Through studies of heat and mass transfer the wall heat and mass transfer coefficient, found that Da number has an important impact on heat and mass transfer, and a smaller Da number has a significant impediment on the heat and mass diffusion; the buoyancy ratio N has a significant impact on the flow characteristics, which dominates the distribution attributes of temperature field and concentration field, and directly impacts on the heat and mass transfer; the interface stress slip factorβ1 andβ2 have a great influence on the speed around the fluid/porous interface, while have small effects on the velocity distribution of the entire field, and have a tiny effect on the distribution of temperature field and concentration field.Based on theoretical analysis and numerical simulation, constructed a compound cavity fluid flow bench, formed a natural convection in the body cavity by the way of supplying a horizontal temperature gradient, adopted two-dimensional particle image velocimetry PIV technology to test the flow field under different Ra number. The results show that:the flow in the cavity gradually intensifies with Ra number increases, and the presence of porous media flow has a huge impact on the fluid flow in the cavity. The comparison between the experimental flow fields and numerical simulations under different Ra number shows a fine agreement.The factors influencing the double-diffusive natural convection in the composite cavity partially filled with porous media are so many that the law is very complicated.This paper mainly studied the effect attributes of the porous medium parameters (porous layer thickness d, Darcy number Da and porosityε),double diffusion parameters (Rayleigh number Ra,the buoyancy ratio N and the Lewis number Le) and the stress slip coefficients at the porous media/fluid interface (the first stress slip coefficientβ1,the second stress slip coefficientβ2), and got the effect law of all parameters on heat and mass transfer, which laid a theoretical foundation for the research of heat and mass transfer in composite cavity.