The Experimental Study On Natural Convection And Heat Transfer In Square Composite Porous/Fluid Cavity

Fluid flow, heat and mass transfer phenomena prevail in nature and practical engineering such as grain drying, building enclosure, insulation materials, groundwater pollution, the use of nuclear energy, micro-electronic technology and so on in the composite system of porous media and fluid. According to its wide existence in nature and engineering application as well as its complex mechanism, the study plays a significant role in science and technology development. Despite of the deep respective study on natural convection and heat transfer within the porous medium and the pure fluid region, little study has been made on the composite cavity with porous media and pure fluid. At the same time taking the limitation of testing technology into account, less study focused on natural convection and heat transfer. However, In practical engineering, there are many factors involved in the composite cavity, as a result, more focus are required on the fluid flow, heat and mass transfer in the composite cavity to provide applicable guidance.In this article, we made the combination of theoretical analysis, numerical simulation and experiments as the solution methods, taking account of the influences of the stress slip condition at the interface between porous medium and pure fluid and mainly discussing about the law of fluid flow and heat transfer in the composite cavity with the existing temperature gradient. We built a two-domain model of the natural convection in the composite cavity, and then utilized the finite element theory with the weak constraint condition at the interface on the dimensionless equations for discretion and solution. In the study, we found that the thickness of the thin porous media layer and the Rayleigh number Ra in the cavity have an important effect on natural convection and heat transfer. Stress slip coefficientβ1 andβ2 at the interface have certain effects on the velocity and temperature distribution, but ignored for the entire field.According to the theoretical analysis, we made thin layers of porous media with different porosities, processed a composite cavity of porous media that is to be used in this experiment. First set the horizontal wall temperature so as to form a natural convection, and then applied the two-dimensional particle image velocimetry PIV technique for the working conditions with different Ra, different porous media thickness and different location of the porous media layer. And on a certain working condition, the calculation shows the flow in the cavity changed from non-steady state to steady-state to verify the feasibility and correctness of the experimental procedures. Through this experiment, it is obviously showed that the flow in the body cavity became more intensified as Rayleigh number increased. And the porous media parameters such as porosity and the placement of the porous media thin layer had a direct effect on the velocity distribution. After analyzing the experimental flow field with the numerical simulation results, we obtained small relative errors so that PIV technology applied to measurement of complex cavity flow proved accurate.There are so many factors influencing the natural convection in the composite cavity that partially filled with porous medium that the law is very complex. This article mainly studied the effects of the porous medium parameters (porous layer thickness d and the location), Rayleigh number Ra and the stress slip coefficients at the porous medium/fluid interface (the first stress slip coefficientβ1, the second stress slip coefficientβ2), and got the effect law of all parameters on fluid flow and heat transfer, which will lay a theoretical foundation for the research of heat transfer in the composite cavity.