Research Of Fluid Flow And Heat Transfer In A Cavity Partially Filled With Compound Porous Medium

The phenomena of fluid flow in porous media are widespread in the human production and life,especially the application of compound area of partly filled with porous medium is more widely, such as drying, filtration, water seepage process, solar thermal collection, heat pipe, nuclear power, fuel cells, oil heat extraction and geothermy engineering, etc. However, there are heterogeneous porous media in the nature and the engineering practice,we named it as compound porous media.Compound porous media covers the hierarchical porous media, the structures and percolation characteristics of each layer porous media are not identical. Hierarchical porous media widely exists in groundwater seepage process, oil exploiting engineering in heterogeneous rock,the heat and mass transfer in composite building wall with thermal insulation material etc.So the mechanism research of the fluid flow and heat transfer in the hierarchical porous media has important practical value and academic value,and it is very significant for the technological progress and the development of science.This paper adapted the simplified model of compound porous media with two layers of porous media filled in the left of the cavity,respectively set up the one-domain mathematical physical model and two-domain regional mathematical physics model of the closed cavities partly filled with compound porous media about natural convection and heat transfer by momentum equations and energy equations, and calculated by finite element method;Contraposed velocity slip weak constraint expression on the interface between two layer porous media,this paper demonstrated the effectiveness of the velocity slip expression by the comparative analysis of the calculating result of one-domain model and two-domain model;At the same time, analyzed the results of the one-domain model to explore the changing laws of natural convection of fluid flow and heat transfer about the cavities partly filled with compound porous media,and analyzed the influences of compound porous media Structure characteristics,Physical properties,Rayleigh number,Prandtl number on the fliud flow and heat transfer in the cavity,focused on the change of two kinds of interfaces velocity slip coefficient to analysis the mechanism of the interface velocity slip effect.Meanwhile,used the X-CT experiment to get the images of bricks and sponge structures,then calculated the cavity filled with compound porous media composed with bricks and sponge structures,and analysised the velocity distribution in the areas of interfaces and the laws of heat transfer.The results of the phenomenon of veocity slip and the validation of formula on the interface showed that:l)There was a velocity slip phenomenon on the interface between two layers of porous media constructed by cylinders;2)Velocity slip phenomenon on the two kinds of interfaces were emerged in the cavity partly filled with compound porous media made of bricks and sponge got by X-CT experiment,it was consistent to the cavity partly filled with compound porous media constructed by cylinders;3)By contrasting the simulated results of one-domain model and two-domain model, the velocity slip weak constraint on the interface between two layers of porous media in this article was effective and feasible to solve the problem of the velocity continuity on the interface between two layers of porous media.The results of each factor’s influence on the fliud flow and heat transfer of free convection showed that:l)Fluid flow resistance increased with the increase of the proportion N of compound porous medium in the cavity,and the nusselt number Nu of left wall grew smaller;2)Fluid flow resistance strengthened with the increase of D-value of two layers porous medium porosities,and the non-dimensional temperature 6 of the half height in the pure liquid part had been largely enhanced,but the change laws of the compound porous media region was opposite;3)the nusselt number Nu of right wall was gradually increasing with the increase of two layers of porous medium ratio coefficient of thermal conductivities Rk;4)The increase of Rayleigh number Ra led to the enhanced liquidity,the average nusselt number Nu of left wall was gradually increasing;5)With the increase of the prandtl number Pr/velocity boundary layer thickness increased,temperature boundary layer thickness was thining,and the average nusselt number Nu of left wall was gradually increasing.The results of the velocity slip effect variations of two kinds of interfaces showed that:1)the increase of porosity D-value △ε of two layers porous media led to the velocity slip coefficient α1 between two kinds of porous media enhanced.In addition,although velocity slip effect between porous media and pure fluid field gradually decreased,but there were limitations in the compound porous media constituted by cylindrical structures,so the velocity slip coefficient a.2 gradually increased;2)With the increase of Rayleigh number, the velocity slip coefficients α1 and α2 of two kinds of interfaces gradually increased; 3)the velocity slip coefficients α1 and α2 of the cavity partly filled with the ordinal cylinders was larger than the cavity partly filled with the stagger cylinders;4)In spite of cavity’ fluid flow and heat transfer enhanced with the increase of the proportion N and Prandtl number Pr,but they didn’t affect the velocity slip effect and velocity slip coefficients of two kinds of interfaces.