Simulation Of Double Diffusion Natural Convection Based On Three-dimensional Reconstruction Of Real Porous Media

There are many natural porous organisms in nature.After biological evolution,they have formed a variety of porous structures with complex structures and excellent heat and mass transfer performance.Based on the research of flow,heat and mass transfer in porous media,it has been applied in many fields,such as building energy conservation,energy chemical industry,food processing,life science,etc.,and with the demand of social development,higher requirements are put forward for the structural performance of the applied porous media.Therefore,the study of heat and mass transfer based on bionic natural biological porous structure is of great practical significance to improve the existing application of porous media structure and reduce the energy consumption in construction,industry and other fields.In this paper,Lentinus edodes is taken as the research object,and the double diffusion natural convection phenomenon of real porous media structure is studied based on the pore scale by the method of experimental research and numerical simulationIn this paper,three-dimensional reconstruction of real porous media structure is completed.The cross-section scanning image sequence of Lentinus edodes' pore structure was acquired by using the computer tomography technology,and then it was filtered,denoised and segmented to realize the three-dimensional visualization of the image sequence.Finally,the three-dimensional micro pore structure of the real porous media was obtained.In this paper,a mathematical model of double diffusion natural convection in a real porous medium cavity is established.In this paper,the finite element method is used to verify the mathematical model from two aspects: the doublediffusion numerical simulation of pure fluid and the coupling between porous media framework and fluid.The numerical results are compared with the numerical results in the existing literature to verify the correctness of the mathematical model.The numerical analysis of double diffusion natural convection in a real porous medium cavity is carried out.Through Numerical simulation,the effects of double diffusion parameters such as buoyancy ratio N,Rayleigh number Ra,Lewis number Le and fiber horizontal and vertical distribution on the flow field,temperature field,concentration field,average Nu number and average Sh number at the wall surface in porous medium cavity are analyzed.The conclusions are as follows: 1)the buoyancy ratio N is related to the flow direction of the fluid in the porous medium cavity.When the buoyancy ratio N is negative,the direction of mass buoyancy lift is the same as the direction of thermal buoyancy lift,and the two assist each other to enhance the fluid flow in the cavity.The fluid flows in a clockwise direction.When the buoyancy ratio N is positive,the mass buoyancy lift and thermal buoyancy lift begin to reduce each other Weak,when N = 1,the fluid flows in a counter clockwise direction;with the increase of the absolute value of the buoyancy ratio number N,the heat and mass transfer are generally enhanced.2)The Rayleigh number Ra represents the intensity of natural convection.When the Rayleigh number is low,the distribution of temperature field and concentration field is almost perpendicular to the upper and lower walls,and the diffusion is dominant.With the increase of Ra number,the convection in the porous medium cavity increases,the average Nu number and Sh number increase,and the heat and mass transfer effect increases.3)Lewis number Le is the ratio of thermal diffusion coefficient to mass diffusion coefficient.With the increase of Le number,the concentration boundary layer becomes thinner,the bending degree of concentration field increases,and the mass transfer rate increases obviously.However,the increase of Le number has little effect on heat transfer.4)When the fiber layer is vertically distributed,the degree of heat and mass transfer is stronger than thatof the fiber layer.The difference between the horizontal and vertical distribution of the fiber layer on the heat and mass transfer intensity reveals the anisotropic characteristics of the real porous media at the pore scale.