Filtration Performance For Voronoi-based Structural Fibrous Mediaand Cross-scale Simulation During Dust Loading Stage

In terms of metallurgy,chemical industry,energy,building environment,etc,fiber filtration equipment(e.g.bag-type and cartridge-type dust collector,air filter)have been widely used in the emission control of particulate matter and the purification of fine particles in the indoor environment because of their effectiveness and low costs.The fiber filtration technology has been popularly studied on the micro-scale level(i.e.micro-structure of fibrous material)and the macro-scale level(i.e.fiber filtration equipment).However,the current 3-D reconstruction method of the micro-structure of the fibrous media is still in the development stage,which severely limits the study of its filtration performance.In addition,the structure of fiber filtration equipment involves a large scale span,and currently there is no effective data transfer mechanism,which links the gas-solid two phase flow at the micro-scale and the macro scale.Therefore,based on the experiment and simulation,the present work is devoted to the research of 3-D reconstruction of fibrous media and its filtration performance during dust loading stage as well as cross-scale simulation.3-D micro-scale model of fibrous media with controllable structural parameters(such as fiber diameter and solid volume fraction)was constructed by using Voronoi algorithm in this study.The gas-solid flow characteristics in fibrous media having Voronoi-based topology under different structural and operating parameters were examined numerically and semi-analytically.Moreover,the accuracy of the numerical results was verified by the experimental data in the literature.Furthermore,an effective data transfer mechanism between scales was established based on the method of cross-scale simulation,which connects the micro-scale flow with the macro-scale flow.The CFD porous media model was redeveloped and the pressure drop model of fibrous media during the dust loading stage(i.e.the macro-scale model)was developed.In addition,the accuracy of the macro-scale model was verified by comparing the experimental data with the numerical results of the macro-scale model.The results show:(1)Compared with the fibrous media model having layer-structured topology,The modeling process of Voronoi-based structure is based on the spatial topological information constructed by creating points and lines in the 3-D space,which can well characterize the penetration behavior between fibers and layer connections.In addition,the spherical cap connection was adopted to calculate the volume of the node cluster,which can obtain more accurate solid volume fraction.(2)The flow field of the Voronoi-based model considering the connection between layers is more significantly affected by the internal structure.The numerical results of pressure drop are higher than those of the layered structure,and the deviation from the experimental value is basically within 15%.Moreover,based on the results of numerical simulation,a new pressure drop correlation for fibrous media with SVF ranging from 5% to 25% and fiber diameters ranging from 15 to 25 μm was fitted.It can provide Darcian permeability for macro-scale model research on pressure drop of fibrous media during dust loading stage.(3)For submicron particles,the Stokes-Cunningham drag law combined with Saffman’s lift force and Brownian force can accurately predict the capture action dominated by the combination of diffusion and inertia.Furthermore,the deviation of the filtration efficiency between numerical results and theoretical predictions increases with the increase of the Peclet number and SVF.For micron particles,the filtration efficiency determined by the semi-analytical model is generally higher than the numerical results by adopting the spherical drag law and considering the gravity effect.In addition,a threshold value of the Stokes number is presumably exhibited,and the deviation between the numerical simulations and semi-analytical approaches is relatively small when the Stokes number is greater than the threshold value.(4)The flow field of the micro-scale model was numerically simulated,and the viscous resistance under the clean state is obtained,which is provided to the CFD porous media as the initial parameter.Based on the Euler-Lagrangian method by implementing the user-defined function(UDF)in ANSYS-Fluent,the CFD porous media model was redeveloped to realize particle trapping and the dynamic change of pressure drop with particle loading.(5)By controlling the threshold of the cell in porous media,the different trapping mechanism programs are developed to realize the different distribution forms of particles along the thickness of porous media.Under the same particle loading,with the increase of threshold,the growth rate of pressure drop decreases.For the calibrated macro-scale model with different SVFs,the deviation between the numerical results and the values calculated by the empirical model is within 20%.(6)According to the air filter performance test standard(EN779: 2012),an air filter performance test bench was built.By comparing the experimental data(i.e.pressure drop versus dust loading capacity)of the 592*592*292-4V-F9 filter with the simulation result of the macro-scale model,the deviation is basically within 30%.Therefore,the macro-scale model proposed in this paper broadens broadens the way of studying the pressure drop of fibrous media during dust loading stage.In addition,the method of cross-scale simulation can provides guidance for the simulation of corresponding gas-solid two phase flow.