3D Reconstruction Of The Structural Model Of Fibrous Media And Numerical Simulation Its Filtration Characteristics

Dust particles in industrial production may cause harm to the environment andhuman health. With the improvements of the public environmental awareness and thestandards for pollutants discharge, so it is crucial to filtrate fine particles in the airpollutant effectively. Fibrous media can filter particulate matter, and the filtration canreach the national standard. Therefore, studying the filtration performance of thefibrous media can provide the basis for optimizing its structure.The2D microstructure of the fibrous media was observed by scanning electronmicroscopy (SEM), and then Matlab software was employed to process the obtainedimage and to write the corresponding program that will reconstruct the fibrous mediamodel, finally the actual3D filtration medium model was generated using Gambitsoftware; Changing the structural parameters of the model, including the fiber diameterdf, the distance that the fiber deviates from the former cross section L and the length offibrous media H, the influences of the structural parameters and the face velocity on itssolid volume fraction (SVF) and the pressure drop were analyzed using the responsesurface methodology (RSM), and the simulation data was compared with the results ofthe classic empirical models and experimental correlations; The Computational FluidDynamics (CFD)–Discrete Element Method (DEM) coupled method was applied tosimulate the gas-solid flow characteristic within the fibrous media and to study theinfluence of the fibers and particles’ properties on particle deposition andagglomeration in the filtration process. In addition, the RSM was also used to analyzethe impact of the structural parameters of the fibrous media on the filtrationcharacteristics (including the pressure drop and filtration efficiency).The results showthat:(1) The3D fibrous media models reconstructed by Matlab and Gambit are based onthe2D images of the actual fibrous media, and the reconstructed models have a lot ofsimilarities with the actual ones, so the study of these models can provide a basis tospeculate the filtration performance of actual fibrous model.(2) The fiber diameter is a significant factor that influences SVF and the pressuredrop, and large fiber diameter can increase SVF and the pressure drop. In addition, thedistance that the fiber deviates from the former cross section, L and the length offibrous media, H have little influence on SVF. The pressure drop increases first and then decreases by increasing L and H, and it reaches the maximum when they are atintermediate level.(3) The internal gas flow field of the fibrous media is inhomogeneous. The pressuredrop increases when increasing SVF and the face velocity. If the structural parametersof fibrous media are different while keeping SVF constant, the pressure drops are alsodifferent, which indicates that the pressure drop of the fibrous media is relevant to thefiber arrangement. Moreover, the simulation values of the pressure drop in this studyagree well with Davies experimental correlation data, and the error is less than5%,which demonstrates that the numerical calculation model in this study is reasonable,and the simulation results are believable.(4) The numerical simulation of gas-solid flow inside the fibrous media is studiedby the use of CFD-DEM coupling method, and the influence of the fibrous mediastructural parameters on their pressure drop, filtration efficiency, particle depositionand agglomeration are also analyzed. The simulation value of the filtration efficiencyof the fibrous media is consistent with the calculation value of the empirical correlation,which shows that the CFD-DEM model in this study is reasonable. In addition, thecomparison between the simulation image of particles deposition and agglomeratationon the fibers with the experimental observations indicates that using CFD-DEM tostudy particles deposition and agglomeration on the fiber surface is convenient andfeasible.(5) With the increase in the filtration time, the deposition mass of the particles on thesurface of the fibrous media increases. When the distance that the fiber deviates fromthe former cross section, L and the length of fibrous media, H are constant, the fiberdiameter, dfincreases, the contribution of the surface filtration is larger, most ofparticles are trapped in the surface of the fibrous media, and only a portion of particleswith small size get into the internal media and are captured by the depth filtration.(6) The comparison between the increase in pressure drop, Δp’ when the fibrousmedia filtrates particles under different conditions with that of the gas flow field showsthat the pressure drop increases with increasing filtration time under various conditions,and the growth shows the exponential trend, which indicates that the depositedparticles change the internal porosity of the fibrous media, thereby changing thepressure drop. The fiber diameter, dfis a main factor that influences the total pressuredrop of the fibrous media, and the total pressure drop increases with increasing df.When L and H change, i.e., the arrangement of the fiber changes, the total pressure drop of the fibrous media changes with the specific conditions. Overall, the moreintensive the fiber distribution is, the larger the total pressure drop of the media is.When dfand H keep unchanged, increasing L will decrease the filtration efficiency. Inaddition, H has basically no effect on the efficiency if dfand L are unchanged.