Probing the Effective Diffusion Coefficient and Filtration Performance of Micro/Nanofibrous Composite Layered Filters

Abstract

Diffusion is an important filtration mechanism of fibrous filters for removing fine particles from gas streams. An analytical model is proposed in this work, based on fractal theory, to quantify the effective diffusion coefficient (EDC) across micro/nanofibrous filters with a layered structure. To show the influence of macroscopic parameters of fibrous filters on EDC, the present models are expressed in terms of fiber diameter. Polyacrylonitrile (PAN) nanofibers were prepared by electrospinning on melt-blown polypropylene (PP) microfiber filter materials to form micro/nanofibrous filters. To validate this model, a three-dimensional (3D) fiber model with physical parameters of the samples was reconstructed using the GeoDict code, and the Brownian movement of nanoparticles was simulated to calculate the EDC. Two kinds of pore size distributions for the layer-structured fibrous filters have been identified, which also shows the internal heterogeneity of the filter media. With decreasing fiber diameter, the tortuosity of the pore channel increases, while the EDC decreases. Compared with the numerical simulation and the experimental data reported in the literature, the current model gives a better theoretical prediction. In addition, the diffusion mechanism in classical filtration theory was modified to reduce the deviation between theoretical prediction and experimental results.

Prediction and Optimization of Interlayer-Interface Resistance for Expanded Polytetrafluoroethylene-Laminated Polyphenylene Sulfide Composite Membranes

“…The viscous resistance increased because of the increase of fiber surface area contacted by air flow, resulting in a higher pressure drop. 12,36 A number of previous studies had focused on the effect of fiber orientation and porosity on the pressure drop. 22,24−29 The comparison of the experimental and simulation results with the prediction model results proposed by Davies, 24 Happel, 25 Spielman and Goren, 26 Drummond, 27 Tomadakis and Robertson, 28 Yang, 29 and Woudberg 22,37 is plotted in Figure 9.…”

“…The lamination process caused the gap between the fibers to become smaller, and it could be seen that the tortuosity of the streamlines after lamination was significantly greater than before lamination. The viscous resistance increased because of the increase of fiber surface area contacted by air flow, resulting in a higher pressure drop. , …”

Investigation on the Collection Mechanism of van der Waals Force in Air Filtration by Numerical Simulation and Empirical Model Development

“…35 In the numerical study, the straight fiber is also commonly used to generate a virtual filter model and assess filter performance, compared to curved fiber. 25,28 Soltani et al conducted a numerical study to compare the permeability of curved and straight fibers. The curved fiber was obtained from X-ray μCT, while the straight fiber was developed by a MATLAB-based program from morphological analysis of X-ray μCT.…”

“…Several researchers have modeled fibrous media using Cartesian grids to reduce computational costs. Bai et al 25 and Maddideni et al 26 reconstructed the 3D fiber structure of an actual filter using the commercial solver GeoDict software based on the voxel method. Pradhan et al 27 used the same voxel method and developed an artificial 3D model of a fibrous filter.…”

Sequential Multiscale Simulation of a Filtering Facepiece for Prediction of Filtration Efficiency and Resistance in Varied Particulate Scenarios

“…As a first step, a virtual model is created by reflecting the actual material characteristics, either by reconstructing a resolved model from an actual sample analyzed by X-ray computed tomography (Xμ-CT) or by generating a digital model (unresolved model) with key input parameters such as fiber diameter, porosity, density, and thickness. , Validation of a virtual model can be attained by comparing the characteristics of virtual and actual materials; thus, physical experiments are accompanied to verify the simulation process. , An earlier study by Pan et al reported that a reconstructed filter model (resolved model) exhibited a better fit with the experimental data than a digital model. The main focus of the simulation study has been in understanding the particle behavior in the air flow − and optimizing the structural design of filter materials. − In other cases, the simulation was conducted on filter media to predict the initial resistance and efficiency at specific test conditions. , However, in most simulation cases, the time factor has been hardly considered, whereas the filtration characteristic with a timeframe may be important for a comprehensive understanding of filtration behavior in practical scenarios.…”