@article{tafreshi_rahman_jaganathan_wang_pourdeyhimi_2009, title={Analytical expressions for predicting permeability of bimodal fibrous porous media}, volume={64}, ISSN={["0009-2509"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-59349120565&partnerID=MN8TOARS}, DOI={10.1016/j.ces.2008.11.013}, abstractNote={Pressure drop is one of the most important characteristics of a fibrous media. While numerous analytical, numerical, and experimental published works are available for predicting the permeability of media made up of fibers with a unimodal fiber diameter distribution (referred to as unimodal media here), there are almost no easy-to-use expressions available for media with a bimodal fiber diameter distribution (referred to as bimodal media). In the present work, the permeability of bimodal media is calculated by solving the Stokes flow governing equations in a series of 3-D virtual geometries that mimic the microstructure of fibrous materials. These simulations are designed to establish a unimodal equivalent diameter for the bimodal media thereby taking advantage of the existing expressions of unimodal materials for permeability prediction. We evaluated eight different methods of defining an equivalent diameter for bimodal media and concluded that the area-weighted average diameter of Brown and Thorpe [2001. Glass-fiber filters with bimodal fiber size distributions. Powder Technology 118, 3–9], volume-weighted resistivity model of Clague and Phillips [1997. A numerical calculation of the hydraulic permeability of three dimensional disordered fibrous media. Physics of Fluids 9 (6), 1562–1572], and the cube root relation of the current paper offer the best predictions for the entire range of mass (number) fractions, 0⩽nc⩽1, with fiber diameter ratios, 1⩽Rcf⩽5, and solidities, 5⩽α⩽15.}, number={6}, journal={CHEMICAL ENGINEERING SCIENCE}, author={Tafreshi, H. Vahedi and Rahman, M. S. A. and Jaganathan, S. and Wang, Q. and Pourdeyhimi, B.}, year={2009}, month={Mar}, pages={1154–1159} }
 @article{maze_tafreshi_wang_pourdeyhimi_2007, title={A simulation of un-steady-state filtration via nanofiber media at reduced operating pressures}, volume={38}, ISSN={["1879-1964"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-34249003346&partnerID=MN8TOARS}, DOI={10.1016/j.jaerosci.2007.03.008}, abstractNote={In this work, 3-D structures resembling nanofiber (df<200nm) filter media are simulated and challenged with nanoparticle aerosols at reduced operating pressures. For the range of fiber diameters considered in this paper, the free molecular flow regime is dominant. Therefore, the disturbances to the air flow field caused by the fibers are neglected. Nanoparticle capture efficiency of nanofiber webs, due to Brownian diffusion and interception, is calculated for particle diameters ranging from 50 to 500 nm. Our simulations show that by decreasing the fiber diameter, the minimum collection efficiency of filtration media having identical pressure drops increases. This effect is accompanied by a decrease in the particle diameter associated with these minimum efficiencies—the most penetrating particle diameter. Moreover, it is demonstrated that increasing the flow temperature enhances the nanoparticle capture efficiency of nanofiber filters. Allowing the particles to deposit on the fibers as well as each other, the caking process of such nanofiber filters is simulated for different monodisperse and polydisperse aerosols at different temperatures. The statistical information regarding the composition of nanoparticle cakes formed at high and low temperatures is presented and discussed.}, number={5}, journal={JOURNAL OF AEROSOL SCIENCE}, author={Maze, B. and Tafreshi, H. Vahedi and Wang, Q. and Pourdeyhimi, B.}, year={2007}, month={May}, pages={550–571} }
 @article{zobel_maze_tafreshi_wang_pourdeyhimi_2007, title={Simulating permeability of 3-D calendered fibrous structures}, volume={62}, ISSN={["1873-4405"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-34848892122&partnerID=MN8TOARS}, DOI={10.1016/j.ces.2007.07.007}, abstractNote={Many fibrous materials such as nonwoven materials are often consolidated by means of hot calenders, i.e., hot compaction rolls. Hot calendering compresses the fiber assembly and can cause changes in the structure. In nonwovens, calendering has an added function of thermally bonding the fibers at their respective crossovers to form a strong but yet somewhat porous material. Calendering causes a significant increase in the solid volume fraction (SVF) of the media and therefore, affects their permeability. To our knowledge, no work in the literature has been dedicated to modeling the permeability of calendered nonwovens. In this study, virtual nonwoven structures are generated and compressed from top and bottom to resemble the hot calendering process. In agreement with our experimental observations, it was found that the average SVF profile across the material's thickness turns into a U-shape profile after the calendering. In this work, the dimensionless permeability of the calendered media is computed using CFD tools and reported for different compaction ratios. Results of our simulations are compared with the experiment as well as the available empirical and/or analytical permeability models in the literature and good agreement, depending upon the SVF, is observed. We also studied the influence of orientation distribution of the fibers on the dimensionless permeability of the fabric and noticed that permeability decreases by increasing the directionality of the fibers. This is found to be primarily due to the fact that highly oriented uncompressed fiber-webs tend to have a higher SVF. Fiber-webs of identical SVF, however, exhibited almost identical permeabilities regardless of their fiber orientations.}, number={22}, journal={CHEMICAL ENGINEERING SCIENCE}, author={Zobel, S. and Maze, B. and Tafreshi, H. Vahedi and Wang, Q. and Pourdeyhimi, B.}, year={2007}, month={Nov}, pages={6285–6296} }
 @article{wang_maze_tafreshi_pourdeyhimi_2007, title={Simulating through-plane permeability of fibrous materials with different fiber lengths}, volume={15}, ISSN={["0965-0393"]}, DOI={10.1088/0965-0393/15/8/003}, abstractNote={Assuming that fibers can be represented as straight cylinders, an algorithm for generating virtual 3D layered fibrous media made up of fibers having identical diameters but different lengths is presented. It is shown that for a given basis weight and computational box (sample size), reducing the fiber length causes the solid volume fraction (SVF) to increase as the fibers pack next to one another more efficiently. The air permeability of these media is numerically simulated and discussed in detail with respect to the available 2D and 3D studies in the literature. Our permeability calculations show an excellent agreement with the predictions of the empirical equation of Davies [1] as well as the analytical model of Spielman and Goren [2]. Such an agreement indicates that, within the range of dimensions considered, the fiber length has no significant influence on the materials' through-plane permeability as long as the SVF remains constant. While this concept has been empirically observed in the past, our work is the first numerical simulation devised to confirm it.}, number={8}, journal={MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING}, author={Wang, Q. and Maze, B. and Tafreshi, H. Vahedi and Pourdeyhimi, B.}, year={2007}, month={Dec}, pages={855–868} }
 @article{wang_maze_tafreshi_pourdeyhimi_2006, title={A case study of simulating submicron aerosol filtration via lightweight spun-bonded filter media}, volume={61}, ISSN={["1873-4405"]}, DOI={10.1016/j.ces.2006.03.039}, abstractNote={The most common method of filtration is via fibrous nonwoven media. Fibrous filters are generally characterized by their collection efficiency and pressure drop. Traditional computational studies in this area are typically based on unrealistic 2-D geometries with the fibers simply placed in a lattice (regular array) perpendicular to the flow. The traditional approaches however, do not permit studying the relation between the 3-D structure of a filter media and its performance. In this study, for the first time, a virtual 3-D web is generated based on the fiber orientation information obtained from analyzing microscopic images of lightweight spun-bonded filter media. Pressure drop and collection efficiency of our virtual filter are simulated and compared with the previous 2-D analytical and numerical models as well as experiment. Our pressure drop calculation, unlike the previous models, showed a perfect agreement with the predictions of the Davies' empirical equation. The collection efficiencies obtained from simulating a thin spun-bonded filter media challenged with submicron particles having diameters ranging from 50 to 500 nm showed a similar trend as that of the previous 2-D models. For the solid volume fraction (SVF), filter thickness, and the fiber and particle diameters considered in this study, we found collection efficiencies higher than that of the above mentioned 2-D models with a relatively good agreement with experimental data obtained from a TSI 8130 filter tester.}, number={15}, journal={CHEMICAL ENGINEERING SCIENCE}, author={Wang, Q. and Maze, B. and Tafreshi, H. Vahedi and Pourdeyhimi, B.}, year={2006}, month={Aug}, pages={4871–4883} }
 @article{wang_maze_tafreshi_pourdeyhimi_2006, title={A note on permeability simulation of multifilament woven fabrics}, volume={61}, ISSN={["1873-4405"]}, DOI={10.1016/j.ces.2006.09.043}, abstractNote={A conventional approach for modeling permeability of multifilament fabrics is to consider their warps and wefts to be individual thick filament made of homogeneous porous media and solve the flow equations for such monofilament fabrics. In this work, for the first time, the full 3-D geometry of an idealized multifilament woven fabric, wherein the filaments are packed in hexagonal arrangement, is generated to compute its permeability and compare with the homogeneous anisotropic lumped model of Gebart (1992. Permeability of unidirectional reinforcements for RTM. Journal of Composite Materials 26(8), 1100–1133). While a relatively good agreement is obtained, our results indicate that Gebart's model slightly underestimate the permeability of multifilament fabrics even at high yarn's solid volume fractions.}, number={24}, journal={CHEMICAL ENGINEERING SCIENCE}, author={Wang, Q. and Maze, B. and Tafreshi, H. Vahedi and Pourdeyhimi, B.}, year={2006}, month={Dec}, pages={8085–8088} }