Fibrous Media Research Articles

Modelling of Escherichia coli removal by a low-cost combined drinking water treatment system

AbstractThis work presents mathematical modelling of Escherichia coli (E.coli) removal by a multi-barrier point-of-use drinking water system. The modelled system is a combination of three treatment stages: filtration by geotextile fabric followed by filtration and disinfection by silver-coated ceramic granular media (SCCGM) then granular activated carbon (GAC) filtration. The presented models accounted for removal mechanisms by each treatment stage. E.coli was modelled as a microbial particle. E.coli inactivation by SCCGM was modelled using the Chick's, Chick-Watson, Collins-Selleck and complete mix system bacterial inactivation kinetic models, which were considered adequately representative for describing the removal. Geotextile removal was modelled using colloidal filtration theory (CFT) for hydrosol deposition in fibrous media. The filtration removal contributions by the SCCGM and GAC were modelled using CFT for removal of colloidal particles by granular media. The model results showed that inactivation by silver in the SCCGM was the main bacterial removal mechanism. Geotextile and GAC also depicted appreciable removals. The theoretical modelling approach used is important for design and optimization of the multi-barrier system and can support future research in terms of material combinations, system costs, etc. Collector diameter, particle size, filtration velocity and contact time were identified as critical parameters for E.coli removal efficiency.

Adhesion modulates cell morphology and migration within dense fibrous networks

One of the most fundamental abilities required for the sustainability of complex life forms is active cell migration, since it is essential in diverse processes from morphogenesis to leukocyte chemotaxis in immune response. The movement of a cell is the result of intricate mechanisms, that involve the coordination between mechanical forces, biochemical regulatory pathways and environmental cues. In particular, epithelial cancer cells have to employ mechanical strategies in order to migrate through the tissue’s basement membrane and infiltrate the bloodstream during the invasion stage of metastasis. In this work we explore how mechanical interactions such as spatial restriction and adhesion affect migration of a self-propelled droplet in dense fibrous media. We have performed a systematic analysis using a phase-field model and we propose a novel approach to simulate cell migration with dissipative particle dynamics modelling. With this purpose we have measured in our simulation the cell’s velocity and quantified its morphology as a function of the fibre density and of its adhesiveness to the matrix fibres. Furthermore, we have compared our results to a previous in vitro migration assay of fibrosarcoma cells in fibrous matrices. The results show good agreement between the two methodologies and experiments in the literature, which indicates that these minimalist descriptions are able to capture the main features of the system. Our results indicate that adhesiveness is critical for cell migration, by modulating cell morphology in crowded environments and by enhancing cell velocity. In addition, our analysis suggests that matrix metalloproteinases (MMPs) play an important role as adhesiveness modulators. We propose that new assays should be carried out to address the role of adhesion and the effect of different MMPs in cell migration under confined conditions.

Capillary wicking in bio-based reinforcements undergoing swelling – Dual scale consideration of porous medium

Capillary wicking of liquids in natural fibrous reinforcements is a significant phenomenon in fibre-reinforced composites manufacturing through Liquid Composite Moulding (LCM) processes. Such phenomenon is however difficult to analyse due to heterogeneous, multiscale and variable fibrous medium during flow. Taking into account the fibre swelling, a modified Washburn’s model is proposed to predict the capillary rise of liquids in flax fibres. Particularly, swelling and wicking are studied at two different scales, i.e. elementary fibres and individual yarns. Swelling effects have been considered in the model and a modified Washburn’s theory has been developed. The proposed model satisfactory fits experimental results from capillary wicking tests, and hold for a 60% fibre volume fraction (Vf) of fabric on a relatively short duration while it fits well on a longer duration for lower Vf.

Resin Radial and Isothermal Infiltration in Fibrous Media: A New Mathematical Formulation

The objective of this work is to describe the fluid flow in porous media including the sorption term of the fluid by the fibers. The study has been applied to the manufacture of fiber-reinforced polymer composites by resin transfer molding, giving emphasis to radial resin infiltration in a one-dimensional approach. The mass conservation equation and Darcy’s law are presented and the solution of the governing equation is obtained. The advanced mathematical modeling includes the effect of fluid sorption by the porous media. Predicted flow front results and resin pressure fields within the mold during the injection process are presented, and the effects of the sorption term, injection pressure and fibrous medium permeability analyzed.

Prediction of flow characteristics in fibrous porous medium using a novel modeling algorithm and lattice Boltzmann method

Three flow types and previous modeling methods for the fibrous porous media (FPM) are summarized. A novel algorithm for modeling FPM structures was proposed to overcome shortcomings of other modeling methods. Carbon fiber felts were observed by a scanning electron microscopy to obtain geometrical information. Lattice Boltzmann method (LBM) was used in simulations for predicting flow properties. Permeability measurements and other correlations validated the new simulation method. Compared with other two common algorithms, the new algorithm predicted the flow properties in FPM more precisely. Results indicate that tortuosity in FPM increases as the porosity decreases, and the general range of the tortuosity is larger than that in the granular porous media. The effect of fiber diameter on the dimensionless permeability and the tortuosity is less than that of the porosity. A slight decline in dimensionless permeability was observed as the fiber diameter increases from 0.5 to 300 µm.

Air filter media functionalized with β‐Cyclodextrin for efficient adsorption of volatile organic compounds

AbstractRespiratory air filter media invariably comprise a nonwoven textile fabric. The limitation of the existing fibrous air filter medium is negligible protection against hazardous volatile organic compounds (VOCs). In this study, the filter media was cross‐linked with β‐Cyclodextrin for the surface functionalization. The VOC adsorption performance of the functional fabric was explored for styrene, benzene, and formaldehyde and also compared with a commercial nonwoven face mask. The functionalized fabric performed much better than commercial masks with adsorption capabilities of 18.80 μg mg−1 (for xylene), 14.75 μg mg−1 (for benzene), and 0.06 μg mg−1 (for formaldehyde). Further, the cross‐linking did not affect the air permeability (204 cm3 cm−2 s−1) thus showing no resistance to breathing. β‐Cyclodextrin functionalized textiles can be promising respiratory air filter media having the potential to capture a variety of VOCs yet remain breathable.

Water filtration using nonwoven cartridge filter system

A cartridge based fibrous filtration system has been designed and investigated. For the fibrous medium, needle-punch nonwoven structure has been selected and different nonwoven samples are analysed for the water purification. A series of different needle-punched nonwovens made of polypropylene have been produced by changing mass per unit area, needling density and fibre linear density. A chemical oxygen demand test has been employed to obtain the filtration efficiency (FE). The FE obtained for these samples ranges from 8.84% to 78.04% in purifying the reference water (mud water). It has been found that the FE increases with increase in mass per unit area and needling density (p < 0.01). Also, the filter media made of finer fibres displays higher FE than coarser fibre (p < 0.01). On examining the filter performance in multiple filtration cycles, it is found that the FE increases initially and finally reaches to a saturation value. A good correlation (r2 > 0.95) has been found for the FE of each cycle with the air permeability, thickness and weight density of the loaded filter. The FE of the bare nonwoven (maximum FE) further improves (95%) by incorporating activated particles.

Numerical simulation of solute removal from a cross-flow past a row of parallel hollow-fiber membranes

A multi-parametric simulation of the 2-D steady transverse flow of viscous incompressible fluid and diffusion transport of a dissolved solute past a model fibrous medium – a row of parallel sorbent fibers or hollow-fiber membranes is performed in a wide range of Schmidt (Sc) and Peclet (Pe) numbers for fiber Reynolds numbers up to Re = 100. The Navier-Stokes and convection-diffusion equations are solved numerically and the fiber capture efficiency for solute molecules is calculated as a function of Re, Sc and inter-fiber distance. The field of solute concentration and the fiber capture efficiency are found with zero concentration-fixed and diffusion flux boundary conditions set at the streamlined fiber surface, and the difference between the results of simulations with the two boundary conditions is shown for high Peclet numbers. It is also shown that the fiber capture efficiencies estimated with both boundary conditions tend to a constant maximum value for low Peclet numbers. The results of simulations for the fiber capture efficiency are validated by comparison with existing analytical asymptotic solutions for low and high Peclet numbers, and the agreement is shown.

Modeling of Designed Textile Fibrous Media for Liquid Filtration

This study is undertaken to provide a mathematical model designed by using colloidal filtration theory based on the orientation of fibers in the textile media for bacteria filtration. A model of colloidal filtration process is formulated based on the previous published works by considering relevant parameters affecting the filtration process like fiber orientation, fiber diameter, fiber length, and porosity of the media. The output value of the filtration efficiency of the model and the experimental data are compared. It is noted that the trends in the filtration efficiency data of the model and the experimental values are similar in nature which indicates the validity of the model.

Study on filtration performance of elliptical fiber with different arrangements

The fibrous media composed of elliptical fibers is widely used owing to the high filtration efficiency. However, there are few studies on the arrangement of non-circular fibers, although the single non-circular fiber has been clearly investigated. In this article, two-dimensional numerical geometries of fibrous media with different elliptical fiber arrangements, namely, random distribution structure, dense–sparse structure, and bimodal structure, are developed for studying filtration performance. The results show that the large aspect ratio and solid volume fraction represent low particle penetration. When the particle diameter ( Dp) is small, the quality factor of bimodal structure is higher than the dense–sparse structure, especially at Dp = 50 nm. For the large Dp, the opposite is true. Meanwhile, reducing fiber diameter ( Df) is more significant than increasing solid volume fraction in terms of improving penetration. As for dense–sparse structure, replacing the elliptical fibers in sparse layers with circular fibers can comprehensively improve the quality factor of fibrous media. However, if the replacement between elliptical fiber and circular fiber occurs in dense layer, it will result in high quality factor at Dp ⩽ 500 nm, while low quality factor at Dp > 500 nm.

Heat transfer enhancement in mini-channel using a fibrous porous medium

Heat transfer enhancement in mini-channel using a fibrous porous medium

Yield Loci of Reinforced Plates Made from Rigid-Plastic Unequiresistant Materials Considering the Two-Dimensional Stress State in Fibers I. Unidirectional Reinforcement

Structural models of hybrid fiber composites orthogonally reinforced in the plane are constructed. They allow one to calculate the yield loci taking into account the plane stress state in all composition components with different tensile and compressive yield stresses. Materials of the components are homogeneous and isotropic, and their mechanical behavior is described by the associated flow rule for a rigid-plastic body with the piecewise linear yield criteria of Johansen, Hu, and Tresca–Hu types. The fibers are located along the directions of principal stresses in the reinforced body. Analytical expressions for the equations of regimes on the yield loci of the composition are obtained, which can be used further in practical calculations. Different limit processes, from orthogonally reinforced composites to unidirectional reinforced ones and from fibrous media to homogeneous ones, are analyzed. It is proved that the plastic flow in a reinforced medium is associated with the yield loci constructed for it. The yield loci obtained for the composition are compared with those determined on the basis of the structural model with a one-dimensional stress state in fibers.

Use of an internal fibrous biofilter for intermittent nitrification and denitrification treatments in a zero-discharge shrimp culture tank

To achieve water reuse in recirculating aquaculture systems, intermittent nitrification and denitrification processes using internal fibrous media was proposed. A pre-acclimated Biocord biofilter, with an initial nitrification rate of 17.1 ± 12.4 mg total ammonia nitrogen-N/m2/d was applied in a marine whiteleg shrimp (Litopenaeus vannamei) culture tank. Throughout the experiment, the aerobic nitrification activity of the biofilter was sufficient to control the ammonia and nitrite levels below 0.2 mg-N/L with an accumulation of nitrate up to 50 mg-N/L. The remaining nitrate was successfully removed after shrimp harvest with the same biofilter through anoxic denitrification in conjunction with a methanol supplement at a chemical oxygen demand: nitrate-N ratio of 5:1. With complete nitrogen removal, the water was re-aerated and the next crop of shrimp culture was initiated. In this study, a two-crop shrimp cultivation was performed in sequence in the same tank without water exchange. The microbial diversity was monitored using high-throughput sequencing on Illumina MiSeq, which demonstrated that Proteobacteria (45.3 %), Chloroflexi (18.4 %), and Bacteroidetes (17.1 %) were the most abundant phyla. With an emphasis on nitrogen removal, the family Nitrosomonadaceae and Nitrospiraceae were the dominant nitrifying bacteria during the aerobic nitrification, while a high relative abundance of the Methylophaga and Methylotenera genera was observed under the anoxic condition.

Stochastic modelling of the heat and moisture transfer in a porous medium

A multi-phase and multi-component flow model with inherent stochastic terms is derived and is used to study the heat and moisture transfer in a fibrous porous medium. The materials’ porosity, velocity derived from Darcy’s law and ambient temperature at the external boundary are treated as white Gaussian noises. An effective multistep implicit splitting finite difference method (FDM) is adopted to solve the strongly coupled non-linear water, energy, vapour and air equations. The existence of a unique solution is analysed through the Lipschitz, monotonicity, growth, hemicontinuity and coercivity conditions. The notion of better thermal comfort arises from the results, as fluctuations are seen to dissipate on approaching the inner boundary (human body). Also, attention is drawn to the significance of considering all necessary uncertain variables in the system of equations. Four scenarios are considered in order to investigate the degree of contribution of the fluctuating terms. Clearly, ignoring certain vital stochastic elements can influence the results. Consequently, a combination of the stochastic porosity, velocity and ambient temperature incorporated into the same multi-phase and multi-component flow model is expected to provide more realistic results.

Evaluation of solids removal and optimisation of backwashing for an upflow stormwater filtration system utilising novel floating fibrous media

ABSTRACT Although filtration devices are already widely used for stormwater runoff treatment, there are much to be improved to ensure the required performance. Additionally, the performance of a device should be verified before on-site installation. In this context, an upflow filtration system using novel high porosity floating fibrous media formed into spherical shape was proposed and evaluated for solid capture and backwashing. At filtration velocities of 20–40 m/h, the maximum head loss was about 2 cm even under a solid load of 30 kg/m2, and suspended solid (SS) removal efficiency was >96% throughout 300 min. A considerable amount of SS was removed in the pretreatment chamber, so the load on the media was reduced. Several models were tried to describe the solid capture in the media. The coefficients of solid attachment/detachment showed good correlations with filtration velocity. Other parameters indicated a variation of solid capture and permeability, which is unique to the media in this study. The backwashing with air and water for 1–2 min each showed good head loss recovery under the SS load up to 550–600 kg/m2, and the SS discharge was more efficient when the stagnant water was drained before water backwashing. The results in this study suggest the high potential of the combination of fibrous media and upflow filtration system for the efficient control of the nonpoint source pollutants in stormwater runoff.

Electrokinetic Flow of Salt-Free Solutions in a Fibrous Porous Medium.

The electrokinetic flow of a salt-free solution in the fibrous porous medium constituted by an array of parallel charged circular cylinders subject to a pressure gradient and an electric field imposed in the axial direction is analytically studied via the use of a unit cell model. The Poisson-Boltzmann equation and modified Navier-Stokes equation applicable to a unit cell accommodating the salt-free solution around an individual cylinder are solved to determine the electric potential profile and fluid velocity distribution. Results of the electroosmotic velocity and effective electric conductivity in the fiber matrix are obtained as functions of the surface charge density of the dielectric cylinders and the porosity of the fiber matrix. The effects of the porosity or interactions among the cylinders on the electric potential distribution, electroosmotic velocity, and effective electric conductivity are significant and interesting under practical conditions. The apparent zeta potential, electroosmotic velocity, and effective electric conductivity increase monotonically with an increase in the surface charge density of the cylinders. When the porosity of the fiber matrix and surface charge density of the cylinders are high, the increases of the apparent zeta potential and electroosmotic velocity with the surface charge density are substantially suppressed due to the counterion condensation effect. However, this effect becomes weak when the porosity is low.

Transport through random bimodal and multimodal fiber structures

Random walk simulation results are reported for the transport and structural properties of random bimodal fibrous media for a range of values of the porosity, relative fiber size, and relative fiber density. Analytical expressions are derived for the mean intercept length of random bimodal and multimodal fiber structures, and are validated through simulations. A fiber dispersity factor emerges from the derivations, accounting for the deviation of the mean intercept length of such structures from that of unimodal fiber beds of the same porosity. Tortuosity factors in all diffusion regimes for in-plane and transverse flow through bimodal fibrous media of moderate or high porosity are practically independent of the relative fiber size and density and equal to those reported earlier for beds of unimodal fibers. The same holds for the formation factor of such structures, accounting for the dimensionless effective bulk diffusivity, thermal and electrical conductivity, magnetic permeability, dielectric constant and refractive index. The dimensionless viscous permeability of bimodal and multimodal fiber structures of moderate or high porosity may be obtained from that of unimodal fiber structures through simple multiplication by the square of the dispersity factor. This result is in line with a multitude of experimental data of the literature.

Modeling electrospun fibrous structures with embedded spacer particles: Application to aerosol filtration

This work presents a physics-based modeling technique to simulate the 3-D microstructure of electrospun fibrous media with embedded spacer particles. The model accepts inputs like diameter, basis weight, deposition velocity, and bending properties for the fibers as well as diameter and basis weight for the spacer particles. The model then predicts morphological parameters like filter porosity and filter thickness, among many others. The work presented in this paper is the first to report the effects of spacer particles with different diameters or basis weights on the thickness and solid volume fraction of spacer-embedded fibrous media. Such morphological information is then used for collection efficiency and pressure drop predictions when challenged with aerosol particles in the particle diameter range of 20 nm to 5 µm at a face velocity of 10 cm/s. Our results indicate that adding spacer particles to a fibrous filter can lower its collection efficiency and pressure drop, but the reduction in the pressure drop will be at a higher rate resulting in better filters, i.e., filters with better quality factors.

A novel-charged fibrous media characterized by higher efficiency and lower pressure drop

AbstractA new porous fiber shape was produced, one with a longitudinal notch. This new shape increases the surface area and therefore the overall number of pores, which in turn leads to a higher pe...

Semi-analytical and computational investigation of different fibrous structures affecting the performance of fibrous media.

Three arrangement types of fibrous media have been established including "Mesh" (layered distribution), "Para" (unidirectional distribution), and "Nurbs" (random distribution), with fiber diameters ranging from 5 to 7 µm and solid volume fractions ranging from 14.58% to 21.95%. To describe the filtration performance, particles trajectories, and the influence of structural parameters of fibrous media, the computation fluid dynamics is adopted. The filtration efficiency and the pressure drop of fibrous media are calculated in computation fluid dynamics and semi-analytical model. It is found that the arrangement types have significant effects on the filtration efficiency and show the limitation of the semi-analytical model. With the Stokes number larger than 1, the numerical results and semi-analytical model have great consistency in the filtration efficiency for the "Mesh" and "Para" types than "Nurbs" type. Meanwhile, the pressure drop between the numerical results and the semi-analytical model is always consistent.