The Impacts of Surface Microchannels on the Transport Properties of Porous Fibrous Media Using Stochastic Pore Network Modeling

A stochastic pore network modeling method with tailored structures is proposed to investigate the impacts of surface microchannels on the transport properties of porous fibrous media. Firstly, we simplify the original pore network extracted from the 3D images. Secondly, a repeat sampling strategy is applied during the stochastic modeling of the porous structure at the macroscale while honoring the structural property of the original network. Thirdly, the microchannel is added as a spherical chain and replaces the overlapped elements of the original network. Finally, we verify our model via a comparison of the structure and flow properties. The results show that the microchannel increases the permeability of flow both in the directions parallel and vertical to the microchannel direction. The microchannel plays as the highway for the pass of reactants while the rest of the smaller pore size provides higher resistance for better catalyst support, and the propagation path in the network with microchannels is more even and predictable. This work indicates that our modeling framework is a promising methodology for the design optimization of cross-scale porous structures.

Fibrous coalescence filtration in treating oily wastewater: A review

Many industries discharge oil-in-water emulsion in the waste stream, often above the permissible limit causing serious environmental hazards. Porous media such as membrane and coalescence beds are employed to treat oily wastewater. A coalescence bed filter consists of either fibrous or granular packing and is used for removing larger oil droplets less than 100 μm from secondary emulsions. Fibrous media have higher porosities and specific surface areas than coarse granular media and hence give higher oil removal efficiency. To design an efficient fibrous coalescence bed filter for treating industrial discharge, understanding the mechanism of oil separation is important. This involves the surface wettability of fibers relating to surface chemistry and roughness. Further, fiber diameter, filter bed’s height, porosity, and pore size in relation to the oil droplet size and throughput and influent oil concentration are interactive parameters that affect the efficiency of coalescence. The performance of coalescence filtration is evaluated by analyzing the oil concentrations and D50 droplet sizes in the influent and effluent. In this article, the above-mentioned subjects are comprehensively reviewed from the reported research works, which highlights the complex nature of fibrous coalescence filtration.

Low-frequency noise control using layered granular aerogel and limp porous media

The acoustic absorption of granular aerogel layers with a granule sizes in the range of 2 to 40 μm is dominated by narrow-banded, high absorption regions in the low-frequency range and by reduced absorption values at higher frequencies. In this paper, we investigate the possibility of developing new, low-frequency noise reduction materials by layering granular aerogels with traditional porous sound absorbing materials such as glass fibers. The acoustic behavior of the layered configurations is predicted using the arbitrary coefficient method, wherein the granular aerogel layers are modeled as an equivalent poro-elastic material while the fibrous media and membrane are modeled as limp media. The analytical predictions are verified using experimental measurements conducted using the normal incidence, two-microphone impedance tube method. Our results show that layered configurations including granular aerogels, fibrous materials, and limp membranes provide enhanced sound absorption properties that can be tuned for specific noise control applications over a broad frequency range.

Electroosmosis and Electric Conduction of Electrolyte Solutions in Charge-Regulating Fibrous Media

An analytical study of the electroosmosis and electric conduction of electrolyte solutions in a fibrous medium composed of parallel charge-regulating cylinders with arbitrary electric double layer thickness is presented. A linearized charge regulation model was adopted for the association and dissociation reactions occurring at the amphoteric functional groups over the surfaces of the cylinders, and a unit cell model was employed to accommodate interactions among the cylinders. The electrokinetic equations governing the ionic concentration, electric potential, and liquid flow fields were solved at low zeta potential for the cylinders. Explicit formulas for the electroosmotic mobility and effective electric conductivity in the fiber matrix were obtained. The results indicate that the charge regulation characteristics, such as the equilibrium constants of the reactions occurring at the cylinders’ surfaces and the bulk concentration of the charge-determining ions, influence the surface charge density and potential, electroosmotic mobility, and effective electric conductivity substantially.