Filtration Of Suspensions Research Articles

Nanocellulose films as air and water vapour barriers: A recyclable and biodegradable alternative to polyolefin packaging

Synthetic polymer packaging is neither reprocessable, renewable nor biodegradable and is difficult to recycle into useful barrier materials. Cellulose fibre based packaging is renewable, easily reprocessable, recyclable and biodegradable, however, it is a poor barrier material both before and after recycling, especially against air and water vapour. Nanocellulose (NC), formed by breaking down cellulose fibres into nanoscale diameter fibres, is a renewable alternative to synthetic polymer packaging barrier layers. This research investigates the recyclability of virgin NC films. Nanocellulose films were recycled and prepared into films, using standard dispersion-based laboratory papermaking techniques through mixing and vacuum filtration of the resultant suspension. The recycled films retained ˜70% of the strength of the virgin films. Although the water vapour permeability (WVP) approximately doubled, increasing to 1.29 × 10−10 g.m−1.s−1 Pa−1, it is still comparable to synthetic polymer packaging materials such as Polyethylene(PE), Plasticized PVC, Oriented Nylon 6 and Polystyrene (PS). SEM micrographs reveal no fibre agglomeration and no damage to the fibres during the recycling process. The optical uniformity measurements of recycled NC film confirms a drop in uniformity of the film at smaller length scales and an increase in uniformity at larger length scales, compared with virgin NC film. The retained strength and barrier properties combined with easy reprocessability of the product promises a sustainable and recyclable alternative to conventional polyolefin packaging, providing a very attractive alternative for the packaging industry.

Polyhydroxybutyrate/Chitosan 3D Scaffolds Promote In Vitro and In Vivo Chondrogenesis

The articular cartilage is an avascular and aneural tissue and its injuries result mostly in osteoarthritic changes and formation of fibrous tissue. Efforts of scientists worldwide are focused on restoration of cartilage with increase in life quality of patients. Novel polymeric polyhydroxybutyrate/chitosan (PCH) porous 3D scaffolds were developed and characterized. The rat mesenchymal stem cells (MSCs) were seeded in vitro on PCH scaffolds by a simple filtration of MSCs suspension over scaffolds using syringe. The chondrogenesis of cell-scaffold constructs was carried out in supplemented chondrogenic cultivation medium. After 2 and 4weeks of in vitro culturing cell-scaffold constructs in chondrogenic differentiation medium, the cartilage extracellular matrix components like glycosaminoglycans and collagens were identified in scaffolds by biochemical assays and histological and immunohistochemical staining. Preliminary in vivo experiments with acellular scaffolds, which filled the artificially created cartilage defect in sheep knee were done and evaluated. Cells released from the bone marrow cavity have penetrated into acellular PCH scaffold in cartilage defect and induced tissue formation similar to hyaline cartilage. The results demonstrated that PCH scaffolds supported chondrogenic differentiation of MSCs in vitro. Acellular PCH scaffolds were successfully utilized in vivo for reparation of artificially created knee cartilage defects in sheep and supported wound healing and formation of hyaline cartilage-like tissue.

Modelling of the technological process of multiple filtering suspensions with multi-layered filter

Although a technological process of filtration with multi-layered filters is well-known in industry (purification of such liquid solutions as spinning solutions, liquid fuels, drinking liquids, pharmaceuticals, etc.), very few studies have systematically quantified its mechanism, and even less have characterized the affect of its parameters on operating costs and the quality of the final product. In this study, there was developed a mathematical model of multiple filtration of suspensions with multi-layered filter, a computational algorithm for solving the problem as well as software for carrying out computational experiments. The developed mathematical software allows to carry out many-sided study and forecast the technological process of filtration in order to make appropriate management decisions.

Optimisation of the Microbial Cell Concentration Procedure in Plague Vaccine Production

To date, the technology of live plague vaccine production uses a combined method of concentrating microbial cells which consists of three operations with a total duration of 18 hours. The procedure of obtaining concentrate, which is used in the current vaccine production technology, has a number of disadvantages, namely: multiple operations, high energy consumption, long duration, and, as a consequence, low yield of concentrated suspension (0.04 l from 1 l of native culture). The aim of the study was to optimise the procedure of Yersinia pestis ЕV microbial cell concentration using the system for tangential flow microfiltration with the ASF-020 filter support unit. Materials and methods: the vaccine strain used in the study was Yersinia pestis ЕV derived from NIIEG cell line (the strain of the Research Institute of Epidemiology and Hygiene). Submerged cultivation of the native culture was performed using the BIOR-0.25 reactor. The content of live microbial cells was determined by cytorefractometry. Oxidative metabolism was assessed using the chronoamperometric method. Physico-chemical and immunobiological properties of the dry live plague vaccine were assessed according to the monograph FS.3.3.1.0022.15 of the State Pharmacopoeia of the Russian Federation, 14 edition. Results: the equipment’s design features made it possible to carry out membrane filtration of the microbial suspension using the BIOR-0.25 reactor as an intermediate storage unit, thereby excluding three technological stages. The total concentration of microbes in the suspension obtained by the routine and the optimised methods was not less than 120 billion microbial cells/ml. A comparative study of the effect of various hydrodynamic regimes in the working cavities of ASF-009 and ASF020 filter units did not significantly affect the morphometric and physiological properties of microbial cultures. Experimental data helped to determine the process mass balance of membrane filtration. The optimised technology gave 0.17 l yield of the concentrate from 1 l of native culture, and the process duration was reduced to 4 hours. Conclusions: the process of concentrating Y. pestis EV microbial cells during production of plague vaccines was optimised. A comparative study of morphometric and physiological properties of plague microbe cultures that was carried out during their concentration using the optimised technology did not reveal any significant differences as compared to the routine one.

Formation damage and cleanup in the vicinity of flooding wells: Multi-fluid suspension flow model and calibration on lab data

Injection of water into a rock formation through the flooding wells is a common practice to maintain reservoir pressure and increase ultimate recovery of hydrocarbons. While flowing through the well from surface to the rock formation, injected water typically transports fine particles, which are introduced either externally (untreated water) or internally (e.g., particles detached from the inner surface of a pipeline due to erosion and abrasion as well as mineral particles detached from pore surface). In the framework of the two-fluid approach, we formulate mathematical model for filtration of a particle-laden suspension in the vicinity of flooding wells. Two mechanisms affecting transport of non-colloidal fines are considered: trapping and mobilization. Trapped particles reduce permeability and porosity of the rock, which leads to the injectivity decline of the well. The model contains minimal set of tuning parameters describing particle trapping and mobilization rates. This is achieved by critical overview of existing models. We calibrate suspension filtration model against existing experimental (laboratory) data on fines mobilization and trapping in porous media. A parametric study of different flooding scenarios is carried out numerically. In particular, we investigate the effectiveness of periodic flooding regime, when the periods of injection are followed by flowback in order to wash out trapped fines from the near-wellbore zone and restore well injectivity. Implications to formation damage and cleanup phenomena peculiar to hydraulic fracturing and drilling are discussed. Practical recommendations are given.

Attapulgite nanofibers and graphene oxide composite membrane for high-performance molecular separation

Graphene oxide (GO) based membranes are widely adopted in molecular separation based on size exclusion effect by stacked GO sheets. Both high flux and efficient rejection of GO-based membranes for long-term operation are highly expected for practical applications. Here, an attapulgite (ATP) nanofibers/ GO composite (ATP/GO) membrane is assembled by filtration of mixed aqueous colloidal suspensions of ATP and GO. Due to the modification of interlayer distance and surface property of GO membrane by ATP, the ATP/GO membrane demonstrates excellent separation performance, with a high water flux of 221.16 Lm-2 h-1bar−1, 7.7 times higher than that of pure GO membrane. Meanwhile, the rejection of ATP/GO is also slightly improved comparing with that of GO membrane. It is also found that increasing the thickness of the membrane is effective to enhance rejection percentage. The ATP/GO membranes reported here show high efficiency for molecular separation, which demonstrates potential applications in water purification and environmental protection.

A Specific NH<sub>3</sub> Gas Sensor of a Thick MWCNTs-OH Network for Detection at Room Temperature

NH3 gas sensor was fabricated based on deposited of Functionalized Multi-Walled Carbon Nanotubes (MWCNTs-OH) suspension on filter paper substrates using suspension filtration method. The structural, morphological and optical properties of the MWCNTs film were characterized by XRD, AFM and FTIR techniques. XRD measurement confirmed that the structure of MWCNTs is not affected by the preparation method. The AFM images reflected highly ordered network in the form of a mat. The functional groups and types of bonding have appeared in the FTIR spectra. The fingerprint (C-C stretch) of MWCNTs appears in 1365 cm-1, and the backbone of CNTs observed at 1645 cm-1. A homemade sensing device was used to evaluate the fabrication network toward NH3 gas at ppm levels as well as the response to sensitivity by changing the concentration. MWCNTs-OH network of 8mm thickness showed an increase in resistance upon exposure to the NH3 gas. The sensor exhibits a good sensitivity for low concentration of NH3 gas at room temperature. The sensitivities of the network were 2.5% at 14ppm, 5.3% at 27ppm and 17.6% at 68ppm. Further investigations showed that the network was specific sensitive to NH3 gas in the environment and not affected by the amount of ambient air.

Antibiofouling Performance by Polyethersulfone Membranes Cast with Oxidized Multiwalled Carbon Nanotubes and Arabic Gum

Despite extensive research efforts focusing on tackling membrane biofouling, one of the biggest problems associated with membrane technology, there has been little headway in this area. This study presents novel polyethersulfone (PES) membranes synthesized via a phase inversion method at incremental loadings of functionalized oxidized multiwalled carbon nanotubes (OMWCNT) along with 1 wt. % arabic gum (AG). The synthesized OMWCNT were examined using scanning electron microscopy and transmission electron microscopy for morphological changes compared to the commercially obtained carbon nanotubes. Additionally energy-dispersive X-ray spectroscopy was carried out on the raw and OMWCNT materials, indicating an almost 2-fold increase in oxygen content in the latter sample. The cast PES/OMWCNT membranes were extensively characterized, and underwent a series of performance testing using bovine serum albumin solution for fouling tests and model Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) bacterial species for anti-biofouling experiments. Results indicated that the composite PES membranes, which incorporated the OMWCNT and AG, possessed significantly stronger hydrophilicity and negative surface charge as evidenced by water contact angle and zeta potential data, respectively, when compared to plain PES membranes. Furthermore atomic force microscopy analysis showed that the PES/OMWCNT membranes exhibited significantly lower surface roughness values. Together, these membrane surface features were held responsible for the anti-adhesive nature of the hybrid membranes seen during biofouling tests. Importantly, the prepared membranes were able to inhibit bacterial colonization upon incubation with both Gram-positive and Gram-negative bacterial suspensions. The PES/OMWCNT membranes also presented more resilient normalized flux values when compared to neat PES and commercial membrane samples during filtration of both bacterial suspensions and real treated sewage effluents. Taken together, the results of this study allude to OMWCNT and AG as promising additives, for incorporation into polymeric membranes to enhance biofouling resistance.

Optimization of Triton X-100 removal and ultrasound probe parameters in the preparation of multiwalled carbon nanotube buckypaper

A highly porous film composed of a three-dimensional network of multi-walled carbon nanotube (MWCNT), also known as buckypaper (BP), was prepared by vacuum filtration of a well-dispersed suspension of MWCNT/H20 with the aid Triton X-100 surfactant. The key contribution of this work is to achieve the best parameters during the preparation of the suspension and find the best way to remove the excess triton X-100 from the nanotube network. The stability of suspension in different pH, the adsorption capacity, and the reusability of MWCNT was also evaluated. The effects of ultrasound parameters on the BP properties were systematically investigated and characterized by Raman Spectroscopy, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), and electric resistivity using a four-point probe technique. In addition, the results of using different solvents to wash the BP after filtration process were analyzed by Thermogravimetric analyses (TGA), Fourier transform infrared spectroscopy (FT-IR), and Field emission gun scanning electron microscopy (FEG-SEM). The optimum condition employed in this work (25 min–40%) exhibited the ID/IG ratio of 2.17 and L002 of 5.597 nm, which suggests less damage to MWCNT. This study confirms that MWCNT-BP can be used to fabricate high-loading CNT/polymer composites with improved electrical properties.

Global asymptotics of filtration in porous media

Filtration problems are actual for the design of underground structures and foundations, strengthening of loose soil and construction of watertight walls in the porous rock. A liquid grout pumped under pressure penetrates deep into the porous rock. Solid particles of the suspension retained in the pores, strengthen the loose soil and create watertight partitions. The aim of the study is to construct an explicit analytical solution of the filtration problem. A one-dimensional model of deep bed filtration of a monodisperse suspension in a homogeneous porous medium with size-exclusion mechanism of particles retention is considered. Solid particles are freely transferred by the carrier fluid through large pores and get stuck in the throats of small pores. The mathematical model of deep bed filtration includes the mass balance equation for suspended and retained particles and the kinetic equation for the deposit growth. The model describes the movement of concentrations front of suspended and retained particles in an empty porous medium. Behind the concentrations front, solid particles are transported by a carrier fluid, accompanied by the formation of a deposit. The complex model has no explicit exact solution. To construct the asymptotic solution in explicit form, methods of nonlinear asymptotic analysis are used. The new coordinate transformation allows to obtain a parameter that is small at all points of the porous sample at any time. In this paper, a global asymptotic solution of the filtration problem is constructed using a new small parameter. Numerical calculations are performed for a nonlinear filtration coefficient found experimentally. Calculations confirm the closeness of the asymptotics to the solution in the entire filtration domain. For a nonlinear filtration coefficient, the asymptotics is closer to the numerical solution than the exact solution of the problem with a linear coefficient. The analytical solution obtained in the paper can be used to analyze solutions of problems of underground fluid mechanics and fine-tune laboratory experiments.

Numerical solution of filtration in porous rock

The filtration problem is one of the most relevant in the design of retaining hydraulic structures, water supply channels, drainage systems, in the drainage of the soil foundation, etc. Construction of transport tunnels and underground structures requires careful study of the soil properties and special work to prevent dangerous geological processes. The model of particle transport in the porous rock, which is based on the mechanical-geometric interaction of particles with a porous medium, is considered in the paper. The suspension particles pass freely through large pores and get stuck in small pores. The deposit concentration increases, the porosity and the permissible flow of particles through large pores changes. The model of one-dimensional filtration of a monodisperse suspension in a porous medium with variable porosity and fractional flow through accessible pores is determined by the quasi-linear equation of mass balance of suspended and retained particles and the kinetic equation of deposit growth. This complex system of differential equations has no explicit analytical solution. An equivalent differential equation is used in the paper. The solution of this equation by the characteristics method yields a system of integral equations. Integration of the resulting equations leads to a cumbersome system of transcendental equations, which has no explicit solution. The system is solved numerically at the nodes of a rectangular grid. All calculations are performed for non-linear filtration coefficients obtained experimentally. It is shown that the solution of the transcendental system of equations and the numerical solution of the original hyperbolic system of partial differential equations by the finite difference method are very close. The obtained solution can be used to analyze the results of laboratory research and to optimize the grout composition pumped into the porous soil.

Oil Filtration in a Porous Medium in the Presence of Graphene Nanoparticles

The filtration of a graphene suspension through a core sample has been studied experimentally. It has been found that at the oil–water interface in the porous medium of the core sample, a transient multilayer microheterophase structure consisting of planar graphene nanoparticles, hydrocarbon oil molecules, and surfactants is formed. It has been found that with an increase in the concentration of graphene nanoparticles, the volume fraction of displaced oil increases and the water volume fraction in oil decreases.

Filtration in porous rock with initial deposit

The problems of underground fluid mechanics play an important role in the design and preparation for the construction of tunnels and underground structures. To strengthen the insecure soil a grout solution is pumped under pressure in the porous rock. The liquid solution filters in the pores of the rock and strengthens the soil after hardening. A macroscopic model of deep bed filtration of a monodisperse suspension in a porous medium with a size-exclusion mechanism for the suspended particles capture in the absence of mobilization of retained particles is considered. The solids are transported by the carrier fluid through large pores and get stuck at the inlet of small pores. It is assumed that the accessibility factor of pores and the fractional flow of particles depend on the concentration of the retained particles, and at the initial moment the porous medium contains an unevenly distributed deposit. The latter assumption leads to inhomogeneity of the porous medium. A quasilinear hyperbolic system of two first-order equations serves as a mathematical model of the problem. The aim of the work is to obtain the asymptotic solution near the moving curvilinear boundary - the concentration front of suspended particles of the suspension. To obtain a solution to the problem, methods of nonlinear asymptotic analysis are used. The asymptotic solution is based on a small-time parameter, measured from the moment of the concentration front passage at each point of the porous medium. The terms of the asymptotics are determined explicitly from a recurrent system of ordinary differential and algebraic equations. The numerical calculation is performed by the finite difference method using an explicit TVD scheme. Calculations for three types of microscopic suspended particles show that the asymptotics is close to the solution of the problem. The time interval of applicability of the asymptotic solution is determined on the basis of numerical calculation. The constructed asymptotics, which explicitly determines the dependence on the parameters of the system, allows to plan experiments and reduce the amount of laboratory research.

A self-cleaning piezoelectric PVDF membrane system for filtration of kaolin suspension

Exploring innovative membrane material is an important approach to mitigate membrane fouling. This study investigated a self-cleaning polyvinylidene fluoride (PVDF) piezoelectric membrane system which can vibrate at controlled frequencies, amplitudes and waveforms to mitigate membrane fouling. Among different PVDF films, the one of the highest content of β-phase PVDF was selected because of the greatest piezoelectric coefficient. The film was pin punched to 0.14 ± 0.02 mm holes for filtration purpose. The characteristic peaks of vibration velocity and amplitude were identified by measurements of a Scanning Laser-Doppler vibrometer with tiered driving voltages. The piezoelectric membrane was tested in a dead-end filtration system fed with 0.5 g L−1 kaolin suspension of 907.7 nm Z-average diameter at a constant filtration pressure of 34.5 kPa. The results indicate vibration velocity is more important than amplitude to choose the vibration frequency in order to optimize membrane fouling control. The piezoelectric membrane with continued vibration driven by 24 V (peak-to-peak) and sine wave at the frequency of 1601 Hz (the peak of vibration velocity) yielded 87 ± 3% higher permeate flux than control test, compared to 30 ± 3% increase at the frequency of 664 Hz (the peak of vibration amplitude). However, the antifouling effect was not apparent with intermittent vibration, possibly due to interrupted processes of cleaning and fouling prevention. The mechanistic explanation of cleaning suggests lift force brought by hydraulic shearing is more important than inertial lift force of vibration.

Determination of filtration and consolidation properties of protein crystal suspensions using analytical photocentrifuges with low volume samples

Proteins and in particular pharmaceutical proteins like monoclonal antibodies are expensive products. Protein crystallization is an interesting alternative process step to the common purification and formulation of such proteins. The solid-liquid separation of proteins however, is a challenging task because the proteins are sensitive to mechanical stress, which could lead to crystal breakage and often are only available in small amounts for research and development. In this study a newly developed filtration cell for the LUMiSizer® centrifuge is used to analyze the filtration behavior with low volume samples. Isometric and needle shaped lysozyme crystals serve as model protein crystals. The needle shaped crystals showed about twice as high compressibility and much higher cake resistance than the isometric lysozyme crystals. After the filtration at maximum pressure in the centrifuge the mean particle diameter decreased compared to the unstressed median diameter. With the filtration cell the cake height and filter cake compression can be monitored in situ and the filter cake resistance and solids volume fraction can be calculated with one experiment using 200–300 μl sample.

Filtration of the catalyst suspension in hydrogenated oil through the woven cloth: Mathematical model of the process accounting for dynamics of the cake growth and filter pore blockage

Catalytic hydrogenation of the plant oils includes a filtration stage in which the solid catalyst must be separated from its suspension in the melted hydrogenation products. For effective separation of the catalyst, a proper selection of the filter cloth and filtration conditions is necessary.The subject of this study is filtration of finely dispersed carbon material Sibunit through a porous woven filtering cloth in circulation mode. Sibunit is the carrier for Pd catalysts that are regarded as prospective for hydrogenation of vegetable oils; the carbon-based catalysts can be reused and can therefore be more economical than conventional nickel catalysts. To reliably predict the efficiency and duration of filtration of the catalyst suspended in the hydrogenated products, the mathematical model of the filtration process must adequately describe the complex physical phenomena that occur during the process.In the article, a one-dimensional mathematical model was developed, which took into account the main physical phenomena of the filtration process, such as percolation of the particles through a porous filter, accumulation of the particles along the filter pores, and a gradual cake growth. Woven fabric contains two types of pores: the pores between the threads and the pores between the fibers. Model assumes that polydisperse particles can both penetrate through the filter cloth and accumulate inside the tissue and on its outer surface. It is assumed that the hydraulic resistance of the cake increases due to the growth of its height only, and the hydraulic resistance of the filter cloth increases due to particles trapped in the pores.Numerical analysis of the model was carried out in the range of parameters typical for industrial conditions. It has been found that the process efficiency, which was defined as the minimum time required filtering a certain amount of hydrogenated oil to the maximum degree of catalyst purification, depends mainly on the time taken to form a cake layer of sufficient height. Higher efficiency of the filtration process is favored by the higher filter porosity, the greater thread diameter, and the smaller pore size between the fibers. In contrast to the thin pores formed by the fibers, the large pores between threads allow more particles to pass through the filter; therefore, for practical use it is necessary to adjust the filter cloth porous structure with the particles size distribution.The model was verified by comparing the predicted results with experimental data.

Graphene-based papers as substrates for cell growth: Characterisation and impact on mammalian cells

Graphene based material (GBM) substrates are promising candidates for tissue engineering and as cell scaffolds owing to their outstanding properties that favour cell adhesion and growth. In this study, we report the fabrication and use of different oxidised graphene-based ‘papers’ as substrates for cell culture, using starting materials of different thickness and lateral dimensions. Graphite oxide (GTO) consisted of thicker sheets than the thinner large graphene oxide (l-GO) and small graphene oxide (s-GO) sheets. The ‘papers’ were prepared by vacuum filtration of the material suspensions and characterised by an array of experimental techniques. The substrates were then evaluated for cellular adhesion and proliferation with two epithelial cell lines that differ in their morphologies, the human lung cell culture (A549) model and the human neural cell culture (SH-SY5Y) model using microscopic analysis. Release of lactate dehydrogenase (LDH) in cell supernatants was measured to assess any cytotoxic responses. Our results revealed that the GO papers had similar physicochemical properties but differing topographies. The papers supported cell growth and no cytotoxicity was observed. These results suggest that substrates based on graphite and graphene oxide papers are suitable biocompatible cellular supports for anchorage-dependent cell growth and can be further explored for tissue engineering, regenerative medicine, substrates for cell growth and bionic applications.

Fabrication of high-performance antibiofouling ultrafiltration membranes with potential application in membrane bioreactors (MBRs) comprising polyethersulfone (PES) and polycitrate-Alumoxane (PC-A)

Novel nanocomposite ultrafiltration (UF) membranes were designed and fabricated using hydrophilic polycitrate-Alumoxane (PC-A) nanoparticles and polyethersulfone (PES) to achieve desirable performance for membrane bioreactor (MBR) system. Pure water flux (PWF) and fouling tests were employed to examine the effects of PC-A nanoparticles on the UF performance. FTIR spectra of the PC-A nanoparticles revealed that carboxylic acid and hydroxyl groups are created on the surface of the PC-A. The presence of these hydrophilic groups in PC-A resulted in greater hydrophilicity for the PC-A-modified UF membranes. Therefore, the PC-A-modified UF membranes exhibited higher PWFs compared to the unfilled PES membrane. Fouling resistance of the membranes was evaluated by activated sludge suspension filtration disclosed that the membrane modified with only 0.5 wt% of PC-A had the best antifouling characteristic as well as the greatest PWF. Hence, this optimal nanocomposite membrane was used in the MBR and variations of fluxes exanimated at different mixed liquor suspended solids (MLSS) concentrations of 6000, 10,000 and 14,000 mg/L. During filtration of the activated sludge, the fluxes increased with an increase in MLSS. A decrease in soluble microbial products, extracellular polymeric substance (EPS) from the bacterial cells, and cake formation fouling may result in gentler permeation flux decline over time.

Novel device for in situ process characterization of oxide/oxide ceramic matrix composites fabricated by flexible injection

AbstractIn this work, a new manufacturing process of CMC by liquid molding was studied. An instrumented device has been developed to characterize the through‐thickness impregnation of ceramic fibers by a slurry charged with submicron ceramic particles. This instrument was used to characterize the permeability of the fibrous reinforcement and the formation of the ceramic cake by filtration of a ceramic particle suspension. Slurries containing different concentrations (10, 25, 33, and 40 vol%) of mono‐dispersed alumina particles were filtered under different pressure conditions (345, 415, 485 kPa) to optimize the cake formation and filling of fibrous reinforcements while controlling the porosity level. Ceramic cakes exhibited an average permeability of 1.0 × 10−17 m2 while the manufactured all‐oxide composites resulted in a permeability of 0.6 × 10−17 m2. Furthermore, a mathematical model based on Darcy's law was developed in this study to predict the rate of filtering and cake formation during injection using the permeability and filtration data measured with the experimental device. This mathematical model allows to determine the filtration time to produce a dense ceramic composite with an accuracy of ±15%, which corresponds to an error of less than 0.1 mm on the thickness of formed CMC.

Modeling of fouling in cross‐flow microfiltration of suspensions

Cross‐flow filtration of fine suspensions through microsieves occurs in microprocessing. The interaction of particles with surfaces in microenvironments has been extensively studied, but predominantly in monolayers and not with an eye to microfiltration. Here, we introduce a microfiltration model that pertains to particles that might be seen as fine in a macroscopic environment, but are large enough to intrude significantly into the shear layer of a microchannel. Thus, particle accumulation upon the sieve couples the steady‐state filtrate flux and the suspension flow through the microchannel that feeds the sieve. We envision and create a stable, stationary multilayer of particles whose thickness is shear‐limited and we identify and verify the structure and parameters that limit steady filtration in this environment. At first, a packed bed of particles forms, growing into and regulated by the micro channel's shear flow. A critical shear stress is shown to determine the thickness of the bed, seen as a stationary and stable multilayer of particles through which filtration may occur. As the bed thickens, at the expense of channel area for suspension flow, surface shear stress increases until no further particle adherence is possible. We built a simple example using hard noninteracting polymer microspheres and conducted cross‐flow filtration experiments over Aquamarijn™ microsieves (uniform pore size of 0.8 μm). We observed a steady cake‐layer thickness and because of the simple geometry afforded by uniform spheres, we could approximate the force balance, cake resistance, and filtration rate from first principles. The good fit of our data to the proposed mechanism lays a firm basis for the semiquantitative analysis of the behavior of more complex suspensions. © 2018 American Institute of Chemical Engineers AIChE J, 65: 207–213, 2019