•The permeation of O/W emulsion through a coalescing filter was numerically studied.•A simulation model was developed based on the free-energy lattice Boltzmann method.•The effects of filter ...properties on the coalescing behaviors were investigated.•Our simulations demonstrated the effectiveness of the bilayer structure of filters.
The permeation of an oil-in-water (O/W) emulsion through a coalescing filter was numerically studied using the lattice Boltzmann method (LBM). A numerical simulation model for the coalescing phenomena was developed based on the free-energy LBM. We investigated the effects of the wettability of fibers, filter porosity, and fiber diameter on the coalescing behaviors by performing two-dimensional permeation simulations for the O/W emulsions through modeled fibrous filters. We mainly focused on hydrophilic filters because they did not generate small secondary droplets during oil droplet detachment from the filter, and this is preferred for precise separation of oil and water. Our simulations demonstrated that filters with larger pore spacings enable formation of larger droplets but allow more droplets to pass without coalescing. To solve this problem, we designed bi-layered filters composed of a small-pore filter to accurately catch the droplets and a large-pore filter to enlarge the droplets; we demonstrated the effectiveness of the bilayer structure for membrane coalescence.
We present a three-dimensional phase-field simulation of membrane porous structure formation via spinodal decomposition by the thermally induced phase separation (TIPS) method. The free energy of the ...polymer solution system was described based on the Flory–Huggins theory, and the mobility was calculated from the solvent self-diffusion coefficients estimated by the free-volume theory of Vrentas and Duta. We explored the effects of initial polymer concentration, quench temperature, and gradient energy parameter on the membrane morphology evolution. The initial domain size increased with the decreasing driving force for the spinodal decomposition and the increasing contribution of the gradient energy to the total energy. The morphology evolution during the intermediate and late stage of spinodal decomposition also depended on the membrane morphology formed at the initial stage, such as bicontinuous or droplet structures. We also simulated the membrane formation under the influence of a polymer concentration gradient in the TIPS process. The polymer concentration gradient led to the formation of membranes with anisotropic pore structures.
•We conducted a phase-field simulation of membrane formation via the TIPS process.•Driving force for the SD affected the membrane morphology.•The contribution of the gradient energy term affected the membrane morphology.•Morphology evolution during the late stage of SD depended on membrane morphology.•Polymer concentration gradient led to the formation of anisotropic membranes.
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•Particulate flow passing through membrane pore was numerically studied.•A simulation model was developed based on LBM and DEM.•The effects of rolling friction on pore clogging ...behavior were investigated.•Permeation of suspensions including two types of particles was investigated.•A few particles with a large friction coefficient potentially accelerate clogging.
We present simulations showing the particulate flows passing through a single membrane pore under a dead-end and constant-pressure condition. We investigate the effects of the rolling friction acting on particles and the particle concentration on the pore clogging phenomena. A decrease in the rolling friction coefficient of particles shifts the clogging position toward the permeate side and decelerates the permeating flux decline. This effect of the rolling friction coefficient decreases with increasing particle concentration. Furthermore, we simulate the permeation of two-component suspensions, which include two types of particles with large and small rolling friction coefficients. The small number of particles with a large friction coefficient drastically accelerate the pore clogging because they first deposit near the pore entrance and trap subsequent particles. This result indicates that particles that are less accumulated on the membrane under a single-component condition may be primary foulants in a multicomponent system.
Owing to the limitations of visualization techniques in experimental studies and low-resolution numerical models based on computational fluid dynamics (CFD), the detailed behavior of oil droplets ...during microfiltration is not well understood. Hence, a high-resolution CFD model based on an in-house direct numerical simulation (DNS) code was constructed in this study to analyze the detailed dynamics of an oil-in-water (O/W) emulsion using a microfiltration membrane. The realistic microporous structure of commercial ceramic microfiltration membranes (mullite and α-alumina membranes) was obtained using an image processing technique based on focused ion beam scanning electron microscopy (FIB-SEM). Numerical simulations of microfiltration of O/W emulsions on the membrane microstructure obtained by FIB-SEM were performed, and the effects of different parameters, including contact angle, transmembrane pressure, and membrane microporous structure, on filtration performance were studied. Droplet deformation had a strong impact on filtration behavior because coalesced droplets with diameters larger than the pore diameter permeated the membrane pores. The permeability, oil hold-up fraction inside the pores, and rejection were considerably influenced by the contact angle, while the transmembrane pressure had a little impact on the permeability and oil hold-up fraction. The membrane structure, especially the pore size distribution, also had a significant effect on the microfiltration behavior and performance.
In this study, we investigated the permeation behavior of particles through a polyphenylene sulfide (PPS) fibrous filter using a numerical simulation approach. To represent realistic flow inside the ...filter during simulation, voxel data obtained from X-ray computed tomography (CT) images of the PPS filter microstructure were used. To calculate the contact force between the particle and the fiber surface, we propose a new method to create a signed distance function (SDF) of the PPS filter structure by utilizing the phase-field model and the level set method. Our method successfully constructs SDF from the complex filter microstructures created from the X-ray CT images. As a demonstration of the application of this method, the permeation of four particles through a realistic filter microstructure was simulated. The effect of the filter microstructure, such as the fiber orientation and porosity, on the permeation behavior of the particles was investigated using several filter domains. Our simulations demonstrate that the behavior of the particles in contact with the fiber surface can be reasonably described by applying SDF. The particles tend to contact the fibers oriented perpendicularly to the main flow direction rather than the fibers oriented parallelly. In addition, particles remain inside lower porous filter domains for longer durations because of an increase in the probability of contact with the fiber surfaces.
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•We developed a method to create signed distance function (SDF) from X-ray CT images of fibrous filter.•The method utilized phase-field model and level set method.•Our model successfully calculated the contact between particles and filter media.•The particles tend to contact the fibers perpendicular to the main flow direction.
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•Cake formation in cross-flow microfiltration was numerically studied.•Our simulation model used lattice Boltzmann method and discrete element method.•The effects of attractive forces ...and particle concentrations were studied.•The attractive force between particles affected the cake layer growth.•The effects of particle concentration depended on the attractive interactions.
We present a two-dimensional simulation model to explore cake formation in cross-flow filtration. The model uses the lattice Boltzmann method (LBM) for fluid computation and the discrete element method (DEM) for particle computation; they were fully coupled with the smoothed profile method. We verified our model by simulating filtration under different transmembrane pressures. We then investigated the effects of attractive forces and particle concentration on the cake formation mechanism. Generally, as the attractive interaction and particle concentration increased, the particles formed a cake layer with a looser body and rough surface, due to the decrease in the mobility of the particles in contact with the cake surface. It is concluded that the effects of particle concentration are affected by the different conditions of attractive interactions between the particles.
Cluster arrays composed of metal nanoparticles are promising for application in sensing devices because of their interesting surface plasmon characteristics. Herein, we report the spontaneous ...formation of cluster arrays of gold colloids on flat substrates by vertical-deposition convective self-assembly. In this technique, under controlled temperature, a hydrophilic substrate is vertically immersed in a colloid suspension. Cluster arrays form when the particle concentration is extremely low (in the order of 10–6–10–8 v/v). These arrays are arranged in a hierarchically ordered structure, where the particles form clusters that are deposited at a certain separation distance from each other, to form “dotted” lines that are in turn aligned with a constant spacing. The size of the cluster can be controlled by varying the particle concentration and temperature while an equal separation distance is maintained between the lines formed by the clusters. Our technique thus demonstrates a one-step, template-free fabrication method for cluster arrays. In addition, through the direct observation of the assembly process, the spacing between the dotted lines is found to result from the “stick-and-slip” behavior of the meniscus tip, which is entirely different from the formation processes observed for the striped patterns, which we reported previously at higher particle concentrations. The difference in the meniscus behavior possibly comes from the difference in colloidal morphology at the meniscus tip. These results demonstrate the self-regulating characteristics of the convective self-assembly process to produce colloidal patterns, whose structure depends on particle concentration and temperature.
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•We synthesized Fe3O4/SiO2 core/shell particles functionalized with polyelectrolytes.•Grafted PNaAA provides a high osmotic pressure required to transport water.•SiO2 shell enables ...chemical immobilization of PNaAA on the particle surface.•Synthesized particles can be used as a draw solute for FO membrane processes.
The forward osmosis (FO) membrane separation process is one of the emerging membrane technologies that can meet the increasing global demand for clean water. We synthesize the Fe3O4/SiO2 core/shell particles functionalized with sodium polyacrylate (PNaAA) as a draw solute, which generates the driving force to transport water through an FO membrane in this process. The Fe3O4 core enables the recovery and dispersion of the particles using a magnetic field, while the grafted PNaAA provides the high osmotic pressure required to transport water. Preparing an SiO2 shell over the Fe3O4 core of the particles enables the chemical immobilization of the PNaAA on the particle surface and increases their stability as a draw solute. Here, Fe3O4 core particles with a controlled size of the submicron-meter order are prepared by a solvothermal method, followed by the formation of the SiO2 shell. Subsequently, the Fe3O4/SiO2 core/shell particles are modified with PNaAA using surface-initiated atom transfer radical polymerization (SI-ATRP). The effects of the amount of grafted PNaAA and the particle size on the performance as a draw solute are investigated by conducting osmolality measurements and recovery tests. The synthesized particles are able to maintain a stable dispersion even after ten cycles of assembling/dispersing operations.
A computational method for the simulation of particulate flows that can efficiently treat the particle-fluid boundary in systems containing many particles was developed based on the smoothed-profile ...lattice Boltzmann method (SPLBM). In our proposed method, which we call the improved SPLBM (iSPLBM), for an accurate and stable simulation of particulate flows, the hydrodynamic force on a moving solid particle is exactly formulated with consideration of the effect of internal fluid mass. To validate the accuracy and stability of iSPLBM, we conducted numerical simulations of several particulate flow systems and compared our results with those of other simulations and some experiments. In addition, we performed simulations on flotation of many lightweight particles with a wide range of particle size distribution, the results of which demonstrated the effectiveness of iSPLBM. Our proposed model is a promising method to accurately and stably simulate extensive particulate flows.
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