Simulation of particle deposition on filter fiber in an external electric field

Particle deposition onto a filter fiber was numerically simulated when a uniform external electric field was applied. The effects of electric field strength, particle inertia, and electrical conductivity of particles on particle deposition characteristics such as particle loading patterns and collection efficiency were qualitatively investigated. As a result, the electrostatic forces between a newly introduced particle and the already captured particles on the fiber were found to have a great influence on the particle deposition patterns compared with the results where the electrostatic forces were neglected. Conductive particles and filter fibers lead to higher collection efficiency and more linear structure of particle deposits than those of dielectrics, and the particle inertia could also be more important to the collection efficiency of a fibrous filter when electric fields are present. The simulated particle deposits obtained from this work agreed well with the existing experimental results, in which the photographs of particle loaded fibers, within an external electric field, were reported.     

Appraisal of three-dimensional numerical simulation for sub-micron particle deposition in a micro-porous ceramic filter

A computational, three-dimensional approach to investigate the behavior of diesel soot particles in the micro-channels of a wall-flow, porous-ceramic particulate filter is presented. Particle size examined is in the PM2.5 range. The flow field is simulated with a finite-volume Navier-Stokes solver and the Ergun equation is used to model the porous material. The permeability coefficients were obtained by fitting experimental data. Particle flow, dispersion, deposition and wall-particle interactions are investigated tracking large swarms of 2 and diameter particles in a Lagrangian frame of reference. Particle dynamics included rarefied gas hypotheses (the Knudsen number being larger than unity) and bounce/capture models based on impact kinetic energy loss. The influence of gas molecules-particle interaction on overall particle behavior is also examined by including Brownian motion and partial slip in particle equation of motion. Simulations help to highlight three-dimensional non-uniform particle deposition, mainly due to flow distribution in the micro-channel. All particles deposit onto the porous filter wall following the distribution of the through-wall velocity. The larger, , particles show a larger tendency to deposit at the end of the filter. Due to the flow contraction at the inlet, virtually no particle deposit in the inlet section of the filter. Reasons for the scarce influence on particle deposition due to particle-flow slip and Brownian motion are given.     

A direct sampling particle filter from approximate conditional density function supported on constrained state space

Constraints on the state vector must be taken into account in the state estimation problem. Recently, acceptance/rejection and projection methods are proposed in the particle filter framework for constraining the particles. A weighted least squares formulation is used for constraining samples in unscented and ensemble Kalman filters. In this paper, direct sampling from an approximate conditional probability density function (pdf) is proposed. It is obtained by approximating the a priori pdf as a Gaussian. The support of the conditional density is a subset of the intersection of two supports, the 3-sigma bounds of the priori Gaussian and the constrained state space. A direct sampling algorithm is proposed for handling linear and nonlinear equality and inequality constraints. The algorithm uses the constrained mode for nonlinear constraints.     

Dendritic deposition of aerosol particles in fibrous media by inertial impaction and interception

When an aerosol of fine solid particles flows through a fibrous filter, particles deposit on fibers and form chainlike agglomerates known as dendrites (see for instance, Fig. 1). These dendritic structures grow relatively unhindered for an initial period of time, but eventually they begin to interfere with each other's growth and to intermesh (Fig. 2). This pattern of deposition has profound effects on the filtration efficiency and pressure drop, both of which increase rapidly with time. Therefore, rational design, optimization, operation, troubleshooting and innovation require intimate understanding and accurate analysis of the dendritic deposition process. A theoretical model of dendritic deposition for the period during which dendrites do not intermesh was developed by Payatakes [1], subject to the assumption that interception is the dominant capture mechanism. In the present work the model is extended to include deposition by inertial impaction and interception, mechanisms which are dominant for particles larger than about 1 μm. The “shadow effect” is also incorporated in the analysis.     

Structure of silane layer formed on silica particle surfaces by treatment with silane coupling agents having various functional groups

The surface treatment of spherical silica particles with silane coupling agents having various organic functional groups was conducted and the effect of the alkoxy group number on the molecular flexibility of the silane chain with multilayer coverage was investigated using ¹H-pulse nuclear magnetic resonance spectroscopy. The silica particles were treated with 2-propanol solution and heated at 120?°C for 24?h after solvent evaporation to accelerate the polycondensation reaction of silanol groups. For multilayer coverage, flexible linear chain and rigid network structures were expected to form on the surface from the di- and trialkoxy structures, respectively. However, the rigid network structure was formed from both the di- and trialkoxy structures with glycidoxy, amino, and methacryloxy functional silanes. Ring opening of the epoxy group occurred, followed by reaction to form the network structure, even with the dialkoxy structure of the glycidoxy functionality. Ring opening of the epoxy group could be reduced by pH adjustment of the treatment solution and the linear chain structure was formed from the dialkoxy structure. In the case of amino and methacryloxy functional groups, hydrogen bonds were formed between the amino or methacryloxy groups and the silanol groups on the silica surface or silane molecules.     

The effect of the contact between platinum and soot particles on the catalytic oxidation of soot deposits on a diesel particle filter

Experiments were performed with two model soot aerosols brought into different forms of contact with Pt aerosol particles, to investigate the effectiveness of this contact in lowering the catalytic soot oxidation temperature. The contact was either generated between individual particles in the aerosol state (Pt-doped soot to simulate a fuel borne catalyst), or by sequential or simultaneous deposition of separately generated soot and Pt aerosols onto a sintered metal filter. (Formation of a soot cake on previously deposited Pt aerosol would simulate a catalyst coated diesel particle filter.) The catalytic activity was determined in all cases from temperature ramped oxidation in air of the filtered particles, and defined as the 50% conversion temperature.

It was found that Pt-doped soot and simultaneously filtered aerosols were both equally effective in reducing the oxidation temperature by up to 140–250 °C for the spark discharge soot (with 3–47 wt% Pt concentration in the soot cake), and by up to 140 °C for the pyrolysis soot (3 wt% Pt). Conversely, the deposition of a thin soot layer of 5–10 μm thickness onto Pt, or vice versa, produced only a slight temperature reduction on the order of about 13–42 °C. These results suggest that the distance between soot and Pt particles plays a key role in promoting an effective oxidation on the filter, which is consistent with the role of Pt particles as local generators of activated oxygen.     

Effects of airway obstruction induced by asthma attack on particle deposition

Two computational models of the airway tree up to six generations deep were reconstructed from computed tomography scans from a single patient. The first scan was taken a day after an acute asthma episode while the second scan was taken 30 days later when the patient had recovered. The reconstructed models were used to investigate the effects of acute asthma on realistic airway geometry, the airflow patterns, the pressure drop, and the implications it has on targeted drug delivery. Comparisons in the geometry found that in general the average increase in diameter was larger in the right airway the airway is larger in diameter than the left side. The average airway branch difference from the Asthma Model to the Recovered Model was found to be 10.4% in the right airway and 4.8% in the left airway; however the airway dilation during the recovery stage was not consistent through the entire branch airway. Instead there were local branches that exhibited a very high local dilation recovery (≈30% recovery). This inconsistent dilation recovery makes it difficult to predict where and how much each branch will recover from an asthma episode. In terms of targeted drug delivery studies in the lung airways, the deposition patterns will be under-predicted for airway models that are reconstructed from a healthy or non-asthma affected lung airway. The discrepancy may reach as high as 13% between the two models for particles ≥10 μm under a turbulent flow. For particles <10 μm, the discrepancy reduces to 1% as the particle size reduces to 1 μm under a turbulent flow. This means that drug delivery studies in the lung airway should consider the effects of airway narrowing and that if a recovered or a healthy airway is used, then the deposition fraction and efficiencies are expected to be under-predicted.     

Fabrication of aluminum nitride coatings by electrophoretic deposition: Effect of particle size on deposition and drying behavior

Electrophoretic technique was used to deposit micro- and nano-sized aluminum nitride coatings on stainless steel surfaces by using a well-dispersed stable suspension produced by addition of AlN powder plus a small amount of iodine to ethanol. Parabolic regime governed the deposition. Electrophoretic deposition for 240 s at 100 V resulted in formation of a uniformly dense film on the top, but a porous inhomogeneous layer at the bottom. This was attributed to fast deposition of coarse particles and/or agglomerates at large electric fields. After drying, micro-sized particles led to a uniform crack-free interface while nano-particles resulted in fragmented non-cohesive layers. Weight loss measurements revealed higher drying rates for micro-layer as compared to nano-cover. This seemed owing to the larger pore sizes and lower specific surfaces of the former. Stress inducement by lateral drying of small capillaries led to crack initiation from the edges and its propagation across the surfaces. This resulted in fragmentation of the samples due to their delamination. Effect of deposition rate on particles packability was also investigated.     

The effect of re-entrainment on particle deposition

The effect of particle removal on observed deposition rates is considered by combining previous sublayer analyses. Wall shear stress is shown to be a controlling parameter; below a critical value where removal can occur, deposition varies linearly with time but above this value the observed deposition rate is dependent on the choice of time interval over which measurements are made. For monodisperse particles, a discontinuity in deposition plot is predicted although this may be smoothed out for particles with a wide size distribution. It is suggested that the measurement of the critical wall shear stress may be useful for estimating adhesion forces under dynamic conditions such as occur for redeposition problems.The functional dependence of deposition on wall shear stress for combined deposition and removal has been derived for the cases where diffusional, inertial and gravitational forces are dominant. Comparison with data from the literature confirms the general trends but precise matchings have not been attempted.     

Gas marbles: ultra-long-lasting and ultra-robust bubbles formed by particle stabilization

Bubbles and foams are ubiquitous in daily life and industrial processes. Studying their dynamic behaviors is of key importance for foam manufacturing processes in food packaging, cosmetics and pharmaceuticals. Bare bubbles are inherently fragile and transient; enhancing their robustness and shelf lives is an ongoing challenge. Their rupture can be attributed to liquid evaporation, thin film drainage and the nuclei of environmental dust. Inspired by particle-stabilized interfaces in Pickering emulsions, armored bubbles and liquid marble, bubbles are protected by an enclosed particle-entrapping liquid thin film, and the resultant soft object is termed gas marble. The gas marble exhibits mechanical strength orders of magnitude higher than that of soap bubbles when subjected to overpressure and underpressure, owing to the compact particle monolayer straddling the surface liquid film. By using a water-absorbent glycerol solution, the resulting gas marble can persist for 465 d in normal atmospheric settings. This particle-stabilizing approach not only has practical implications for foam manufacturing processes but also can inspire the new design and fabrication of functional biomaterials and biomedicines.     

Sonochemical deposition of silver nanoparticles on wool fibers

Silver nanoparticles were deposited on the surface of natural wool with the aid of powered ultrasound. The average particle size was 5–10 nm, but larger aggregates of 50–100 nm were also observed. The sonochemical irradiation of a slurry containing wool fibers, silver nitrate, and ammonia in an aqueous medium for 120 min under an argon atmosphere yielded a silver–wool nanocomposite. By varying the gas and reaction conditions, we could achieve control over the deposition of the metallic silver particles on the surface of the wool fibers. The resulting silver‐deposited wool samples were characterized with X‐ray diffraction, transmission electron microscopy, high‐resolution transmission electron microscopy, high‐resolution scanning electron microscopy, electron‐dispersive X‐ray analysis, Brunauer, Emmett, and Teller physical adsorption method, X‐ray photoelectron spectroscopy, and Raman and diffused reflection optical spectroscopy. The results showed that the strong adhesion of the silver to the wool was a result of the adsorption and interaction of silver with sulfur moieties related to the cysteine group. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1732–1737, 2007     

Effects of air temperature and humidity on particle deposition

Particle deposition in a fully developed turbulent duct flow was studied. The random walk model of Lagrangian approach was used to predict the trajectories of 3000 particles with a density of 900 kg/m³. The effects of thermophoretic force and air humidity were also considered. The results were compared with the previous studies with a particle size range of 0.01–50 μm and air flow velocity of 5 m/s. The profile of dimensionless deposition velocity with relaxation time presents a V-shaped curve and the results are in good agreement with the previous studies.The effects of air temperature and humidity on particle deposition with a particle size of 1 μm were also investigated. The results show that thermophoretic force accelerates particle deposition onto the duct walls with increasing temperature difference between air flow and the duct wall surface. Meanwhile, it was found that particle deposition velocity increases with air humidity.     

Study of deposition technology on spray formed silicon-aluminum alloy

研究了喷射成形硅铝合金(CE11)材料表面化学镀镍和镀金工艺,使用电子显微镜(SEM)及能谱分析仪(EDS)分析了沉积过程中CE11硅铝合金表面形貌和沉积层化学成分,采用热震、高温烘烤、焊接试验等方法检测了硅铝合金样件的镀层质量.结果发现,CE11硅铝合金经氟化氢铵和硝酸混合溶液粗化、超声波去膜、浸锌、预镀镍后化学镀镍,可以获得结合力良好的化学镀层,镀金后能耐400℃烘烤而仍然保持很好的结合力,能够满足金锗、金锡等合金的共晶焊接使用要求.     

Experimental analysis of particle deposition on single collectors

Experimental studies of particle deposition from liquid suspensions of monodispersed particles flowing past single spherical collectors were carried out and compared with theoretical results based on trajectory calculations. The experimental observations indicate the significant effect of particle flocculation and thus suggest the importance of sedimentation as a collection mechanism. The agreement between the theoretical results and the experimental data is good when the surface force interactions are favorable for collection. However, when the electrokinetic repulsion dominates in the neighborhood of the collector, the rate of collection drops rapidly, although not to zero as predicted by theory.