Particle Deposition Experiments Research Articles

Comprehensive adhesion model based on the surface characteristics of the coal particles

A comprehensive model for the adhesion of coal ash or char particle was established in this study, which includes the particles’ properties and slag layer. The physical properties of the particles include their kinetic parameters and surface characteristics. The particle surface characteristics, such as particle ash ratio and melting fraction, play an important role in particle adhesion. A sub-model of adhesion probability, constructed based on particle surface properties, was also introduced as a part of this comprehensive model. The particle adhesion propensity was determined by considering the kinetic energy criterion of the particles. The model was validated using two sets of particle deposition experiments at different temperatures. Discussion of the model shows that, when the particle kinetic energy is within the medium range, more significant than the critical velocity and less than the critical kinetic energy required to overcome viscosity or surface tension, the particle adhesion is determined by the probability corresponding to the surface characteristics. Furthermore, it is found that the adhesion probability increases with ash-carbon ratio and carbon conversion, and exhibits different trends above and below the flow temperature.

Influence of chemical nature of carrier materials on the dissolution behavior of racemic ibuprofen

The poor aqueous solubility of ibuprofen due to its hydrophobicity limits the bioavailability of the drug in the aqueous environment of the human body. Therefore particle deposition experiments were performed with ibuprofen and different carrier materials. Furthermore, the dissolution behavior of the untreated ibuprofen and the ibuprofen loaded carriers has been investigated at 310K and pH=2.0 and pH=5.5.The results of this investigation demonstrate that drug loadings up to 50 wt% drug onto silica materials could be achieved and that the drug loading increases nearly linear with increasing surface area of the silica materials. Furthermore, the study reveals that the highest dissolution rate was obtained with β-cyclodextrin and that the dissolution rate of all materials investigated increases with increasing pHvalue.

Experimental and CFD study of particle deposition on the outer surface of vortex finder of a cyclone separator

Based on the industrial background of carbonaceous deposition in secondary cyclone separators of FCC units, this paper focuses on particle deposition pattern and investigation of factors on deposition on the outer surface of vortex finder of secondary cyclone. Particle deposition experiments were carried out with a 500mm-diameter cyclone in a cold-model pilot test platform. Deposition patterns were obtained under different inlet gas velocities, particle concentrations and experimental materials etc. Furthermore, discrete phase model (DPM) was applied to obtain particles distribution in the annular space and the effect of particle properties and operational conditions on mass of deposited particles was also investigated. In addition, Gas shielding method was preliminarily explored to avoid particle deposition. The results will provide experimental evidence for analyzing the deposition process and help to further understand the deposition mechanism.

Particle deposition on the patterned membrane surface: Simulation and experiments

Mitigation of membrane fouling is important for the sustainable operation of waste-water treatment. A wide range of physical, chemical and biological anti-fouling techniques has been proposed to reduce membrane fouling. Through these efforts, patterned membranes on which micro-sized surface patterns are engraved are known to exhibit effective anti-fouling performance without any chemical or biological treatment. To optimize anti-fouling properties of patterned membranes, particle deposition on the patterned membrane surface needs to be understood. In this study, both Brownian dynamics simulation and particle deposition experiments were conducted to understand the mechanism of particle deposition on the patterned membrane surface. A model experimental system was developed, in which poly(methyl methacrylate) (PMMA) colloidal suspension was pumped into a microfiltration module containing a patterned membrane. Stagnant flow zone was formed in the valley region of the surface pattern, in which more particles were deposited. High shear stress was distributed near the apex region, where few particles were deposited. Both the simulation and the experimental results confirmed these observations. Flow characteristics near the patterned membrane surface were found to be strongly correlated with the particle deposition. This study will provide a useful insight for the design of efficient micro-structured membranes.

Ionic Strength Dependent Transport of Microparticles in Saturated Porous Media: Modeling Mobilization and Immobilization Phenomena under Transient Chemical Conditions

This study investigates ionic strength dependent deposition and release of microparticles in saturated porous media. Controlled micrometer-sized particle deposition experiments were conducted, followed by stepwise modifications in porewater chemistry to induce retained particle mobilization. A transient dual site transport model was tested against deposition and release, systematically addressing the effect of variations in solution ionic strength by coupling the equations for colloid transport with that for solute transport. The attachment and detachment coefficients of the model equations were explicitly tied to the salt concentration through proposed empirical functions, derived from experimental and theoretical considerations. Two regimes of attachment (and detachment) were hypothesized, showing favorable behavior beyond modeled values of a critical deposition concentration (and critical release concentration). Blocking phenomena were accounted for as well. This work shows how the intimate inclusion of salt concentration in a unique model equation system is able to describe both deposition and release behaviors of the particles under transient chemical conditions.

Characterization of poly(ethylene imine) layers on mica by the streaming potential and particle deposition methods

Deposition kinetics of polystyrene latex (averaged particle size of 0.66 μm) on mica covered by poly(ethylene imine) (PEI), a cationic polyelectrolyte having an average molecular mass of 75,000 g mol −1, was studied using the impinging-jet method. The hydrodynamic radius of PEI, determined by PCS measurements, was 5.3 nm. The electrophoretic mobility of PEI was measured as a function of pH for ionic strengths of 10 −3 and 10 −2 M, which made it possible one to determine the amount of electrokinetic charge of the molecule and its zeta potential. Formation of the polyelectrolyte layer on mica was followed by measuring the streaming potential in the parallel-plate channel. From these measurements, the dependence of the apparent zeta potential of mica on the surface coverage of PEI was determined. The amount of adsorbed PEI on mica was calculated from the convective diffusion theory. These results were quantitatively interpreted in terms of the theoretical model postulating a particle-like adsorption mechanism for PEI with not too significant shape deformation upon adsorption. On the other hand, the Gouy–Chapman model postulating the adsorption in the form of flat disks was proved inappropriate. After the surface was fully characterized, particle deposition experiments were carried out with the aim of finding the correlation between the polymer coverage and the initial rate of latex particle deposition. In the range of small polyelectrolyte coverage, a monotonic relation between the polymer coverage and the initial deposition rate of particles, as well as the jamming coverage, was found. For Θ PEI > 0.25 , the initial particle deposition rate attained the value predicted from the convective diffusion theory for homogeneous surfaces. These results were interpreted theoretically by postulating that an effective immobilization of colloid particles occurred on local polyelectrolyte assemblages containing between two and three PEI molecules.

Polyelectrolyte adsorption layers studied by streaming potential and particle deposition

Adsorption of a cationic polyelectrolyte, polyallylamine hydrochloride (PAH), having a molecular weight of 70,000 on mica was characterized by the streaming potential method and by deposition of negative polystyrene latex particles. Formation of PAH layers was followed by determining the apparent zeta potential of surface ζ as function of bulk PAH concentration. The zeta potential was calculated from the streaming potential measured in the parallel-plate channel formed by two mica plates precovered by the polyelectrolyte. The experimental data were expressed as the dependence of the reduced zeta potential ζ / ζ 0 on the PAH coverage Θ PAH , calculated using the convective diffusion theory. It was found that for the ionic strength of 10 −2 M, the dependence of ζ / ζ 0 on Θ PAH can be reflected by the theoretical model formulated previously for surfaces covered by colloid particles. The electrokinetic measurements were complemented by particle deposition experiments on PAH-covered mica surfaces. A direct correlation between the polymer coverage and the initial deposition rate of particles, as well as the jamming coverage, was found. For Θ PAH > 0.3 the initial deposition rate attained the value predicted from the convective diffusion theory for homogeneous surfaces. The initial deposition rates for surfaces modified by PAH were compared with previous experimental and theoretical results obtained for heterogeneous surfaces formed by preadsorption of colloid particles. It was revealed that negative latex deposition occurred at surfaces exhibiting negative apparent zeta potential, which explained the anomalous deposition of particles observed in previous works. It was suggested that the combined electrokinetic and particle deposition methods can be used for detecting adsorbed polyelectrolytes at surfaces for coverage range of a percent. This enables one to measure bulk polyelectrolyte concentrations at the level of 0.05 ppm.

Coupled Influence of Colloidal and Hydrodynamic Interactions on the RSA Dynamic Blocking Function for Particle Deposition onto Packed Spherical Collectors

The influence of electrostatic double-layer and hydrodynamic interactions on random sequential adsorption (RSA) of colloidal particles onto packed spherical collectors was investigated using inverse analysis of colloid breakthrough data obtained from well-controlled particle deposition experiments. Deposition experiments were carried out using monodisperse aqueous suspensions of positively charged latex colloids and packed columns of negatively charged uniform glass beads for different combinations of ionic strength, particle size, and approach velocity. From the experimental particle breakthrough data, the initial particle deposition rates and the virial coefficients of the dynamic blocking function based on RSA mechanics were determined. The magnitudes of the virial coefficients were observed to increase from the hard sphere values with increasing flow rates and decreasing ionic strengths of the background electrolyte. Particle size also plays a significant role in governing the deposition dynamics. The deviation from the hard sphere RSA behavior becomes more prominent for larger particles.

Dynamics of Silica Colloid Deposition and Release in Packed Beds of Aminosilane-Modified Glass Beads

The transport and deposition dynamics of colloidal particles in packed porous media were investigated. The colloids were negatively charged silica particles (0.1 and 0.3 μm in diameter), and the packed-bed columns comprised aminosilane-modified glass beads. The glass beads acquired a positive surface charge by anhydrous chemical reaction with aminoethyl(N-aminopropyl)dimethoxymethylsilane. Maximum attainable surface-coverage (θmax) and excluded-area-parameter (β) values were determined for particle deposition experiments under various physicochemical conditions, namely, solution ionic strength, flow velocity, and particle size. The results demonstrated that excluded-area-parameter values increased with decreasing ionic strength and increasing flow velocity and particle size. Observed excluded-area-parameter values smaller than 1.83, the hard-sphere jamming limit according to random-sequential-adsorption (RSA) mechanics, alluded to the occurrence of multilayer deposition. The release of deposited particles after complete breakthrough was also investigated by reducing the ionic strength of the solution and by reversing the collector surface charge with an anionic surfactant (sodium dodecyl sulfate). Because colloid release was predominantly observed following deposition runs with higher values of surface coverage, which suggested the possible presence of multilayer deposition, it could be inferred that particle−particle repulsion was mainly responsible for the observed colloid release.

Effect of Particle Size on the Kinetics of Particle Deposition under Attractive Double Layer Interactions

The effect of particle size on the kinetics of particle deposition in the presence of attractive double layer interactions has been studied theoretically and experimentally. Particle deposition experiments were carried out with several model suspensions of positively charged latex particles and negatively charged glass beads using the packed bed column technique. The model particles used in the deposition experiments covered a wide size range, from 0.08 to 2.51 μm. Experimental deposition rates were compared to theoretical predictions based on a numerical solution of the convective diffusion equation with colloidal, hydrodynamic, and gravitational forces fully incorporated. Theoretical and experimental results reveal that the enhancement in particle deposition rate (i.e,, the deposition rate in the presence of double layer interaction divided by the rate in the absence of double layer interaction) is dependent on particle size. At low ionic strengths, the enhancement in deposition rate passes through a maximum as the particle size increases. This maximum corresponds to particles with a size around 1 μm. It is also concluded that this maximum is determined by the interplay between the size of the particles and the range of the attractive double layer interactions.

Enhanced deposition to pits: A local food source for benthos

Particle deposition experiments using mimics of biogenous negative relief (“pits”) and low-excess-density particles in a small annular flume indicate a significantly enhanced deposition rate (number of particles per time) compared to smooth, flat patches of the same diameter. This study included flow visualizations as well as observations of particle residence times, particle concentrations in the pits, and particle fluxes to the pits from the main flow. Experimental conditions of particle concentration, shear velocity, and particle settling velocity mimicked the dynamic characteristics (low excess density and large size) of organic-rich floes and flow conditions in the subtidal and deep sea where biogenous pits are common features. Results suggest that pits provide benthic organisms an important capture mechanism for such floes. Flow visualizations concur qualitatively with previously reported results for twodimensional cavity flow, with unique features due to the conical shape of the pits. When the Rouse number (settling velocity/shear velocity) was much less than 1, pit deposition rate increased with increasing pit aspect ratio (AR = depth/diameter; ranging from 0.25 to 2) and always exceeded deposition to a flat patch of comparable diameter. For the single aspect ratio tested (AR = 0.5) under conditions of increasing turbulence, deposition to the pit increased under transitional flow, but then decreased to near zero when conditions reached fully rough flow. Relative enhancement of deposition to this pit decreased with increased ambient bed roughness since grave1 beds also effectively collect particles. Particle concentration inside pits decreased weakly with pit aspect ratio but greatly increased with increasing roughness Reynolds number. Particle residence time increased somewhat with pit aspect ratio but decreased significantly with increasing roughness Reynolds number. Particle flux into pits from the main flow increased with both increasing aspect ratio and increasing roughness Reynolds number. Enhancement of food supply to pit inhabitants thus depends on the flow regime.

Theoretical and experimental study of particle transport in vacuum chambers

Particle deposition models applicable to low pressure were developed by incorporating known pressure dependencies into well established atmospheric deposition models. Contributions by various particle deposition mechanisms such as sedimentation, diffusion, and other external forces are accounted for in the particle deposition model. Particle deposition experiments were conducted at both the University of Duisburg (UD) and the Research Triangle Institute (RTI). Each organization used its own customized vacuum chamber and differing methods of particle generation and detection. Results from both experimental setups are compared with the deposition models to assess the capability of the models in describing particle deposition in semiconductor vacuum processing equipments.

Measurement of particle deposition on wafers in vacuum chambers

To determine the applicability of electrical fields to control particle deposition on wafers in vacuum chambers, particle deposition experiments were conducted in an idealized vacuum chamber and in an e-beam evaporator in the metallization section of the fab line of the Microelectronics Center of North Carolina (MCNC). For the evaporator, particles created naturally during the pumpdown and venting operation of the chamber were used to measure particle deposition on wafers. Bias voltages were applied to the wafer to control particle deposition during pumpdown and venting. In the idealized chamber, monodisperse particles of known size, charge, and concentration, generated at low pressres by a modified Vibrating Orifice Aerosol Generator (VOAG), were used to cant' out particle deposition experiments. The effectiveness of do deflection plates in minimizing particle deposition on wafers was studied in this chamber. Results from both chambers and the predictions from a two dimensional, particle deposition model for a low pressure chamber are presented here.