Deposition Of Solid Particles Research Articles

Warm Spraying: An improved spray process to deposit novel coatings

Warm Spray is an atmospheric coating process through continuous impact and deposition of solid particles heated and accelerated by a supersonic jet controlled between 800~1900 K and 900~1600 m s − 1 . This paper introduces successful fabrication of dense and less-oxidized metallic titanium (Ti) coatings by Warm Spray and clarification of phenomena occurring upon the spray process. Temperature and velocity of an in-flight Ti particle were compared between measurement by the diagnostic instrument and calculation based on the fluid dynamics simulation. Deformation behaviour of particle from impact to deposition was analyzed through the finite element method (FEM). Densification of stacking particles was attained by applying bi-modal size distribution to the feedstock Ti powder. Qualitative restriction of changes in chemical composition of Ti coating obtained was demonstrated by elemental analysis and by calculation based on the oxidation model. Warm Spray enables various materials to fabricate coatings without thermal deterioration of the original characteristics such as purity and crystallographic phase.

Modelling film formation and degradation of semi-transparent exterior wood coatings

Deposition and aggregation of small solid particles are encountered in many natural and industrial environments. These processes are of substantial significance for the development of a coating film on a wooden substrate. Formulating new coatings with improved performance and lower cost for exterior wooden joinery, mainly a trial-and-error approach, has a large influence on the initial film forming stage in a coating's life. Therefore modelling can supply insight in the particle–particle–substrate interaction. Two approaches are proposed. The first one uses a random point process to position the cluster centres and particles in a dry film. The second strategy starts with a random scattering of the particles in a wet film followed by Monte Carlo sampling and subsequently minimization of the total energy of the particle system. Surface roughness and gloss are calculated from the simulated surface structure. Next to these simulations, surface reconstruction of coated wood with confocal scanning laser microscopy (CSLM) is used to obtain surface roughness values and deduction of gloss applying the bidirectional reflection distribution function (BRDF) theory. As semi-transparent systems are the subject of gloss calculation on surfaces measured by CSLM and computer simulation, refractive index is estimated using an analytical solution of the reflectance and transmittance problem. Withal, coating and subsequent degradation simulation can become a valuable tool for screening purposes.

A numerical study of particle wall-deposition in a turbulent square duct flow

The deposition of dense solid particles in a downward, fully developed turbulent square duct flow at Re τ = 360, based on the mean friction velocity and the duct width, is studied using large eddy simulations of the fluid flow. The fluid and the particulate phases are treated using Eulerian and Lagrangian approaches, respectively. A finite-volume based, second-order accurate fractional step scheme is used to integrate the incompressible form of the unsteady, three-dimensional, filtered Navier–Stokes equations on an 80 × 80 × 128 grid. A dynamic subgrid kinetic energy model is used to account for the unresolved scales. The Lagrangian particle equation of motion includes the drag, lift, and gravity forces and is integrated using the fourth-order accurate Runge–Kutta scheme. Two values of particle to fluid density ratio ( ρ p/ ρ f = 1000 and 8900) and five values of dimensionless particle diameter ( d p/ δ × 10 6 = 100, 250, 500, 1000 and 2000, δ is the duct width) are studied. Two particle number densities, consisting of 10 5 and 1.5 × 10 6 particles initially in the domain, are examined. Variations in the probability distribution function (PDF) of the particle deposition location with dimensionless particle response time, i.e. Stokes number, are presented. The deposition is seen to occur with greater probability near the center of the duct walls, than at the corners. The average streamwise and wall-normal deposition velocities of the particles increase with Stokes number, with their maxima occurring near the center of the duct wall. The computed deposition rates are compared to previously reported results for a circular pipe flow. It is observed that the deposition rates in a square duct are greater than those in a pipe flow, especially for the low Stokes number particles. Also, wall-deposition of the low Stokes number particles increases significantly by including the subgrid velocity fluctuations in computing the fluid forces on the particles. Two-way coupling and, to a greater extent, four-way coupling are seen to increase the deposition rates.

Formation Damage vs. Solid Particles Deposition Profile During Laboratory-Simulated Produced-Water Reinjection

SummaryThe importance of produced water reinjection (PWRI) is unquestionable. It is in many cases the cheapest and most environmentally friendly solution for wastewater disposal. It is also a feasible method for enhanced oil recovery (EOR) as a waterflooding mechanism.PWRI, however, suffers from a major limitation, which is the current inability in accurately predicting the lifespan and performance of its injection wells. This is because of the multitude of parameters that affect it. Current models1,2 that incorporate the thermal effects3 of PWRI leading to fracture growth exist. However, the leakoff pattern of this injection differs from that of clean water (seawater) injection because of the damage caused by the produced water to the formation, especially to the fracture faces. Thus, static filtration experiments with refined post-mortem analysis have been conducted to obtain quantitative deposition profiles along the core. This allows for the testing and verification of existing models.4–8The post-mortem analysis introduced in this paper will be used for future dynamic filtration experiments as well as experiments specifically devised to simulate the fracture tip area. A unified model that will accurately reproduce the permeability decline and deposition profile for all three sets of experiments will follow, thus advancing the predictability of injectivity decline associated with PWRI.The purpose of this paper is to provide a detailed description of the post-mortem analysis, while rigorous testing of the existing heuristic models (for instance, Wennberg and Sharma6 and Bedrikovedski et al.7) will be published in the near future.9

Piezoelectric droplet ejector for ink-jet printing of fluids and solid particles

In this article, we present a technique for the deposition of inks, organic polymers, and solid particles, using a fluid ejector. The ejector design is based on a flextensional transducer that excites axisymmetric resonant modes in a clamped circular plate. It is constructed by bonding a thin piezoelectric annular disk to a thin edge clamped circular plate. Liquids or solid particles are placed behind one face of the plate which has a small orifice (50–200 μm diameter) at its center. By applying an ac signal across the piezoelectric element, continuous or drop-on-demand ejection of photoresist (Shipley Microposit S1400-21, S1400-27, S1805, and S1813), oil-based ink, water, or talcum powder [Mg3Si4O10(OH)2] has been achieved. Successful deposition of a photoresist has been accomplished without spinning, and thus without waste. A boundary integral method was used to numerically simulate drop formation from the vibrating orifice. Simulations have been used to optimize ejection performance.

Controlled ink-jet printing and deposition of organic polymers and solid particles

In this letter, we present a technique for the deposition of inks, organic polymers and solid particles, using a fluid ejector. The ejector design is based on a flextensional transducer that excites axisymmetric resonant modes in a clamped circular membrane. It is constructed by bonding a thin piezoelectric annular ring to a thin, edge supported, circular membrane. Liquids or solid particles are placed behind one face of the membrane which has a small orifice (50–200 μm diam) at its center. By applying an ac signal across the piezoelectric element, continuous or drop-on-demand ejection of photoresist (Shipley Microposit S1400-21, S1400-27, S1805, and S1813), oil-based ink, water, or talcum powder [Mg3Si4O10(OH)2] has been achieved. Successful deposition of photoresist has been accomplished without spinning, and thus without waste. Patterning of 10 μm features, by baking, exposure, and developing, has revealed no defects in the deposition process. A boundary integral method was used to numerically simulate drop formation from the vibrating orifice. Simulations have been used to optimize ejection performance.

Erosion and deposition of solid particles in porous media: Homogenization analysis of a formation damage

The aim of the paper is to model at a large scale, the formation damage in porous media by erosion and deposition of solid particles. We start from the equations governing the pore-scale processes of erosion, deposition, convection and diffusion. The macroscopic equivalent behaviour is investigated by using a homogenization method. Four characteristic models with different dominating phenomena at the pore scale are determined. The main results are twofold: first dispersion-deposition and dispersion-erosion phenomena are shown at the macroscopic scale for peculiar values of the dimensionless numbers; furthermore, and contrarily to phenomenological models, erosion and deposition generally occur in regions of intense and slow flow, respectively.

Numerical analysis of motion and deposition of particles in cascade impactors

The motion and deposition of small solid particles (1–10 μm) in an idealized six-stage cascade impactor is investigated numerically. The flow of air is simulated using commercial software, and the trajectories of solid particles are predicted by integrating equations of motion that include gravitational forces, inertia and viscous friction. Particle-wall interactions are modeled in terms of a sticking probability and a restitution coefficient. The model correctly predicts the typical S-shaped trapping efficiency curves. As expected, the sticking probability has the greatest impact on trapping profiles. The restitution coefficient has only a very small effect, which becomes negligible for large sticking probability. However, a large unanticipated effect is uncovered by the model. The flow inside the impactor displays large recirculation regions that act as efficient traps of particles of specific sizes. Particles trapped in these regions do not deposit on collection plates, possibly biasing analysis results. This effect, which is magnified at low sticking probabilities, provides an alternative explanation for the ‘wall losses’ reported in several experimental studies that have examined impactors similar to the one studied here.

Simulation of Paraffin Deposition in Reservoirs

Summary Certain reservoirs have a recurring wellbore damage problem caused by deposition of solid paraffin particles in the pore space. This paper describes the simulation of the reservoir processes of paraffin precipitation, convection, and deposition. The effect of reservoir heating treatments is included.

Particle deposition and plugging in tubes and cracks (with special reference to fission product retention)

The main function of a containment structure enclosing a nuclear reactor is to retain any accidental release of radioactive materials. However, if the containment has leak paths due, for example, to cracks or failed seals, then there is the possibility of particulate matter and gas passing through the opening due to the pressure difference. The work presented in this paper describes in some detail the three main steps reqired to assess the amount of gas and particulate matter that pass into the environment. Step one involves calculation of the gas flow through a tube of non-uniform cross sectional area, step two is concerned with the deposition of small solid particles suspended in the host gas, onto the walls of the tube and, in step three, the rate of buildup of deposit on the tube wall is calculated with the aim of determining the rapidity with which the tube is plugged. We recast the gas dynamics equation into a form suitable for calculating gas flow in non-uniform tubes in the laminar and turbulent flow regimes, from low speed up to critical flow conditions. The results of these calculations are compared with an extensive set of experiments and excellent agreement is found. We briefly outline the various deposition processes that particles can undergo on surfaces and show how the particle concentration in the tube may be calculated. Finally, an equation that determines the shape and rate of formation of a plug is developed. This equation is non-linear and integro-differential in nature, and in order to solve it we develope a method which involves prescibing a geometrical plug shape but allowing the parameters within it to be time dependent. Plugging times and the amounts of particulate and gas that have escaped prior to plugging are calculated. Comparison with experiment is made and reasonable agreement found. A general discussion of the shortcomings of the approach is given together with suggestions for further work.

Shear stress induced erosion of filtration cake studied by a flat rotating disk method. Determination of the critical shear stress of erosion

Many authors choose wall shear stress as a fundamental parameters for controlling re-entrainment of particles. Therefore shear stress induced erosion of filtration cake from a colloidal suspension of active carbon is studied using a rotating flat microfiltration membrane. The critical shear stress of erosion, τ* of the macroscopic deposit of solid particles for a given system is thus determined. τ* represents the minimal value of shear stress needed to create erosion. Furthermore the influence of the transmembrane pressure, the thickness of the initial deposit and the pore size on the critical shear stress is investigated and described by empirical fits. Transmembrane pressure and pore size act independently in the same way: the larger they are, the higher τ*. Consequently fouling is more efficiently eliminated at high Δ P m and large pore size.

Modeling of Compressible Cake Filtration

The transport of suspended solid particles in a liquid through porous media has importance from the viewpoint of engineering practice and industrial applications. Deposition of solid particles on a filter cloth or on a pervious porous medium forms the filter cakes. Following a literature survey, a governing equation for the cake thickness is obtained by considering an instantaneous material balance. In addition to the conservation of mass equations for the liquid, and for suspended and captured solid particles, functional relations among porosity, permeability, and pressure are obtained from literature and solved simultaneously. Later, numerical solutions for cake porosity, pore pressure, cake permeability, velocity of solid particles, concentration of suspended solid particles, and net rate of deposition are obtained. At each instant of time, the porosity decreases throughout the cake from the surface to the filter septum where it has the smallest value. As the cake thickness increases, the trends in pressure variation are similar to data obtained by other researchers. This comparison shows the validity of the theory and the associated solution presented. A sensitivity analysis shows higher pressure values at the filter septum for a less pervious membrane. Finally, a reduction in compressibility parameter provides a thicker cake, causes more particles to be captured inside the cake, and reduces the volumetric filtrate rate. The increase of solid velocity with the reduction in compressibility parameter shows that more rigid cakes compress less.

Modelling of transport phenomena in semiconductor processing

Two-dimensional predictions of complex gas flows are presented in this work for various chemical vapor deposition (CVD) processes and crystal pulling from a melt system (Czochralski crystal growth). The model used in the calculations involves momentum, energy and mass conservation equations with corresponding boundary conditions. The structure of convective heat and mass transfer has been studied in vertical CVD reactors with emphasis on their effect on non-uniformity in epüayer thickness and composition. Three kind of CVD reactors with various inlet jet directions and wall temperatures have been considered for typical operating conditions. Strong buoyancy-driven recirculations were found near the susceptor edge in all predictions. Another object for the numerical investigation was the mixed convection in the gas region around a crystal for the encapsulated Czochralski growth. The gas flow over a crystal protects its surface from some negative effects such as a solid particle deposition. Different stages of crystal pulling from a melt have been considered and an improved construction for gas inlets/outlets, based on the numerical results, have been proposed.

水平輸送管路内の堆積層の厚みの算定式 堆積層を伴うスラリーの流動機構に関する理論的考察

With increasing industrial applications of the method of the transporting settling slurries, a better understanding of the mechanism of the slurry flow at lower velocities has become essential. Below the critical deposition velocity Vd of flow, the deposition of solid particles occurs on the bottom of the horizontal pipe. If the deposited particles are sufficient, the plugging of the pipeline can be induced through the large surge of flow or the sudden change of flow conditions, such as a rise in concentration or a drop in velocity V. However, some papers confirm the possibility of the stable flow configuration in pipe despite of a stationary bed.One of the main problems in the hydraulic transport for V < Vd is the assessment for bed thickness h and hydraulic gradient im. The accuracy of one of the factors is interdependent upon that of the other. Since the correlations have been basically proposed by empirical methods, the bed thickness cannot be reasonably well predicted with flow conditions.The purpose of this paper is to derive the general correlation which determine the relationships between the bed thickness and the corresponding flow condition, and to give the procedure for the pipeline design with the aid of the authors' previous results. Based on the concept of the suspension behavior introduced by Bagnold, this paper estimated the normal stress on the particle at the surface of the bed. The flow condition of initial motion of the particle, then, was considered, and thus these theoretical analyses made possible to present the general correlation of h and to simulate the slurry flow for V<Vd. Experimental values obtained were fairly well coincided with the predicted values.The results of this study may be summarized as follows:(1) For a given system and particle properties the Froude number, Fr V/√4gR, is approximately as a function of concentration alone, such as Durand's results for 0.2<hr <0.6, in which hr is the ratio of the bed thickness to the pipe diameter.(2) The predictions for the critical deposition velocity Vd agree with those by Durand for particles greater than 2mm, while for ones less than 1mm both predictions are incompatible with each other, when the equivalent thickness de/2 is substituted for the bed thickness at the initial condition of Vd.(3) The relationship between hydraulic gradient and slurry velocity, which is the im-V cure predicted, shows that the critical velocities are always less than the critical deposit velocities, and considerable care, therefore, should be exercised to determine the practical velocity in the pipeline design.

Note on the experimental measurement of particles embedded in one and two in-line tubes in a high speed gas stream

Solid particle deposition on one and two in-line tubes has been measured. Experiments were conducted in a vertical duct containing the tube(s) oriented perpendicular to the mean flow. Dilute particle concentrations corresponding to 40 or 97 μm glass beads, at mass loading ratios less than 0.007, were investigated. Air approaching the tube(s) at 18.5 m s −1 and 1.4% turbulence intensity was used as the carrier fluid. Various differences observed in the circumferential depositions for the two bead sizes are attributed to the fivefold difference between their respective inertia numbers. In the case of two in-line tubes, the wake of the first substantially alters the deposition characteristics of the second. Some photographic evidence of this effect was obtained.

Studies on microencapsulation. Part IV: Effect of ethylene-vinyl acetate as a coacervation-inducing agent on the production and release behavior of chlorpromazine hydrochloride microcapsules and tabletted microcapsules

A highly water-soluble drug, chlorpromazine hydrochloride, was microencapsulated by phase separation using ethylene-vinyl acetate (EVA) as a coaceruation-inducing agent. The effect of EVA concentration on the preparation, micromeritic and drug release properties of chlorpromazine hydrochloride microcapsules and tabletted microcapsules was studied. Microcapsules were prepared by the deposition of ethyl cellulose round solid chlorpromazine hydrochloride particles, using 0–6% EVA as a coacervation-inducing agent. The particle size of the microcapsules decreased with increasing EVA concentration. The surface topography of the microcapsules became compact and the wall thickness was increased by increasing EVA concentration. Atmospheric stability and powder flowability were also affected by the EVA concentration used. Moreover, the release rate from untabletted or tabletted microcapsules was also influenced by the concentration of EVA. The thicker wall and less porous, more compact surface structure were responsible for the release of drug from untabletted microcapsules. However, the reduced surface area and porosity of the tabletted microcapsules, and the ethyl cellulose content of the insoluble tabletted micro-capsule matrix were important in drug release from tabletted microcapsules.

Longitudinal diffusion of solid particle admixture in a flow through a tube

The propagation of solid particle admixture in a flow through a flat channel is studied. The processes of diffusion and convective transfer as well as solid particle deposition due to gravity result in varying admixture concentration both in depth and longtitudinally. The study of admixture longitudinal distribution is of great interest in a lot of applications, therefore this paper gives the derivation of longitudinal diffusion equation for a mean cross-section admixture concentration. The equation contains three effective parameters; i.e. convective tranfer velocity, longitudinal diffusion coefficient and particle deposition time. These parameters integrally reflect local processes of matter transfer as well as momentum. The proposed model is specific and differs from Taylor equation for longitudinal diffusion, since the fact of particle deposition and adhesion is taken into account. As a result of particle deposition a sediment layer is formed on the channel bottom which increases in thickness with time. To describe this process balance conditions for the whole flow mass and admixture mass on sediment sediment surface are formulated and a condition for matter movement towards the channel bottom is derived that is different from zero due to particle adhesion.

A Pilot Test of Simultaneous Removal of NOx and SOx from the Flue Gas of Coal-Fired Boiler

Simultaneous removal of NOx and SOx from the flue gas was performed under the gas feed rate from 50 to 80Nm3/hr using the slurry liquid of MgSO3-Mg (OH) 2-e (II) edta system in a column packed with “SAN” packing.It was shown that the removal ratio of NOx exceed 90% for liquid-gas ratio above 30kg-liquid/kg-gas. More than 99% of SO2 was removed. It was found that NOx removal ratio can be estimated by means of Porter's equation.As the results, deposition of solid particles in the apparatus does not occur when concentration of solid particles in the slurry liquid is in the range of 2-5%. Any increase in the initial concentration of MgSO3 or Fe (II)-edta increases NOx absorption capacity of the absorbing liquid.NOx absorption capacity of the liquid did not increased so much at O2 cocentration above 5% when the concentration of MgSO3 and Fe (II)-edta in the liquid were increased.

Deposition of solid particles on a collector: Formulation of a new theory

AbstractTwo concepts concerning the deposition of particles from suspension onto a collector, the shadow effect due to deposited particles and the singular and random behavior of approaching particles, are presented and discussed. Based on these concepts, a new theory of particle deposition is proposed and procedures for the simulation of deposition process outlined. The simulation results give the rate of deposition and the deposit morphology. Potential applications of this model to a number of technical problems are outlined.

Effect of preliminary heating on process of explosive deposition of solid particles on flat surfaces

Effect of preliminary heating on process of explosive deposition of solid particles on flat surfaces