Deposition Of Brownian Particles Research Articles

Diffusion deposition of submicron aerosol particles in screen filters

The deposition of submicron aerosol particles on metal screens has been studied at small Reynolds numbers. The obtained experimental data have been compared with theoretical estimates of the deposition of Brownian particles in a model fibrous filter with allowance for a finite particle size and the existence of a Knudsen boundary layer on a wire surface, with the thickness of the layer being, under normal conditions, comparable with particle sizes. The possibility of using screen diffusion batteries for determining the average diffusion coefficient of submicron particles and as test filters has been discussed.

Using the DEM-CFD method to predict Brownian particle deposition in a constricted tube

Modelling of the agglomeration and deposition on a constricted tube collector of colloidal size particles immersed in a liquid is investigated using the discrete element method (DEM). The ability of this method to represent surface interactions allows the simulation of agglomeration and deposition at the particle scale. The numerical model adopts a mechanistic approach to represent the forces involved in colloidal suspensions by including near-wall drag retardation, surface interaction and Brownian forces. The model is implemented using the commercially available DEM package EDEM 2.3®, so that results can be replicated in a standard and user-friendly framework. The effects of various particle-to-collector size ratios, inlet fluid flow-rates and particle concentrations are examined and it is found that deposition efficiency is strongly dependent on the inter-relation of these parameters. Particle deposition and re-suspension mechanisms have been identified and analyzed thanks to EDEM's post processing capability. One-way coupling with computational fluid dynamics (CFD) is considered and results are compared with a two-way coupling between EDEM 2.3® and FLUENT 12.1®. It is found that two-way coupling requires circa 500% more time than one-way coupling for similar results.

Deposition of Brownian particles during evaporation of two-dimensional sessile droplets

Abstract Evaporation of sessile droplets gives rise to internal flow that, in turn, affects drastically the deposition of the suspended particles on the substrate. Analytical expressions for the flow field are used to compute the local velocity inside an evaporating two-dimensional droplet as a function of position and time of evaporation. Trajectories of a sample of suspended Brownian particles are computed along the progress of the evaporation process and terminate upon collision with the solid substrate. Traveling particles are allowed to interact with the evaporating free surface and are either rebounced into the main body of the droplet or float on the surface until they are collected on the substrate. The dependence of the diffusion coefficient on the distance from the substrate is taken into account giving rise to anisotropic diffusional effects that, however, are shown to affect slightly the deposition rate profile except in the case of flow-dominated transport. Results for hydrophilic and strongly hydrophobic substrates are presented and the conditions for the development of the two-dimensional variant of the famous “coffee stain phenomenon” are investigated. Comparison of the simulated deposition profiles with the corresponding predictions of a convection-diffusion lattice–Boltzmann model revealed excellent agreement for various Peclet number values. Simulation of stick-slip evaporation leads to well-defined multiple stripes, the density of which depends strongly on the difference between the initial contact angle and the angle at which the slip step is activated.

A Correlation for the Collector Efficiency of Brownian Particles in Clean-Bed Filtration in Sphere Packings by a Lattice-Boltzmann Method

In this paper, we develop a new correlation for the clean-bed filter coefficient (lambda0) for Brownian particles, for which diffusion is the main deposition mechanism. The correlation is based on numerical Lattice-Boltzmann (LB) simulations in random packings of spheres of uniform diameter. We use LB methods to solve the Navier-Stokes equation for flow and then the advection-diffusion equation for particle transport. We determine a correlation for an "equivalent" single-collector diffusion efficiency, etaD, so that we can compare our predictions to "true" single-collector correlations stemming from unit-cell modeling approaches. We compared our new correlation to experiments on the filtration of latex particles. For small particle diameters, 50 nm < dp < 300 nm, when gravity and interception are negligible, our correlation for etaD predicts measurements better than unit-cell correlations, which overestimate etaD. The good agreement suggests that the representation of three-dimensional transport pathways in porous media plays an important role when modeling transport and deposition of Brownian particles. To model larger particles, for which gravity and interception are important too, we build a correlation for the overall single-collector efficiency eta0 by adding corresponding etaG and nI terms from unit-cell correlations to our etaD model. The resulting correlation predicts experiments with latex particles of dp > 300 nm well.

Effect of particle size distribution on the collection efficiency of Brownian particles

The main purpose of the present paper is to investigate the effect of the normal Gaussian size distribution on the deposition of Brownian particles onto a spherical collector, by applying the Brownian dynamic simulation method and the Kuwabara flow field model with different types of DLVO interaction energy curves and the shadow effect. The simulation results show that the collection efficiency of Brownian particles always increases with a wider particle size distribution region. The same increased tendencies are also observed for the case of increasing Reynolds number and for the case of increasing the particle size to the collector size ratio. When compared to the available experimental data, the present simulation method fits well with the experimental data when the specific deposit per collector is not large.

06/02831 A Lagrangian stochastic model for the dispersion and deposition of Brownian particles in the presence of a temperature gradientLo Iacono, G. and Reynolds, A, M. Journal of Aerosol Science, 2005, 36, (10), 1238–1250.

06/02831 A Lagrangian stochastic model for the dispersion and deposition of Brownian particles in the presence of a temperature gradientLo Iacono, G. and Reynolds, A, M. Journal of Aerosol Science, 2005, 36, (10), 1238–1250.

A Lagrangian stochastic model for the dispersion and deposition of Brownian particles in the presence of a temperature gradient

A Lagrangian stochastic model has been formulated to simulate the dispersion of Brownian (submicron-sized) particles in turbulent flows and their deposition onto adjacent flow boundaries. The model is applied to the prediction of Brownian-particle dispersion and deposition under non-isothermal conditions. Thermophoresis is shown to arise naturally from the modelling approach which is based upon a natural extension of Thomson's (1987, Journal of Fluid Mechanics, 180, 529–556) well-mixed condition. In accordance with results present in the literature, it is found that thermophoresis has a significant impact upon model predictions for the deposition of Brownian particles from fully developed turbulence onto hydraulically smooth surfaces.

Effect of the Energy Barrier of DLVO Theory on the Deposition of Brownian Particles in Porous Media Using the Constricted Tube Model

The deposition problem of colloidal particles in porous media is investigated theoretically by using the Brownian dynamics simulation method. The pore structure was characterized by the constricted tube model, and the effects of the particle size and the total interaction energy curve of the DLVO theory of various shapes on the collection efficiencies of particles are examined. The simulation results show that: (1) a particle size with a minimum collection efficiency exists when the value of Reynolds number is small, and (2) the dimensionless groups, NE1, NE2, NDL, and NLO which characterize the height of the primary maximum and the depth of the secondary minimum in the total interaction energy curve play a major role in determining the collection efficiencies of Brownian particles with low Reynolds numbers. numbers. In addition, when comparing the present model with the available experimental data (Bai and tien, 1999), it is found that the simulation results obtained from the present model coincide more closely with the experimental data than that of the convective diffusion model in the unfavorable deposition region.

Prediction of Brownian particle deposition in porous media using the constricted tube model

The deposition of colloidal particles onto the collector surfaces of porous media is investigated using the Brownian dynamics simulation method. The pore structure in a filter bed was characterized by the constricted tube model. The effects of various shapes of the total interaction energy curves of DLVO theory and the effects of different particle diameters on the collection efficiencies of particles are examined. The simulation results show that the particle collection efficiency is strongly dependent on the geometry of the tube and on the shape of the total interaction energy curve. In a comparison with the available experimental measurements of the filter coefficient, it is found that the present model can give a smaller discrepancy than that of the convective diffusion model in the unfavorable deposition region.

A Lagrangian Stochastic Model for the Dispersion and Deposition of Brownian Particles

A Lagrangian stochastic model for the dispersion and deposition of submicron-size particles is formulated and validated. The model satisfies the well-mixed condition, incorporates molecular diffusivity, and accounts for the effects of Reynolds number upon Lagrangian particle statistics. Reynolds number effects are found to be significant in the viscous sublayer and the buffer zone of a turbulent shear flow. The effects are due almost entirely to the change in the Lagrangian integral time scale. Sawford's correction to first-order Lagrangian stochastic models for the effects of Reynolds number is found to be appropriate for inhomogeneous turbulence even when the Taylor–Reynolds number Rλ ∼ O(0.1). The model predicts, in close accord with experiment and the results of direct numerical simulations, that the nondimensional particle deposition velocity K+ = 0.06Sc−2/3, where Sc is the Schmidt number. When Reynolds number effects are neglected, K+ is overpredicted by several orders of magnitude.

Particle deposition behavior simulated by the stochastic method

The deposition of colloidal particles onto the collector surface in two-dimensional flows is studied using the Brownian dynamics simulation method. By using the Kuwabara model to characterize the flow field, the effects of the total interaction energy curves of various shapes on the collection efficiencies of Brownian particles are examined. The simulation results are tested against published experimental data of the deposition rates of Brownian particles, for the cases of the repulsive double layer interactions (Elimelech, M., O'Melia, R.C., 1990. Effect of particle size on collision efficiency in the deposition of Brownian particles with electrostatic energy barriers. Langmuir, 6 (6) 1153–1163.) and of the attractive double layer interactions (Elimelech, M., 1991. Kinetics of capture of colloidal particles in packed beds under attractive double layer interactions. J. Colloid Interface Sci., 146 (2), 337–352). The simulation results with the Brownian diffusion taken into account in the particle deposition mechanisms give a better fit with these experimental data than that obtained without considering the Brownian diffusion.

Deposition of Brownian particles in the presence of energy barriers of DLVO theory: effect of the dimensionless groups

The problem of deposition of colloidal particles onto a collector surface is investigated theoretically using Brownian dynamics simulations. Using the Kuwabara model for the flow field around the collector surface, we examine the effects of the total interaction energy profiles of the DLVO theory on the collection efficiencies. The simulation results show that: (1) the Brownian diffusion effect of particles becomes pronounced when the value of Reynolds number is close to the laminar flow region, (2) a particle size with a minimum collection efficiency exists, and (3) the dimensionless groups, N L0 , N DL , N E1 and N E2 which characterize the height of the primary maximum and the depth of the secondary minimum in the total interaction energy curve play a major role in determining the collection efficiency of Brownian particles with low Reynolds numbers. In addition, we compare the present theoretical results with the available experimental data [FitzPatrick J. A. and Spielman L. A. (1973) J. Colloid Interface Sci. 43, 350–369], and find that the simulation results obtained from the present model coincide more closely with the experimental data than those results obtained from the case where the Brownain diffusion effect is neglected.

Kinetic coefficients for brownian particle deposition on a filter

Kinetic coefficients for brownian particle deposition on a filter

Brownian particle deposition in a directly simulated turbulent channel flow

Diffusion of submicron particles in a simulated turbulent channel flow field is studied. The turbulent flow velocity field is generated by a direct numerical integration of the Navier–Stokes equation with the pseudospectral method. The equation of motion of particles including the Brownian effects is used and ensembles of particle trajectories are numerically evaluated and statistically analyzed. A uniform initial concentration of particles is used in the analysis. Effects of size on particle dispersion and wall deposition processes are studied. The results are compared with the existing models for the submicron particle deposition rate.

Deposition of Brownian particles in porous media: Modified boundary conditions for the sphere-in-cell model

Modified boundary conditions for solving the convective diffusion equation for Brownian particles as applied in the Happel sphere-in-cell porous medium model are presented. With the modified boundary conditions, the convective diffusion equation correctly predicts the deposition rates of Brownian particles at low Peclet numbers. At moderate and large Peclet numbers, colloid deposition rates are similar to those calculated with existing models.

Dispersion and deposition of Brownian particles from point sources in a simulated turbulent channel flow

The diffusion of Brownian submicrometer-size particles from a point source in a simulated turbulent channel flow field is studied. The turbulent flow velocity field is generated by a direct numerical simulation of the Navier-Stokes equation with the pseudospectral method. The equation of motion of particles including the Brownian effects is used, and ensembles of 8192 particle trajectories are evaluated and statistically analyzed. Effects of particle size, density ratio, and source distance from the wall on the particle concentration profile and wall deposition rate are studied. The results are compared with those obtained from the exact solution to the corresponding convective diffusion equation in the absence of turbulent fluctuations. The relative importance of the Brownian motion and turbulence in the diffusion of small particles near the channel walls is also assessed.

PHASE-SPACE DIFFUSION EQUATIONS FOR SINGLE BROWNIAN PARTICLE MOTION NEAR SURFACES

In numerous physical processes involving the motion of micron and submicron sized particles near surfaces, such as the filtration of hydrosols and aerosols, the particle motion is the net result of the combined effects of fluid convection, external forces, particle inertia, Brownian particle motion, and particle-surface fluid dynamic interactions. The most general method of describing particle motion under the combined action of these effects is through the so-called Fokker-Planck equation. In the absence of particle-surface fluid dynamic interactions, the Fokker-Planck equation is well-known, and it has been applied in a general way to problems involving the adsorption or deposition of Brownian particles onto surfaces through a solution technique known as the Brownian dynamics simulation method. In this study, the Fokker-Planck equation for Brownian particle motion near surfaces is generalized to include particle-surface fluid dynamic interactions. The Fokker-Planck equation is shown to follow from the L...

Approximate analytical solutions for particle deposition in viscous stagnation-point flow in the inertial-diffusion regime with external forces

In a previous paper (1) the effects of particle inertia on the diffusional deposition of Brownian particles onto a surface in viscous, axisymmetric stagnation-point flow were investigated using the method of Brownian dynamics. Following Fernandez de la Mora and Rosner (2), under the conditions of large Schmidt numbers and small Stokes numbers (less than the critical Stokes number), an approximate analytical solution is obtained here that also includes an arbitrary external force acting on the particles. This solution is shown to be in excellent agreement with the results from Brownian dynamics simulations. An important characteristic of these solutions is inertial particle concentration “enrichment” outside the diffusion boundary layer near the adsorbing surface at subcritical Stokes numbers. In general, it is shown that attractive external particle forces only slightly reduce the amount of this enrichment. On the other hand, in the absence of inertia, attractive external particle forces increase the surface flux of particles beyond that for solely diffusional deposition. The combination of inertial particle concentration enrichment and an attractive external particle force leads to a synergistic-type increase in the surface flux of particles beyond that for solely diffusional deposition. Finally, Robinson's theorem (6) is extended to formally prove these results for inviscid-type flows.

Application of mixing and deposition data of Brownian particles in a model alveolus to human alveoli.

Air-mixing in an expanding and contracting vessel influences the deposition of Brownian particles. In the present work, by using a previously developed technique to measure mixing and deposition of aerosol particles in a balloon extensive data were collected to cover a wide range of balloon expansion and contraction conditions

Kinetics of deposition of colloidal particles in porous media

A theoretical framework for chemical-colloidal effects on the kinetics of deposition of Brownian particles in porous media has been presented. The theory was tested rigorously by conducting deposition experiments with model colloids and collectors under controlled chemical conditions in a well-defined experimental system