Modeling particle transport in downward and upward flows

The prediction of particle and scalar transport in a complex geometry with turbulent flow driven by fans is considered. The effects of using different turbulence models, anisotropy, flow unsteadiness, fan swirl, and electrostatic forces on particle trajectories are shown. The turbulence models explored include k−l, zonal k−ε/k−l, and nonlinear eddy viscosity models. Particle transport is predicted using a stochastic technique. A simple algorithm to compute electrostatic image forces acting on particles, in complex geometries, is presented. Validation cases for the particle transport and fluid flow model are shown. Comparison is made with new smoke flow visualization data and particle deposition data. Turbulence anisotropy, fan swirl, and flow unsteadiness are shown to significantly affect particle paths as does the choice of isotropic turbulence model. For lighter particles, electrostatic forces are found to have less effect. Results suggest, centrifugal forces, arising from regions of strong streamline curvature, play a key particle deposition role. They also indicate that weaknesses in conventional eddy viscosity based turbulence models make the accurate prediction of complex geometry particle deposition a difficult task. Axial fans are found in many fluid systems. The sensitivity of results to their modeling suggests caution should be used when making predictions involving fans and that more numerical characterization studies for them could be carried out (especially when considering particle deposition). Overall, the work suggests that, for many complex-engineering systems, at best (without excessive model calibration time), only qualitative particle deposition information can be gained from numerical predictions.

The green's function method in quantum statistics

Modeling particle deposition in the pig respiratory tract

A simplified method for assessing particle deposition rate in aircraft cabins

Computational investigation of particle inertia effects on submicron aerosol deposition in the respiratory tract

Summary form only given. A stagnation point flow (SPF) setup was used to directly observe deposition kinetics of colloidal particles onto micropatterned glass surfaces with well-defined surface charge heterogeneity features. The SPF system consists of a microscope focused on a small collector surface area, with an automated computer controlled image-capturing device comprising a CCD camera. Surface charge heterogeneity was microfabricated onto glass surfaces by chemically modifying well-controlled fractions of glass surface with aminosilane using a soft lithographic technique. Particle deposition was observed for a wide range of flow rates (Peclet numbers) and solution ionic strengths. The observed experimental particle deposition rates at various physicochemical conditions were compared to predictions based on a patchwise charge-heterogeneity model. Comparisons revealed that (1) deviation from patch model occurs at high flow rates (or Peclet numbers), (2) patch model approximates deposition rate at lower Peclet numbers, and (3) deviation from patch model predictions occurs at a lower flow velocity for lower ionic strength runs. The particle deposition behavior and breakdown of patch model are attributed to coupling between hydrodynamic and electrostatic double layer interactions. A mechanistic model which we term the bump effect is used to describe deposition behavior on micropatterned glass surfaces.

The main goal of this study is the quantification of the particle transport and deposition within the human airways during light, normal and exercise breathing conditions using the computational fluid dynamics. In particular we presented a comparison between healthy and stented airways. The considered tracheobronchial model is based on the Weibel symmetric model in which we have inserted the Dumon prosthesis at different locations and on the CT-based geometries of a healthy and a stented airway. The results indicate an important redistribution of the particle deposition locations. Local overdoses can be found in the proximal regions of the prostheses, independently of the breathing conditions, of the particle size and of the considered geometry. The presented work is aimed to contribute to the understanding of the particle deposition in the human lung and to improve drug-aerosol therapies. For patients that underwent airways reconstructive surgery, it can give detailed information about the deposition efficiency and it may help targeting specific airways regions.

Artificial groundwater recharge utilizing stormwater is an effective tool to reduce urban flooding and artificially increase groundwater resources. However, porous media clogging due to the solid polydisperse particles carried in stormwater severely restricts the application of recharge technology. In addition, solid particles play a crucial role in aquifer contamination. If particles are easily transport in groundwater flows, they can act as contaminant carriers to facilitate the movement of contaminants. Conversely, if particles cause porous media clogging, they can form barriers that prevent contaminant migration. While the transport and clogging mechanism of particles has been explored by many macroscopic physical experiments, the intrinsic connection between the deposition behavior of particles in pore scale and the macroscopic presentation of clogging phenomenon remains unclear. In this study, laboratory-scale sand column experiments were combined with scanning electron microscopy (SEM) observations to explore the effect of polydisperse particle size on the mechanism of particle transport and clogging. The median particle sizes (dp50) of the polydisperse particles used in the experiments were 0.66, 4.05, and 11.83 μm, respectively. The interaction energy between particles and porous media grains was calculated using XDLVO theory, indicating that the experiments were conducted under unfavorable condition. The sand column experiments revealed that the influence of large particles on the porous media permeability is limited to shallow layers, and small particles are more likely to transport to deeper layers. Particles with dp50=0.66 μm were tend to form aggregates, reducing particle recovery rate and promoting clogging. The pore-scale observations illustrated that the vast majority of the particles are preferentially deposited in concave regions of the media grain surface. The larger the particle size, the higher the proportion of deposition in concave regions. Due to the different transport mechanisms of particles in pore space, the ratio of dp50 to porous media grain size is not the only basis for identifying the type of clogging. The results proved that the particles with dp50=0.66 μm can form mixed clogging faster than particles with dp50=4.05 μm. The proposed results provide a reference for the theoretical study of the particle transport and deposition mechanism, the prevention and control of aquifer pollution, as well as the development of more effective artificial groundwater recharge scheme.

Combined effects of thermophoresis and electrophoresis on particle deposition onto a vertical flat plate from mixed convection flow through a porous medium

Gas flow and particle deposition in the hot-gas filter vessel of the Pinon Pine project

Dry powder inhalation (DPI) has attracted much attention as a treatment for respiratory diseases owing to the large effective absorption area in a human respiratory system. Understanding the drug particle motion in the respiratory system and the deposition behavior is necessary to improve the efficiency of DPI. We conducted computer simulations using a model coupling a discrete element method and a computational fluid dynamics method (DEM-CFD) to evaluate the particle deposition in human respiratory system. A simple artificial respiratory model was developed, which numerically investigated the effect of particle properties and inhalation patterns on the particle deposition behavior. The DEM-CFD simulations demonstrated that the smaller- and lower-density particles showed higher reachability into the simple respiratory model, and the particle arrival ratio to the deep region strongly depended on the aerodynamic diameter. The particle arrival ratio can be described as an exponential function of the aerodynamic diameter. Furthermore, the exponential relationship between the particle reachability into the depth of the simple respiratory model and the aerodynamic diameter predicted the particle aerodynamic diameter based on the required reachability. The particle shape also had an impact on the particle deposition behavior. The rod-like particles with a larger aspect ratio indicated higher reachability into the depth of the simple respiratory model. This was attributed to the high velocity motion of the particles whose long axis was in the direction of the deep region.

The two-dimensional laminar and turbulent stagnation-point flow over a wafer surface within a cleanroom environment are numerically simulated. This study shows the relationship between particle capture area on the wafer and the particle size and flow conditions. The mean flow field is simulated using a two-equation k-ϵ turbulence model. Trajectories of aerosol particles are evaluated by solving the corresponding Lagrangian equation of motion that includes effects of drag, gravity, lift force, Brownian motion and turbulence fluctuations. The Brownian motion is modeled as a white noise process and turbulence fluctuation is assumed to behave as Gaussian random process. Simulations are carried out for aerosol particles (of various sizes) released at different locations over the surface. Depositions of particles on the wafer are evaluated and a capture area which varies with particle size is produced. The results show that Brownian motion becomes very significant when turbulence fluctuations start to disappear near the wall for particles smaller than 1 μm in diameter. The results also show that deposition of particles in turbulent flows is usually higher than that in laminar flows for all particle sizes considered. The effect of the fluid state (gas or liquid) on the particle deposition rate is predicted for air and water. The results show that particles deposition rate in air is higher than that in water.

Laminar cross-flow convective heat transfer of a finned cylindrical tube in the presence of particle deposition and deposit erosion

Rates of particle deposition from aqueous suspensions in turbulent flow: a comparison of theory with experiment

Eye diseases such as Krukenberg Spindle, Hyphema and Hypopyon are related to the deposition of specific particles such as pigmentary cells, leukocytes and erythrocytes. These particles are circulated by the aqueous humor (AH), and tend to deposit in regions of low velocities or high resistance. In the present paper, numerical simulations are reported of the AH flow and particle transport, and the particle concentration predictions are qualitatively compared with clinical images. The particle concentration distributions provide an understanding of the likely sources of deposition, and the origin of the deposited particles. Pigmentary cells are seen to concentrate in a vertical band on the corneal surface consistent with clinical observations of Krukenberg Spindle. Leukocytes and erythrocytes are seen to collect at the bottom of the anterior chamber similar to the observations made for Hypopyon and Hyphema. These results confirm the potential of using numerical calculations in order to obtain a better understanding of the particle transport and deposition patterns in the anterior chamber of the eye.