Particle Deposition Velocity Research Articles

Modeling deposition of particles in vertical square ventilation duct flows

The presence, flow, and distribution of particle in heating, ventilation, and air-conditioning (HVAC) ducts influence the quality of air in buildings and hence the health of building occupants. To shed a better light on the flow of particles in HVAC ducts this a paper has considered the effects of drag, lift force, gravity, Brownian diffusion, and turbulent diffusion on the dimensionless deposition velocity of particles in smooth vertical ventilation ducts using fully developed and developing velocity profiles. Based on the Reynolds stress transport model (RSM) at two different air velocities, 3.0 m/s and 7.0 m/s, the aforementioned effects were predicted using Reynolds-averaged Navier–Stokes (RANS)–Lagrangian simulation on square shaped ducts under vertical flows. Preliminary results suggest that the gravity of particles does not directly change the dimensionless deposition velocity in vertical flows. Nevertheless, the gravity of particles contributes to changing the Saffman lift force. It is thus the Saffman lift force that directly changes the dimensionless deposition velocity of particles in vertical flows. In addition, the difference in the dimensionless deposition velocities between fully developed and developing flows is owing to the turbulent diffusion, turbulent intensity, and needless to say, the Saffman lift force under different dimensionless particle relaxation time.

Effects of thermophoresis on the forced convective laminar flow of a viscous incompressible fluid over a rotating disk

In this paper we investigate the effects of thermophoresis on the forced convective laminar flow of a viscous incompressible fluid due to a rapidly rotating disk whose surface temperature is lower than the temperature of its surrounding fluid. The governing equations of continuity, momentum, energy and concentration are transformed using similarity analysis, and the solutions are obtained through numerical techniques. The results show that if the thermophoretic coefficient increases, thermophoretic velocity increases and it intensifies significantly when the relative temperature difference parameter increases. The results also show that axial particle deposition velocity increases as the thermophoretic coefficient as well as Schmidt number increases.

Particle deposition velocity onto a face-up flat surface in a laminar parallel flow considering Brownian diffusion and gravitational settling

The Gaussian Diffusion Sphere Model (GDSM) was developed and improved to reflect the effects of gravitational settling as well as Brownian diffusion of aerosol particles on deposition velocity onto a face-up flat surface in a laminar parallel flow. The model improvement also includes the applicability of the GDSM to a flat surface of any shape with finite dimensions. When deposition velocity for a face-up circular flat plate of 45cm diameter, representing e.g. a semiconductor wafer in a laminar parallel flow, was calculated by the GDSM and compared with that by the theory of Liu and Ahn (1987). Particle deposition on semiconductor wafers. Aerosol Science and Technology, 6, 215–224, the agreement was good for the tested particle sizes ranging 0.003–1μm and free stream velocities ranging 5–500cm/s. Based on this result, deposition velocities onto the face-up square flat plates with different orientations in a laminar parallel flow, simulating e.g. photomasks, were predicted.

The effects of the canopy medium on dry deposition velocities of aerosol particles in the canopy sub-layer above forested ecosystems

Understanding how the leaf area density (a(z)) and its depth integrated value, the leaf area index (LAI), modify dry deposition velocities (Vd) of aerosol particles within the canopy sub-layer is needed for progressing on a plethora of aerosol related problems in climate change, air quality, and ecosystem service evaluation. Here, the interplay between a(z) (and LAI) of tall and densely forested canopies, the flow dynamics, and Vd are explored via model calculations. A multi-layer size-resolving deposition model (hereafter referred to as MLM) is coupled to a second-order closure model (WS77), which are then used to explore a subset of the manifold of a(z) and LAI variations and their concomitant effects on the relationship between Vd and particle diameter (dp). The combined MLM-WS77 calculations are evaluated against Vd measurements collected above a Scots pine stand in Hyytiälä (southern Finland) in which a(z) was experimentally manipulated via forest thinning. Three key findings are derived from these model calculations: (1) at a given LAI, a near-constant a(z) yields the lowest Vd for a given dp class, (2) when the foliage is concentrated in the upper layers of the canopy, increasing LAI predictably increases Vd at a given dp, though some saturation occurs thereafter, but (3) suppressing turbo-phoresis leads to an opposite conclusion, decrease of Vd with LAI increase, for a dp class between 0.5 and 5 μm. Comparison between the combined MLM-WS77 calculations and a recently proposed pipe-flow analogy formulation that includes turbo-phoresis are also presented.

Particle Deposition Velocity onto a Wafer or a Photomask in a Laminar Parallel Flow

Particulate contamination is one of the critical problems that decrease product yield in semiconductor manufacturing. It is therefore important to quickly and correctly predict the particle deposition velocity for controlling the level of particulate contamination. Gaussian diffusion sphere model (GDSM) was employed to predict the mean mass transfer coefficient over a flat plate in a laminar parallel flow. The GDSM was validated for the one-dimensional flat plate by comparing with the laminar boundary layer theory in wide ranges of Schmidt number and fluid temperature. The GDSM was then used to predict the mean mass transfer coefficient over finite flat plates of common areal shapes, i.e., square, rectangle, circle, ellipse, and rhombus, with various aspect ratios. From the GDSM results, the mean Sherwood number correlation was suggested in the form of . The correlation constant was determined as for square/rectangular flat plates, for circular/elliptical flat plates, and for rhombic flat plates. The applicable Reynolds number range of the correlation was proposed by comparing with the simulation data. Finally, the equation to predict the particle deposition velocity onto a wafer or a photomask surface exposed to a parallel flow was suggested.

Significant influence of particle surface oxidation on deposition efficiency, interface microstructure and adhesive strength of cold-sprayed copper coatings

The critical velocity for particle deposition in cold spraying is a key parameter, which depends not only on the material type, but also the particle temperature and oxidation condition. The dependency of deposition efficiency of cold spray Cu particles on the particle temperature and surface oxidation was examined. The effect of particle surface oxide scales on the interfacial microstructure and adhesive strength of the cold-sprayed Cu coatings was investigated. The results show that the deposition efficiency significantly increases with increasing the gas temperature but decreases with augmenting the oxygen content of the starting powder. The oxide inclusions at the interfaces between the deposited particles inhibit the effective bonding of fresh metals and remarkably lower the bond strength of the deposited Cu coatings on steel.

Particle Deposition on a 300 mm Wafer Moving in the Opposite Direction of the Airflow in a Uni-directional Cleanroom

An investigation of the particle deposition velocity (vd) onto an upward moving 300 mm (dw) wafer in a cleanroom with a 0.3 m/s downward velocity (vo) was performed by the dynamic mesh model of FLUENT CFD code. The results show that the air simultaneously replenishes the vacant space induced by the movement of the wafer and new recirculation zones were formed around the wafer. These phenomena are apparently different from those of the wafer fixed (free-standing) in the flowing fluids. Compared with a free-standing wafer, the particle deposition velocity on a moving wafer was increased significantly. The deposition velocity increases with the increase of wafer moving velocity (vb). When the dimensionless moving velocity of the wafer Vb (= vb/vo) was 0.3, 1.0, and 3.3, the time averaged (over the dimensionless time τ (= tvo/dw) from 0 to 1.0) particle deposition velocity of particles with diameter of 0.1 μm was 11.4%, 20.8% and 37.8% greater than that of a free-standing wafer (vfs), respectively. In the computing range, the mean vd can be estimated by an equation of vd = vfs (0.208 Vb1/2 + 1.0).

A DNS study of effects of particle–particle collisions and two-way coupling on particle deposition and phasic fluctuations

This study is concerned with the effects of particle–particle collisions and the two-way coupling on the dispersed and carrier phase turbulence fluctuations in a channel flow. The time history of the instantaneous turbulent velocity vector was generated by the two-way coupled direct numerical simulation of the Navier–Stokes equations via a pseudo-spectral method. The particle equation of motion included the wall-corrected nonlinear drag force and the wall-induced and shear-induced lift force. The effect of particles on the flow was included in the analysis via a feedback force that acted on the computational grid points. Several simulations for different particle relaxation times and particle mass loadings were performed, and the effects of particle–particle collisions, particle feedback force and inter-particle interactions on the particle deposition velocity, fluid and particle fluctuating velocities, and particle concentration profiles were determined. The effect of particle aerodynamic interactions was also examined for certain cases.The simulation results indicated that when particle–particle collisions were included in the computation but two-way coupling effects were ignored, the particle normal fluctuating velocity increased in the wall region causing an increase in the particle deposition velocity. When the particle collisions were neglected but the particle–fluid two-way coupling effects were accounted for, the two-way coupling and the particle normal fluctuating velocity decreased near the wall causing a decrease in the particle deposition velocity. In the case of the four-way coupling in which both inter-particle collisions and two-way coupling effects were present, it was found that the particle deposition velocity increased compared with the one-way coupling case. When the particle aerodynamic interactions were added to the four-way coupled case (termed six-way coupled case), no significant changes in the mean fluid and particle velocities and the fluid and particle fluctuating velocities were obtained.The results for the particle concentration profile indicated that the inclusion of two-way coupling or inter-particle collisions into the computation reduced the accumulation of particles near the wall. It was also observed that particle–particle collisions and two-way coupling weakened the preferential distribution of particles.

Simulation of particle deposition in ventilation duct with a particle–wall impact model

Particle deposition velocities and locations in horizontal ventilation ducts are investigated by incorporating the effect of particle–wall collision. Particle deposition onto two types of surfaces, stainless steel surface and tedlar surface, are simulated and compared. The RNG k–ɛ model is employed to predict the air turbulence, and the Lagrangian particle tracking method integrated with particle–wall impact model is used to reveal particle physical behaviors. Turbulent dispersion of the particles is taken into account by adopting the discrete random walk (DRW) model. Particle deposition velocities and distributions onto the wall, ceiling and floor are simulated and analyzed. For both stainless steel and tedlar ducts, reasonable agreements are achieved between the simulation data and experimental data for particles with larger relaxation time. Particle deposition velocity is related to particle relaxation time and surface materials. The particle–wall impact model affects the prediction of deposition velocity and distribution. As the effects of Brownian diffusion and turbulent fluctuation on particle deposition are not considered, the presented model applies better to the particles with relatively large relaxation time.

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

Suspended dust particles are usually correlated to indoor air quality, filtration processes, and environmental problems. Dealing with air mixed with suspended particles is a matter of great urgency. This paper presents a theoretical study on aerosol particles responding to thermophoresis, electrophoresis and the particle deposition rate onto a vertical flat wall with wall heat flux in a porous medium. The non-Darcian model is employed to analyze this process. The flow is modeled as a two-dimensional, incompressible, steady-state laminar mixed convection flow. The particle transport mechanisms are promoted by convection, Brownian diffusion, thermophoresis and electrophoresis. Similarity analysis is used to transform the governing equations for continuity, momentum, energy and concentration into a system of partial differential equations. Using numerical techniques, the particle concentration profiles and deposition velocities are obtained to improve the particle filtration technology and remove contaminants from the air.

Processes affecting the movement of organochlorine pesticides (OCPs) between soil and air in an industrial site in Turkey

Soil and atmospheric concentrations, dry deposition and soil-air gas exchange of organochlorine pesticides (OCPs) were investigated at an industrial site in Aliaga, Izmir, Turkey. Current-use pesticides, endosulfan and chlorpyrifos, had the highest atmospheric levels in summer and winter. Summertime total (gas + particle) OCP concentrations in air were higher, probably due to increased volatilization at higher temperatures and seasonal local/regional applications of current-use pesticides. Particle deposition fluxes were generally higher in summer than in winter. Overall average dry particle deposition velocity for all the OCPs was 4.9 ± 4.1 cm s −1 (average ± SD). ΣDDXs (sum of p,p′-DDT, p,p′-DDD, and p,p′-DDE) were the most abundant OCPs in Aliaga soils ( n = 48), probably due to their heavy historical use and persistence. Calculated fugacity ratios and average net gas fluxes across the soil-air interface indicated volatilization for α-CHL, γ-CHL, heptachlorepoxide, cis-nonachlor, trans-nonachlor, and p,p′-DDT in summer, and for α-CHL, γ-CHL, trans-nonachlor, endosulfan sulfate, and p,p′-DDT in winter. For the remaining OCPs, soil acted as a sink during both seasons. Comparison of the determined fluxes showed that dry particle, gas-phase, and wet deposition are significant OCP input mechanisms to the soil in the study area.

Size‐resolved fluxes of sub‐100‐nm particles over forests

Dry deposition of atmospheric particles is critically dependent on particle size and plays a key role in dictating the mass and number distributions of atmospheric particles. However, modeling dry deposition is constrained by a lack of understanding of controlling dependencies and accurate size‐resolved observations. We present size‐resolved particle number fluxes for sub‐100‐nm particle diameters (Dp) over a deciduous forest derived using eddy covariance applied to data from a fast mobility particle sizer. The size‐resolved particle number fluxes in 18 diameters between 8 and 100 nm were collected during leaf‐on and are statistically robust. Particle deposition velocities normalized by friction velocity (vd+) are approximately four times smaller than comparable values for coniferous forests reported elsewhere. Comparison of the data with output from a new one‐dimensional mechanistic particle deposition model designed for broadleaf forest exhibits greater accord with the measurements than two previous analytical models, but modeled vd+ underestimate observed values by at least a factor of two for all Dp between 6 and 100 nm. When size‐resolved particle deposition velocities for Dp < 100 nm are normalized by friction velocity, the key controlling role of particle diffusivity is strongly manifest. On the basis of analyses of these new measurements and recently published size‐resolved particle number fluxes from a conifer forest, we present working parameterizations for size‐resolved particle deposition velocities over forests that could reasonably be applied in regional and global atmospheric chemistry transport models.

Aerosol fluxes and particle growth above managed grassland

Abstract. Particle deposition velocities (11–3000 nm diameter) measured above grassland by eddy covariance during the EU GRAMINAE experiment in June 2000 averaged 0.24 and 0.03 mm s−1 to long (0.75 m) and short (0.07 m) grass, respectively. After fertilisation with 108 kg N ha−1 as calcium ammonium nitrate, sustained apparent upward fluxes of particles were observed. Analysis of concentrations and fluxes of potential precursor gases, including NH3, HNO3, HCl and selected VOCs, shows that condensation of HNO3 and NH3 on the surface of existing particles is responsible for this effect. A novel approach is developed to derive particle growth rates at the field scale, from a combination of measurements of vertical fluxes and particle size-distributions. For the first 9 days after fertilization, growth rates of 11 nm particles of 7.04 nm hr−1 and 1.68 nm hr−1 were derived for day and night-time conditions, respectively. This implies total NH4NO3 production rates of 1.11 and 0.44 μg m−3 h−1, respectively. The effect translates into a small error in measured ammonia fluxes (0.06% day, 0.56% night) and a large error in NH4+ and NO3− aerosol fluxes of 3.6% and 10%, respectively. By converting rapidly exchanged NH3 and HNO3 into slowly depositing NH4NO3, the reaction modifies the total N budget, though this effect is small (<1% for the 10 days following fertilization), as NH3 emission dominates the net flux. It is estimated that 3.8% of the fertilizer N was volatilised as NH3, of which 0.05% re-condensed to form NH4NO3 particles within the lowest 2 m of the surface layer. This surface induced process would at least scale up to a global NH4NO3 formation of ca. 0.21 kt N yr−1 from NH4NO3 fertilisers and potentially 45 kt N yr−1 from NH3 emissions in general.

Formulation for predicting deposition velocity of particles in turbulence

Relationships for the particle concentration and convection velocity profile has been obtained by the adaptation of the random surface renewal model [1–5] to the particle continuity and momentum equations of the nonisothermal turbulence boundary-layer flows; particle transport mechanisms of Brownian and turbulent diffusion, eddy impaction, particle inertia, and thermophoresis are included. This proposed model provides a useful framework for coupling these modeling parameters with analytical equation of the particle deposition velocity. The predictions obtained on the basis of this equation have been found to be in good agreement with experimental values of deposition velocity for fully-developed turbulent pipe flow.

Some aspects on 3D numerical modeling of high velocity impact of particles in cold spraying by explicit finite element analysis

Three-dimensional modeling of particle impacting behavior in cold spraying by using ABAQUS/Explicit was conducted for copper and other materials. Various combinations of calculation settings concerning material damage, Arbitrary Lagrangian Eulerian adaptive meshing, distortion control and contact interaction were examined. The effects of meshing size and particle size on the impact behavior were analyzed compared to the previous results. The results show that the simulations with material damage cope well with the element excessive distortion and the resultant output is more reasonable than that obtained without material damage. In addition, the meshing size has less effect on the output with the material damage than without material damage. Although particle size has little effect on the morphologies of the deformed particles, it has some effect on the failure of elements at contact interfaces. The critical velocity for particle deposition could be estimated given the appropriate material properties.

Prediction of particle deposition onto indoor surfaces by CFD with a modified Lagrangian method

Accurate prediction of particle deposition indoors is important to estimate exposure risk of building occupants to particulate matter. The prediction requires accurate modeling of airflow, turbulence, and interactions between particles and eddies close to indoor surfaces. This study used a v ′ 2 ¯ − f turbulence model with a modified Lagrangian method to predict the particle deposition in enclosed environments. The v ′ 2 ¯ − f model can accurately calculate the normal turbulence fluctuation v ′ 2 ¯ , which mainly represents the anisotropy of turbulence near walls. Based on the predicted v ′ 2 ¯ , we proposed an anisotropic particle–eddy interaction model for the prediction of particle deposition by the Lagrangian method. The model performance was assessed by comparing the computed particle deposition onto differently oriented surfaces with the experimental data in a turbulent channel flow and in a naturally convected cavity available from the literature. The predicted particle deposition velocities agreed reasonably with the experimental data for different sizes of particles ranging from 0.01 μm to 50 μm in diameter. This study concluded that the Lagrangian method can predict indoor particle deposition with reasonable accuracy provided the near-wall turbulence and its interactions with particles are correctly modeled.

Focused ion beam micro-dissection of cold-sprayed particles

Three different modes of cold-spray impact were compared; aluminium particles onto a piezoelectric ceramic (PZT), aluminium particles onto copper, and deep penetration of copper particles into aluminium. Adhered particles were dissected using a dual-beam scanning electron microscope/focused ion beam (SEM/FIB) for morphological and microstructural examination. It was shown that the extent of substrate deformation substantially altered the behaviour displayed during bonding of the particles. In aluminium-on-ceramic impact, no permanent deformation of the substrate was seen. Shearing of layers of metal over the ceramic left a thin coating of debris on the surface. In contrast, aluminium particles caused plastic deformation and cratering of the copper. The critical velocity for aluminium particle deposition was lower on this substrate. Copper impact onto aluminium caused adiabatic shear of the substrate, with local temperatures reaching melting point. Copper particles embedded deeply into the aluminium surface without rebounding.

Modeling deposition of particles in typical horizontal ventilation duct flows

Particles carried by airflows through ventilation ducts in heating, ventilation and air-conditioning (HVAC) systems have adverse effects on human health. Knowledge of particle deposition rates in ventilation ducts is useful for modeling exposures to particles within buildings and more completely understanding particle fates. To meet these objectives, deposition rates of particles to various internal surfaces in a smooth horizontal square ventilation duct are predicted by Reynolds-Averaged Navier-Stokes (RANS)-Lagrangian simulation at all three air speeds of 3.0 m/s, 7.0 m/s and 9.0 m/s. Drag, lift force, gravity, inertial force and turbulent diffusions are considered in the computation of particle motion. The influences of relaxation time, particle size, air speed, turbulent flow development profiles and surface orientations on predicted deposition rates (dimensionless deposition velocities) of particles is discussed. For particles larger than 10 μm, it is shown that vertical wall deposition rates in a smooth horizontal square ventilation duct where the turbulent flow profiles is fully developed first increase with dimensionless relaxation time increase and then slightly decrease with dimensionless relaxation time increasing at three different air speeds. The maximum of the sidewall deposition rates is 0.12. Floor deposition rates increase with dimensionless relaxing time increase and attain the maximum value of 9.6. Ceiling deposition rates firstly gradually decrease and then rapidly decrease to zero with dimensionless relaxing time increasing at different air speeds. The maximum of the ceiling deposition rates is 0.054. Particle deposition rates to the ceiling, wall and floor in the horizontal duct with a fully developed turbulent flow profile are all lower than that in the horizontal duct with a developing turbulent flow profile. Particle deposition rates are mainly dependent on friction velocity (air speed) and particle size. The differences in deposition rates to the duct floor, wall and ceiling decrease with increasing air speed. The results of Lagrangian simulations in this work are valuable for more accurately predicting and understanding particle deposition in typical ventilation ducts.

SU-GG-J-25: Aerosols/Nanoparticle Therapy for Malignancy Involving the Lung - a Transport Phenomenon Study

Purpose: Study the nanoparticles/aerosols localized deposition patterns in morphometrically realistic lung bifurcations geometry using computational fluid dynamics code FLUENT®. Method and Materials: Chest CT scan data from an unidentified patient, with 3 mm slices in the axial direction are used to reconstruct the lung airway bifurcation geometry using Amira 4.0 (Mercury Inc.) program. The 3D rendered airway bifurcations are exported to FLUENT® preprocessor GAMBIT where further meshing was performed and exported for FLUENT® computation. Species Transport and Reaction model in FLUENT® was used to explore the local deposition patterns of nanoparticles/aerosols. At this time, only the inspiratory phase of the breathing cycle has been studied in realistic bifurcation geometry for 3rd and 4th generations. Modeling using the CT scan data is currently in progress. N2 has been assumed to be the bulk carrier gas in the flow fields carrying arbitrary particles uniformly sized (smoke, radon daughters, radiopharmaceuticals, etc.) with defined physical and diffusional properties. In this initial study a mass fraction of 10−8 was used for particle mass concentration. The particles interacting with the the airway wall surface are assumed to be deposited. Results: Results from preliminary studies of localized particle deposition velocities and deposition fractions using unrealistic symmetric airway bifurcations geometries for 3rd and 4th generations using FLUENT® model for Po-218 nanoparticles are in close agreement with the experimental data of Kinsara et al. (Health Phys. 68(3), 1995). Further, results obtained with the realistic bifurcation geometry for 3rd and 4th generations, suggest that the particle deposition is maximum at the carinal region of the bifurcations. Conclusion: Maximum particle deposition concentration was observed to occur at the carinal regions in the bifurcations. Further, the deposition patterns provide very useful information for the design of the inhalation drugs, with detail on where the particles end up after one breath in.

CFD simulation of particle deposition in a horizontal turbulent duct flow

Deposition of particles in turbulent duct flows is crucial process in a number of industrial and environmental applications. Therefore, in this paper, particle deposition in a horizontal turbulent duct flow is simulated by CFD (computational fluid dynamics) modeling. Dimensionless deposition velocities of particles ranging from 10 to 200 μm are predicted by one-way coupling Lagrangian eddy lifetime model combined with a computation model of particle deposition in the turbulent duct flow with a fully developed velocity profiles based on RANS (Reynolds-averaged Navier–Stokes) equations at all three air speeds of 3.0, 5.0 and 7.0 m s −1. It is shown that deposition rates (dimensionless deposition velocities) of particles to floors are higher than that to vertical wall and ceiling surfaces. Floor deposition rates increase with dimensionless relaxing time increasing, ceiling deposition rates decrease to zero with dimensionless relaxing time increasing, and wall deposition rates show the increase first and then a subtle decrease with dimensionless relaxing time increase at different air speeds. Wall and ceiling deposition rates increase with air speed increase at the same dimensionless relaxing time. Floor deposition rates decrease with air speed increase at the same dimensionless relaxing time. The simulation results are expected to be helpful for evaluating particle deposition rates in some environmental and industrial square ducts.