Particle Deposition Velocity Research Articles

Defiltering turbulent flow fields for Lagrangian particle tracking using machine learning techniques

We propose a defiltering method of turbulent flow fields for Lagrangian particle tracking using machine learning techniques. Numerical simulation of Lagrangian particle tracking is commonly used in various fields. In general, practical applications require an affordable grid size due to the limitation of computational resources; for instance, a large-eddy simulation reduces the number of grid points with a filtering operator. However, low resolution flow fields usually underestimate the fluctuations of particle velocity. We thus present a novel approach to defilter the fluid velocity to improve the particle motion in coarse-grid (i.e., filtered) fields. The proposed method, which is based on the machine learning techniques, intends to reconstruct the fluid velocity at a particle location. We assess this method in a priori manner using a turbulent channel flow at the friction Reynolds number Reτ=180. The investigation is conducted for the filter size, nfilter, of 4, 8, and 16. In the case of nfilter=4, the proposed method can perfectly reconstruct the fluid velocity fluctuations. The results of nfilter=8 and 16 also exhibit substantial improvements in the fluctuation statistics although with some underestimations. Subsequently, the particle motion computed using the present method is analyzed. The trajectories, the velocity fluctuations, and the deposition velocity of particles are reconstructed accurately. Moreover, the generalizability of the present method is also demonstrated using the fields whose computational domain is larger than that used for the training. The present findings suggest that machine learning-based velocity reconstruction will enable us precise particle tracking in coarse-grid flow fields.

Influence of modeling conditions on the estimation of the dry deposition velocity of aerosols on highly inhomogeneous surfaces

An approach to estimating the dry deposition velocity of aerosol particles on the surfaces of Arctic regions, where snow-covered surfaces, open water surface, tundra and coniferous forest predominate, is proposed and numerically investigated. Optimal modeling conditions are proposed, taking into account the characteristic sizes and densities of aerosol particles involved in transport in the planetary boundary layer, and the interaction of air flows with the surface through the parameter u*, calculated using the WRF-ARW model. The proposed approach is compared with other known models and experimental data. The dependence of the dry deposition velocity obtained by the proposed approach on the diameter, density of aerosol particles and dynamic velocity u* for the surfaces in the Far North is estimated.

Modeling Indoor Inorganic Aerosol Concentrations During the ATHLETIC Campaign with IMAGES.

In 2018, the ATHLETIC campaign was conducted at the University of Colorado Dal Ward Athletic Center and characterized dynamic indoor air composition in a gym environment. Among other parameters, inorganic particle and gas-phase species were alternatingly measured in the gym's supply duct and weight room. The Indoor Model of Aerosols, Gases, Emissions, and Surfaces (IMAGES) uses the inorganic aerosol thermodynamic equilibrium model, ISORROPIA, to estimate the partitioning of inorganic aerosols and corresponding gases. In this study herein, measurements from the ATHLETIC campaign were used to evaluate IMAGES' performance. Ammonia emission rates, nitric acid deposition, and particle deposition velocities were related to observed occupancy, which informed these rates in IMAGES runs. Initially, modeled indoor inorganic aerosol concentrations were not in good agreement with measurements. A parametric investigation revealed that lowering the temperature or raising the relative humidity used in the ISORROPIA model drove the semivolatile species more toward the particle phase, substantially improving modeled-measured agreement. One speculated reason for these solutions is that aerosol water was enhanced by increasing the RH or decreasing the temperature. Another is that thermodynamic equilibrium was not established in this indoor setting or that the thermodynamic parametrizations in ISORROPIA are less accurate for typical indoor settings. This result suggests that applying ISORROPIA indoors requires further careful experimental validation.

Experimental study on the effect of adjacent near-wall heat sources on the particle deposition

Adjacent near-wall heat sources are widely used in indoor environments. It is important to investigate the particle deposition under the influence of coupled thermal plumes arising from adjacent near-wall heat sources to improve indoor air quality and control harmful particle deposition. Thus, this study scrutinizes the behavior of thermal plumes emanating from adjacent near-wall heat sources, focusing on the deposition of particles with diameters of 0.3 μm, 0.5 μm, 1.0 μm and 3.0 μm on the wall behind the heat sources. These findings are juxtaposed with the pattern of particles with varying sizes situated above the single near-wall heat source and away from the heat sources. The study delves into the impact of varying surface temperatures and the distance from the wall behind the heat sources, as well as the top surface of the heat source, on particle deposition in 29 distinct cases. The results indicate that the deposition velocity of particles with the same size is highest above the adjacent near-wall heat sources, followed by that of a single near-wall heat source, and finally, locations away from the near-wall heat source. Also, the decay rate loss coefficient of particles with the same size above the adjacent near-wall heat sources increases with a decrease in the distance of the heat sources from the wall behind them, an increase in the temperature of the heat sources, and a reduction in distance from the top surface of heat sources.

Stochastic subgrid-scale modeling for particles dispersion and deposition for a filtered DNS channel flow field

The effect of subgrid-scale velocity fluctuations on the deposition and dispersion of solid particles in a filtered DNS turbulent channel flow at Reτ=180, and for particles with Stokes numbers of St = 1, 2, 5, 24 was studied. First, the turbulent flow field was simulated using the DNS on a high-resolution grid. Then, the filtered DNS flow fields were generated using several low-resolution grids. Particle tracking was performed for the DNS and filtered DNS channel flow fields, and the effects of filtering on particle deposition and concentration were studied. It was shown that filtering significantly decreases the particle deposition velocities at lower Stokes numbers (St = 1, 2, 5). However, at higher Stokes numbers (St = 24), the deposition velocity was less affected. Next, the ability of a stochastic model to generate the correct particle deposition velocities and concentration profiles was studied. A Langevin stochastic equation for modeling the subgrid-scale (SGS) fluid velocity fluctuations as seen by particles was developed and tested. The two input parameters of the stochastic model are the variance of SGS fluctuations in the wall-normal direction and the Lagrangian SGS time-scale. It was seen that the model prediction is sensitive to the SGS time scale used in the Langevin equation. The model was capable of predicting the correct deposition velocities and concentration profiles of lower inertia particles when the proper time-scale was used. For higher inertia particles and when a larger amount of energy was removed by filtering, the model was unable to predict the deposition velocities.

Investigation of a solid particle deposition velocity in drag reducing fluids with salinity

Optimal and cost-effective drilling operations in extended-reach horizontal wells depend on efficient solid cuttings removal from the borehole. Several solids-suspended multiphase processes such as crude petroleum transportation, separation, and processing of oil and gas streams also require the efficient removal of these solids. The terminal settling velocity (Vts) of the solid particle is a vital parameter that controls the removal efficiency of these solids. In a drilling scenario when there is a hold on fluid circulation such as connection time, the accurate estimation of Vs provides the driller with time available to prevent solid deposition. In severe conditions, this can result in a stuck pipe, especially for extended-reach horizontal wells. In this work, both spherical and non-spherical particle deposition were experimentally investigated in several fluid rheology and salinity. Two concentrations (0.1vol% and 0.05vol%.) of partially-hydrolyzed polyacrylamide (PHPA) were used as a drag-reducing additive for water-based drilling mud. The PHPA drag-reducing fluid (reduced pressure loss) acts as a turbulence inhibitor. The PHPA polymer chain suppresses any turbulence in the flow, reducing the turbulent eddy viscosity. The effects of salinity (3wt.%NaCl and 3wt.%CaCl2 contamination) on solid particle settling velocity (Vs) in drag-reducing fluids were also investigated. Terminal velocity was achieved for all experiments and seemed to increase with increased diameter/sphericity. However, cases when this trend was not consistent were observed and therefore a new parameter of Φ (sphericity index × diameter) was proposed. Vs increases with Φ value for all cases. During drilling, PHPA also aids in sealing the fracture in the formation. With and without salt in the fluid, how lowering drag affected the settling velocity of solid particles (drill cuttings) could be observed. The settling velocity tests will be improved in drag-reducing PHPA solutions with the knowledge from this study.

Simulation and evaluation study of atmospheric aerosol nonsphericity as a function of particle size

Aerosol nonsphericity causes great uncertainty in radiative forcing assessments and climate simulations. Although considerable studies have attempted to quantify this uncertainty, the relationship between aerosol nonsphericity and particle size is usually not considered, thus reducing the accuracy of the results. In this study, a coupled inversion algorithm combining an improved stochastic particle swarm optimization algorithm and angular light scattering is used for the nonparametric estimation of aerosol nonsphericity variation with particle size, and the optimal sample selection method is employed to screen the data. Based on the verification of inversion accuracy, the variation of aerosol aspect ratio with particle size based on the ellipsoidal model in global regions has been obtained from Aerosol Robotic Network (AERONET) data, and the effect of nonsphericity on radiative forcing and dry deposition has been studied. The results show that the aspect ratio increases with particle size in all regions, with the maximum ranging from 1.4 to 1.8 in the desert, reflecting the differences in aerosol composition at different particle sizes. In radiation calculations, considering aerosol nonsphericity makes the aerosol cooling effect weaker and surface radiative fluxes increase, but hardly changes the aerosol absorption, with maximum differences of 9.22% and 22.12% at the bottom and top of the atmosphere, respectively. Meanwhile, the differences in radiative forcing between aspect ratios as a function of particle size and not varying with particle size are not significant, averaging less than 2%. Besides, the aspect ratio not varying with particle size underestimates the deposition velocity of small particles and overestimates that of large particles compared to that as a function of particle size, with maximum differences of 7% and 4%, respectively.

Numerical simulation of the particle wall mass transfer rates on rough surfaces confining turbulent natural convection flows

We performed numerical simulations of the particle mass transfer rates on the horizontal and vertical thermally active rough walls confining a turbulent natural convection flow. We considered the air flow conditions in a cubical cavity (L=1.22m, Ra=5.4·108, Pr=0.71) with two opposed pairs of consecutive walls at different temperatures, for which measurements of the particle deposition velocities are reported in the literature. The simulations were carried out by solving the momentum, thermal energy and particle mass transfer equations using a series of two-dimensional computational cell units to determine spatial evolution and development of the particle concentration boundary layer in the vicinity of hot and cold rough walls. Different flow conditions, wall orientations, sizes of roughness elements, particle diameters and temperature increments between the wall and the bulk fluid, typically found in indoor environments, have been considered and consequently, results can be used to estimate the particle deposition rates in real scenarios. At large mass transfer particle Péclet numbers, corresponding to spherical particles with diameters of 0.5–1 μm, the wall mass transfer rates of particles on rough textures typically increase by a factor of about 3 in comparison with the deposition on smooth surfaces. The thermophoretic effect significantly decreases the particle deposition on hot surfaces and increases it on cold surfaces, especially at large particle Péclet numbers. The numerical predictions of the deposition velocities are in good agreement with the measurements reported in the literature for the same flow conditions considered.

Influence of inclined magnetic field and cross diffusion on transient forced convective heat and mass transfer flow along a porous wedge with variable Prandtl number

The unsteady 2-D forced convective mass and heat transfer flow of an incompressible, viscous and electrically conducting fluid along a porous wedge is examined in this article using numerical analysis to survey the effects of a magnetic field and thermophoresis. This is done in the existence of temperature-dependent thermal conductivity, a variable Prandtl number, and the effect of cross diffusion. The governing nonlinear PDEs have been converted into nonlinear ODEs by using a similarity transformation. The modified ODEs are solved for similar solutions using the shooting technique and the Runge–Kutta fourth-order method. The temperature, velocity, concentration, thermophoretic velocity, and thermophoretic particle deposition velocity results for various parameters are provided. The Dufour number’s effect enhances the temperature profile and rate of heat transfer. Moreover, it is noted that the rate of mass transfer is meaningfully influenced by the variation of the thermophoresis parameter and Soret number. Thus, in any physical model where the thermal conductivity of the fluid is temperature dependent, the Prandtl number within the BL have to be treated as variable rather than constant.

Numerical Study of Flow and Particle Deposition in a Block Duct

The primary of this study is to evaluate the characteristics of airflow organization and particle deposition in blocked ducts with various subgrid models. Five popular sublattice models are chosen to conduct this and the LES method is utilized to simulate the flow field and particle deposition properties of the duct. The results demonstrate that the features of the flow field varied amongst the different sub-grid models. The Smagorinsky and WALE models provide comparable findings, with only one pair of separated vortices in the leeward region. With small separated vortices and a small vortex structure near the wall in the leeward region, the WALES model, the WALES-Omega model, and the KET model are more informative. Simultaneously, a large number of particle groups with particle sizes ranging from 1nm to 50μm were selected for particle phase analysis. It was discovered that the deposition velocity of ultrafine particles below 1μm steadily reduced as particle size grew, whereas the deposition velocity of particles larger than 1μm rose as particle size increased.

Numerical study of dry deposition of dust-PM10 on leaves of coniferous forest

The present study aims to investigate the effect of forests on PM distribution following dust events in a region prone to frequent dust storms (Northern Negev, Israel). 3D numerical modeling of the particulate flow using a discrete phase model, based on the Eulerian-Lagrangian approach, has been performed to investigate the dust deposition to the vegetation element. The modeling considered several deposition mechanisms, namely, the drag force, buoyancy force, Brownian force, and Saffman's lift force. The vegetation element is considered as a prolate ellipsoid approximating in shape to a leaf of Aleppo pine (Pinus halepensis), the dominant tree species in Lahav Forest. Based on CFD modeling, the novel parameterization of the average collection rate is suggested. The validity of the model prediction is evaluated by comparison with experimental data available in the literature. It is shown that using a correlation based on dimensionless mass transfer parameters leads to an overestimation of the dust concentration at the leeward side of the forest by 23% compared to the measurement data. By contrast, the model supplemented with CFD-based average collection rate parameterization yields an overestimation of only 8%. It was also found that both models estimate the dust concentration with a difference of less than 5% in a location inside the forest in the area adjacent to the windward side of the forest. The influences of other essential factors, such as particle size and wind velocity, on deposition efficiency and the deposition velocity of dust particles on the vegetation element, are also analyzed and discussed.

A particle deposition model considering particle size distribution based on the Eulerian approach

The problem of ash deposition on heat exchange surfaces is one of the main causes hindering the safe and efficient operation of conventional boilers. Hence, looking into the particle deposition characteristics on heat transfer surfaces as well as the formation process and the deposition mechanism is essential. In this study, a particle deposition model considering the particle size distribution based on the Eulerian approach is presented to predict the dynamic deposition process of multi-sized particles on the surfaces of heat exchange tubes. The model harnesses the advantages of the Eulerian approach and takes into account the particle size distribution as well as the interaction between them. By coupling computational fluid dynamics (CFD) analysis with the population balance model, and the embedding user-defined function code with the deposition model, the deposition characteristics of the multi-sized particles are predicted. It is established that the simulation findings of this model, as opposed to models for average-sized particles, are in greater accord with the experimental data by comparing the model predictions against published experimental results, with the average relative deviations are reduced by 9.28%, 8.11%, and 7.14%, respectively. The weighted average of the latter three dimensionless deposition velocities of multi-sized particles are all greater than those of average-sized particles. Moreover, the net deposition mass of multi-sized particles is 9.34% higher than that of average-sized particles.

Modeling atmospheric microplastic cycle by GEOS-Chem: An optimized estimation by a global dataset suggests likely 50 times lower ocean emissions

Modeling atmospheric microplastic cycle by GEOS-Chem: An optimized estimation by a global dataset suggests likely 50 times lower ocean emissions

DEPOSITION BEHAVIOR OF INDOOR AIRBORNE PARTICULATE MATTER ON HUMAN BODY SURFACES

In this study, we investigated the deposition behavior of particles in air using a thermal manikin and a silicon wafer as a surface on which particles are deposited. As a result, it was confirmed that the particle deposition velocity on the heated manikin was reduced compared to that on the unheated manikin, due to the effect of thermophoretic forces. The deposition velocities obtained from the experiments were compared with existing models of particle deposition on the human body, and the order and trend of the experimental values were generally consistent, confirming the validity of the models.

Seasonal variations in total deposition velocity and washout ratio of fine aerosols revealed from beryllium-7 (7Be) measurements in Sevastopol, the Black Sea region

Washout ratios and deposition velocities are crucial in fine aerosols as they affect their atmospheric concentration, which in turn impacts human health. The only method to estimate the total (dry and wet) aerosol deposition velocity or washout ratio is by using a tracer such as beryllium-7 (7Be). This study collected field data on the temporal variability of monthly total deposition flux of 7Be and monthly mean 7Be activity in Sevastopol station, the Black Sea region from March 2011 to December 2013. From these data, the washout ratio and deposition velocity of fine aerosol particles were derived. The monthly mean values of the washout ratio and deposition velocity ranged from 388 to 3533 (mean 1112 ± 793) and from 0.1 to 1.5 cm s−1 (mean 0.6 ± 0.4 cm s−1), respectively. The dry deposition velocity in the four precipitation-free months varied between 0.10 and 0.15 cm s−1 with an average of 0.13 ± 0.02 cm s−1. The precipitation amount and frequency strongly influenced the seasonal variability of the deposition velocity, whereas the seasonal variability of the washout ratio was controlled only by the precipitation amount. The reduced washout ratio and the increased deposition velocity were associated with the increased precipitation. Thus, the results obtained allowed for parameterizations to estimate the monthly mean values of the washout ratio and deposition velocity from the data of the monthly precipitation amount.

Particle dispersion and deposition in wall-bounded turbulent flow

Particle dispersion and deposition in a fully developed turbulent channel flow at a friction Reynolds number of Reτ=180 for a wide range of Stokes numbers (St = 1-130) are investigated using the direct numerical simulation (DNS). The combined effect of gravity and the Saffman lift force on the particle deposition velocities in upward and downward flows are considered. The results are compared with recent experimental measurements and numerical benchmark solutions. For particle–wall collisions, two scenarios of fully elastic and no-rebound (trap-wall) collisions are considered. Due to the turbophoresis effect and the steady migration of particles toward the walls, a stationary state cannot be reached for particle concentration with the fully elastic assumption. To alleviate this problem, for every particle that impacts the wall a new particle is added to the computational domain with the trap-wall assumption. The stationary particle field is further time-averaged to present the average particle velocities, particle concentrations, and particle velocity fluctuations profiles. It is shown that at lower Stokes numbers, the deposition velocity of downward channel flow is higher than the upward flow, whereas at higher Stokes numbers the upward flow has a higher deposition rate but a lower near-wall particle concentration. This higher deposition rate is attributed to the combined effect of gravity and the positive Saffman lift force that brings the inactive particles trapped in the viscous sublayer to the buffer layer, resulting in an increase of their wall-normal turbulent fluctuations and their wall-collision rates.

Deposition of non-spherical particles on indoor surfaces: Modification of diffusion coefficient

Although there have been studies on gravitational settling of non-spherical particles, only few studies have incorporated the diffusion of non-spherical particles into particle deposition. Non-spherical particles occupy a large proportion of particles in indoor environments, and their deposition is a key factor that influences the level of indoor particulate matter pollution. In this study, we modified drag coefficient and diffusion coefficient based on settling experiment and Langevin equation to fulfill a semi-analytical modeling of particle deposition on indoor surfaces. The modified diffusion coefficient and deposition velocity agree well with the experimental results for fibers. With the modified diffusion coefficient, we further modeled the deposition of non-spherical particles on indoor surfaces under typical air friction velocity conditions. The results showed that the deposition velocity between spherical and non-spherical particle deviated by 10–25% with the same aerodynamic diameter for diffusion-controlled region, while the application of aerodynamic diameter would lead to 10% to over 100% deviation with 10 μm particle for particle depositing on side walls. However, the deposition of non-spherical particle can be estimated rightly through spherical particle with the same aerodynamic diameter when gravitational settling dominates the deposition process. The modification of the diffusion coefficient and deposition velocity of non-spherical particles is expected to help in understanding the effect of particle shape on its deposition and may be further applied to indoor particle pollution modeling. Copyright © 2022 American Association for Aerosol Research

Deposition velocity of inertial particles driven by wall-normal external force in turbulent channel flow

The effect of wall-normal external force and particle inertia on the deposition of particles in wall-bounded turbulence has been investigated by a point-particle Lagrange simulation. The preferential distribution of particles in the near-wall regions and the insufficient deceleration in the viscous sublayer jointly cause the enhancement of deposition velocity. The external forces strongly affect the clustering of particles in coherent flow structures. The increasing of the wall-normal force inhibits the clustering of particles, which further affects the deposition velocity.

Experiment and calculation of deposition velocity of suspended particles in storm drainage.

Deposition particles can lead to blockage, odor, and corrosion of pipes, and the deposition process of suspended particles is particularly complicated. In order to quantify the deposition process of suspended particles and mastered the critical conditions for the deposition in storm drainage, the process was simulated experimentally, and the deposition states of suspended particles under the different roughness of pipe wall, particle size, and density were analyzed. Two mathematical models of deposition critical velocity and easy deposition velocity were established. Results showed that with the increase of particle size and density, the gravity of particles increased and deposition was more likely to occur. In the rough pipeline, the kinetic energy consumption of water flow increased, the ability to carry particles was weakened, and the deposition rate would increase accordingly. The higher the flow velocity, the lower the deposition rate. The deposition states of particles in the pipeline could be divided into three types according to the deposition rates: "no deposition," "minor deposition," and "bulk deposition." Verification showed that the difference rates between the calculated values and measured values of the deposition critical velocity ranged from - 3.23 to 2.86%, and the difference rates of the easy deposition velocity were - 4.14-4.72%, showing good consistency.

Improving the particle dry deposition scheme in the CMAQ photochemical modeling system

Dry deposition of atmospheric aerosols in large-scale models is a critical, but highly uncertain, sink process with a strong dependence on particle size, meteorological conditions, and land surface properties. This study investigates the particle dry deposition scheme implemented in the standard Community Multiscale Air Quality (CMAQ) model v5.2.1, characterizes its underlying parameterized components with comparison to a similar scheme in a contemporary regional-scale model, and proposes two updated schemes that are then evaluated with available ambient particle deposition velocity (Vd) measurements. Both updated schemes reduce the surprisingly strong dependence of deposition velocity on the aerosol mode width, with one scheme further introducing a dependence on vegetation coverage that is broadly consistent with variability in observations between vegetated and non-vegetated surfaces. Compared to the base scheme, the updated scheme with vegetation dependence increases Vd for submicron particles and decreases it for larger particles by an average of 37% and −66%, respectively. This scheme performs statistically better than the base scheme, reducing fractional biases by 56%–97% for vegetated land-use types and has roughly equivalent performance over water. The base and updated schemes are tested with three annual CMAQ (v5.2.1) simulations for the year 2011; predicted ambient aerosol concentrations are evaluated with routine monitoring network observations and predicted dry deposition fluxes are evaluated with data from the Clean Air Status and Trends Network (CASTNET). The updated scheme with vegetation dependence reduces negative fractional biases for PM10 by 41% and positive fractional biases for PM2.5 organic carbon by 15%. This scheme has been incorporated into the most recent publicly accessible versions of CMAQ (v5.3 and beyond) to replace the scheme used in previous versions of CMAQ (v4.5 through v5.2.1).