Particle deposition in ventilation duct with convex or concave wall cavity

A numerical study is carried out on particle deposition in ducts with either convex or concave wall cavity.Results show that,if compared with smooth duct,particle deposition velocitiesVd^+increase greatly in ducts with wall cavities.More specifically,forτ+<1,Vd^+increase by about 2–4 orders of magnitude in the cases with the convex and concave wall cavities;forτ+>1,Vd^+grows relatively slower.Enhancement of particle deposition with wall cavities is caused by the following mechanisms,i.e.,interception by the wall cavities,expanded deposition area,and the enhanced flow turbulence.In general,addition of wall cavities is contributive for particle deposition,so it provides an efficient approach to remove particles,especially with small size,e.g.,PM2.5.Moreover,the convex wall cavity leads to a larger increment ofVd^+than the concave wall cavity.However,taking pressure loss into account,thoughVd^+is relatively lower,duct with the concave wall cavity is more efficient than that with the convex wall cavity.

Heavy-organic particle deposition from petroleum fluid flow in oil wells and pipelines

Suspended asphaltenic heavy organic particles in petroleum fluids may stick to the inner walls of oil wells and pipelines. This is the major reason for fouling and arterial blockage in the petroleum industry. This report is devoted the study of the mechanism of migration of suspended heavy organic particles towards the walls in oil-producing wells and pipelines. In this report we present a detailed analytical model for the heavy organics suspended particle deposition coefficient corresponding to petroleum fluids flow production conditions in oil wells. We predict the rate of particle deposition during various turbulent flow regimes. The turbulent boundary layer theory and the concepts of mass transfer are utilized to model and calculate the particle deposition rates on the walls of flowing conduits. The developed model accounts for the eddy diffusivity, and Brownian diffusivity as well as for inertial effects. The analysis presented in this paper shows that rates of particle deposition （during petroleum fluid production） on the walls of the flowing channel due solely to diffusion effects are small. It is also shown that deposition rates decrease with increasing particle size. However, when the process is momentum controlled （large particle sizes） higher deposition rates are expected.

Numerical simulation of particle deposition in obstructive human airways

To investigate airflow pattern and its impact on particle deposition, finite-volume based computational fluid dynamics （CFD） simulations were conducted in the diseased triple-bifitrcation airways. Computations were carried out for twenty Reynolds numbers ranging from 100 to 2 000 in the step of 100. Particles in the size range of 1-10 μm were conducted. Two particle deposition mechanisms （gravitational sedimentation and inertial impaction） were considered. The results indicate that there are strong relationship between airflow structures and particle deposition patterns. Deposition efficiency is different for different particles in the whole range of the respiratory rates. Particles in different sizes can deposit at different sites. Smaller particles can be uniformly deposited at the inside wall of the considered model. Larger particles can be mainly deposited in the proximal bifurcations. Deposition fraction varies a lot for different inlet Reynolds numbers. For lower Reynolds numbers, deposition fraction is relatively small and varies a little with varying the diameters. For Reynolds number to target the aerosols at the specific site. higher Reynolds numbers, there is a most efficient diameter for each

Lie group analysis for the effect of temperature-dependent fluid viscosity and thermophoresis particle deposition on free convective heat and mass transfer under variable stream conditions

This paper examines a steady two-dimensional flow of incompressible fluid over a vertical stretching sheet. The fluid viscosity is assumed to vary as a linear function of temperature. A scaling group of transformations is applied to the governing equa- tions. The system remains invariant due to some relations among the transformation parameters. After finding three absolute invariants, a third-order ordinary differential equation corresponding to the momentum equation and two second-order ordinary differential equations corresponding to energy and diffusion equations are derived. The equations along with the boundary conditions are solved numerically. It is found that the decrease in the temperature-dependent fluid viscosity makes the velocity decrease with the increasing distance of the stretching sheet. At a particular point of the sheet, the fluid velocity decreases but the temperature increases with the decreasing viscosity. The impact of the thermophoresis particle deposition plays an important role in the concentration boundary layer. The obtained results are presented graphically and discussed.

Self-cleaning effect and secondary swirling clean gas for suppressing particle deposition on vortex finder of gas cyclones

In order to suppressing the particle deposition on vortex finder,a series of gas cyclones with the secondary swirling clean gas were developed inspired by the gas purge effect.Effects of the width and extension length of the flow channel as well as the secondary inlet velocity and running time on the particle deposition pattern,the deposited particle mass and the cyclones'performance were experimentally investigated,respectively.The results show that the ultrafine particles(Stokes number Stk<0.0358)are mainly loose deposited on the walls under the secondary gas.Compare to the conventional cyclone with single tangential inlet,the total deposited particle mass of the improved cyclone has a maximum reduction more than 60%,and the collecting efficiency is increased up to 97.5%under the basically same pressure drop.The corresponding no-deposition area is increased by about 13%,and remains constant in spite of extending the running time.Moreover,an interesting phenomenon named"self-cleaning effect"of the vortex finder was captured for the gas cyclones,and mechanism of the secondary clean gas on the particle deposition is preliminarily analyzed.The results can deepen the understanding of the particle deposition on the vortex finder and guide the design of the anti-coking gas cyclones.

Incense smoke(IS)inhalation exposure system:Physicochemical characterization,IS particle deposition and clearance in human airway using MPPD model

Incense smoke(IS)is source of indoor air pollution and key risk for diverse human diseases.Less in-formation is available regarding controlled IS rodent inhalation exposure system and IS particulate matter(PM)deposition in human airways.Study aimed to demonstrate stable ISPM physicochemical parameters of 10 incense products inside the customized whole body inhalation exposure chamber(without animal)connected to smoke generation unit via aerosol mixing device.IS analyzed for size segregated PM emission,ISPM in vitro aerodynamics(MMAD and GSD determination),fine and ultrafine particle's SEM,SEM-EDX and PAH analysis.Using real life exposure scenario by utilizing MMAD,GSD and PM concentration after Tier 1 exposure assessment as key input parameters,ISPM dosimetry in infant(3 months)and adult(21 years male and female)human airways was calculated using multiple-path particle dosimetry(MPPD 3.04)modeling.Mass median aerodynamic diameter(MMAD)and geo-metric standard deviation(GSD)ranged between 0.55 and 2.10μm and 1.22 to 1.77(polydisperse)respectively.PM1.0 and PM0.1 showed multiple morphology and presence of heavy and trace elements.PAH like acenaphthylene,anthracene,fluorene,naphthalene and phenanthrene were detected(0.84-143.17μg/g).MPPD results showed higher ISPM deposition in pulmonary region and lowest in trachea bronchial region.ISPM deposition in tissue was higher in lower,peripheral lung as compared to upper and central lung tissue.Whole body inhalation exposure system showed stable IS atmosphere(physi-cochemical parameters)indicating the device suitability in future inhalation studies.MPPD ISPM deposition fraction and clearance data showed deep lung penetrating and retention behavior with higher risk in infant followed by female and then male.These modeled particle deposition and clearance data may be useful in risk assessment analysis of IS.

A review on numerical studies of airflow dynamics and particle deposition in human respiratory system Author links open overlay panel

Accurate assessment and prediction of airflow dynamics and particle deposition in the human respiratory tract are essential for human health,involving inhaled drugs for treating various diseases and toxic particles that can cause illnesses.This intricate process involves complex multiphase flow with distinct respiratory characteristics.Computational fluid dynamics(CFD)acts as a bridge,overcoming the limitations of in vivo and in vitro experiments and providing a means to fully comprehend and reveal the fundamental mechanisms of respiratory flow and particle behavior on a microscopic scale.This paper provides a comprehensive overview and concise summary of recent advancements in the numerical simulation of airflow and particle deposition in the human respiratory tract.Particularly,it summarizes the transition of respiratory tract models from segmented models to emerging physiological characteristic models and whole-lung airway models,and the latest developments on the effects of key factors such as geometric variations,respiratory patterns,and particle physical/chemical properties on respiratory flow and particle deposition.A notable focus of this review is on emerging physiological characteristics models and their associated complex airflow and particle dynamics inside it.The paper concludes with recommendations for future research to further advance the development of this field.

Numerical investigation of non-spherical particle deposition characteristics on filter media

In the building environment,PM2.5 seriously affects people’s health and quality of life,so it is necessary to study the particle deposition characteristics.In addition,it is essential for a thorough investigation of the dust removal mechanism to understand the non-spherical particles deposition characteristics.The stacking angle experiment was used to calibrate the discrete element simulation parameters.And four simulation methods(CFD-DPM,CFD-DEM,API interface loading drag model based on EDEM software and EDEM simulation)were used to numerically simulate the non-spherical particles deposition characteristics.The optimal simulation method EDEM was applied to study the non-spherical particles deposition characteristics in filter media,which saves the calculation time obviously.On this basis,the particle parameters on the particle deposition characteristics of filter media were investigated.The results show that the deposition rate of non-spherical(special shape)particles with the same volume is basically consistent on the filter media,hence it is more realistic that the dust actual shape is simplified into the triangular-shaped particles.As the particle size increases,the number of deposited particles on the filter media decreases.And the larger the particle size,the more dispersed the distribution.It has a significant impact on the number of particles deposited on the filter media when the particle velocity is 0.1 m/s.The particle deposits to the lower part of the filter media in the form of a parabola and deviates from the outlet seriously at 0.1 m/s.Moreover,it has little effect on the number of particle deposition at the other velocities,and most particles are deposited on the upper part of the filter media with the increase of particle velocity.

Bioconvective nanofluid flow over an exponential stretched sheet with thermophoretic particle deposition

The current work is being done to investigate the flow of nanofluids across a porous exponential stretching surface in the presence of a heat source/sink,thermophoretic particle deposition,and bioconvection.The collection of PDEs(partial differential equations)that represent the fluid moment is converted to a system of ODEs(ordinary differential equations)with the use of suitable similarity variables,and these equations are then numerically solved using Runge Kutta Fehlberg and the shooting approach.For different physical limitations,the numerical results are visually represented.The results show that increasing the porosity characteristics reduces velocity.The mass transfer decreases as the thermophoretic limitation increases.Increases in the porosity parameter reduce skin friction,increases in the solid volume fraction improve the rate of thermal distribution,and increases in the thermophoretic parameter increase the rate of mass transfer.

Modeling micro-particle deposition in human upper respiratory tract under steady inhalation

A representative human upper respiratory tract （URT） with idealized oral region and asymmetric tracheo- bronchial （TB） airway has been modeled, and laminar-to-turbulent airflow for typical inhalation modes as well as micro-particle transport and deposition has been simulated using CFX10.0 software from Ansys Inc. on a personal computer. The asymmetric TB airway could not be replaced by an extended straight tube as outlet of the oral region while investigating the tracheal airflow field and particle deposition. Compared to an idealized oral airway with an extended straight tube, several differences could be noted： （i） The laryngeal jet extends further down the trachea and inclines towards the anterior wall; （ii） the turbulence level in trachea is less and decays more quickly; （iii） three recirculation zones are visible with intense adverse current after the glottis; （iv） deposition of small particles in trachea is reduced due to lower turbulence. Refined unstructured mesh with densified boundary layer mesh could be a proper substitute for the structured mesh in the human URT model with asymmetric TB airway. Based on the refined unstructured mesh, the physiological structure of uvula in the soft palate is properly simulated in the present human URT model.

Particle deposition patterns on high-pressure turbine vanes with aggressive inlet swirl

Characteristics of particle migration and deposition were numerically investigated in presence of aggressive swirl at the turbine inlet.The isolated effects of the inlet swirl were considered in detail by shifting the circumferential position of the swirl and by implementing positive and negative swirling directions.Particles were released from the turbine inlet and the resulting deposition on the vanes was determined by using the critical velocity model in a range of particle diameters from 1 to 25 lm.Results show that the particles are more likely to move outwards to the boundary walls of the passage by the action of the swirling flow.However,this could be relieved by increasing the particle size.An imbalance problem of the deposition is found between the adjacent vanes,which could introduce additional inlet non-uniformities towards the downstream rotor and thus accelerate performance degradation of the turbine stage.Overall,the negative swirl case has higher overall capture efficiency within the entire turbine than the positive swirl case for larger particles,and when the inlet swirl is shifted to the mid-passage of the turbine,more deposits could be produced in comparison with the case in which the swirl aims at the vane leading edge.

Particle Deposition in Oral-tracheal Airway Models with Very Low Inhalation Profiles

Considerable progress has been made on modeling particle deposition in the oral-tracheal airway under some normal breathing conditions, i.e., resting, light activity and moderate exercise. None of these standard breathing patterns correspond to very low inhalation profiles. It is known that particle deposition in the oral-tracheal airway is greatly influenced by flow and particle inlet conditions. In this work, very low inhalation flow rates are considered. Particle deposition is numerically investigated in different oral-tracheal airway models, i.e., circular, elliptic and realistic oral-tracheal airway models. Both micro- and nano-particles that are normally present in cigarette smoke are considered. Results show that inhalation profiles greatly influence the particle deposition. Due to relatively low flow rate, for ultra-fine particles, the oral deposition is enhanced due to longer residence time in oral cavity and stronger Brownian motion. However, for larger particles, less particles deposit in the oral-tracheal airway due to the weaker impaction. The transition happens when particle size changes from 0.01 μm to 0.1 μm. The influence of the limited entrance area is shown and discussed. Under the low inhalation profiles, the highest deposition fraction could be in either circular or realistic models depending on the particle property and the geometric characteristic of oral cavity. The knowledge obtained in this study may be beneficial for the design of bionic inhaler and understanding of health effect from smoke particle on human being.

Characterization of particle deposition during crossflow filtration as influenced by permeate flux and crossflow velocity using a microfluidic filtration system

Particle deposition during crossflow filtration is significantly influenced by the operating conditions,in particular the permeate flux and crossflow velocity.However,there is a lack of detailed knowledge about how deposit layer structures and distributions depend on operating parameters.This study uses a microfluidic visualisation filtration system to examine the influence of operating conditions on the deposition process during crossflow ultrafiltration from a microscopic perspective.Increasing the permeate flux caused an increasing amount of deposition and a thicker deposit layer.Higher crossflow velocities reduced the extent of deposition.The degree of deposition varied over a range of operating conditions due to the altered hydrodynamic forces exerted on the particles,which can be examined by the deposition probability according to an existing model.Building on this,an empirical correlation between the deposition probability and volume of deposition as a function of filtration time was developed,which gave good agreement with experimental results.The effect of solution conditions was also involved in this correlation as a interaction energies.This could be useful for predicting the dynamic deposition process during crossflow filtration over a range of operating and solution conditions.

Simulating Deposition of Aerosol Particles on Single Fiber Surface

The stochastic simulation method, based on the concept of control window and the numerical solution of the Langevin equation, is applied to solve the deposition problem of particles from the flowing suspensions onto a fiber collector. Using the Kuwabara model to characterize the flow field, the effects of Stokes number, interception parameter, packing density, particle size distribution on the collection efficioncy, and the deposition morphology of particles onto a collector are i examined. The morphology of deposit obtained in the simulated results agrees Well with experimental observations. The estimation of the initial coUection efficiency through the simulations considers that the deposited particles are in good agreement with published experimental data. In addition, the collection efficiency of particles increases in a wider particle size distribution region.

Deposition of duststorm particles during 2000–2012 in the South Yellow Sea,China based on satellite data

In this study,about 220 satellite images between 2000 and 2012 were obtained from FY-series,MODIS,CBERS,HJ-1A and HJ-1B to estimate the impact of duststorms on the South Yellow Sea（SYS）,which serve as an important source of particles there.The analyzing results from the images support a total occurrence of 88 duststorms（including the locally-generated dusty weather） that affected the SYS during 2000–2012.The annual occurrence was about 4–10 times（10 times in 2000 and 2004;four times in 2009 and 2012）,predominantly in March（29%）,April（33%） and May（22%）.By mapping the distribution of their frequency,the duststorms influencing the SYS were found primarily moving from the northwest（39 times,44.3%） and west（37 times,42%） to the study region with only 11 duststorms（12.5%） coming from the north and 1 duststorm（1%） from the southwest.We estimated that an annual amount of 0.5–3.5 million tons of sediment particles was brought to the SYS by the duststorms during 2000–2012.

Investigation of Movement and Deposition Behaviors of Solid Particles in Hydraulic Water Reservoir via the CFD‑DEM Coupling Method

Solid contamination existing as solid particles in power fluid transmission systems may lead to transmission performance reduction,system failures,and component damage.The hydraulic reservoir will deposit the contamination and store hydraulic fluid.To investigate its purification ability for solid contamination,experiments and simulations for the motion and deposition status of the typical hydraulic system particles are carried out to reveal the interaction of particles and fluid in hydraulic water reservoirs.The results show that the CFD-DEM coupling method could predict the accurate deposition position of iron particles and sand particles when ignoring the small-scale turbulence effect in the flow field.Besides,the particle motion traces and deposition patterns in the reservoir illustrate that the flow development on the bottom surface results in the particles turning,and particles tend to settle in the low flow energy position.The motion of particles is also linked to particles Stokes number,and the same-size sand particles are easily driven by the fluid.The contribution of this paper could provide a guide for predicting the particle motion and deposition pattern in the hydraulic reservoir.

Formation of Ultrafine Metal Particles and Metal Oxide Precursor on Anodized Al by Electrolysis Deposition

Nickel was deposited by ac electrolysis deposition in the pores of the porous oxide film of Al produced by anodizing in phosphoric acid. Ultrafine rod-shaped Ni particles were formed in the pores. At the same time a film of Ni oxide precursor was developed on the surface of the porous oxide film. The Ni particles and the Ni oxide precursor were examined by SEM, TEM and X-ray diffraction. The thickness of the barrier layer of the porous oxide film was thin and it attributed to the formation of the metal particles, while the formation of the oxide precursor was associated with the surface pits which were developed in the pretreatment of Al.

Deep bed filtration model for cake filtration and erosion

Many phenomena in nature and technology are associated with the filtration of suspensions and colloids in porous media. Two main types of particle deposition,namely, cake filtration at the inlet and deep bed filtration throughout the entire porous medium, are studied by different models. A unified approach for the transport and deposition of particles based on the deep bed filtration model is proposed. A variable suspension flow rate, proportional to the number of free pores at the inlet of the porous medium, is considered. To model cake filtration, this flow rate is introduced into the mass balance equation of deep bed filtration. For the cake filtration without deposit erosion,the suspension flow rate decreases to zero, and the suspension does not penetrate deep into the porous medium. In the case of the cake filtration with erosion, the suspension flow rate is nonzero, and the deposit is distributed throughout the entire porous medium. An exact solution is obtained for a constant filtration function. The method of characteristics is used to construct the asymptotics of the concentration front of suspended and retained particles for a filtration function in a general form. Explicit formulae are obtained for a linear filtration function. The properties of these solutions are studied in detail.

Prediction of wall deposition behaviour in a pilot-scale spray dryer using deposition correlations for pipe flows

The particle deposition behaviour of skim milk, water and maltodextrin in the conical section of a pilot-scale spray dryer was predicted using simple correlations for particle depositions in pipes. The predicted particle deposition fluxes of these materials were then compared with the measured deposition fluxes. The predicted particle deposition regimes of the spray dryer were expected to be in the diffusional and mixed (diffusional and inertial) regimes, but the experimental results suggested that the particle deposition was mainly in the inertial regime. Therefore, using the pipe correlations for predicting deposition in a pilot-scale spray dryer suggests that they do not sufficiently represent the actual deposition behaviour. This outcome indicates that a further study of particle flow patterns needs to be carried out using numerical simulations (computational fluid dynamics, CFD) in view of the additional geometrical complexity of the spray dryer.

Effects of cartilaginous rings on airflow and particle transport through simplified and realistic models of human upper respiratory tracts

In the present study, computational fluid dynamics （CFD） is used to investigate inspiratory and expiratory airflow characteristics in the human upper respiratory tract for the purpose of identifying the probable locations of particle deposition and the wall injury. Computed tomography （CT） scan data was used to reconstruct a three dimensional respiratory tract from trachea to first generation bronchi. To compare, a simplified model of respiratory tract based on Weibel was also used in the study. The steady state results are obtained for an airflow rate of 45 L/min, corresponding to the heavy breathing condition. The velocity distribution, wall shear stress, static pressure and particle deposition are compared for inspiratory flows in simplified and realistic models and expiratory flows in realistic model only. The results show that the location of cartilaginous rings is susceptible to wall injury and local particle deposition.