Location Of Particle Deposition Research Articles

A comprehensive approach to simulation of cartridge filtration using CFD

Household water treatment (HWT) systems are widely used for the provision of potable water in many countries with their low-cost key to attaining universal and equitable access to safe and affordable drinking water, Sustainable Development Goal 6.1. Removal of suspended particles (turbidity) from water sources via cartridge filters is often the first step of a HWT system, with the primary treatment increasing the efficiency of a subsequent disinfection step.Whilst the performance of cartridge filters (removal efficiency and pressure drop) can be determined experimentally in long experiments with high volumes of water, numerical simulation adds fundamental insight to the influence of fluid dynamics on particle deposition and vice versa. In this study, a novel computational fluid dynamic (CFD) model was developed to simulate the fundamental mechanisms underpinning the removal of particles within the widely used 10 in. cartridge filter, informed by and complemented with laboratory validation. The Eulerian approach was used to simulate fluid flow with the Lagrangian approach adopted for particle tracking. Rosin-Rammler distribution was implemented with respect to the particle size distribution of the diatomaceous earth particles used in the experiments. Given particles were non-spherical (disk shape), Wadell’s sphericity was included to account for the effect of particle shape on drag force. A porous domain was implemented to simulate the filter element through addition of a source term to the momentum equations, with the likelihood of particle deposition, detachment and rebound also considered.Laboratory based validation studies confirmed the novel CFD model to accurately model removal of turbidity and predict the pressure drop across the filter with Root Mean Square Percentage Error (RMSPE) of less than 3%. The simulated location of particle deposition on the filter elements closely matched images taken at several stages during filtration experiments with the model aiding understanding of pattern of particle removal along and within the porous filter structure. This novel and comprehensive modelling methodology can be utilized to simulate the filtration process at the macro-scale, permitting evaluation of new filter designs and materials for advanced filtration systems; ultimately improving HWT system performance and reducing costs to users.

Numerical study of aerodynamic characteristics and particle motion in square cylinder vortex flow with different void ratios

In actual production practice, blunt block structures usually exist in multiple forms simultaneously, such as buildings, bridges, and offshore platforms. Flow around multi-cylinder structures is often accompanied by complex phenomena, including separation and reattachment of shear layers, vortex-structure interactions, and the evolution of wake vortex streets. These phenomena can worsen fatigue damage or local accumulation of harmful substances on bluff block structures. The main purpose of this study is to analyze the complex flow phenomena of square cylinders with different void ratios and the distribution of particulate matter in the flow. The results show that the drag forces applied to the square cylinder under different void conditions will be very different, the flow will also vary greatly, and the location of particle deposition will also change significantly with the change of void ratio conditions.

Numerical Study of Nanoparticle Deposition in a Gaseous Microchannel under the Influence of Various Forces

Nanoparticle deposition in microchannel devices inducing contaminant clogging is a serious barrier to the application of micro-electro-mechanical systems (MEMS). For micro-scale gas flow fields with a high Knudsen number (Kn) in the microchannel, gas rarefaction and velocity slip cannot be ignored. Furthermore, the mechanism of nanoparticle transport and deposition in the microchannel is extremely complex. In this study, the compressible gas model and a second-order slip boundary condition have been applied to the Burnett equations to solve the flow field issue in a microchannel. Drag, Brownian, and thermophoretic forces are concerned in the motion equations of particles. A series of numerical simulations for various particle sizes, flow rates, and temperature gradients have been performed. Some important features such as reasons, efficiencies, and locations of particle deposition have been explored. The results indicate that the particle deposition efficiency varies more or less under the actions of forces such as Brownian force, thermophoretic force, and drag force. Nevertheless, different forces lead to different particle motions and deposition processes. Brownian or thermophoretic force causes particles to move closer to the wall or further away from it. The drag force influence of slip boundary conditions and gas rarefaction changes the particles’ residential time in the channel. In order to find a way to decrease particle deposition on the microchannel surface, the deposition locations of different sizes of particles have been analyzed in detail under the action of thermophoretic force.

Numerical investigation of nanoparticle deposition location and pattern on a sharp-bent tube wall

The characteristics of fluid flow on a sharp-bent tube under various conditions were analyzed. Numerical simulations for analyzing the particle deposition locations and patterns on a sharp-bent tube were conducted by using the modified single-particle tracking analysis based on aerosol mass flow rate. Through the numerical calculation, we showed that after the bending point in a sharp-bent tube, the faster axial velocity occurred near the outer wall, and the boundary layer at high Reynolds number became thinner. Furthermore, the faster radial velocity near the tube wall was observed at less developed-flow region at high Reynolds number owing to the stronger secondary flow. The nanoparticle deposition locations and patterns were systematically examined in various viewpoints including cumulative number of deposited particles, local deposition enhancement factor, and particle deposition pattern according to azimuthal angles. We found that most of the nanoparticles were deposited on the outer wall right after the bending point owing to outward-sloping flow. Moreover, the difference in relative deposition efficiency along the azimuthal angles at each section in the sharp-bent tube was reduced as Reynolds number increased. This is because the nanoparticles near the wall were well mixed due to the strong secondary flow at high Reynolds number.

Modelling Particle Transport and Deposition in the Human Healthy and Stented Tracheobronchial Airways.

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.

Marangoni circulation by UV light modulation on sessile drop for particle agglomeration

An analytical solution of a biharmonic equation is presented in axisymmetric toroidal coordinates for Stokes flow due to surface tension gradient on the free surface of sessile drops. The stream function profiles exhibit clockwise and counter-clockwise toroidal volumes. The ring or dot formed by the downward dividing streamlines between these volumes predicts the experimentally deposited particle ring or dot well. This finding suggests that the downward dividing streamline can be taken to be a reasonable indicator of where deposition occurs. Different light patterns directed at different locations of the droplet can give rise to a single spot or ring. A relationship between the positions of the light intensity peak and possible locations of particle deposition is analysed to demonstrate that the streamlines can be generated on-demand to achieve particle deposition at predetermined locations on the substrate. Toroidal corner vortices called Moffatt eddies have appeared in other corner flows and develop in this optical Marangoni flow as well near the contact line.

A Feasible Computational Fluid Dynamics Study for Relationships of Structural and Functional Alterations with Particle Depositions in Severe Asthmatic Lungs.

This study aims to investigate the effect of altered structures and functions in severe asthma on particle deposition by using computational fluid dynamics (CFD) models. Airway geometrical models of two healthy subjects and two severe asthmatics were reconstructed from computed tomography (CT) images. Subject-specific flow boundary conditions were obtained by image registration to account for regional functional alterations of severe asthmatics. A large eddy simulation (LES) model for transitional and turbulent flows was applied to simulate airflows, and particle transport simulations were then performed for 2.5, 5, and 10 μm particles using CFD-predicted flow fields. Compared to the healthy subjects, the severe asthmatics had a smaller air-volume change in the lower lobes and a larger air-volume change in the upper lobes. Both severe asthmatics had smaller airway circularity (Cr), but one of them had a significant reduction of hydraulic diameter (Dh). In severe asthmatics, the larger air-volume change in the upper lobes resulted in more particles in the upper lobes, especially for the small 2.5 μm particles. The structural alterations measured by Cr and Dh were associated with a higher particle deposition. Dh was found to be the most important metric which affects the specific location of particle deposition. This study demonstrates the relationship of CT-based structural and functional alterations in severe asthma with flow and particle dynamics.

Large Eddy simulations of particulate flows inside a square differentially heated cavity at Rayleigh numbers up to 1011

The Differentially Heated Cavity (DHC) has often served as a suitable geometric model for naturally driven particulate flows inside closed volumes. While providing deep insights of the flow dynamics, 3D DNS or 3D LES simulations of DHC flows are very time-consuming and their potential extension to higher Rayleigh (Ra) numbers typical of room dimensions is problematic. In this study, therefore, a 2D-LES Euler-Lagrange approach is used to predict turbulent particle transport in a DHC.We first validate our predictions against a 2D DNS database at Ra 109 and 1010 with particles having diameters greater than 15 μm. We show that our LES results are in very agreement with the DNS data. In a second step, we extend our simulations to a fully turbulent Ra number 1011 and particle diameters between 0.5 and 10 m. Details are provided on the particle deposition locations and airborne concentration decay rate with time. We show in particular that as the flow becomes more turbulent, the particle settling rates approach those predicted by the simple stirred settling model.

Aerosols in healthy and emphysematous in silico pulmonary acinar rat models

There has been relatively little attention given on predicting particle deposition in the respiratory zone of the diseased lungs despite the high prevalence of chronic obstructive pulmonary disease (COPD). Increased alveolar volume and deterioration of alveolar septum, characteristic of emphysema, may alter the amount and location of particle deposition compared to healthy lungs, which is particularly important for toxic or therapeutic aerosols. In an attempt to shed new light on aerosol transport and deposition in emphysematous lungs, we performed numerical simulations in models of healthy and emphysematous acini motivated by recent experimental lobar-level data in rats (Oakes et al., 2014a). Compared to healthy acinar structures, models of emphysematous subacini were created by removing inter-septal alveolar walls and enhancing the alveolar volume in either a homogeneous or heterogeneous fashion. Flow waveforms and particle properties were implemented to match the experimental data. The occurrence of flow separation and recirculation within alveolar cavities was found in proximal generations of the healthy zones, in contrast to the radial-like airflows observed in the diseased regions. In agreement with experimental data, simulations point to particle deposition concentrations that are more heterogeneously distributed in the diseased models compared with the healthy one. Yet, simulations predicted less deposition in the emphysematous models in contrast to some experimental studies, a likely consequence due to the shallower penetration depths and modified flow topologies in disease compared to health. These spatial-temporal particle transport simulations provide new insight on deposition in the emphysematous acini and shed light on experimental observations.

Comparative numerical modeling of inhaled micron-sized particle deposition in human and rat nasal cavities

Micron-sized particle deposition in anatomically realistic models of a rat and human nasal cavity was numerically investigated. A steady laminar inhalation flow rate was applied and particles were released from the outside air. Particles showing equivalent total particle deposition fractions were classified into low, medium and high inertial particle. Typical particle sizes are 2.5, 9 and 20 μm for the human model and 1, 2 and 3 μm for the rat model, respectively. Using a surface-mapping technique the 3D nasal cavity surface was “unwrapped” into a 2D domain and the particle deposition locations were plotted for complete visual coverage of the domain surface. The total surface area comparison showed that the surface area of the human nasal model was about ten times the size of the rat model. In contrast, the regional surface area percentage analysis revealed the olfactory region of the rat model was significantly larger than all other regions making up ∼55.6% of the total surface area, while that of the human nasal model only occupying 10.5%. Flow pattern comparisons showed rapid airflow acceleration was found at the nasopharynx region and the nostril region for the human and rat model, respectively. For the human model, the main passage is the major deposition region for micro-particles. While for the rat model, it is the vestibule. Through comparing the regional deposition flux between human and rat models, this study can contribute towards better extrapolation approach of inhalation exposure data between inter-subject species.

Numerical Simulation of Particles Deposition in a Human Upper Airway

Based on the CT scanned images, a realistic geometric model from nasal cavity to upper six-generation bronchia is rebuilt. In order to effectively simulate the particle movement and deposition, LES model is used and the particles are tracked in the frame of Lagrange. Seven kinds of typical particles, including micron particles (1, 5, and 10 μm) and nanoparticles (1, 5, 20, and 100 nm), and three representative respiratory intensities are adopted as computational case, respectively. Deposition efficiency ( D E), deposition concentration ( D C), and capture efficiency ( C E) are introduced. Furthermore, the locations of particle deposition are visualized. The results indicate that the injecting particles from different nasal inlet present “transposition effect.”The D E values of micron particles are much higher than nanoparticles. The particle diameter plays a weaker role in nanoparticle depositions than micron particles. The highest values of D E and D C both occur in nasal cavity, while the highest C E up to 99.5% occurs in bronchus region.

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.

Airborne Particulate Matter and Acute Lung Inflammation: Strak et al. Respond

We thank Gangamma for a number of excellent observations and would like to respond to the issues raised. Gangamma points out that the levels of fractional exhaled nitric oxide (FENO) may be influenced by the site of particle deposition in the lung and requests further explanation on how this could affect the analysis and conclusion of our study (Strak et al. 2012). In an observational study such as ours, it is not possible to assess precise locations of particle deposition in the respiratory tract. Although variations in location of particle deposition likely introduced some noise in the FENO readings, we could not take this into account in the regression model. Gangamma notes that many components of particulate matter (PM) can induce neutrophil inflammation in the lung; thus, focusing only on FENO may not sufficiently reflect their effects. FENO is an indicator of airway inflammation that is used fairly often in observational and experimental studies. As we stated above, in a study such as ours (Strak et al. 2012), it would be very challenging to address many possible inflammation pathways. In addition, the focus of our study was more on the components and characteristics of air pollution and associated health effects. We included other inflammatory markers (e.g., interleukin-6, neutrophils) measured both in blood and nasal lavage in our health measurements, but those were outside of the scope of our paper. The next issue raised by Gangamma deals with the suggestion that many of the measured FENO values could be within error range of the measurement instrument; therefore, data on the precision of the measurements should be provided and explanation should be given on how it could affect the regression analysis. Measurement error is an issue in every observational, as well as experimental, study. It reduces the chance of finding associations with external variables (also subject to measurement error); however, in a regression analysis, measurement error in the dependent variable does not introduce bias in the size of the regression coefficient. Gangamma’s last comment concerned the suitability of using the CPC 3007 portable condensation particle counter (TSI, St. Paul, MN) for ambient measurements. We used the CPC 3007 only to characterize the air pollution inside the van during transport of the participants to and from the sampling locations. Measurements at the sampling locations were performed using a CPC 3022a (TSI), which is an instrument commonly used in similar experimental studies for characterization of particle number concentration in ambient air.

Imaging extra-thoracic airways and deposited particles in laboratory animals

Laboratory animals are widely used as models for exploring adverse and beneficial health effects caused by inhalation of suspended particles. Mapping particle deposition throughout the airways of laboratory animals is crucial since the location of particle deposition often determines subsequent clearance, transport and the health effects elicited. Such mapping has yet to be performed systematically due to lack of available methods. In this paper, a new method is presented for imaging both the nasal airways of laboratory animals and particles deposited in them. After inhalation of particles, the rat airways are frozen to lock the particles in place and cast at this temperature to color and support the lumen. Once the cast is cured, an imaging cryomicrotome sections and images the airways as well as the deposited fluorescent particles. Computer software reconstructs the airways and particle maps from these serial images. The method was validated by manually placing boluses of fluorescent particles in nasal airways of a rat and then imaging them to ensure that they were displayed in the correct locations. To demonstrate the method, rats inhaled 2.5 μm particles in a nose-only exposure chamber. Images and reconstructions are presented of the nasal passage and deposited particles for one of these rats demonstrating the method’s usefulness for locating inhaled and deposited therapeutic and toxic particles in the extra-thoracic airways of laboratory animals.

Particle deposition onto a microsieve

The objective of the present work is to investigate experimentally the deposition of micron-sized particles onto the surface of a microsieve membrane, which consists in a thin screen with patterned circular holes. A dilute suspension of spherical, monodisperse, polystyrene particles flows at an imposed flow rate through the membrane, in a frontal filtration mode (i.e., the flow direction is perpendicular to the membrane). The particle-to-pore diameter ratio is inferior to one. The particle and flow Reynolds numbers are both smaller than 0.1 for the flow regimes investigated in the present study. The particles are non-Brownian, inertialess, and their buoyancy is negligible. Direct visualizations of the membrane are made using video microscopy. A statistical analysis of the particle deposition locations, based on an automatic processing of video images of the membrane surface recorded during the experiment, is made possible by the periodicity of the pore distribution. Experiments show the existence of two preferential locations for particle deposition, for the whole range of flow rates investigated in the present study and the three microsieve patterns used. This puzzling result is discussed in the light of earlier theoretical and numerical simulations works, dealing with the low Reynolds number motion of a single particle in the vicinity of a pore, in the presence of physicochemical interactions between the particle and the membrane surface.

Mechanisms of particle deposition in a fully developed turbulent open channel flow

Particle dispersion and deposition in the region near the wall of a turbulent open channel is studied using direct numerical simulation of the flow, combined with Lagrangian particle tracking under conditions of one-way coupling. Particles with response times of 5 and 15, normalized using the wall friction velocity and the fluid kinematic viscosity, are considered. The simulations were performed until the particle phase reached a statistically stationary state before calculating relevant statistics. For both response times, particles are seen to accumulate strongly very close to the wall in the form of streamwise oriented streaks. Deposited particles were divided into two distinct populations; those with large wall-normal deposition velocities and small near-wall residence times referred to as the free-flight population, and particles depositing with negligible wall-normal velocities and large near-wall residence times (more than 1000 wall time units), referred to as the diffusional deposition population. Diffusional deposition (deposition induced by the small residual turbulent fluctuations near the wall) is found to be the dominant mechanism of deposition for both particle response times. The free-flight mechanism is shown to gain in importance only for τp+=15 particles. For τp+=5 particles only 10% deposit because of free flight, whereas the fraction is around 40% for τp+=15 particles. This result runs counter to the widely held opinion that free flight is the dominant mechanism of deposition in wall-bounded flows and clearly quantifies the relative importance of the two mechanisms. A simple relationship between the particle wall-normal velocity on deposition and the residence time for free-flight particles is presented. Particle deposition locations over the period of the entire simulation reveal that, while diffusional deposition occurs mostly along streamwise oriented lines below the near-wall particle accumulation patterns, free-flight particles deposit more evenly over the wall.

Factors affecting the deposition of aerosolized insulin.

The inhalation of insulin for absorption into the bloodstream via the lung seems to be a promising technique for the treatment of diabetes mellitus. A fundamental issue to be resolved in the development of such insulin aerosol delivery systems is their efficiency (measured, for example, in terms of the amount of insulin absorbed in the blood compared to the total amount loaded into an inhalation device). A primary factor that could cause inefficiency of insulin absorption is deposition in the nonalveolated airways with subsequent removal from the lung via mucociliary clearance. Thus, a better understanding of the spatial distribution of insulin particle deposition in the lung can give guidance to the optimization of inhalation therapy. A mathematical model was used to study factors affecting the disposition of aerosolized insulin. The model calculates the trajectories of inhaled particles in the lung and has been validated by data from human subject experiments. Computer simulations were performed describing a wide range of patient breathing maneuvers. The results indicate significant variations in particle deposition patterns within lungs for different tidal volumes, inspiratory flow rates, and breath hold times. These findings indicate that particle sizes and ventilatory parameters are significant factors determining locations of particle deposition within human lungs, and thus the absorption of insulin into the blood stream via alveloated airways. Mathematical modeling is a valuable technique to complement clinical studies in the targeted delivery of inhaled insulin.

Characterisation of Enriched Uranium Dioxide Particles from a Uranium Handling Facility

A case study was conducted on approaches for using a prospective measurement of the particle size distribution of a process powder in a uranium handling facility to assign an appropriate annual limit on intake (ALI) for potential inhalation exposures of workers to that powder. The aerodynamic size distribution was determined for particles to which workers might be exposed during dispersion of dusts in an enriched uranium casting operation. Bulk powders were obtained during cleaning of the casting crucibles. The material was 0.846 uranium by mass, which corresponds to the theoretical uranium mass fraction for U 3 O 8 . The material was aerosolised using a DeVilbis dry powder blower and separated by aerodynamic diameter using a five-stage aerosol cyclone train. Approximately 0.08 of the total mass processed in the casting operation was retained as residual oxide, and approximately 0.01 of that mass was less than 10 μm aerodynamic diameter. Assumptions from ICRP 30 and from ICRP 68 and 69 were used to calculate the appropriate dose coefficients, depending on the fraction of the bulk powder that might be suspended into the workplace. Using the assumptions of ICRP 30 for Class D material, the potential location of particle deposition in the respiratory tract has little influence on assignment of an appropriate dose; using the actual particle size distribution of the powder reduced the ALI to about 90% of the value based on assuming that all re-suspended material had an activity median aerodynamic diameter of I μm. Using the assumptions of ICRP 30 for Class W and Y materials, the ALI was increased by a factor of 2.4, 6.3, 9.2, or 10.9 depending on whether the suspended material was limited to particles of aerodynamic diameter less than 10 μm, 20 μm, 50 μm, or all measured particle sizes, respectively. Using the assumptions of ICRP 68 and 69 the ALI for powders of Type F is more dependent on particle size than the ALI for Class D material and would be increased by a factor of 1.1, 1.5, 1.6, and 1.6 over the ICRP 30 model values for the four assumptions of particle size. The ALI for Type M material was changed by factors of 0.8, 1.8, 2.4, and 2.2 (an overall factor of 3) for the four assumptions of available particle size. For Type S material, the ALI changes by factors of 5.0, 10.4, 13.5, and 12.2 (again, an overall factor of about 3) compared to the ICRP 30 values for the four assumptions of particle size. Thus, the potential radiation doses to workers can vary substantially for Type M and Type S materials depending on which size fractions of the bulk powder are suspended into the breathing zone. The approaches and results of this case study provide insight into when prospective studies of particle size and solubility should be used to improve worker protection.