Simulating Particle Size Distributions over California and Impact on Lung Deposition Fraction

Reliable simulations of particle mass size distributions by regional photochemical air quality models are needed in regulatory applications because the U.S. EPA's National Ambient Air Quality Standards specify limits on the mass concentration of particles in a specific size range (i.e., aerodynamic diameter <2.5 μm). Considering the associations between adverse health effects and exposure to ultrafine particles, air quality models may need to accurately simulate particle number size distributions in addition to mass size distributions in future applications. In this study, predictions of particle number and mass size distributions by the Community Multiscale Air Quality model with the standard and an updated emission size distribution are evaluated using wintertime observations in California. Differences in modeled lung deposition fraction for simulated and observed particle number size distributions are also evaluated. Simulated mass size distributions are generally broader and shifted to larger diameters than observations, and observed differences in inorganic and carbon (elemental and organic) distributions are not captured by the model. These model limitations can be reasonably accounted for in regulatory modeling applications. Simulated number size distributions are considerably less accurate than mass size distributions and are difficult to represent in air quality models due to large sub-grid-scale concentration gradients. However, modeled number size distributions are responsive to updates of the emission size distribution, and reasonable simulation of background number size distributions might be possible with an improved treatment of emission size distributions. Modeled lung deposition fractions for simulated number size distributions peak in the same lung region as those for number size distributions observed in the background. However, differences in modeled and observed total number concentrations generally suggest large differences in the total number of deposited particles. Future model development on simulating particle mass size distributions should focus on improving predictions of the mass fraction of particles <2.5 μm. Model development for particle number size distributions should focus on reducing differences in modeled lung deposition for modeled and observed distributions.     

2D and 3D simulations of an internal airlift loop reactor on the basis of a two-fluid model

Two- and three-dimensional (2D and 3D) simulations of an airlift reactor under steady state conditions at low gas flow rates are presented. The simulations are based on a two-fluid model with a k–ε model for the turbulence and as little as possible ad hoc closure terms. The results are compared with an one-dimensional mechanical energy balance and are found to be in good agreement. The 2D results show sensitivity to the gas inlet geometry: whether or not the gas is partially sparged into the liquid directly next to a wall affects the liquid velocity distribution and thereby the gas disengagement at the top of the airlift. The three-dimensional calculations make a more realistic geometry possible. The friction in the system is found to be about a factor of two larger in the 3D case at the same gas inlet conditions. For a given gas flow rate, the mean gas fraction in the riser is the same for the 2D and 3D simulations, the liquid circulation rate is about 30% higher in the 2D case than in the 3D one. A comparison is made with experimental data obtained in an airlift of the same dimensions. The simulated overall gas fraction is in agreement with the experimental findings. The simulated superficial velocity in the riser is compared to LDA data. For the lowest superficial velocities the LDA data coincide with the results from the 2D simulations, for higher gas flow rates the LDA results switch over towards the 3D results.     

CFD simulations of bubble column reactors: 1D, 2D and 3D approach

CFD simulations have been carried out for the predictions of flow pattern in bubble column reactors using 1D, 2D and 3D k-ε models. An attempt has been made to develop a complete correspondence between the operation of a real column and the simulation. Attention has been focused on the cylindrical bubble columns because of their widespread applications in the industry. All the models showed good agreement with the experimental data for axial liquid velocity and the fractional gas hold-up profiles. However, as regards to eddy diffusivity, only the 3D model predictions agree closely with the experimental data.The CFD model has been extended for the estimation of an axial dispersion coefficient (D_L) using 1D, 2D and 3D models. Excellent agreement was found only between the experimental values and the 3D predictions. The 1D and 2D simulations, however, yielded D_L values, which were lower by 25-50%. For this, a mechanistic explanation has been provided.     

Determination of 3‐D Alumina Grain Orientation,Size, Shape,and Growth Kinetics from 2‐D Data in Nextel™ 610 Fibers

Nextel^? 610 alumina fibers were heat‐treated at 1100°C–1500°C for 1–100 h in air. Grain size distributions (GSDs) and grain orientation distributions (ODs) with respect to the fiber axis were characterized by analysis of TEM images from longitudinal fiber sections. The 2‐D GSDs and ODs were characterized as ellipses. 3‐D GSDs and ODs were calculated by fitting distributions of oriented oblate ellipsoids to 2‐D GSDs and ODs formed by ellipsoid–section‐plane intersections. The standard deviations (SDs) of log‐normal GSDs consistently increased with grain size, which is not diagnostic of normal grain growth. The grain aspect ratio (α) and the tendency of the short grain axis to orient perpendicular to the fiber axis also increased with grain size, resulting in more textured fibers at larger grain sizes. Average 3‐D grain sizes were larger than 2‐D sizes for GSDs with small SDs, but smaller for GSDs with large SDs because of under sampling of small grains. 3‐D grain growth kinetics had the same 815 kJ/mol activation energy as that found by 2‐D analysis, but the grain growth exponent m of 6.0 was larger and the pre‐exponential factor much smaller. Expressions for 3‐D log‐normal GSDs as a function of heat treatment temperature and time were determined. α‐distributions and ODs were determined as a function of grain size. Methods for determining 3‐D GSDs are discussed.     

不同填充率下FDM 3D打印预制件建模及力学性能分析

以拉伸、压缩、弯曲、扭转4种受载情况下的熔融沉积型三维（FDM 3D）打印预制件为研究对象,以填充率、填充单元结构类型为分析参数,通过确定3D打印预制件填充率的影响因素,建立了填充率与格子形填充单元几何参数的通用解析式,据此构建不同填充率下3D打印预制件的三维几何模型;然后对不同受载类型3D打印预制件进行有限元仿真分析,明确填充率对不同载荷工况下3D打印预制件力学特性的影响规律。仿真和实验结果表明,填充率对3D打印预制件所受拉伸应力、压缩应力、弯曲应力均有较大影响,而扭转情况下影响较小,据此进一步确定了一定受载情况下3D打印预制件的较优填充率;基于本文提出的不同填充率下预制件三维模型建立方法,可有效实现对预制件的力学性能仿真分析,对减少产品试验验证次数、降低研发成本具有积极作用。     

Comparison of analytical and CFD models with regard to micron particle deposition in a human 16-generation tracheobronchial airway model

A representative human tracheobronchial tree has been geometrically represented with adjustable triple-bifurcation units (TBUs) in order to effectively simulate local and global micron particle depositions. It is the first comprehensive attempt to compute micron-particle transport in a (Weibel Type A) 16-generation model with realistic inlet conditions. The CFD modeling predictions are compared to experimental observations as well as analytical modeling results. Based on the findings with the validated computer simulation model, the following conclusions can be drawn:(i) Surprisingly, simulated inspiratory deposition fractions for the entire tracheobronchial region (say, G0–G15) with repeated TBUs in parallel and in series agree rather well with those calculated using analytical/semi-empirical expressions. However, the predicted particle-deposition fractions based on such analytical formulas differ greatly from the present simulation results for most local bifurcations, due to the effects of local geometry and resulting local flow features and particle distributions. Clearly, the effects of realistic geometries, flow structures and particle distributions in different individual bifurcations accidentally cancel each other so that the simulated deposition efficiencies during inspiration in a relatively large airway region may agree quite well with those obtained from analytical expressions. Furthermore, with the lack of local resolution, analytical models do not provide any physical insight to the air–particle dynamics in the tracheobronchial region.(ii) The maximum deposition enhancement factors (DEF) may be in the order of 10² to 10³ for micron particles in the tracheobronchial airways, implying potential health effects when the inhaled particles are toxic.(iii) The presence of sedimentation for micron particles in lower bronchial airways may change the local impaction-based deposition patterns seen for larger airways and hence reduces the maximum DEF values.(iv) Rotation of an airway bifurcation cause a significant impact on distal bifurcations rather than on the proximal ones. Such geometric effects are minor when compared to the effects of airflow and particle transport/deposition history, i.e., upstream effects.     

Computational Fluid Dynamic Predictions and Experimental Results for Particle Deposition in an Airway Model

An area identified as having a high priority by the National Research Council (NRC 1998) relating to health effects of exposure to urban particulate matter is the investigation of particle deposition patterns in potentially-susceptible subpopulations. A key task for risk assessment is development and refinement of mathematical models that predict local deposition patterns of inhaled particles in airways. Recently, computational fluid dynamic modeling (CFD) has provided the ability to predict local airflows and particle deposition patterns in various structures of the human respiratory tract. Although CFD results generally agree with available data from human studies, there is a need for experimental particle deposition investigations that provide more detailed comparisons with computed local patterns of particle deposition. Idealized 3-generation hollow tracheo-bronchial models based on the Weibel symmetric morphometry for airway lengths and diameters (generations 3-5) were constructed with physiologically-realistic bifurcations. Monodisperse fluorescent polystyrene latex particles (1 and 10 mu m aerodynamic diameter) were deposited in these models at a steady inspiratory flow of 7.5 L /min (equivalent to heavy exertion with a tracheal flow of 60 L /min). The models were opened and the locations of deposited particles were mapped using fluorescence microscopy. The particle deposition predictions using CFD for 10 mu m particles correlated well with those found experimentally. CFD predictions were not available for the 1 mu m diameter case, but the experimental results for such particles are presented.     

Modelling inhaled particle deposition in the human lung—A review

Particle deposition in the human respiratory tract is determined by biological factors such as lung morphology and breathing patterns, and physical factors such as fluid dynamics, particle properties, and deposition mechanisms. Current particle deposition models may be grouped into two categories referring to the region of interest in the lung, i.e. either deposition in the whole lung (whole lung models), or deposition in a localized region of the lung (local scale models). In whole lung models, particle deposition in individual airways is computed by analytical equations for particle deposition efficiencies and specific flow conditions (analytical models). The present review focuses upon the philosophy of different conceptual whole lung models to determine deposition in bronchial and acinar airway generations, and to compare the deposition patterns predicted by these models. Since any modelling approach requires validation by comparison with the available experimental evidence, predicted deposition data are compared with published experimental data in human subjects. This comparison indicates that, at least during the writing of this review, deposition models can be validated only for total and, to some extent, for regional deposition. In local scale models, particle transport and deposition equations are solved by Computational Fluid and Particle Dynamics (CFPD) methods (numerical models), providing information on particle deposition patterns within selected structural elements of the lung, e.g. bronchial bifurcations. In this review, however, only their potential contribution to improve upon current analytical whole lung models will be considered.     

Particle Deposition in a Cast of Human Tracheobronchial Airways

Abstract

Regional particle deposition efficiency and deposition patterns were studied experimentally in a human airway replica made from an adult cadaver. The replica includes the oral cavity, pharynx, larynx, trachea, and four generations of bronchi. This study reports deposition results in the tracheobronchial (TB) region. Nine different sizes of monodispersed, polystyrene latex fluorescent particles in the size range of 0.93–30 μm were delivered into the lung cast with the flow rates of 15, 30, and 60 l min^{? 1}. Deposition in the TB region appeared to increase with the increasing flow rate and particle size. Comparison of deposition data obtained from physical casts showed agreement with results obtained from realistic airway replicas that included the larynx. Deposition data obtained from idealized airway models or replicas showed lower deposition efficiency. We also compared experimental data with theoretical models based on a simplified bend and bifurcation model. A deposition equation derived from these models was used in a lung dosimetry model for inhaled particles, and we demonstrated that there was general agreement with theoretical models. However, the agreement was not consistent over the large range of Stokes number. The deposition efficiency was found as a function of the Stokes number, bifurcation angle, and the diameters of parent and daughter tubes. An empirical model was developed for the particle deposition efficiency in the TB region based on the experimental data. This model, combined with the oral deposition model developed previously, can be used to predict the particle deposition for inertial effects with improved accuracy.     

Particle Deposition in a Multiple-Path Model of the Human Lung

Predicting the amount of particle deposition in the human lung following exposure to airborne particulate matter is the first step toward evaluating risks associated with exposure to airborne pollutants. Realistic deposition models are needed for accurate predictions of deposition in the lung, but a major limitation is the degree to which the lung geometry can be accurately reconstructed. Morphometric data for the entire airway tree of the human lung are not available. So far, idealistic lung structures have been used for deposition calculations. In this study, 10 statistical lung structures based on morphometric measurements of Raabe et al. (1976) were generated for the conducting airways of the human lung. A symmetric, dichotomous branching alveolar airway structure was attached to the end of the conducting airway tree of each lung structure. The total volume of the alveolar region was the same among the lung geometries. Using a mathematical scheme developed previously (Anjilvel and Asgharian 1995), regional, lobar, and per-generation depositions of particles were calculated in these geometries. The results were compared to deposition predictions using typical-path and five-lobe symmetric lung geometry models. All three lung models showed very similar regional and generation-by-generation deposition results. Lobar deposition was found to strongly depend on the detailed morphometry of the lung structure that was used.     

Cavity size, sorption and transport characteristics of thermally rearranged (TR) polymers

Within a polymer thin film, free volume elements have a wide range of size and topology. This broad range of free volume element sizes determines the ability for a polymer to perform molecular separations. Herein, six permeable thermally rearranged (TR) polymers and their precursors were studied. Using atomistic models, cavity size (free volume) distributions determined by a combination of molecular dynamics and Monte Carlo methods were consistent with experimental observation that TR polymers are more permeable than their precursors. The cavity size distributions determined by simulation were also consistent with free volume distributions determined by positron annihilation lifetime spectroscopy. The diffusion, solubility and permeation of gases in TR polymers and their precursors were also simulated at 308 K, with results that agree qualitatively with experimental data.     

Aerosol deposition in 3D models of the upper airways and trachea of rhesus macaques

Abstract

Little is known about aerosol deposition in macaques, variability in deposition between animals, or how deposition in macaques and humans compare. This is despite the use of macaques in assessments of toxic aerosols that are often translated to estimates of human exposure. We used three dimensional (3D) physical models of the upper airways and trachea (UAT) of Rhesus macaques to begin to fill in this information gap. Models of the UAT of five, living rhesus macaques were produced from CT scans, using 3D printing technology. Models were exposed to a polydisperse aerosol containing 0.54 to 9.65 micron particles, during constant flowrates of 2, 4, and 6 liters per min. Percent deposition in UAT models was quantified using an Aerodynamic Particle Sizer and was compared to in vivo upper airway deposition in ten, adult human subjects. Deposition in the UAT models increased as Stokes number increased. Deposition also varied significantly between models, but intermodel variability was reduced when plotted as a function of Stokes number. Using Stokes number, deposition in four of the five UAT models overlapped with each other and also overlapped with human upper airway deposition. These models could be used to explore the relationship between factors that affect toxic aerosol deposition in the UAT in vitro and pathology following toxic aerosol exposure in Rhesus macaques in vivo. Results from those experiments could also be applicable to humans because of deposition similarities.

Copyright © 2020 American Association for Aerosol Research     

4D Printing of Polyvinyl Chloride (PVC): A Detailed Analysis of Microstructure,Programming, and Shape Memory Performance

In this research, polyvinyl chloride (PVC) with excellent shape-memory effects is 4D printed via fused deposition modeling (FDM) technology. An experimental procedure for successful 3D printing of lab-made filament from PVC granules is introduced. Macro- and microstructural features of 3D printed PVC are investigated by means of wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA) techniques. A promising shape-memory feature of PVC is hypothesized from the presence of small close imperfect thermodynamically stable crystallites as physical crosslinks, which are further reinforced by mesomorphs and possibly molecular entanglement. A detailed analysis of shape fixity and shape recovery performance of 3D printed PVC is carried out considering three programming scenarios of cold (T_g −45 °C), warm (T_g −15 °C), and hot (T_g +15 °C) and two load holding times of 0 s, and 600 s under three-point bending and compression modes. Extensive insightful discussions are presented, and in conclusion, shape-memory effects are promising,ranging from 83.24% to 100%. Due to the absence of similar results in the specialized literature, this paper is likely to fill a gap in the state-of-the-art shape-memory materials library for 4D printing, and provide pertinent results that are instrumental in the 3D printing of shape-memory PVC-based structures.     

Vaporizing Microdroplet Inhalation,Transport, and Deposition in a Human Upper Airway Model

Evaluation of injuries from inhalation exposure to toxic fuel requires detailed knowledge of inhaled aerosol transport and deposition in human airways. Focusing on highly toxic, easily volatized JP-8 fuel droplets, the three-dimensional airflow, temperature distributions, and fluid-particle thermodynamics, i.e., droplet motion as well as evaporation, are simulated and analyzed for laminar as well as locally turbulent flow conditions.

Specifically, using a commercial finite-volume software with user-supplied programs as a solver, the Euler-Lagrange approach for the fluid-particle thermodynamics is employed with: (1) a low Reynolds number k-ω model for laminar-to-turbulent airflow, and (2) a stochastic model for random fluctuations in the droplet trajectories with droplet evaporation. Presently, the respiratory system consists of two major segments of a simplified human cast replica, i.e., a representative oral airway from mouth to trachea (Generation 0) and a symmetric four-generation upper bronchial tree model (G0 to G3). Experimentally validated computational fluid-particle thermodynamics results show that evaporation of JP-8 fuel droplets is greatly affecting deposition in the human airway. Specifically, droplet deposition fractions due to vaporization decrease with increasing ambient temperatures and decreasing inspiratory flow rates. It is also demonstrated that assuming idealized velocity profiles and particle distributions in or after the trachea may greatly overpredict particle deposition efficiencies in the upper bronchial tree.     

Investigating particle emissions and aerosol dynamics from a consumer fused deposition modeling 3D printer with a lognormal moment aerosol model

ABSTRACT

Particle emissions from consumer-fused deposition modeling 3D printers have been reported previously; however, the complex processes leading to observed aerosols have not been investigated. We measured particle concentrations and size distributions between 7 nm and 25 μm emitted from a 3D printer under different conditions in an emission test chamber. The experimental data was combined with a moment lognormal aerosol dynamic model to better understand particle formation and subsequent evolution mechanisms. The model was based on particles being formed from nucleation of unknown semivolatile compounds emitted from the heated filament during printing, which evolve due to condensation of emitted vapors and coagulation, all within a small volume near the printer extruder nozzle. The model captured observed steady state particle number size distribution parameters (total number, geometric mean diameter and geometric standard deviation) with errors nominally within 20%. Model solutions provided a range of vapor generation rates, saturation vapor pressures and vapor condensation factors consistent with measured steady state particle concentrations and size distributions. Vapor generation rate was a crucial factor that was linked to printer extruder temperature and largely accounted for differences between filament material and brands. For the unknown condensing vapor species, saturation vapor pressures were in the range of 10^?3 to 10^?1 Pa. The model suggests particles could be removed by design of collection surfaces near the extruder tip.

Copyright © 2018 American Association for Aerosol Research     

Categorization of Lung Morphology Based on FRC and Height: Computer Simulations of Aerosol Deposition

The aim of this study was to compare the human subject experimental measurements of particle deposition within the lungs using the aerosol bolus technique with the results of analytical modeling as a basis for assessing the influence of lung morphology on inhaled particle deposition patterns. A methodology for scaling the lung morphology, based on a classic symmetric dichotomous model, as a function of both functional residual capacity and height of the investigated population is presented. Because of the availability of deposition data for male and female lung morphologies, these were used as an example to address the importance of adjusting lung morphology in calculating the aerosol deposition rates. In order to represent the 2 groups based on gender enrolled in the experimental study, 2 lung morphologies have been built. An analytical and mechanistic model was used to mimic the bolus delivery technique and simulate the aerosol deposition in each of the 2 groups. Predicted results were compared with experimental data for both total deposition fraction and bolus recovery (fraction of exhaled particles compared with inhaled particles) for 3 flow rates and 3 particle sizes. Good agreement was found between theoretical and measured data, showing the primary importance of the differentiation of the lung morphology to predict the aerosol deposition within human lungs. This study presents a morphological lung model that is adaptable to specific populations (e.g., gender or race), groups (e.g., a clinical study population), or even individuals.

Copyright 2012 American Association for Aerosol Research     

Particle deposition in the pulmonary region of the human lung: Multiple breath aerosol transport and deposition

Comprehensive knowledge of aerosol deposition in the lung during multiple breathing cycles is essential to understanding the long term adverse effects of environmental particulate pollution as well as various therapeutic strategies for aerosolized drug delivery. In this work, a simple semi-empirical model for whole lung aerosol bolus dispersion and deposition developed in an accompanying study [Park, S.S. and Wexler, A.S., 2007. Particle deposition in the pulmonary region of the human lung: A semi-empirical model of single breath transport and deposition. Journal of Aerosol Science 38(2), 228–245] was used to estimate regional particulate dosimetry during multiple breaths. To further validate the transport and deposition model of Park and Wexler [2007. Particle deposition in the pulmonary region of the human lung: A semi-empirical model of single breath transport and deposition. Journal of Aerosol Science 38(2), 228–245], the washin and washout experiments of Davies and coworkers were simulated; predictions compared well to observations. Typical models of pulmonary particle deposition simulated transport to these distal airways by a flow-through approximation where particle-laden air is assumed to flow into the airways and out the alveoli, but resting tidal volumes do not transport particles to the distal pulmonary airways in a single breath. By simulating tidal transport and deposition over a series of breath, we find that the concentration of retained particles as a function of lung depth increases with each tidal cycle and these particles penetrate deeper with succeeding breaths. The retained particle concentration increases more slowly with each breath, so that after the 8th breath, the concentration distribution within the lung attains a steady state. Comparison with observed data and previous model predictions is made in terms of total and generational deposition fractions at steady state. After accounting for the retained fractions, the total predicted deposition fraction was similar to the experimental data while other previous model predictions underestimated it. Predicted deposition fraction per generation showed similar patterns to other model simulations yet higher deposition fractions in the more proximal pulmonary regions. This is a result of the enhanced alveolar deposition in the first half of the acinar generations due to alveoli expansion and contraction.     

Experimental research of drop‐on‐demand droplet jetting 3D printing with molten polymer

Three‐dimensional (3D) printing technology has become an effective method for parts manufacturing and got a certain application in many fields. Now, drop‐on‐demand droplet jetting 3D printing appears as a new method of manufacturing technology which has a proven research progress for metal, colloid, and liquid resin materials. However, there are hardly any researches of droplet jetting 3D printing with molten polymer. So, considering molten polymer as the jetting material with droplet jetting method is an explorative direction. In order to attain the molten polymer droplets and achieve droplet jetting 3D printing with molten polymer, the 3D printing technology of differential melt (3DPDM) is developed independently. According to 3DPDM, a complete set of drop‐on‐demand droplet jetting 3D printer have been developed. In this work, PP (6820) was chosen as the experimental material. Under the different print parameters such as the rotation speed of screw, nozzle diameter, mechanical impact frequency, heating temperature, the space between nozzle and platform, the form, and deposition of droplets were studied. Furthermore, the optimal print parameters were summarized. By printing models with the optimal print parameters, it turned out that the 3DPDM is able to achieve drop‐on‐demand droplet jetting 3D printing with molten polymer. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45933.