@inproceedings{kalia_zhang_singh_2014, title={Estimating trust from agents' interactions via commitments}, volume={263}, booktitle={21st european conference on artificial intelligence (ecai 2014)}, author={Kalia, A. K. and Zhang, Z. and Singh, M. P.}, year={2014}, pages={1043–1044} } @article{hang_zhang_singh_2013, title={Shin: Generalized Trust Propagation with Limited Evidence}, volume={46}, ISSN={["1558-0814"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84875836507&partnerID=MN8TOARS}, DOI={10.1109/mc.2012.116}, abstractNote={Shin incorporates a probabilistic method for revising trust estimates in trustees, yielding higher prediction accuracy than traditional approaches that base trust exclusively on a series of referrals culminating with the trustee.}, number={3}, journal={COMPUTER}, author={Hang, Chung-Wei and Zhang, Zhe and Singh, Munindar P.}, year={2013}, month={Mar}, pages={78–85} } @article{zhang_kleinstreuer_hyun_2012, title={Size-change and deposition of conventional and composite cigarette smoke particles during inhalation in a subject-specific airway model}, volume={46}, ISSN={["1879-1964"]}, DOI={10.1016/j.jaerosci.2011.12.002}, abstractNote={In light of the established health risks of cigarette smoking, less harmful cigarettes (or potential reduced exposure products (PREPs)) have been marketed. Thus, it is of interest to analyze and compare the inhaled droplet dynamics of conventional and new composite cigarette smoke particles (CSPs). Inhalation pattern, hygroscopic growth and deposition of different composite cigarette smoke particles (CSPs) have been simulated numerically in a subject-specific human respiratory airway model from the mouth to generation G9. The validated computer model has been developed to consider the interaction of different deposition mechanisms, including impaction, sedimentation, diffusion, hygroscopic growth, coagulation, as well as possible cloud motion under different exposure and steady breathing conditions (e.g., puffing, post-puffing and two-step inhalation). The computer simulation results are consistent with numerous in-vivo and in-vitro studies as well as whole-lung modeling for deposition of conventional CSPs including hygroscopic growth and cloud motion. It is demonstrated that changes in cigarette composition significantly influence the hygroscopic growth of CSPs. In general, the growth rate of new composite CSPs is larger than the conventional one if the initial water mole-fraction is lower in the droplet. Hygroscopic growth of the new composite CSPs is not a significant mechanism leading to elevated deposition in the oral and tracheobronchial (TB) airways, provided that the relative humidity in the lungs does not exceed 99.5% and the droplet size does not exceed 3 μm; however, enhanced deposition may occur if the particles can grow over 3 μm. In this case, the deposition patterns of CSPs may be controlled by changing the primary composition, especially the initial ratio of water and glycerol. The simulation data with cloud diameters of 0.15–0.2 cm in the oral cavity and 0.5–0.6 cm in the trachea closely match the in-vivo lung deposition measurements of highly dense (conventional) CSPs. Specifically, preferred deposition occurs in the upper airway region, i.e., from the oral cavity to the second bifurcation, with deposition fractions of about 13–22% from the oral cavity to the larynx and 40–57% in the TB airways. This study is helpful for quantitatively evaluating the dose-exposure and subsequent health effects of both conventional and potentially less-harmful cigarettes.}, journal={JOURNAL OF AEROSOL SCIENCE}, author={Zhang, Zhe and Kleinstreuer, Clement and Hyun, Sinjae}, year={2012}, month={Apr}, pages={34–52} } @article{zhang_kleinstreuer_feng_2012, title={Vapor deposition during cigarette smoke inhalation in a subject-specific human airway model}, volume={53}, ISSN={["1879-1964"]}, DOI={10.1016/j.jaerosci.2012.05.008}, abstractNote={Validated computer simulation results of vapor deposition from inhaled cigarette smoke are helpful to assess potential health effects of conventional and so-called less-harmful tobacco products. In this paper, the depositions of four critical tobacco-smoke vapors, i.e., acrolein, 1,3-butadiene, acetaldehyde and CO, in a subject-specific human airway model from mouth to generation G9 under different inhalation conditions have been simulated. The results show that vapor deposition is strongly influenced by its property values as well as inhalation waveform, i.e., puffing behavior. As almost insoluble species in the mucus layer, the deposition of butadiene vapor and CO is very low in the upper airways. The remaining vapors may penetrate further and deposit in deeper lung regions. As medium-to-high soluble vapors, acrolein and acetaldehyde have very high deposition values in the human upper airways from mouth to generation G9. The deposition result for steady matching flow (where the average flow rate between mean and peak values was taken) is a good conservative estimate of the actual deposition fraction under transient normal inhalation condition. However, the vapor transport delay may largely reduce the vapor deposition for transient puffing. A correction factor has been proposed, considering vapor transport delay, in order to calculate efficiently actual deposition fraction values under transient puffing condition. Furthermore, the effect of different puffing waveforms for conventional cigarettes and PREPs (potential reduced exposure products) on smoke vapor deposition has been discussed as well. Finally, a set of deposition correlations have been developed to estimate the deposition of acrolein and acetaldehyde vapors in different segments of the human upper airways under both puffing and normal inhalation (i.e., post-puffing) conditions.}, journal={JOURNAL OF AEROSOL SCIENCE}, author={Zhang, Zhe and Kleinstreuer, Clement and Feng, Yu}, year={2012}, month={Nov}, pages={40–60} } @article{kleinstreuer_zhang_2011, title={Optimal Drug-Aerosol Delivery to Predetermined Lung Sites}, volume={133}, ISSN={["1528-8943"]}, DOI={10.1115/1.4002224}, abstractNote={This review summarizes computer simulation methodologies of air-particle flow, results of drug-aerosol transport/deposition in models of the human respiratory system, as well as aspects of drug-aerosol targeting and associated inhalation devices. After a brief introduction to drug delivery systems in general, the required modeling and simulation steps for optimal drug-aerosol delivery in the lung are outlined. Starting with medical imaging and file conversion of patient-specific lung-airway morphologies, the air-particle transport phenomena are numerically solved for a representative inhalation flow rate of Qtotal=30 l/min. Focusing on microspheres and droplets, the complex airflow and particle dynamics, as well as the droplet heat and mass transfer are illustrated. With this foundation as the background, an overview of present inhaler devices is presented, followed by a discussion of the methodology and features of a new smart inhaler system (SIS). With the SIS, inhaled drug-aerosols can be directly delivered to any predetermined target area in the human lung.}, number={1}, journal={JOURNAL OF HEAT TRANSFER-TRANSACTIONS OF THE ASME}, author={Kleinstreuer, Clement and Zhang, Zhe}, year={2011}, month={Jan} } @article{kleinstreuer_zhang_2010, title={Airflow and Particle Transport in the Human Respiratory System}, volume={42}, ISSN={["0066-4189"]}, DOI={10.1146/annurev-fluid-121108-145453}, abstractNote={ Airflows in the nasal cavities and oral airways are rather complex, possibly featuring a transition to turbulent jet-like flow, recirculating flow, Dean's flow, vortical flows, large pressure drops, prevailing secondary flows, and merging streams in the case of exhalation. Such complex flows propagate subsequently into the tracheobronchial airways. The underlying assumptions for particle transport and deposition are that the aerosols are spherical, noninteracting, and monodisperse and deposit upon contact with the airway surface. Such dilute particle suspensions are typically modeled with the Euler-Lagrange approach for micron particles and in the Euler-Euler framework for nanoparticles. Micron particles deposit nonuniformly with very high concentrations at some local sites (e.g., carinal ridges of large bronchial airways). In contrast, nanomaterial almost coats the airway surfaces, which has implications of detrimental health effects in the case of inhaled toxic nanoparticles. Geometric airway features, as well as histories of airflow fields and particle distributions, may significantly affect particle deposition. }, journal={ANNUAL REVIEW OF FLUID MECHANICS}, author={Kleinstreuer, C. and Zhang, Z.}, year={2010}, pages={301–334} } @article{zhang_kleinstreuer_kim_2009, title={Comparison of analytical and CFD models with regard to micron particle deposition in a human 16-generation tracheobronchial airway model}, volume={40}, ISSN={["1879-1964"]}, DOI={10.1016/j.jaerosci.2008.08.003}, abstractNote={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.}, number={1}, journal={JOURNAL OF AEROSOL SCIENCE}, author={Zhang, Zhe and Kleinstreuer, Clement and Kim, Chong S.}, year={2009}, month={Jan}, pages={16–28} } @article{ma_vazhkudai_zhang_2009, title={Improving Data Availability for Better Access Performance: A Study on Caching Scientific Data on Distributed Desktop Workstations}, volume={7}, ISSN={["1572-9184"]}, DOI={10.1007/s10723-009-9122-7}, abstractNote={Client-side data caching serves as an excellent mechanism to store and analyze the rapidly growing scientific data, motivating distributed, client-side caches built from unreliable desktop storage contributions to store and access large scientific data. They offer several desirable properties, such as performance impedance matching, improved space utilization, and high parallel I/O bandwidth. In this context, we are faced with two key challenges: (1) the finite amount of contributed cache space is stretched by the ever increasing scientific dataset sizes and (2) the transient nature of volunteered storage nodes impacts data availability. In this article, we address these challenges by exploiting the existence of external, primary copies of datasets. We propose a novel combination of prefix caching, collective download, and remote partial data recovery (RPDR), to deal with optimal cache space consumption and storage node volatility. Our evaluation, performed on our FreeLoader prototype, indicates that prefix caching can significantly improve the cache hit rate and partial data recovery is better than (or comparable to) many persistent-data availability techniques.}, number={4}, journal={JOURNAL OF GRID COMPUTING}, author={Ma, Xiaosong and Vazhkudai, Sudharshan S. and Zhang, Zhe}, year={2009}, month={Dec}, pages={419–438} } @article{kleinstreuer_zhang_li_roberts_rojas_2008, title={A new methodology for targeting drug-aerosols in the human respiratory system}, volume={51}, ISSN={["1879-2189"]}, DOI={10.1016/j.ijheatmasstransfer.2008.04.052}, abstractNote={Inhalation of medicine for the treatment of lung and other diseases is becoming more and more a preferred option when compared to injection or oral intake. Unfortunately, existing devices such as the popular pressurized metered dose inhalers and dry powder inhalers have rather low deposition efficiencies and their drug-aerosol deliveries are non-directional. This is acceptable when the medicine is inexpensive and does not cause systemic side effects, as it may be the case for patients with mild asthma. However, the delivery of aggressive chemicals, or expensive insulin, vaccines and genetic material embedded in porous particles or droplets requires optimal targeting of such inhaled drug-aerosols to predetermined lung areas. The new methodology introduces the idea of a controlled air-particle stream which provides maximum, patient-specific drug-aerosol deposition based on optimal particle diameter and density, inhalation waveform, and particle-release position. The efficacy of the new methodology is demonstrated with experimentally validated computer simulations of two-phase flow in a human oral airway model with two different sets of tracheobronchial airways. Physical insight to the dynamics of the controlled air-particle stream is provided as well.}, number={23-24}, journal={INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER}, author={Kleinstreuer, Clement and Zhang, Zhe and Li, Zheng and Roberts, William L. and Rojas, Carlye}, year={2008}, month={Nov}, pages={5578–5589} } @article{zhang_kleinstreuer_kim_2008, title={Airflow and Nanoparticle Deposition in a 16-Generation Tracheobronchial Airway Model}, volume={36}, ISSN={["1573-9686"]}, DOI={10.1007/s10439-008-9583-z}, abstractNote={In order to achieve both manageable simulation and local accuracy of airflow and nanoparticle deposition in a representative human tracheobronchial (TB) region, the complex airway network was decomposed into adjustable triple-bifurcation units, spreading axially and laterally. Given Q(in) = 15 and 30 L/min and a realistic inlet velocity profile, the experimentally validated computer simulation model provided some interesting 3-D airflow patterns, i.e., for each TB-unit they depend on the upstream condition, local geometry and local Reynolds number. Directly coupled to the local airflow fields are the convective-diffusive transport and deposition of nanoparticles, i.e., 1 nm < or = d(p) < or = 100 nm. The CFD modeling predictions were compared to experimental observations as well as analytical modeling results. The CFD-simulated TB deposition values agree astonishingly well with analytical modeling results. However, measurable differences can be observed for bifurcation-by-bifurcation deposition fractions obtained with these two different approaches due to the effects of more realistic inlet conditions and geometric features incorporated in the CFD model. Specifically, while the difference between the total TB deposition fraction (DF) is less than 16%, it may be up to 70% for bifurcation-by-bifurcation DFs. In addition, it was found that fully developed flow and uniform nanoparticle concentrations can be assumed beyond generation G12. For nanoparticles with d(p) > 10 nm, the geometric effects, including daughter-branch rotation, are minor. Furthermore, the deposition efficiencies at each individual bifurcation in the TB region can be well correlated as a function of an effective diffusion parameter.}, number={12}, journal={ANNALS OF BIOMEDICAL ENGINEERING}, author={Zhang, Zhe and Kleinstreuer, Clement and Kim, Chong S.}, year={2008}, month={Dec}, pages={2095–2110} } @misc{kleinstreuer_zhang_li_2008, title={Modeling airflow and particle transport/deposition in pulmonary airways}, volume={163}, ISSN={["1878-1519"]}, DOI={10.1016/j.resp.2008.07.002}, abstractNote={A review of research papers is presented, pertinent to computer modeling of airflow as well as nano- and micron-size particle deposition in pulmonary airway replicas. The key modeling steps are outlined, including construction of suitable airway geometries, mathematical description of the air-particle transport phenomena and computer simulation of micron and nanoparticle depositions. Specifically, diffusion-dominated nanomaterial deposits on airway surfaces much more uniformly than micron particles of the same material. This may imply different toxicity effects. Due to impaction and secondary flows, micron particles tend to accumulate around the carinal ridges and to form "hot spots", i.e., locally high concentrations which may lead to tumor developments. Inhaled particles in the size range of 20nm< or =dp< or =3microm may readily reach the deeper lung region. Concerning inhaled therapeutic particles, optimal parameters for mechanical drug-aerosol targeting of predetermined lung areas can be computed, given representative pulmonary airways.}, number={1-3}, journal={RESPIRATORY PHYSIOLOGY & NEUROBIOLOGY}, author={Kleinstreuer, Clement and Zhang, Zhe and Li, Zheng}, year={2008}, month={Nov}, pages={128–138} } @article{kleinstreuer_zhang_donohue_2008, title={Targeted drug-aerosol delivery in the human respiratory system}, volume={10}, ISSN={["1545-4274"]}, DOI={10.1146/annurev.bioeng.10.061807.160544}, abstractNote={ Inhalation of drug aerosols is a modern pathway to combat lung diseases. It is also becoming the preferred route for insulin delivery, pain management, cancer therapy, and nanotherapeutics. Popular delivery devices include nebulizers, metered-dose inhalers, and dry-powder inhalers. They are all nondirectional and hence have typically low particle deposition efficiencies in desired nasal or lung areas. Thus, for specific disease treatment with costly and/or aggressive medicine, it is necessary to provide targeted drug–aerosol delivery to predetermined sites in the human respiratory system. Experimental measurements and computer models of particle transport and deposition in nasal and lung airway models are presented. Furthermore, the underlying methodology and performance of pressurized metered dose inhalers as well as new smart inhaler systems are discussed. To maximize respiratory drug delivery to specific sites, an optimal combination of particle characteristics, inhalation waveform, particle release position, and drug-aerosol dosage has to be achieved. }, journal={ANNUAL REVIEW OF BIOMEDICAL ENGINEERING}, author={Kleinstreuer, C. and Zhang, Z. and Donohue, J. F.}, year={2008}, pages={195–220} } @article{kleinstreuer_zhang_kim_2007, title={Combined inertial and gravitational deposition of microparticles in small model airways of a human respiratory system}, volume={38}, ISSN={["1879-1964"]}, DOI={10.1016/j.jaerosci.2007.08.010}, abstractNote={Focusing on relatively small airways in terms of the medium-size bronchial generations G6–G9, the interplay of impaction and sedimentation on micron particle transport and deposition has been simulated. A commercial finite-volume code, enhanced with user-supplied programs, has been employed. Although impaction is still a dominant deposition mechanism for microparticle in medium-size airways under normal breathing conditions (say, Qin=15–30L/min), sedimentation may play a role as well. In turn, that can influence the local particle deposition patterns, efficiencies and fractions for a realistic range of Stokes numbers (0.001⩽St⩽0.33). However, deposition due to sedimentation is significantly amplified during slow inhalation; for example, the gravitational deposition may become dominant in the ninth bifurcation (i.e., generations G8–G9) for relatively large microparticles (say, dp>5μm) at Qin=3.75L/min. The occurrence of sedimentation changes the location of the deposition “hot spots” and reduces the order of the maximum deposition enhancement factor. The use of analytical formulas based on inclined tube models for predicting gravitational deposition in local bronchial airway segments as well as the combination of deposition by sedimentation and impaction has to be carefully examined. As shown, more prudent is the use of curve-fitted correlations generated from experimentally validated computer simulation results as a function of Stokes number and sedimentation parameter.}, number={10}, journal={JOURNAL OF AEROSOL SCIENCE}, author={Kleinstreuer, Clement and Zhang, Zhe and Kim, Chong S.}, year={2007}, month={Oct}, pages={1047–1061} } @article{kleinstreuer_shi_zhang_2007, title={Computational analyses of a pressurized metered dose inhaler and a new drug-aerosol targeting methodology}, volume={20}, ISSN={["0894-2684"]}, DOI={10.1089/jam.2006.0617}, abstractNote={The popular pressurized metered dose inhaler (pMDI), especially for asthma treatment, has undergone various changes in terms of propellant use and valve design. Most significant are the choice of hydrofluoroalkane-134a (HFA-134a) as a new propellant (rather than chlorofluorocarbon, CFC), a smaller exit nozzle diameter and attachment of a spacer in order to reduce ultimately droplet size and spray inhalation speed, both contributing to higher deposition efficiencies and hence better asthma therapy. Although asthma medicine is rather inexpensive, the specter of systemic side effects triggered by inefficient pMDI performance and the increasing use of such devices as well as new targeted drug-aerosol delivery for various lung and other diseases make detailed performance analyses imperative. For the first time, experimentally validated computational fluid-particle dynamics technique has been applied to simulate airflow, droplet spray transport and aerosol deposition in a pMDI attached to a human upper airway model, considering different device propellants, nozzle diameters, and spacer use. The results indicate that the use of HFA (replacing CFC), smaller valve orifices (0.25 mm instead of 0.5 mm) and spacers (ID = 4.2 cm) leads to best performance mainly because of smaller droplets generated, which penetrate more readily into the bronchial airways. Experimentally validated computer simulations predict that 46.6% of the inhaled droplets may reach the lung for an HFA-pMDI and 23.2% for a CFC-pMDI, both with a nozzle-exit diameter of 0.25 mm. Commonly used inhalers are nondirectional, and at best only regional drug-aerosol deposition can be achieved. However, when inhaling expensive and aggressive medicine, or critical lung areas have to be reached, locally targeted drug-aerosol delivery is imperative. For that reason the underlying principle of a future line of "smart inhalers" is introduced. Specifically, by generating a controlled air-particle stream, most of the inhaled drug aerosols reach predetermined lung sites, which are associated with specific diseases and/or treatments. Using the same human upper airway model, experimentally confirmed computer predictions of controlled particle transport from mouth to generation 3 are provided.}, number={3}, journal={JOURNAL OF AEROSOL MEDICINE-DEPOSITION CLEARANCE AND EFFECTS IN THE LUNG}, author={Kleinstreuer, Clement and Shi, Huawei and Zhang, Zhe}, year={2007}, pages={294–309} } @article{shi_kleinstreuer_zhang_2007, title={Modeling of inertial particle transport and deposition in human nasal cavities with wall roughness}, volume={38}, ISSN={["1879-1964"]}, DOI={10.1016/j.jaerosci.2007.02.002}, abstractNote={Nasal inhalation helps to protect the lungs from detrimental effects of toxic particles which, however, may also place the nasal and adjacent tissues at risk. Alternatively, drug–aerosol deposition on pre-determined nasal airway surfaces can be a modern pathway for rapid medical treatment. The present study focuses on inertial particles in the range of 1μm⩽dp⩽50μm, subject to steady laminar flow rates of 7.5 and 20 L/min. In contrast to ultrafine particles, for certain fine particle sizes deposition is strongly affected by wall roughness, which was incorporated with a selective micro-size airway-surface layer. The validated computer simulation results show that the inertial particle deposition in human nasal cavities increases with increasing impaction parameter, IP=da2·Q. Most of the deposition occurs in the anterior part of the human nasal cavities, especially in the nasal valve region. Considering drug–aerosol targeting, an optimal impaction parameter value exists which generates for normal inlet conditions the largest deposition in desired areas, e.g., the middle meatus, inferior meatus and olfactory regions. However, the absolute deposition efficiencies, especially in the inferior meatus and olfactory region, are very small because particles hardly reach those regions due to the complex nasal geometric structures. The influence of gravity was also analyzed and an experimentally validated correlation for inertial particle deposition in human nasal cavities has been provided.}, number={4}, journal={JOURNAL OF AEROSOL SCIENCE}, author={Shi, Huawei and Kleinstreuer, Clement and Zhang, Zhe}, year={2007}, month={Apr}, pages={398–419} } @article{li_kleinstreuer_zhang_2007, title={Particle deposition in the human tracheobronchial airways due to transient inspiratory flow patterns}, volume={38}, ISSN={["1879-1964"]}, DOI={10.1016/j.jaerosci.2007.03.010}, abstractNote={Considering realistic tracheobronchial airways, transient airflow structures and micro-particle deposition patterns were simulated with an in-house finite-volume code for typical inhalation waveforms and Stokes numbers, i.e., the average flow rates at the trachea inlet, Qin,av, are 15 and 60L/min and the mean Stokes number at the trachea inlet, Stmean,trachea, is in the range of 0.0229⩽Stmean,trachea⩽0.0915, respectively. While the overall airflow fields exhibit similar characteristics, the local flow patterns which influence particle deposition are largely affected by secondary flows (for both Qin,av=15 and 60L/min) as well as airflow turbulence (when Qin,av=60L/min). The particle deposition fraction is a strongly transient function according to a given inhalation waveform. In light of the importance of targeted drug-aerosol delivery, it is shown that the relation between particle-release positions at the trachea inlet and particle depositions at specific lung sites are greatly influenced by the complex airway geometry and the flow-rate magnitude. For laminar flow, the particle-release points are deterministic and unique, as required for optimal drug-aerosol targeting.}, number={6}, journal={JOURNAL OF AEROSOL SCIENCE}, author={Li, Zheng and Kleinstreuer, Clement and Zhang, Zhe}, year={2007}, month={Jun}, pages={625–644} } @article{li_kleinstreuer_zhang_2007, title={Simulation of airflow fields and microparticle deposition in realistic human lung airway models. Part I: Airflow patterns}, volume={26}, ISSN={["1873-7390"]}, DOI={10.1016/j.euromechflu.2007.02.003}, abstractNote={In Part I, transient and steady laminar airflow fields were simulated with an in-house finite volume code for realistic upper airway models subject to different inlet conditions and geometric features. Axial velocities and secondary flows were compared at key time levels during the acceleration/deceleration phase of inhaled air and for steady-state inhalation. The main results can be summarized as follows. Considering two acceleration and deceleration time levels during transient inhalation as well as steady-state inhalation generating the same inlet Reynolds number, Rein-mean=1201, the airflow patterns are quite similar. However, stronger axial and secondary velocities occur at all upper branch locations during flow deceleration because of the dynamic lingering effect. In general, the axial velocity profiles at steady state are very close to those at the point of deceleration. Variations in upper airway geometry, e.g., in-plane vs. out-of-plane configurations, have a significant effect on the airflow fields, although the primary airflow structures are similar in both idealized and more realistic airway configurations. The type of velocity inlet condition and existence of cartilaginous rings also influence the flow field; however, their impact is less important than changes in spatial angles.}, number={5}, journal={EUROPEAN JOURNAL OF MECHANICS B-FLUIDS}, author={Li, Zheng and Kleinstreuer, Clement and Zhang, Zhe}, year={2007}, pages={632–649} } @article{li_kleinstreuer_zhang_2007, title={Simulation of airflow fields and microparticle deposition in realistic human lung airway models. Part II: Particle transport and deposition}, volume={26}, ISSN={["1873-7390"]}, DOI={10.1016/j.euromechflu.2007.02.004}, abstractNote={In Part II, given the airflow fields discussed in Part I, microparticle deposition for a practical range of Stokes numbers, 0.025⩽St⩽0.102, has been simulated and analyzed, comparing different temporal assumptions, inlet conditions and geometric configurations. The matching steady-state assumption with equivalent Reynolds and Stokes numbers achieves basically the same deposition fraction (DF) values as under transient inhalation conditions. When comparing parabolic vs. realistic inlet velocity profiles, total DF-values are higher for the parabolic inlet flow for all Stokes numbers. Geometric features, such as out-of-plane configurations and cartilaginous rings in the trachea, further change local deposited microparticle concentrations when compared with simple airway models. Furthermore, significant differences were recorded when comparing DFs in some branches of the present realistic model and the Weibel Type A model. For practical purposes, algebraic microparticle-deposition correlations, DF=DF(Re,St), have been obtained for both the left and right upper lung airways. Based on current research results, the out-of-plane model with tracheal rings and realistic inlet condition is recommended for future work.}, number={5}, journal={EUROPEAN JOURNAL OF MECHANICS B-FLUIDS}, author={Li, Zheng and Kleinstreuer, Clement and Zhang, Zhe}, year={2007}, pages={650–668} } @article{zhang_kleinstreuer_kim_2006, title={Isotonic and hypertonic saline droplet deposition in a human upper airway model}, volume={19}, ISSN={["0894-2684"]}, DOI={10.1089/jam.2006.19.184}, abstractNote={The evaporative and hygroscopic effects and deposition of isotonic and hypertonic saline droplets have been simulated from the mouth to the first four generations of the tracheobronchial tree under laminar-transitional-turbulent inspiratory flow conditions. Specifically, the local water vapor transport, droplet evaporation rate, and deposition fractions are analyzed. The effects of inhalation flow rates, thermodynamic air properties and NaCl-droplet concentrations of interest are discussed as well. The validated computer simulation results indicate that the increase of NaCl-solute concentration, increase of inlet relative humidity, or decrease of inlet air temperature may reduce water evaporation and increase water condensation at saline droplet surfaces, resulting in higher droplet depositions due to the increasing particle diameter and density. However, solute concentrations below 10% may not have a very pronounced effect on droplet deposition in the human upper airways.}, number={2}, journal={JOURNAL OF AEROSOL MEDICINE-DEPOSITION CLEARANCE AND EFFECTS IN THE LUNG}, author={Zhang, Zhe and Kleinstreuer, Clement and Kim, Chong S.}, year={2006}, pages={184–198} } @article{shi_kleinstreuer_zhang_2006, title={Laminar airflow and nanoparticle or vapor deposition in a human nasal cavity model}, volume={128}, ISSN={["1528-8951"]}, DOI={10.1115/1.2244574}, abstractNote={The transport and deposition of nanoparticles, i.e., dp=1–2nm, or equivalent vapors, in the human nasal cavities is of interest to engineers, scientists, air-pollution regulators, and healthcare officials alike. Tiny ultrafine particles, i.e., dp≤5nm, are of special interest because they are most rapidly absorbed and hence have an elevated toxic or therapeutic impact when compared to larger particles. Assuming transient laminar 3-D incompressible flow in a representative human nasal cavity, the cyclic airflow pattern as well as local and overall nanoparticle depositions were computationally simulated and analyzed. The focus was on transient effects during inhalation/exhalation as compared to the steady-state assumption typically invoked. Then, an equation for a matching steady-state inhalation flow rate was developed that generates the same deposition results as cyclic inhalation. Of special interest is the olfactory region where the narrow channel surfaces receive only about one-half of a percent of the inhaled nanoparticles because the airflow bypasses these recesses located in the superior-most portions in the geometrically complex nasal cavities.}, number={5}, journal={JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME}, author={Shi, H. and Kleinstreuer, C. and Zhang, Z.}, year={2006}, month={Oct}, pages={697–706} } @article{zhang_kleinstreuer_kim_2006, title={Water vapor transport and its effects on the deposition of hygroscopic droplets in a human upper airway model}, volume={40}, ISSN={["1521-7388"]}, DOI={10.1080/02786820500461154}, abstractNote={The fundamentals of 3-D airflow as well as heat and water vapor transport and droplet vaporization (or hygroscopicity) are described for a human upper airway model under steady laminar-transitional-turbulent inspiratory flow conditions. Water vapor distributions from the mouth to the first four generations of the tracheobronchial tree are given in terms of relative humidity or mass fraction. The mass transfer coefficients of water vapor are correlated as a function of local flow rate and temperature-dependent diffusivity, which can be readily used for estimating the regional water loss or moisture variations in the human upper airways. Furthermore, the dynamics of hygroscopicity and deposition of isotonic saline droplets have been simulated as an example, applying the basic theory. Specifically, droplet evaporation rates and deposition pattern are analyzed and the effects of inhalation flow rates and thermodynamic air properties are discussed.}, number={1}, journal={AEROSOL SCIENCE AND TECHNOLOGY}, author={Zhang, Z and Kleinstreuer, C and Kim, CS}, year={2006}, month={Jan}, pages={1–16} } @article{zhang_kleinstreuer_donohue_kim_2005, title={Comparison of micro- and nano-size particle depositions in a human upper airway model}, volume={36}, ISSN={["1879-1964"]}, DOI={10.1016/j.jaerosci.2004.08.006}, abstractNote={Simulation results of microparticle and nanoparticle deposition patterns, local concentrations, and segmental averages are contrasted for a human upper airway model starting from the mouth to planar airway generation G3 under different inspiratory flow conditions. Specifically, using a commercial finite-volume software with user-supplied programs as a solver, the Euler–Euler (nanoparticles) or the Euler–Lagrange (microparticles) approach was employed with a low-Reynolds-number k–ω model for laminar-to-turbulent airflow and submodels for particle-phase randomization. The results show that depositions of both micro- and nano-size particles vary measurably in the human upper airways; however, the deposition distributions are much more uniform for nanoparticles. The maximum deposition enhancement factor, which is defined as the ratio of local to average deposition concentrations, ranges from about 40 to 2400 for microparticles and about 2 to 11 for nanoparticles with inspiratory flow rates in the range of 15⩽Qin⩽60 l/min. In addition, some airway bifurcations in generations G0 to G3 subjected to high inlet flow rates (say, Qin=60l/min) may receive only very small amounts of large micro-size particles (say, with aerodynamic diameter dae⩾10μm) due to largely preferred upstream deposition. It has been hypothesized that, uniformly deposited nanoparticles of similar concentrations may have greater toxicity effects when compared to microparticles of the same material.}, number={2}, journal={JOURNAL OF AEROSOL SCIENCE}, author={Zhang, Z and Kleinstreuer, C and Donohue, JF and Kim, CS}, year={2005}, month={Feb}, pages={211–233} } @article{zhang_kleinstreuer_2004, title={Airflow structures and nano-particle deposition in a human upper airway model}, volume={198}, ISSN={["1090-2716"]}, DOI={10.1016/j.jcp.2003.11.034}, abstractNote={Considering a human upper airway model, or equivalently complex internal flow conduits, the transport and deposition of nano-particles in the 1–150 nm diameter range are simulated and analyzed for cyclic and steady flow conditions. Specifically, using a commercial finite-volume software with user-supplied programs as a solver, the Euler–Euler approach for the fluid-particle dynamics is employed with a low-Reynolds-number k–ω model for laminar-to-turbulent airflow and the mass transfer equation for dispersion of nano-particles or vapors. Presently, the upper respiratory system consists of two connected segments of a simplified human cast replica, i.e., the oral airways from the mouth to the trachea (Generation G0) and an upper tracheobronchial tree model of G0–G3. Experimentally validated computational fluid-particle dynamics results show the following: (i) transient effects in the oral airways appear most prominently during the decelerating phase of the inspiratory cycle; (ii) selecting matching flow rates, total deposition fractions of nano-size particles for cyclic inspiratory flow are not significantly different from those for steady flow; (iii) turbulent fluctuations which occur after the throat can persist downstream to at least Generation G3 at medium and high inspiratory flow rates (i.e., Qin⩾30 l/min) due to the enhancement of flow instabilities just upstream of the flow dividers; however, the effects of turbulent fluctuations on nano-particle deposition are quite minor in the human upper airways; (iv) deposition of nano-particles occurs to a relatively greater extent around the carinal ridges when compared to the straight tubular segments in the bronchial airways; (v) deposition distributions of nano-particles vary with airway segment, particle size, and inhalation flow rate, where the local deposition is more uniformly distributed for large-size particles (say, dp=100 nm) than for small-size particles (say, dp=1 nm); (vi) dilute 1 nm particle suspensions behave like certain (fuel) vapors which have the same diffusivities; and (vii) new correlations for particle deposition as a function of a diffusion parameter are most useful for global lung modeling.}, number={1}, journal={JOURNAL OF COMPUTATIONAL PHYSICS}, author={Zhang, Z and Kleinstreuer, C}, year={2004}, month={Jul}, pages={178–210} } @article{shi_kleinstreuer_zhang_kim_2004, title={Nanoparticle transport and deposition in bifurcating tubes with different inlet conditions}, volume={16}, ISSN={["1089-7666"]}, DOI={10.1063/1.1724830}, abstractNote={Transport and deposition of ultrafine particles in straight, bent and bifurcating tubes are considered for different inlet Reynolds numbers, velocity profiles, and particle sizes, i.e., 1 nm⩽dp⩽150 nm. A commercial finite-volume code with user-supplied programs was validated with analytical correlations and experimental data sets for nanoparticle depositions, considering a straight tube, a tubular 90° bend, and a G3-G5 double bifurcation with both planar and nonplanar configurations. The focus is on the airflow structures as well as nanoparticle deposition patterns and deposition efficiencies, which were analyzed for planar and nonplanar bifurcating lung airway models representing part of the upper bronchial tree. Deposition takes place primarily by Brownian diffusion, and thus deposition efficiencies increase with decreasing nanoparticle size and lower inlet Reynolds numbers. Deposition in the nonplanar configuration differs only slightly from that in the planar configuration. When compared with axisymmetric inlet conditions, the more realistic, skewed inlet velocity and particle profiles generate nearly axisymmetric deposition patterns as well. This work may elucidate basic physical insight of ultrafine particle transport and deposition relevant to environmental, industrial and biomedical studies.}, number={7}, journal={PHYSICS OF FLUIDS}, author={Shi, H and Kleinstreuer, C and Zhang, Z and Kim, CS}, year={2004}, month={Jul}, pages={2199–2213} } @article{zhang_kleinstreuer_kim_cheng_2004, title={Vaporizing microdroplet inhalation, transport, and deposition in a human upper airway model}, volume={38}, ISSN={["1521-7388"]}, DOI={10.1080/02786820490247597}, abstractNote={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.}, number={1}, journal={AEROSOL SCIENCE AND TECHNOLOGY}, author={Zhang, Z and Kleinstreuer, C and Kim, CS and Cheng, YS}, year={2004}, month={Jan}, pages={36–49} } @article{zhang_kleinstreuer_2003, title={Computational thermodynamics analysis of vaporizing fuel droplets in the human upper airways}, volume={46}, ISSN={["1340-8054"]}, DOI={10.1299/jsmeb.46.563}, abstractNote={The detailed knowledge of air flow structures as well as particle transport and deposition in the human lung for typical inhalation flow rates is an important precursor for dosimetry-and-health-effect studies of toxic particles as well as for targeted drug delivery of therapeutic aerosols. Focusing on highly toxic JP-8 fuel aerosols, 3-D airflow and fluid-particle thermodynamics in a human upper airway model starting from mouth to Generation G3 (G0 is the trachea) are simulated using a user-enhanced and experimentally validated finite-volume code. The temperature distributions and their effects on airflow structures, fuel vapor deposition and droplet motion/evaporation are discussed. The computational results show that the thermal effect on vapor deposition is minor, but it may greatly affect droplet deposition in human airways.}, number={4}, journal={JSME INTERNATIONAL JOURNAL SERIES B-FLUIDS AND THERMAL ENGINEERING}, author={Zhang, Z and Kleinstreuer, C}, year={2003}, month={Nov}, pages={563–571} } @article{kleinstreuer_zhang_2003, title={Laminar-to-turbulent fluid-particle flows in a human airway model}, volume={29}, ISSN={["1879-3533"]}, DOI={10.1016/S0301-9322(02)00131-3}, abstractNote={As in many biomedical and industrial applications, gas–solid two-phase flow fields in a curved tube with local area constrictions may be laminar, transitional and/or turbulent depending upon the inlet flow rate and tube geometry. Assuming steady incompressible air flow and non-interacting spherical micron-particles, the laminar-to-turbulent suspension flow problem was solved for a human airway model using a commercial software with user-supplied pre- and post-processing programs. All flow regimes (500