@article{shi_kleinstreuer_zhang_2008, title={Dilute suspension flow with nanoparticle deposition in a representative nasal airway model}, volume={20}, ISSN={["1089-7666"]}, DOI={10.1063/1.2833468}, abstractNote={The human nasal cavities with an effective length of only 10cm feature a wide array of basic flow phenomena because of their complex geometrics. Employing a realistic nasal airway model and demonstrating that laminar, quasisteady airflow can be assumed, dilute nanoparticle suspension flow and nanoparticle deposition are simulated and analyzed for 7.5⩽Q⩽20L∕min and 1⩽dp⩽150nm. The understanding and quantitative assessment of mixture flow fields and local nanoparticle wall concentrations in nasal airways with a thin mucus layer are very important for estimating the health risks of inhaled toxic aerosols, determining proper drug-aerosol delivery to target sites such as the olfactory regions and developing algebraic transfer functions for overall nasal dose-response analyses. Employing a commercial software package with user-supplied programs, the validated computer modeling results can be summarized as follows: (i) Most of the air flows through the middle-to-low main passageways. Higher airflow rates result in stronger airflow in the olfactory region and relatively lower flow rates in the meatuses. (ii) Nanoparticle deposition in human nasal airways is significant for tiny nanoparticles, i.e., 1⩽dp⩽2nm, which also represent some vapors. The smaller the nanoparticle size and the lower the flow rate, the higher are the total deposition efficiencies because of stronger diffusion and longer residence times. (iii) Nanoparticles with dp<5nm flow preferentially through the middle-to-low main passageway along with the major portion of the airflow. For relatively large nanoparticles (dp⩾5nm), due to the low diffusivities, fewer particles will deposit onto the wall leaving a much thinner nanoparticle gradient layer near the wall, i.e., such nanoparticles pass through the nasal cavities more uniformly with minor wall deposition. (iv) Secondary flows may enhance nanoparticle transport and deposition, especially in the meatuses by convecting nanoparticles into these particular regions. (v) For the olfactory region, an optimal particle size may exist due to the combined effects of nanoparticle transport and local deposition mechanisms. However, because of the low deposition flux and small surface area, the olfactory channels account for only very small total deposition values. (vi) A compact correlation for predicting nanoparticle deposition in human nasal airways has been developed.}, number={1}, journal={PHYSICS OF FLUIDS}, author={Shi, H. and Kleinstreuer, C. and Zhang, Z.}, year={2008}, month={Jan} }
 @article{shi_brenner_2008, title={Jetting and detonation initiation in shock induced collapse of nanometer-scale voids}, volume={112}, ISSN={["1932-7455"]}, DOI={10.1021/jp7119735}, abstractNote={Molecular dynamics simulations have been used to characterize the dynamics of the shock-induced asymmetric collapse of nanometer-scale voids in cubane nitrogen and to characterize how this dynamics couples with local chemistry to increase the shock sensitivity relative to homogeneous initiation. Mesoscopic-scale features of the void collapse correspond well to experimentally observed features of micrometer-scale bubble collapse, including a transition from single to double jetting with an increasing transverse void length. An analytic model is developed for the enhanced shock sensitivity as a function of void size and shape that reproduces the simulation results. At the atomic level, the simulations show vibrational up-pumping of molecules in the jet front because of collisions with the downstream wall followed by bi-molecular reactive dynamics from continued jet impact that triggers the onset of initiation. These results provide important new insights into the coupling of hydrodynamic void collapse and the enhanced shock sensitivity of energetic materials.}, number={16}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Shi, Yunfeng and Brenner, Donald W.}, year={2008}, month={Apr}, pages={6263–6270} }
 @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{shi_kleinstreuer_2007, title={Simulation and analysis of high-speed droplet spray dynamics}, volume={129}, ISSN={["1528-901X"]}, DOI={10.1115/1.2717621}, abstractNote={Abstract
               An experimentally validated computer simulation model has been developed for the analysis of gas-phase and droplet characteristics of isothermal sprays generated by pressure jet atomizers. Employing a coupled Euler-Lagrange approach for the gas-droplet flow, secondary droplet breakup (based on the ETAB model), was assumed to be dominant and the k-ε model was selected for simulating the gas flow. Specifically, transient spray formation in terms of turbulent gas flow as well as droplet velocities and size distributions are provided for different back pressures. Clearly, two-way coupling of the phases is important because of the impact of significant gas entrainment, droplet momentum transfer, and turbulent dispersion. Several spray phenomena are discussed in light of low back-pressure (1atm) and high back-pressure (30atm) environments. At low back-pressure, sprays have long thin geometric features and penetrate faster and deeper than at high back-pressures because of the measurable change in air density and hence drag force. Away from the nozzle exit under relatively high back pressures, there is no distinct droplet size difference between peripheral and core regions because of the high droplet Weber numbers, leading to very small droplets which move randomly. In contrast to transient spray developments, under steady-state conditions droplets are subject to smaller drag forces due to the fully-developed gas entrainment velocities which reduce gas-liquid slip. Turbulent dispersion influences droplet trajectories significantly because of the impact of random gas-phase fluctuations.}, number={5}, journal={JOURNAL OF FLUIDS ENGINEERING-TRANSACTIONS OF THE ASME}, author={Shi, H. and Kleinstreuer, C.}, year={2007}, month={May}, pages={621–633} }