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The crucial parameter in the analysis of impact events is the impact velocity v_i. In case of inertial impactors v_i was assumed to be 85% of the average gas jet velocity, following the work of Marple. Numerical analysis of the im...
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The crucial parameter in the analysis of impact events is the impact velocity v_i. In case of inertial impactors v_i was assumed to be 85% of the average gas jet velocity, following the work of Marple. Numerical analysis of the impact process in low pressure impactors shows that this assumption is inappropriate and leads to overestimation of v_i,- near the inset of particle deposition, while, v_i is underestimated in the regime of high impact velocities. In this paper the whole process of nanoparticle acceleration and impact in low pressure impactors is investigated numerically. In order to assure correct numerical procedures, the employed methods are thoroughly validated by comparison with experimental results. Finally, a new analytical model for the calculation of v_i- on the basis of similarity theory is proposed that is independent of the impactor geometry and particle properties and holds well for the whole incompressible region. The model allows to perform defined collision experiments in low pressure impactors regarding impact velocity, without need of demanding numerical effort that is often beyond the scope of experimental studies. The model replaces the old rule of thumb and allows a quantitative re-evaluation of existing experimental data, e.g. on nanoparticle agglomerate fragmentation.
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Models of drop scavenging of aerosols via inertial impaction proposed by Slinn and by Calvert are compared with published experimental measurements to determine which model is a better predictor of the data. Additionally, a parame...
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Models of drop scavenging of aerosols via inertial impaction proposed by Slinn and by Calvert are compared with published experimental measurements to determine which model is a better predictor of the data. Additionally, a parametric study was performed on the residual of the model predictions from the measurements to identify dimensionless groups not included in these models, which might increase model performance. The study found that the Calvert model predicts scavenging in the inertial regime with less error than the Slinn model. The study also found that two dimensionless groups, the relative Stokes number, Stk(r), and the drop Reynolds number, Re-D, are both well correlated with the residual of these models. They are included in modified versions of both of these models to provide better performance. That these two dimensionless groups improve model performance suggests that an inertial mechanism and an advective mechanism not accounted for in the existing models play some role in aerosol scavenging in the inertial regime. (C) 2016 Elsevier Ltd. All rights reserved.
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The results of theoretical studies and numerical simulations of laser-driven acceleration of a flat foil up to ultrahigh velocity of the order of 1000 km s(-1), which corresponds to the achievement of thermonuclear temperatures du...
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The results of theoretical studies and numerical simulations of laser-driven acceleration of a flat foil up to ultrahigh velocity of the order of 1000 km s(-1), which corresponds to the achievement of thermonuclear temperatures due to kinetic energy transition into thermal energy at an inelastic impact, are reported. The behavior of a foil accelerated to such high velocities, in particular, the distribution of foil density, which defines thermonuclear reaction intensity, has been studied. The calculation results are compared with the results of the experiments performed on the Gekko/HIPER laser, where a laser-driven projectile achieved record-breaking velocity. The laser pulse and foil parameters responsible for acceleration of the projectile up to 'thermonuclear' velocities in a dense state have been determined.
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In this paper, particulate gas flows over a circular cylinder were studied numerically for wide ranges of flow Reynolds numbers (5 < Re < 5 x 10(6)) and P numbers (0.025 < P < 5 x 10(4)). P number is defined as 9Re/S and S is the particle-fluid density ratio. For Re = 10(3) using unsteady Reynolds-averaged Navier-Stokes (URANS) equations. The Reynolds stress model...
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In this paper, particulate gas flows over a circular cylinder were studied numerically for wide ranges of flow Reynolds numbers (5 < Re < 5 x 10(6)) and P numbers (0.025 < P < 5 x 10(4)). P number is defined as 9Re/S and S is the particle-fluid density ratio. For Re = 10(3) using unsteady Reynolds-averaged Navier-Stokes (URANS) equations. The Reynolds stress model (RSM) was used to account for the anisotropic turbulent stresses around the cylinder. The computed drag was compared with the available experimental data and earlier numerical results. It was shown that the RSM could properly predict the drag-drop at the critical flow regime. Deposition of particles on the cylinder surface was also investigated using the Lagrangian trajectory analysis. Particle capture efficiencies were evaluated and compared with the available experimental data and theoretical models. The simulation results indicated that for P >= 10(2), the computed capture efficiencies obtained by the viscous flow analysis coincided with those obtained from the inviscid flows. For 1 = 0.5.
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This paper presents the development and evaluation of a high-volume, multiple rectangular (slit) geometry jet impactor. Operating with a preselective inlet that removes particles larger than 2.5 #mu#m in aerodynamic size, the impa...
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This paper presents the development and evaluation of a high-volume, multiple rectangular (slit) geometry jet impactor. Operating with a preselective inlet that removes particles larger than 2.5 #mu#m in aerodynamic size, the impactor has been designed to separate ultrafine (< 0.15 #mu#m) from the accumulation mode range (0.15 < d_p < 2.5 #mu#m). Particles are accelerated by passing through 10 parallel slits nozzles, each 12.5 cm long by 0.0125 cm wide. The average jet velocity i each rectangular jet is appromately 8500 cm s~(-1). Following acceleration, particles larger than approximately 0.15 #mu#m impact on quartz fiber strips, each 12.5 X 0.5 cm~2, while the aerosol fraction smaller than 0.15 #mu#m penetrates through the outlet of the impactor. The impactor operates at a flow rate 5501 min~(-1) and at a very low pressure drip of 0.020 kPa. The performance of the multi-slit impactor was validated in laboratory and the field tests. Laboratory experiments conducted with the 50% cutpoint of the impactor at 0.15 #mu#m. Field test comparisons between the high-volume multi-slit impactor and the Microorifice Uniform Deposit Impactor (MOUDI) showed that the accumulation and ultrafine mode concentrations of particulate nitrate, sulfate, elemental and organic carbon are in very good agreement (within 10% or less). This impactor has been developed primarily as a separator of ultrafine from accumulation mode particles for use in human exposure studies to concentrated ambient ultrafine aerosols. High-volume collection of size-fractionated particulate matter accomplished by this impactor further enables investigators in the field of environmental health to conduct toxicological studies using ambient accumulation and ultrafine mode particles in vitro as well as by means of intratracheal instillation.
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Increasing the bias voltage is a method of reducing the motional resistance of the capacitive disk resonator to match the impedance of the RF circuit. But there are few reports on the study of reliable working range of bias voltag...
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Increasing the bias voltage is a method of reducing the motional resistance of the capacitive disk resonator to match the impedance of the RF circuit. But there are few reports on the study of reliable working range of bias voltage under the shock and vibration environment. Therefore, the reliability of disk resonator under the step and pulse acceleration impact respectively is systematically analyzed in this paper. By the expression of the biggest inertial acceleration the disk can bear under the reliable condition, the maximal reliable range curves of the disk resonator under the dynamic impact environment are obtained. According to the actual sizes of disk in the literature, it can be seen that when a step shock of 13000g is supplied, the reliability range is reduced to 75% compared with the original state. For the pulse shock, the reliability range is related to the pulse amplitude and time width. Research of this paper can provide the basis for the selection of bias voltage of disk resonator under the inertial shock.
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In this study, elliptical concave impaction plate was suggested for lowering cut-off size and therefore enhancing collection efficiency of the inertial impactor. Statistical Lagrangian Particle Tracking (SLPT) model was employed f...
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In this study, elliptical concave impaction plate was suggested for lowering cut-off size and therefore enhancing collection efficiency of the inertial impactor. Statistical Lagrangian Particle Tracking (SLPT) model was employed for calculating impactor collection efficiency and validated by comparing with the experimental data of Tsai, C.J., Cheng, Y.H. ((1995). Solid particle collection characteristics on impaction surfaces of different designs. Aerosol Science Technology, 23, 96-106), for three different shapes of impaction plates. Then, the effect of the ratio of major axis length (A) to minor axis length (B) for determining the curvature of elliptical concave impaction plate, on impactor collection efficiency was numerically investigated using the SLPT model, with nozzle Reynolds numbers ranging from 1440 to 2600. It was found that there existed an optimum range of the A/B ratio for minimizing the cut-off size, i.e. the A/B ratio ranged between 3.2 and 4.2 for the PM10 inertial impactor, or between 3.2 and 3.5 for the PM2.5 inertial impactor. When the elliptical concave impaction plates with the A/B ratio of 4.0 and 3.5 were applied to the MST indoor air sampling impactor having PM10 and PM2.5 stages, the cut-off size was predicted to decrease from 10 to 6.5 um and from 2.5 to 1.6 urn, respectively, while the impactor collection efficiency curves became less steep.
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Aerosol deposition (AD) can lead to the formation of dense coatings via deposition of particles from a gas flow; in AD the aerosol is passed through a converging-diverging nozzle, facilitating inertial particle impaction on a desi...
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Aerosol deposition (AD) can lead to the formation of dense coatings via deposition of particles from a gas flow; in AD the aerosol is passed through a converging-diverging nozzle, facilitating inertial particle impaction on a desired substrate at supersonic particle velocities. Unique from thermal spray methods, AD can be applied near room temperature and unique from cold spray, in AD the aerosol is typically at atmospheric pressure upstream of the nozzle. Though AD has been successfully demonstrated previously, a number of aspects related to particle motion in AD systems remain poorly understood. In this work, we simulated compressible flow field profiles and particle trajectories for typical AD working conditions for a slit type converging-diverging nozzle with a planar substrate. In examining the fluid flow profile, we show that the velocity and pressure profiles, as well as the shock structure are sensitive to the upstream and downstream operating pressures of the nozzle. These ultimately affect particle impaction speed. Importantly, in AD, the particle drag regime is dynamic; both particle Knudsen numbers and Mach numbers can vary by orders of magnitude. To aid particle trajectory simulations, we trained a neural network to predict the drag force on the particles based on existing experimental data, theoretical limits, and new direct simulation Monte Carlo (DMSC) results. The neural network based drag law, which depends upon both Mach and Knudsen numbers, shows better agreement with the DSMC simulation data than preexisting correlations. With it, particle trajectory simulation results reveal that for a given particle density, there exists an optimal particle diameter to maximize particle impaction speed. We also find that in AD particles undergo size dependent inertial focusing, i.e. there is a particular particle diameter where the particle deposition linewidth is minimized. Particles smaller than this diameter are underfocused, and particles larger than this are overfocused, and hence have larger deposition linewidths in both cases. Using trajectory simulations, we additionally developed a framework that can be used to evaluate the position-dependent mass, momentum and kinetic energy fluxes to the deposition substrate for any aerosol size distribution function upstream of the nozzle. It is shown for typical aerosol concentrations achievable in the laboratory, the kinetic energy flux can approach a magnitude normally observed in convective heat transfer with phase change, hence translational kinetic energy to thermal energy transfer in AD is likely a key contributor to the formation of dense coatings. (C) 2018 Elsevier Ltd. All rights reserved.
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Whether a particle sticks or rebounds upon impact on a flat surface is rather well understood for normal incidence.In this case the fate of the particle (stuck or bounced) is determined by a criterion expressed in terms of the nor...
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Whether a particle sticks or rebounds upon impact on a flat surface is rather well understood for normal incidence.In this case the fate of the particle (stuck or bounced) is determined by a criterion expressed in terms of the normal impact velocity being larger than a "critical velocity".The "critical velocity" is in principle function of physical and material properties of the particle-surface combination and it can be measured in well-defined experiments.In addition,theoretical estimates for it can be made depending on the prevailing particle-surface contact mechanics.Oblique impact is not as well characterized and a simple particle sticking/rebounding criterion analogous to that for normal impact is not available.In the present study,we introduce and test the validity of such a criterion.The new criterion is cast in terms of a "critical impact angle" of incidence,beyond which no particle deposition is possible,irrespective of the value of the normal velocity.For elastic-frictional-adhesive contacts the criterion can be expressed in terms of the friction coefficient and the effective Young and Shear moduli of the particle-surface combination.The sticking/rebound criteria for normal and oblique incidence in conjunction with particle trajectory calculations are applied to analyze several sets of experimental data in the literature and they are shown to explain very well the sticking fraction of inertially impacting aerosol particles on cylindrical and spherical collectors,over the entire range of Stokes numbers.
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Cervical pain and injuries are a major health problem globally. Existing neck injury criteria are based on experimental studies that included sled tests performed with volunteers, post-mortem human surrogates and animals. However,...
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Cervical pain and injuries are a major health problem globally. Existing neck injury criteria are based on experimental studies that included sled tests performed with volunteers, post-mortem human surrogates and animals. However, none of these studies have addressed the differences between young adults and elderly volunteers to date. Thus, this work analyzed the estimated axial and shear forces, and the bending moment at the craniocervical junction of nine young volunteers (18-30 years old) and four elderly volunteers (>65 years old) in a low-speed frontal deceleration. The study proposed new methods to estimate the inertial properties of the head of the volunteers based on external measurements that reduced the error of previously published methods. The estimated mean peak axial force (Fz) was -164.38 ±35.04 N in the young group and -170.62±49.82 N in the elderly group. The average maximum shear force (Fx) was -224.42±54.39 N and -232.41±19.23 N in the young and elderly group, respectively. Last, the estimated peak bending moment (My) was 13.63±1.09 Nm in the young group and 14.81±1.36 Nm in the elderly group. The neck loads experienced by the elderly group were within the highest values in the present study. Nevertheless, for the group of volunteers included in this study, no substantial differences with age were observed.
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