A. D. Eisner

Airflow Around a Child-Size Manikin in a Low-Speed Wind Environment

This work provides an understanding of how airflow patterns around humans can affect the concentrations and particle size distributions of particulate matter (PM) in the breathing zone. The focus of the experiments reported here is the flow around a child-size manikin under various conditions, including changes in body heat, breathing, wind speed, and body orientation relative to the wind direction. The airflow patterns that develop were investigated using laser Doppler anemometry. The presence of body heat changes the flow pattern most dramatically. With the manikin at room temperature, the flow pattern on the downstream side of the manikin consists of two slowly recirculating eddies. With the addition of body heat to the manikin, the flow pattern downstream of the manikin changes to a rising vertical plume with velocities on the order of 0.1 m/s. This vertical plume is capable of transporting PM into the breathing zone from near the floor. Increased wind speed decreases the relative importance of buoyancy. As the wind speed increases from 0.1 to 0.3 m/s, the vertical plume on the downstream side of the manikin is replaced by two recirculating eddies, a flow pattern similar to that with the unheated manikin. Changes in the relative importance of body heat and free-stream wind speed are quantified using a type of Richardson number.

Coupled mass and energy transport phenomena in aerosol/vapor-laden gases-I. theory of the hygroscopic aerosol effects on temperature and relative humidity patterns of inspired air

Abstract A quantitative theory has been developed to predict coupled energy and mass transport phenomena during inhalation of hygroscopic aerosol-laden air. It is shown that hygroscopic particle-induced vapor scavenging will influence temperature and relative humidity patterns within the respiratory system. Consequently, particle growth kinetics will depend on its number concentration. Monodisperse hygroscopic aerosol will become polydisperse and stratified, which may subsequently affect the deposition probabilities.

Development of a Versatile Aerosol Generation System for Use in a Large Wind Tunnel

A novel aerosol generation system has been constructed for use in a large wind tunnel for two distinct research projects. One project requires a uniform aerosol concentration over the wind tunnel cross section, while the other project demands a stratified aerosol concentration distribution. The system consists of an array of venturi nozzles, which entrains particulate matter from a moving conveyor belt and disperses it into the tunnel under the force provided by a compressed air source. For the stratified release configuration, only the bottom row of nozzles was used and a confinement sleeve was installed to prevent mixing with clean air; the mixing fans were omitted from this configuration. The uniform release arrangement was tested by gravimetrically measuring particle concentration over the cross section of the tunnel for tunnel speeds of 0.1 and 1.0 m/s; uniformity was achieved within a coefficient of variation of 6.4%. The stratified distribution results show a high concentration near the floor, which diminishes with increased height. Particle size distribution was also determined on filter samples using scanning electron microscopy analysis for the uniform release experiments. No appreciable difference in mass median diameter or geometric standard deviation could be discerned for the various sampling points.

Simulation of heat and mass transfer processes in a surrogate bronchial system developed for hygroscopic aerosol studies

In order to study quantitatively the behavior of inhaled hygroscopic aerosol particles, a surrogate tracheobronchial system, capable of simulating the in vivo atmosphere (i.e., temperature and relative humidity) in a physiologically realistic manner, was developed and is reported here. This surrogate tracheobronchial system is a tubular, multicomponent physical model in which the average Reynolds number value for the airflow within each respective compartment, or section, equals the value within the corresponding bronchial airway generation of Weibels Model A network. The mass transport phenomenon (i.e., the in vivo water flow through a tracheobronchial wall and its membrane, and subsequent water evaporation into inhaled air) was simulated using this system. Detailed information regarding localized air temperature and water vapor concentration patterns for the steady flow rate of 13.5 L/min is reported in this work. The impact of the laryngeal simulator was studied, and average values of Nusselt and Sher...

Considerations for Modeling Particle Entrainment into the Wake of a Circular Cylinder

The objective of this work is to evaluate the performance of the steady state Reynolds Averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) models for estimating concentration of low Stokes number aerosols (Stk = O(10−4)) in the wake of a bluff body. These simulations are compared with experimental data. In the simulations and experiments, particles are released upstream of the body and convected downstream, where some are entrained into the wake. The air velocity is computed using a steady state renormalized group k ∼ ϵ model. Lagrangian particle trajectory simulations are performed in conjunction with each airflow model to calculate concentrations. The experiments are performed in an aerosol wind tunnel in which phase Doppler velocimetry measurements are obtained for the velocity field and aerosol concentration. The RANS model yields a wake concentration deficit that extends downstream past x/D = 10, while the experiments produce elevated concentrations immediately downstream of the near wake. It is postulated that the concentration peak is at least in part attributed to particle interaction with the boundary layer by the following mechanism. Particles are transported into the boundary layer by turbulent diffusion, turbophoresis, and/or inertial forces. Particles then separate from the cylinder with the airflow and travel in a sheath around the periphery of the near wake to converge at the downstream edge of the near wake. Underestimation of the wake concentration by the RANS model is potentially due to inadequacy in the boundary layer approximation used in the model.

On the Impact of the Human (Child) Microclimate on Passive Aerosol Monitor Performance

Research into the wind microclimate and its effect on the accuracy and effectiveness of passive aerosol monitors is expanding as the importance of personal monitoring versus regional monitoring increases. The important phenomena for investigation include thermal and dynamic effects of the human body, contaminant dispersion around a human body and within a building complex, and the wind environment within a building (indoor/outdoor) complex. This paper demonstrates that the microclimate around the human body plays a critical role in contaminant transport near the body and thus can affect particle concentration measurements by personal samplers.

Coupled mass and energy transport phenomena in aerosol/vapor-laden gases-II. computer modeling of water vapor/droplet interaction and entrainment

Abstract A computer program has been developed to simulate vapor and heat transfer processes in multiphase flow in a tube. The primary purpose is to apply it to the respiratory conditions at which aerosol-laden air is inhaled in the human respiratory tract. The method of evaluating the analytical solution and the input needed to run the program are described. Aerosol-induced coupling between temperature and vapor concentration fields under different respiratory conditions is investigated. Simulation results for air-water vapor mixtures agree well with both simplified analytical solutions and with the results of Barrett and Clement [(1986) J. Aerosol Sci. 17 , 129–143] for an infinite plane. The effect of tube radius on temperature, relative humidity and particle size is also demonstrated.

Simultaneous Production of Two Monodisperse Aerosols Using a Spinning-Top Aerosol Generator

A relatively simple laboratory technique for the simultaneous production of two monodisperse aerosols of different size has been developed and tested. This technique utilizes a standard May spinning-top aerosol generator that has been modified and enclosed under a special dual-cone fractionator. The fractionator efficiently separates the primary and satellite droplets. Illustrative Nacl aerosol generation data, obtained in a series of experiments, show that satellite droplets can provide an important source of the monodisperse aerosol.

Discussion and Evaluation of the Volatility Test for Equivalency of Other Methods to the Federal Reference Method for Fine Particulate Matter

In July, 1997, the EPA promulgated a new National Ambient Air Quality Standard (NAAQS) for fine particulate matter (PM 2.5 ). This new standard was based on the collection of an integrated mass sample on a filter. Field studies have demonstrated that the collection of semivolatile compounds leads to artifacts and imprecision among methods. In view of such sampling artifacts, a test requirement was promulgated in Title 40, Part 53, Subpart F, Section 53.66 of the Code of Federal Regulations (40CFR53.66) to aid in the determination of methodological equivalency. In this paper, this requirement is critically reviewed and tested in terms of its feasibility and precision. The results show that the test is capable of demonstrating acceptable precision for FRM-type samplers and repeatable differences in performance among different methods. In order to maintain high precision within the entire test procedure, the loading time should be extended to 2 h for flow rates of 16.7 lpm and proportionately longer for lower flow rates.

Properties of satellite and primary aerosols from a modified may spinning-top aerosol generator

Abstract Primary and satellite droplets are produced during the atomization process of the May spinning-top aerosol generator. The satellites have been commonly considered as secondary, or nuisance, aerosol and eliminated from the desired, or primary droplet, aerosol. Here, NaCl aerosol data for the satellite and primary droplets, including size distribution, production rate, and number density, were obtained in a series of experiments with a novel fractionation method. It was found that without using a centripeter, satellite droplets can be produced to serve as an important source of aerosol that is uniform in size, having a coefficient of variation of 20% vs that for primary droplets of 25%. The number density of the secondary droplets produced can be almost two orders of magnitude higher than that of the primary aerosol, and the size of the former can vary from between 10 and 70% of the size of the latter.