Particle deposition in ventilation ducts

Sippola, Mark R.

doi:10.2172/810494

Cited by 35 publications

(43 citation statements)

References 113 publications

(286 reference statements)

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“…The top, middle, and bottom rows of plots display data collected at the duct ceiling, wall, and floor, respectively. The uncertainties in the reported enhancement factors have been estimated to be in the range 5-15% (Sippola 2002). Data with similar results to those shown in Table 3 and Figures 6 and 7 were collected in test duct 3 (Sippola 2002).…”

Section: Ducts With Developing Turbulent Flowsupporting

confidence: 63%

Particle Deposition in Ventilation Ducts: Connectors, Bends and Developing Turbulent Flow

Sippola

Nazaroff

2005

Aerosol Science & Technology

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In ventilation ducts the turbulent flow profile is commonly disturbed or not fully developed, and these conditions are likely to influence particle deposition to duct surfaces. Particle deposition rates at eight S-connectors, in two 90• duct bends and in two ducts where the turbulent flow profile was not fully developed were measured in a laboratory duct system with both bare steel and internally insulated ducts with hydraulic diameters of 15.2 cm. In the bare-steel duct system, experiments with nominal particle diameters of 1, 3, 5, 9, and 16 µm were conducted at each of three nominal air speeds: 2.2, 5.3, and 9.0 m/s. In the insulated duct system, deposition of particles with nominal diameters of 1, 3, 5, 8, and 13 µm was measured at nominal air speeds of 2.2, 5.3 and 8.8 m/s. Fluorescent techniques were used to measure directly the deposition velocities of monodisperse fluorescent particles to duct surfaces. Deposition at S-connectors, in bends, and in straight ducts with developing turbulence was often greater than deposition in straight ducts with fully developed turbulence for equal particle sizes, air speeds, and duct surface orientations. Deposition rates at all locations were found to increase with an increase in particle size or air speed. High deposition rates at S-connectors resulted from impaction, and these rates were nearly independent of the orientation of the S-connector. Deposition rates in the two 90• bends differed by more than an order of magnitude in some cases, probably because of the difference in turbulence conditions at the bend inlets. In straight sections of bare steel ducts where the turbulent flow profile was developing, the deposition enhancement relative to fully developed turbulence generally increased with air speed and decreased with downstream distance from the duct inlet. This enhancement was greater at the duct ceiling and wall than at the duct floor. In insulated ducts, deposition enhancement was less pronounced overall than in bare steel ducts. Trends that were

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Section: Ducts With Developing Turbulent Flowsupporting

confidence: 63%

Particle Deposition in Ventilation Ducts: Connectors, Bends and Developing Turbulent Flow

Sippola

Nazaroff

2005

Aerosol Science & Technology

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“…An ensemble of 30,000 trajectories ensured sufficient statistical confidence of the predicted deposition velocities. Figure 4 shows the comparison of predicted results and experimental data from the literature collected by Sippola (2002). The deposition velocity and the particle relaxation time were normalized by the friction velocity u * and the turbulence time scale *2 u /ν .…”

Section: Predicting Particle Deposition In a Channel Flowmentioning

confidence: 99%

Prediction of particle deposition onto indoor surfaces by CFD with a modified Lagrangian method

Zhang¹,

Chen²

2009

Atmospheric Environment

162

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Accurate prediction of particle deposition indoors is important to estimate exposure risk of building occupants to particulate matter. The prediction requires accurate modeling of airflow, turbulence, and interactions between particles and eddies close to indoor surfaces. This study used a 2 ′ − v f turbulence model with a modified Lagrangian method to predict the particle deposition in enclosed environments. The 2 ′ − v f model can accurately calculate the normal turbulence fluctuation 2 ′ v , which mainly represents the anisotropy of turbulence near walls.Based on the predicted 2 ′ v , we proposed an anisotropic particle-eddy interaction model for the prediction of particle deposition by the Lagrangian method. The model performance was assessed by comparing the computed particle deposition onto differently oriented surfaces with the experimental data in a turbulent channel flow and in a naturally convected cavity available from the literature. The predicted particle deposition velocities agreed reasonably with the experimental data for different sizes of particles ranging from 0.01μm to 50μm in diameter. This study concluded that the Lagrangian method can predict indoor particle deposition with reasonable accuracy provided the near-wall turbulence and its interactions with particles are correctly modeled.

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“…Such systems can become entry points or distribution systems for hazardous contaminants, including biological weapon agents (BWA) (15). Air circulation in ordinary buildings can assist the spread of airborne disease and can disperse contaminants (11,22). Reaerosolization of these hazardous bioparticles deposited onto surfaces can be a continuing source of contamination.…”

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confidence: 99%

Reaerosolization of Fluidized Spores in Ventilation Systems

Krauter

Biermann

2007

Appl Environ Microbiol

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This project examined dry, fluidized spore reaerosolization in a heating, ventilating, and air conditioning duct system. Experiments using spores of Bacillus atrophaeus, a nonpathogenic surrogate for Bacillus anthracis, were conducted to delineate the extent of spore reaerosolization behavior under normal indoor airflow conditions. Short-term (five air-volume exchanges), long-term (up to 21,000 air-volume exchanges), and cycled (on-off) reaerosolization tests were conducted using two common duct materials. Spores were released into the test apparatus in turbulent airflow (Reynolds number, 26,000). After the initial pulse of spores (approximately 10 10 to 10 11 viable spores) was released, high-efficiency particulate air filters were added to the air intake. Airflow was again used to perturb the spores that had previously deposited onto the duct. Resuspension rates on both steel and plastic duct materials were between 10 ؊3 and 10 ؊5 per second, which decreased to 10 times less than initial rates within 30 min. Pulsed flow caused an initial spike in spore resuspension concentration that rapidly decreased. The resuspension rates were greater than those predicted by resuspension models for contamination in the environment, a result attributed to surface roughness differences. There was no difference between spore reaerosolization from metal and that from plastic duct surfaces over 5 hours of constant airflow. The spores that deposited onto the duct remained a persistent source of contamination over a period of several hours.The threat from a bioweapon agent such as anthrax remains problematic. Because of the biological, technical, and pathological characteristics of Bacillus anthracis, it is attractive as a bioweapon (2, 10). When used as a weapon of mass destruction, the agent is dispersed in particles less than 5 m in diameter, a size that allows penetration into the pulmonary alveoli (18). Minimal data on human infective doses for inhalational Bacillus anthracis are available (14,24,25). The problem is further compounded by variations in individual susceptibility, B. anthracis strain virulence and spore preparation technique, and physical characteristics of the bioparticle. Thus, studying the fate and transport of fluidized spore concentrations is necessary in order to better predict the area of contamination and to more accurately model potential health risk.Ventilation systems provide a conduit to contaminate a building and the surrounding area. Such systems can become entry points or distribution systems for hazardous contaminants, including biological weapon agents (BWA) (15). Air circulation in ordinary buildings can assist the spread of airborne disease and can disperse contaminants (11,22). Reaerosolization of these hazardous bioparticles deposited onto surfaces can be a continuing source of contamination. For example, a study of reaerosolization of B. anthracis after dispersal in a postal facility found that a mail sorter remained contaminated many days after processing B. anthracis-contaminated letters ...

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Particle deposition in ventilation ducts

Cited by 35 publications

References 113 publications

Particle Deposition in Ventilation Ducts: Connectors, Bends and Developing Turbulent Flow

Particle Deposition in Ventilation Ducts: Connectors, Bends and Developing Turbulent Flow

Prediction of particle deposition onto indoor surfaces by CFD with a modified Lagrangian method

Reaerosolization of Fluidized Spores in Ventilation Systems

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