Transport of gases and particles to surfaces with widely spaced roughness elements

Chamberlain, A. C.; Garland, Jeffery S.; Wells, A. C.

doi:10.1007/bf00120534

Cited by 39 publications

(20 citation statements)

References 12 publications

(13 reference statements)

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“…When particle deposition is the concern, quantification of surface roughness is needed rather than simple classification of the surface as hydraulically smooth. Macroscale roughness, in the form of fibers or grasses (Chamberlain, 1967;Wells & Chamberlain, 1967;Sehmel, 1970a), repeated ribs (Chamberlain et al, 1984;Hahn et al, 1985;Lai, 1997) and uniform three-dimensional elements (Lai, 1997), has been more frequently characterized and its influence on deposition more systematically investigated. Roughnesses reported in Tables 2.2-2.5 include both microscale and macroscale conditions.…”

Section: Details About Experiments In Straight Tubes and Ductsmentioning

confidence: 99%

“…Their data confirmed the expected decrease in deposition with increases in particle size within the diffusion regime until Brownian diffusion becomes negligible. Chamberlain et al (1984) made a single observation of deposition in the diffusion regime. Shimada et al (1993) provided a larger data set of reasonable quality for deposition in the diffusion regime, showing increasing deposition for decreasing particle size.…”

Section: 33a Particle Size and Air Velocitymentioning

confidence: 99%

“…In addition, the distribution of three-dimensional roughness blocks on the surface slightly influenced deposition. Chamberlain et al (1984) studied the effects of repeated rib roughness on the deposition of large particles and Hahn et al (1985) performed similar experiments for small, diffusive particles. Effects of spacing between the ribs were unclear in both cases and neither work compared deposition rates to a similar smooth surface.…”

Section: 33c Fibrous and Macroscale Roughnessmentioning

confidence: 99%

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Particle deposition in ventilation ducts

Sippola¹

2002

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Exposure to airborne particles is detrimental to human health and indoor exposures dominate total exposures for most people. The accidental or intentional release of aerosolized chemical and biological agents within or near a building can lead to exposures of building occupants to hazardous agents and costly building remediation.Particle deposition in heating, ventilation and air-conditioning (HVAC) systems may significantly influence exposures to particles indoors, diminish HVAC performance and lead to secondary pollutant release within buildings. This dissertation advances the understanding of particle behavior in HVAC systems and the fates of indoor particles by means of experiments and modeling.Laboratory experiments were conducted to quantify particle deposition rates in horizontal ventilation ducts using real HVAC materials. Particle deposition experiments were conducted in steel and internally insulated ducts at air speeds typically found in ventilation ducts, 2-9 m/s. Behaviors of monodisperse particles with diameters in the size range 1-16 µm were investigated. Deposition rates were measured in straight ducts with 1 2 a fully developed turbulent flow profile, straight ducts with a developing turbulent flow profile, in duct bends and at S-connector pieces located at duct junctions. In straight ducts with fully developed turbulence, experiments showed deposition rates to be highest at duct floors, intermediate at duct walls, and lowest at duct ceilings. Deposition rates to a given surface increased with an increase in particle size or air speed. Deposition was much higher in internally insulated ducts than in uninsulated steel ducts. In most cases, deposition in straight ducts with developing turbulence, in duct bends and at S-connectors at duct junctions was higher than in straight ducts with fully developed turbulence.Measured deposition rates were generally higher than predicted by published models.A model incorporating empirical equations based on the experimental measurements was applied to evaluate particle losses in supply and return duct runs. Model results suggest that duct losses are negligible for particle sizes less than 1 µm and complete for particle sizes greater than 50 µm. Deposition to insulated ducts, horizontal duct floors and bends are predicted to control losses in duct systems. When combined with models for HVAC filtration and deposition to indoor surfaces to predict the ultimate fates of particles within buildings, these results suggest that ventilation ducts play only a small role in determining indoor particle concentrations, especially when HVAC filtration is present.However, the measured and modeled particle deposition rates are expected to be important for ventilation system contamination. ChairDate

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Section: Details About Experiments In Straight Tubes and Ductsmentioning

confidence: 99%

Section: 33a Particle Size and Air Velocitymentioning

confidence: 99%

Section: 33c Fibrous and Macroscale Roughnessmentioning

confidence: 99%

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Particle deposition in ventilation ducts

Sippola¹

2002

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“…Chamberlain, Garland, and Wells (1984) found that transfer correlated well with: This relationship is based on lead-121 and iodine-131 data.…”

Section: 34mentioning

confidence: 90%

Improved Formulations for Air-Surface Exchanges Related to National Security Needs: Dry Deposition Models

Droppo¹

2006

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SummaryThe Department of Homeland Security and others rely on results from atmospheric dispersion models for threat evaluation, event management, and post-event analyses. The ability to simulate dry deposition rates is a crucial part of our emergency preparedness capabilities. Deposited materials pose potential hazards from radioactive shine, inhalation, and ingestion pathways. A reliable characterization of these potential exposures is critical for management and mitigation of these hazards.A review was conducted of the current status of dry deposition formulations used in these atmospheric dispersion models. The formulations for dry deposition of particulate materials considered an event such as a radiological attack involving a Radiological Detonation Device (RDD). The results of this effort are applicable to current emergency preparedness capabilities, such as are deployed in the Interagency Modeling and Atmospheric Assessment Center (IMAAC), other similar national/regional emergency response systems, and stand-alone emergency response models.The review concludes that dry deposition formulations need to consider the full range of particle sizes, including: 1) the accumulation mode range (0.1 to 1 micron in diameter) and its minimum deposition velocity, 2) smaller particles (less than 0.01 micron diameter) deposited mainly by molecular diffusion, 3) 10 to 50 micron diameter particles deposited mainly by impaction and gravitational settling, and 4) larger particles (greater than 100 micron diameter) deposited mainly by gravitational settling. The effects of the local turbulence intensity, particle characteristics, and surface element properties must also be addressed in the formulations.Specific improvements recommended for dry deposition formulations are 1) the capability of simulating near-field dry deposition patterns, 2) the capability of addressing the full range of potential particle properties, 3) the incorporation of particle surface retention/rebound processes, and 4) the development of dry deposition formulations applicable to urban areas. Also, to improve dry deposition modeling capabilities, atmospheric dispersion models in which the dry deposition formulations are imbedded need better source-term plume initialization and improved in-plume treatment of particle growth processes.Dry deposition formulations used in current models are largely inapplicable to the complex urban environment. An improved capability is urgently needed to provide surface-specific information to assess local-exposure hazard levels in both urban and non-urban areas on roads, buildings, crops, rivers, etc.A model improvement plan is developed with a near-term and far-term component. Despite some conceptual limitations, the current formulations for particle deposition based on a resistance approach have proven to be reasonable dry deposition simulations. For many models with inadequate dry deposition formulations, adding or improving a resistance approach will be the desirable near-term update. Resistance models, however, are i...

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“…Several empirical formulae have been proposed for excess resistance (and, therefore, implicitly z p ) under different conditions (e.g. Thom 1972;Stewart and Thom, 1973;Brutsaert, 1982;Chamberlain, 1984) Fortunately, investigation of the effective value of z p (e.g. Garratt and Francey, 1978) for a range of surfaces covered in permeable (fibrous) vegetation has suggested that ln(z 0 /z p ) ~ 2 (Fig.…”

Section: Fig 4 Conceptual Framework Of the Rutter Model (Rutter Et mentioning

confidence: 99%

Putting the "vap" into evaporation

Shuttleworth¹

2007

Hydrol. Earth Syst. Sci.

212

147

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In the spirit of the Special Issue of HESS to which it contributes, this paper documents the origin and development of the science of natural evaporation from land surfaces over the last 3035 years, since the symposium A View from the Watershed was held to commemorate the opening of the new Institute of Hydrology (IH) building in 1973. Important subsequent technical progress includes the ability to measure routinely the diurnal cycle of near-surface meteorological variables using automatic weather stations, and of surface energy and momentum exchanges using automated implementations of the Bowen Ratio/Energy Budget technique and the Eddy Correlation technique, along with the capability to estimate the fetch for which these measurements apply. These improvements have been complemented by new methods to measure the separate components of evaporation, including: the interception process using randomly relocated below-canopy gauges, transpiration fluxes from individual leaves/shoots using porometers and from plants/plant components using stem-flow gauges and soil evaporation using micro-lysimeters and soil moisture depletion methods. In recent years progress has been made in making theory-based areaaverage estimates of evaporation using scintillometers, and model-based area-average estimates by assembling many streams of relevant data into Land Data Assimilation Systems. Theoretical progress has been made in extending near-surface turbulence theory to accommodate the effect of the excess boundary layer resistance to leaf-to-air transfer of energy and mass fluxes relative to that for momentum, and to allow for observed shortcoming in stability factors in the transition layer immediately above vegetation. Controversy regarding the relative merits of multi-layer model and big leaf representations of whole-canopy exchanges has been resolved in favour of the latter approach. Important gaps in the theory of canopy-atmosphere interactions have been filled, including recognising the need, separately, to represent dry-canopy and wet-canopy evaporation in models and the capability to describe wet-to-dry canopy transitions as well as the ability to describe sparse vegetation canopies which only partly cover the underlying soil. There is progress in methods of estimating crop water requirements, but an important recommendation of this paper is that this progress should continue by introducing use of an effective stomatal resistance rather than crop factors. The paper draws attention to relevant theoretical insight on this issue. Progress in theoretical understanding of evaporation processes has been used in the creation of numerous Land Surface Parameterisations (LSPs), the models used to represent land-surface interaction in climate and weather forecast models, and there have been important advances in describing the behaviour of plant stomata in LSPs. A major investment over the last 25 years in conducting Large-Scale Field Experiments, the better to measure, understand and model coupled land-surface/atmosphere intera...

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Transport of gases and particles to surfaces with widely spaced roughness elements

Cited by 39 publications

References 12 publications

Particle deposition in ventilation ducts

Particle deposition in ventilation ducts

Improved Formulations for Air-Surface Exchanges Related to National Security Needs: Dry Deposition Models

Putting the "vap" into evaporation

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Transport of gases and particles to surfaces with widely spaced roughness elements

Cited by 39 publications

References 12 publications

Particle deposition in ventilation ducts

Particle deposition in ventilation ducts

Improved Formulations for Air-Surface Exchanges Related to National Security Needs: Dry Deposition Models

Putting the &quot;vap&quot; into evaporation

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Putting the "vap" into evaporation