Dispersion, airflows

Transport of outdoor contaminants is controlled by both the mean motion of winds and dispersal by turbulence. Since airflow around buildings has... 

Contaminant concentrations Dispersal of airborne contaminants such as odors, fumes, smoke, VOCs, etc. transported by these airflows and transformed by a variety of processes including chemical and radiochemical transformation, adsorption, desorption to building materials, filtration, and deposition to surfaces evolution of contaminant concentrations in the individual zones air quality checks in terms of CO2 levels cross-contamination evaluation of zones air quality evaluations in relation to perception as well as health. Methods ate also applicable to smoke control design. 

CONTAM96 is based on earlier programs by NIST (National Institute ol Standards and Technology), AIRNET (airflows), CONTAM (contaminant dispersal), and ASCOS (smoke transport). ... 

All three experimental approaches are presented in this chapter visualization of airflow and contaminant dispersion (Section 12.2), measurement techniques including laser-based-techniques (Section 12.3), and scale model experiments (Section 12.4). 

The main purpose with flow visualization is to make the airflow field or the emission and transport of air contaminants visible and thereby possible to study. In technical terms, flow visualization gives possibilities to study airflow field and contaminant dispersion and changes in it depending on general changes in geometry, boundary conditions, inlet and exhaust airflow, etc. It is... 

The reasons for using airflow or contaminant dispersion visualization techniques may be divided into purely technical and pedagogical, both with the purpose to give a base for the design and proper use of a contaminant control technology for workplaces with a good air quality. 

In this chapter the most common and/or well-evaluated techniques for the visualization of airflow and contaminant dispersion are described. The strategy for its use as a pedagogic tool is not included this can be found elsewhere. To separate the different methods according to either airflow or contaminant dispersion studies is meaningless and not always possible. For example, smoke may many times be used for both purposes. The emitted smoke acts like a substitute for the contaminant in question and visualizes its dispersion to, e.g., the... 

There are of course a number of methods that can be classific d a- methods for the visualization of airflow and contaminant dispersion. This i.hapter describes some of these that are useful for designers of industrial vcntilatiou. Methods that not are presented in more detail here are, for example, to fill small soap bubbles or ordinary balloons with helium in order to stuiiy the airflow field in large rooms. A large number of textbooks focus on flow- visualization. The research in this area can also be followed in The lournal of Floif Visualization and Image Processing. -... 

Air contaminants in solid or liquid state (aerosols), e.g., wood dust, welding smoke, or oil mist, are all in principle directly visible. The dispersion of those contaminants and the airflow patterns around the source may therefore be studied without any special tools. It is, however, not always possible to see the contaminant if, for example, the concentration in the air is low, the size of the particles is small, or the lighting is poor. The fact that the contaminant can t be seen may stem from the acceptable low level of the concentration but that can of course not be used to conclude that the control is acceptable. That conclusion depends not only on the contaminant s toxicological qualities but on how visible it is iit air. The ability to see the particles directly is also, as said above, a function of their size. Small particles, able to be transported deep into the thinner airways of the lungs, are many times also difficult to see directly. 

In industrial ventilation the majority of air velocity measurements are related to different means of controlling indoor conditions, like prediction of thermal comfort contaminant dispersion analysis adjustment of supply airflow patterns, and testing of local exhausts, air curtains, and other devices. In all these applications the nature of the flow is highly turbulent and the velocity has a wide range, from O.l m in the occupied zone to 5-15 m s" in supply jets and up to 30-40 m s in air curtain devices. Furthermore, the flow velocity and direction as well as air temperature often have significant variations in time, which make measurement difficult. 

Additional dispersal problems may occur when the prevailing wind occurs perpendicular to the valley or hill ridgeline. This may lead to speed up and turbulence over the valley or it may simply reduce the effect of airflow carrying away airborne pollutants. 

Take advantage of ongoing research aimed at the development of models of the airflow within aircraft, terminals, and so forth, based on empirical studies of specific facilities, and explore the dispersal of chemical/biological simulants under various release scenarios ... 

Computational fluid dynamic simulator ht-MAH CFD simulation OT indoor airflow and pollutant dispersion Trained %... 

The aim of dispersion models is the prediction of atmospheric dilution of pollutants in order to prevent or avoid nuisance. Established dispersion models, designed for the large scale of industrial air pollution have to be modified to the small scale of agricultural pollutions. An experimental setup is described to measure atmospheric dilution of tracer gas under agricultural conditions. The experimental results deliver the data base to identify the parameters of the models, For undisturbed airflow modified Gaussian models are applicable. For the consideration of obstacles more sophisticated models are necessary,... 

Move the sample tube in toward the smoke source from all directions at this level to the point where particle counts show a sudden and rapid rise to high levels (lO per cubic foot). This defines the envelope of dispersion away from the smoke source and demonstrates the airflow parallelism control of the room. Repeat for all grid areas. Prepare a diagram showing grid areas and corresponding dispersion envelopes. 

The purpose is to verify the parallelism of airflow throughout the work zone and the capability of the cleanroom to limit the dispersion. 

Powder-layer reactors are not appropriate for full-scale commercial applications, however. Loose catalyst powders are generally not compatible with high-flow-rate situations, as the powder may become compressed or dispersed into the airstream, depending on the direction of the airflow. Powder-layers are also a poor choice in situations where the reactor may be subjected to vibrations or sudden shocks, as might be expected in reactors associated with certain mobile... 

Radiotracers have been employed in studies of physical and biological processes in the atmosphere and the hydrosphere. Among the quantities that have been measured in atmospheric studies are the natural airflow patterns in large- and small-scale investigations, the dispersion of atmospheric pollutants from various sources, and the identification of the sources of various pollutants. In studies of... 

Comparing these airflow intervals with those permeable zones induced by conventional hydraulic fracturing indicated that explosive fracturing created additional communication paths to wells 2 and 5 at the 73-ft level. However, the injection capacity of well 3 was reduced 64%. This may have resulted from too wide a dispersion of the liquid explosive, so that the shot was not strong enough to lift and fracture the overburden rock permanently, or the fractures may have been plugged by fine oil-shale particles or mud. 

To maximize drug particle dispersion, mechanical means may be introduced into the flow path to generate a turbulent airflow that exerts... 

The coarse carrier particles blended with micronized drug form an ordered or interactive mixture (Fig. 8.11) (Hersey 1975) stabilized by adhesive Lifshitz—van der Waals and electrostatic forces (Podczeck 1998 Hickey et al. 1994). The shear forces exerted in the airflow of a DPI device must be greater than the adhesive forces in order to provide sufficient deaggregation and dispersion of the drug particles. Unfortunately, however, this process is more or less incomplete and disperses only a proportion of the agglomerated drug particles depending on the inhalation airflow (Zanen et al. 1992). 

Dispersion arises from the fact that, even in a relatively homogenous porous medium, small-scale heterogeneities exist which cause airflow to proceed along various channels at different rates. Barometric pumping causes a significant increase in the coefficient of hydrodynamic dispersion over a pure diffusion-based transport model, thus increasing the overall transport rate. 

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