Plume releases

The Britter and McQuaid model is not appropriate for jets or two-phase plume releases. However, it would be appropriate at a minimal distance of 100 m from these types of releases since the initial release effect is usually minimal beyond these distances. 

Gaussian techniques, discussed in Chapter 19, are reasonable for estimates of concentrations of nonreative pollutants within 20 km of point sources. It is preferable to utilize on-site wind fluctuation measurements to estimate the horizontal and vertical spreading of a pollutant plume released from a point source. 

Consider the important time scales involved, and decide whether a puff or plume model is indicated. If this choice is unclear, assume a plume release. 

This should provide direction as to how operations staff, emergency responders, and the public should respond to a potential toxic release (e.g., chemical plumes released), including facility evacuation, personnel accountability, proper personal protective equipment (PPE) as dictated by the Risk Management Program and Process Safety Management Plan, and whether the nearby public should be in-place sheltered or evacuated. 

Figure 5.1 Closeup, overhead view of a plume released isokinetically into a turbulent boundary layer in an open-channel flow. Flow direction is from left to right.

Several laboratory studies have contributed to our understanding of turbulent chemical plumes and the effects of various flow configurations. Fackrell and Robins [25] released an isokinetic neutrally buoyant plume in a wind tunnel at elevated and bed-level locations. Bara et al. [26], Yee et al. [27], Crimaldi and Koseff [28], and Crimaldi et al. [29] studied plumes released in water channels from bed-level and elevated positions. Airborne plumes in atmospheric boundary layers also have been studied in the field by Murlis and Jones [30], Jones [31], Murlis [32], Hanna and Insley [33], Mylne [34, 35], and Yee et al. [36, 37], In addition, aqueous plumes in coastal environments have been studied by Stacey et al. [38] and Fong and Stacey [39], The combined information of these and other studies reveals that the plume structure is influenced by several factors including the bulk velocity, fluid environment, release conditions, bed conditions, flow meander, and surface waves. 

As explained in Section 2.2, where obstacles are located in rows with separation gaps d that are comparable with their height H, (i.e. streets), the recirculating flow in the wake of the upwind row tends to extend across the gap or street , and there is usually a significant mean velocity Vs along the street (see Figures 2.5 and 2.15. Note that for convenience separate streamline coordinate systems are used within and above the canyon, with denoting the coordinate relative to the canyon flow. First consider a cloud/plume released below the top of the obstacles. 

This review has mainly focused on models for mean concentrations. However, fluctuations need to be estimated in order to assess all the risks associated with accidental releases. There is some evidence from the experiments, Davidson et al., 1995 [143], that the intensity of fluctuations is lower in clouds/plumes released among buildings, and are also qualitatively different. There is much less chance of a large scale of wind gust reducing the concentration to zero, so that the probability density function is closer to a log-normal distribution than to a cut-off Gaussian (Mylne, 1992 [440]). 

The effect of temperature stratification on the atmosphere can be illustrated by considering the different forms a plume may assume. The form of a plume is determined essentially by the relation of the plume release point to any stable, neutral, and unstable layers that may be present the basic forms have been summarized by Slade (1968) and Arya (1999). In a stable layer, vertical mixing of the plume will be limited, and the plume will fan out in the horizontal plane. If a plume is released into a neutral layer capped by a stable layer, the plume will mix vertically throughout the entire depth of the neutral layer. If a plume is released into a neutral layer... 

Figure 7. a) Typical flight behaviour of a male moth tracking a pheromone plume released by a female moth, b) Trace of a typical pheromone search compared to the structure of the pheromone plume. (Image on top by Ishida Morizumi 2002 [40] bottom image by J.Hildebrand). 

The relative importance of convection and the turbulence generated by mechanical shear can be judged by the Richardson number. In defining the Richardson number, it is convenient first to define a stability parameter s, which will be used later in modeling smoke plume releases,... 

Wind tunnel (8 ft X 16 ft X 96 ft) an environmental test chamber, allows mixing and mitigation technology research as well as plume releases... 

Herbivores can typically sense suitable host plants using olfactory cues from long distance. Many volatile terpenoids bear the essential information in their molecular structure. Different stereo isomers of the same compound may result in different response when sensed by insect antennae or the olfactory sensors in the nose of vertebrate animals. Another important factor affecting signal perception and behavioral response in herbivore is the relative proportion of different volatile compounds, terpenoids or other volatiles, in the odor plume released by a plant. CombinatiOTi of certain monoterpenes and sesquiterpenes are very distinctive in certain plant families. Specialist herbivore species can separate these combinations from similar monoterpenes released by other plants, because of their strict ratio in the host species. 

FIGURE 2.33. Spreadsheet output for Example 13 Plume Release 1. 

FIGURE 2.34. Spreadsheet output for Example 14 Plume Release 2. 

The Britter and McQuaid model is not appropriate for jets or two-phase plume releases due to the entrainment effect noted earlier. 

Unlike separation devices generally encountered in the laboratory or used for industrial operations, in this case nature and natural phenomena provide the environment for the separation of dust particles from the gaseous plume released into the atmosphere from the stack. The key unknowns in the equation (7.3.178) for Tground,rp(z) are Ox and Oy, although there is some empiricism involved in estimating Upyt also. Turner (1969) provides charts to estimate values of Ox (his a,), a, (his ttj) as a function of the axial distance z (his x) from the source for six types of atmospheric conditions. 

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