Cloud concentration

FIG. 17-14 Biihhling-hed model of Kunii and Levenspiel. dy = effective hiih-ble diameter, = concentration of A in hiihhle, = concentration of A in cloud, = concentration of A in emulsion, y = volumetric gas flow into or out of hiihhle, ky,- = mass-transfer coefficient between bubble and cloud, and k,. = mass-transfer coefficient between cloud and emulsion. (From Kunii and Leoen-spiel, Fluidization Engineering, Wiley, New York, 1.96.9, and Ktieger, Malahar, Fla., 1977.)... 

As Brenguier (2003) noted, a contributing factor to the uncertainty is drizzle in clouds that form in the atmospheric boundary layer (ABL). In particular, this circumstance illustrates the importance of the adequate retrieval of cloud cover dynamics in the ABL. Another problem is connected with consideration (parameterization) of small-scale processes in the ABL and their non-linearity. For instance, aerosols acting as cloud concentration nuclei (CCN) can be determined from upward motions at the cloud bottom which should be reproduced at a spatial resolution (in the horizontal) of the order of 100 m. The present parameterization schemes still do not meet these requirements. 

Meroney, R. N. 1991. Numerical Simulation of the Mitigation of HF Cloud Concentrations by Means of Vapor Barriers and Water Spray Curtains. Proceedings of the International Conference and Workshop on Modeling and Mitigating the Consequences of Accidental Releases of Hazardous Materials, pp. 431-442. New York American Institute of Chemical Engineers. 

The effective virtual source is at the same location as for the plume. The cloud concentration in relation to the plume concentration (2.67) is... 

The maximum explosion pressure and maximum rate of pressure rise values are determined by using the 20 L sphere apparatus. The dust sample is dispersed within the sphere, ignited by chemical igniters, and the pressure of the resulting explosion is measured. The sample size is varied to determine the optimal dust cloud concentration. The maximum pressure and rate of pressure rise are measured and used to calculate the explosion severity (Kst) value of the dust cloud. These data can be used for the purpose of designing dust explosion protection measures. 

Figure 5.68. Reaction scheme responsible for rapid ozone destruction in polar regions when large amounts of chlorine and bromine are activated by polar stratospheric clouds. Concentrations (cm-3) and fluxes (cm-3s-1) associated with chemical reactions are calculated for Antarctic springtime conditions (lower stratosphere). After Zellner (1999).

Cloud concentration (x seconds per cubic metre) is the measure of air contamination at a certain position for health protection evaluations. Sometimes, the S5mbol xlQ is used for the same quantity, where Q is the activity release (Bq). Cloud concentration is inversely proportional to wind speed... 

Program DJil is for an instantaneous radioactivity release and calculates the cloud-concentration, X (Ci s m ), and the ground concentration, Ct (Ci m ), in a ground position chosen downwind from the release point. 

Program DJi2 calculates the cloud-concentration, x (Ci s m ), for a continuous release. 

This indicates that crude oils (meeting the criteria outlined in paragraph 6) and toluene also have the potential to form a large vapour cloud in the event of an overfill. For toluene, the cloud concentration at the base of a tank has been shown by research to be just above its lower flammable limit. However, there is a degree of uncertainty over whether its subsequent movement and dilution would lead to the formation of a large flammable vapour cloud. Taking a precautionary approach it would seem sensible to consider that it would. 

The basis for specification of Vi LFL (e.g.. Department of Transportation, 1980) is to allow for variations in instantaneous cloud concentrations. Pasquill-Giflford Gaussian models have an implicit 10 min averaging time. Benarie (1987) notes that transient concentrations may differ from the average predicted by a factor up to 4 at the 5% confidence level. A problem with using Vi LFL is that hazard zones will be consistently overpredicted based on the Canvey Study (Health Sc Safety Executive, 1981), this overprediction is typically about 15-20% in distance. While individual flammable pockets may ignite at the Vi LFL distance, there is a probability that the whole cloud will not. 

For toxic gas clouds, concentration-time information is estimated using dispersion models (Section 2.3). Probit models are used to develop exposure estimates for situations involving continuous emissions (approximately constant concentration over time at a fixed downwind location) or puff emissions (concentration varying with time at a downwind location). It is much more difficult to apply other criteria that are based on a standard exposure duration (e.g., 30 or 60 min) particularly for puff releases that involve short exposure times and varying concentrations over those exposure times. The object of the toxic effects model is to determine whether an adverse health outcome can be expected following a release and, if data permit, to estimate the extent of injury or fatalities that are likely to result. 

Two p orbitals may also overlap laterally (side-to-side) to form a PI (tt) bond (Fig. 18.9). The bonding ir MO consists of two electron charge clouds concentrated above and below the axis joining the two nuclei. The MO has a nodal plane (in which the electron density is zero) incorporating the bond axis as shown in Fig. 18,9a. The antibonding MO is depicted in Fig. 18.9b. A strong rt bond can result... 

The pool vaporization is evaluated based on heat transfer from the substrate, solar radiation, convective heat transfer from the air, local wind speed, turbulence levels and local vapor pressure. All these variables are calculated at each time step and locally, for each grid cell (Gavelli et al., 2011). The cloud concentration also will be influenced by atmospheric turbulence, atmospheric stability and density changes. FLACS models flow in the atmospheric boundary layer by profiles of wind, temperature and turbulence parameters on the inlet boundaries (GexCon AS, 2013). 

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