Aerodynamic Processes

Older works on the kinetic theory of gases quite uniformly show the following attitude toward the application of probability theory The goal is the explanation of the observable aerodynamic processes on the basis of two groups of assumptions. These are ... 

The kinetic interpretation of an aerodynamic process, just as any other "explanation of a physical phenomenon, consists of the representation of the observed sequence of states by a purely conceptual scheme. A special feature of kinetic interpretations, however, is the statistical character of these schemes. Each single process which takes place in the given gas quantum is made to correspond to a whole group of motions of the gas model. This is done with the help of the following concluding assertion ... 

This statement is clearly not a direct expression of an experimental fact. Apart from a very small group of aerodynamical processes, we always deal with turbulent motions of the gas, where it is impossible to follow the visible state with our measuring instruments. Furthermore, even the best insulation against thermal conduction and radiation is completely unsatisfactory unless we deal with very short periods of observation. 

UPfi is the only compound of uraruum volatile at room temperature. It is used as working fluid in the gaseous diffusion, gas centrifuge, and aerodynamic processes for uranium enrichment discussed in Chap. 14. Its principal physical and chemical properties are summarized in Sec. 4.7. 

Numerous other schemes for separating isotopes in flowing gas streams have been conceived and subjected to small-scale test, but none has appeared sufflciently promising to enlist the major development support given the nozzle and UCOR processes. Summary descriptions of other aerodynamic processes are in references [T2] and [M2]. 

T in aerodynamic processes, absolute temperature after isentropic expansion... 

Wind speed and the type of wind flow have a pronounced effect on the atmospheric corrosion rate. This is illustrated by the dry deposition velocity, which is defined as the ratio of deposition rate of any gaseous compound and the concentration of that compound in the atmosphere. The factors controlling dry deposition are composed of aerodynamic and surface processes. Aerodynamic processes are related to the actual depletion of the gaseous constituent (e.g., SO2) in the atmospheric region adjacent to the aqueous phase and the ability of the system to add new SO2 to the region. This ability... 

A comparison has been made of detailed CFD predictions, which have included all the aerodynamic processes involved in falling sprays, and a simple momentum conservation model which ignores the induced shear flow on the spray periphery. This has shown that for the scenarios considered here it is adequate to use the latter, simpler treatment, which is described in Annex 1. Typical results obtained using the simple momentum conservation model are shown in Figure 16. In overfilling incidents the mass flux density is likely to be in the range 1 to 10 kg/mVs. This corresponds to maximum droplet velocities of 10-13 m/s and vapour velocities of 4-6 m/s. 

In general, the dry deposition velocity will be the combined effect of both resistances. However, at highly turbulent air flow conditions R =0 and the dry deposition velocity is dependent only on the surface processes. Alkaline surfaces, such as lead peroxide or triethanolamine, are ideal absorbers of SO2 for which = 0. In this case, the dry deposition velocity if dependent on the aerodynamic processes. Typical ranges for dry deposition velocities onto various materials imder outdoor and indoor conditions are given in Table 2.1. 

A useful parameter is the dry deposition velocity, which is defined as the ratio of deposition rate or surface flux per time unit of any gaseous compound and the concentration of the same compound in the atmosphere [46]. The concept of dry deposition velocity of SO2 and its relevance to atmospheric corrosion rates is well established [47]. By examining data based on both field and laboratory exposures, it can be concluded that the factors controlling dry deposition fall into aerodynamic processes and surface processes. Aerodynamic processes are connected with the actual depletion of the gaseous constituent (e.g., SO2) in the atmospheric region next to the aqueous phase and the ability of the system to mix new SO2 into this region. This ability depends on, for instance, the actual wind speed, type of wind flow, and shape of sample. Surface processes, on the other hand, are connected with the ability of the aqueous layer to accommodate SO2. This ability increases with the thickness of the aqueous layer and, hence, with the relative humidity, the pH of the solution (as discussed earlier), and the alkalinity of the solid surface. 

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