Wake Region/zone

Workers could be either inside the supply airflow or outside. If a worker is inside the airflow, it is possible that the breathing zone of the worker is within the wake region and he or she may be exposed to the contaminated airflow. To reduce the exposure the worker should always be upstream of the source and should try not to have his or her back to the supply airflow. 

The recirculating wake zone is of particular importance for dispersion prediction. The dispersing species can become trapped in the wake region, remaining present at elevated concentrations well after a puff might be expected to have passed. 

The order of magnitude of the characteristic dimensions of diffusion wake regions past a spherical drop and a solid particle in a translational flow is shown in Table 4.9. These estimates remain valid at moderate Reynolds numbers, when the stagnation zones past a drop or a solid particle are absent. 

The bed is assumed to consist of three zones, the bubble, cloud and emulsion, with the wake region considered to be a part of the cloud zone. 

If a bottle is placed in the bench, a wake is easily created in the legitni with horizontal flow. This is depicted visually with smoke in Fig. 10.58. If the bottle is situated close to the opening of the unit, ambient air will be entrained intt> the dean zone in the bench. The length of the reversed region can be < sti mated to two to three times the diameter of the bottle, and can reach twice this length w hen the bottle is situated just beside the side wall. 

FIGURE 4.54 Recirculation zone and flame-spreading region for a fully developed turbulent wake behind a bluff body (after Williams [57]). 

Stirred reactor theory was initially applied to stabilization in gas turbine combustor cans in which the primary zone was treated as a completely stirred region. This theory has sometimes been extended to bluff-body stabilization, even though aspects of the theory appear inconsistent with experimental measurements made in the wake of a flame holder. Nevertheless, it would appear that stirred reactor theory gives the same functional dependence as the other correlations developed. In the previous section, it was found from stirred reactor considerations that... 

A number of parasitic diseases result in a coexisting liver reaction or even lead to coexisting liver disease. However, most of these parasitoses are rarely encountered in the temperate zones, and if at all, they occur only sporadically in the wake of immigration and tourist travel to endemic regions. 

Note that the dispersion terms described in equation (6.18) are valid only in the limit of Fickian behavior. From the central limit theorem, this regime is reached when every particle has amply sampled each region (wakes, gaps, recirculation zones). The average time-scale to advect through a wake is (a(u)Yl, and the average time-scale to experience trapping within a recirculation zone is r/ (yad). Then, the Fickian limit is reached at time t r/ (yad) and (fl(M 1. 

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