Recirculation region

Cavity Recirculation Region - The cavity calculations are based largely on results published by Hosker (1984). If non-zero building dimensions are input to SCREEN for either point or flare releases, then cavity calculations will be made as follows. The cavity height, h,.(m), is estimated based on the following equation from Hosker (1984) ... 

The length of the recirculation region is calculated using the formula ... 

The ground-level concentration in the recirculation region is calculated assuming the mass fraction of the plume, below HR at the downwind end of the region, is captured into the region. The calculation assumes a Gaussian... 

Sandberg, M., B. Wiren, and I,. Claesson. 1992. Attachment of a cold plane jet to the ceiling—length of recirculation region and separation distance. In Roomvent 92, vol, 1, Aalborg, Denmark. 

Wilson indicates that for a flat-roofed building, the recirculation region maximum height at location X and the reattachment length L, shown m Fig. 7.96 can be evaluated using the following equations " ... 

Establishing a criterion for blowoff during opposed-jet stabilization is difficult owing to the sensitivity of the recirculation region formed to its stoichiometry. This stoichiometry is well defined only if the main stream and opposed jet compositions are the same. Since the combustor pressure drop is of the same order as that found with bluff bodies [76], the utility of this means of stabilization is questionable. 

The needle valve oscillated up to 12% of the total fuel, and flow rates larger than around 3% of the total implied that the bulk mean velocity in the axial jet was greater than the bulk flow in the swirler and the mean equivalence ratio was greater than unity. It was found that the amplitude of oscillations was unaffected by values of bulk mean velocity of the axial jet greater than 2.5 times that in the swirler for a main flow swirl number of 1.35, and 4 times that value for a swirl number of 0.6. Larger values of axial jet velocity led to a decrease in amplitude due to the penetration of the swirl-induced recirculation region by the jet and the consequences for the distribution of heat release. 

Figure 9. Boundaries of the internal recirculation region in the modulated swirl combustor—propane fuel...

The possibility of prompt NO was arbitrarily neglected since its importance under lean conditions is likely to be small. These kinetic estimates probably cannot be considered as predictions for the complex recirculation region produced by the flameholder, but they do serve as a reference for one limit of NO. production. 

The approach developed by Newman for the treatment of both mass-transfer and electric-field effects in boundary-layer flows has had considerable success.L2 6 However, many flows of practical interest have separation and recirculation regions, features not amenable to a boundary-layer analysis. Fortunately, there has been significant progress in the heat-transfer and other communities in computational fluid dynamics (CFD), providing numerical methods applicable to problems important to electrochemistry. The pioneers in using CFD for electrochemical applications are Alkire and co-workers, who have been largely interested in flow effects in localized corrosion. The literature is briefly reviewed in the next section. 

Figure 1.7. Flow separation and the onset of a recirculation region in flow past a cylinder...

Figs. 11.7a and 11.7c). In particular, the comparisons clearly show similar trends in the distributions, such as relatively thinner mixing layers, a shorter recirculation region, and more pronounced expansion effects in Case III. 

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