Impingement zone

Fig. 2. A brief view of SCISR 1—Drawing tube 2—Propeller 3—Impingement zone 4 —Outlet...

Barratt P A, Baumgartl A, Hannay N, Vetter M, Xiong F (1996) CHEMOX Advanced waste water treatment with the impinging zone reactor in Clausthaler Umwelt-Akademie Oxidation of Water and Wastewater, A Vogelpohl (Hrsg.), Goslar 20.-22. Mai. 

Two-phase gaslwater injector nozzles are mostly used in pilot- or full-scale bubble column applications (Krost, 1995) or in specialized, newly developed reactor types. An example is the Submerged Impinging Zone Reactor (IZR) (Gaddis and Vogelpohl, 1992 Air Products, 1998), which is constructed for very high mass-transfer rates. 

In addition, according to the feature and number of impingement planes, devices can also be classified as stationary, moving, and multi impingement zone, etc. Readers may refer to Ref. [5]. 

When the jet on the right-hand side is at the top and that on the left-hand side is at the bottom, the twisting is clockwise while for opposite positions of the jets, it is anticlockwise. The deflection and twisting of the jets result in the formation of vortices on both sides of the outflow plane. Ihe intensities of which depend on the parameters of the jets in impingement. The researchers considered that the collision between the two jets is associated with retardation of the liquid, resulting in an increase in pressure in the impingement zone. The experimental measurements were correlated in terms of the period T of the auto oscillation as a function of the operation parameters. For two equal jets ejected from the nozzles at the same velocity, the relationship they obtained is... 

Figures 1.6(c) and (d) show the pressure profile in the impinging streams. The profile is characterized by the considerable pressure gradients in the direction of the chamber axis, as shown in Fig. 1.6(c), and also in the perpendicular plane, as shown in Fig. 1.6(d). Obviously, in the region a little distance away from the impingement plane, the pressure profile is independent of the impinging distance. A decrease in the impinging distance leads to a more rapid increase in pressure only in the impingement zone.

Figure 2.2 Particles leaving impingement zone in various directions.

Obviously, the situations are very complex. To describe every possible condition is very difficult and troublesome while, on the other hand, it is not necessary to do so from a practical point of view. In the following discussions the motion of the particle will be analyzed based on certain idealized assumptions for the most number of oscillation times possible and the longest residence time possible of the particle in the impingement zone in extreme cases. 

From the point of view of practical application, it is certainly of interest to understand, even primarily, the possible residence time of the particle in the impingement zone by a theoretical analysis. In principle, the total residence time of the particle, fr, can be calculated as the summation of the residence times in all the motion stages ... 

Despite possible error(s), it is still helpful and of significance to get some rough or semi-quantitative understanding about the residence time of particles in the impingement zone from the analysis using the equations given above. The results estimated with Eq. (2.31) can be considered as being about the possible maximum residence time of particles. 

Figure 2.6 shows the relationship between the residence time of a single particle in the impingement zone, tf, and the length of the accelerating tube, /ac. As can be seen, in the range of /ac smaller than 1.0, t increases quickly as /ac increases while after /ac = 1.0, the increase in /, with /ac is smoothed. 

Figure 2.6 Residence time of particle in the impingement zone vs. the length of accelerating...

A theoretical analysis is helpful for understanding the basic characteristics of impinging stream processes and the performances of the related devices. In an impinging stream device, where the residence time distribution of particles is most important is in the impingement zone, because this zone is the major active region for heat and mass transfer between phases in such a device. Unfortunately, it is basically... 

Because of the importance of the residence time distribution in the impingement zone, the basic requirement when designing the experimental equipment is that it should be suitable for understanding the residence time and its distribution of particles in the impingement zone. For this purpose, the rest of the equipment should be as simple as possible. From the point of view of residence time distribution, this means shortening the residence times in the spaces other than the impingement zone as much as possible. 

Part of the experimental results on the residence time of a single particle in the impingement zone was given in Fig. 2.6 in Chapter 2. These results, at least, can bound... 

The particles may leave the impingement zone in various directions, as shown in Fig. 3.2. To calculate the residence time in the falling down region, only the motion in the vertical direction needs to be considered. If the direction vertically downward is set to be the positive direction for both the vertical velocity of particles, p h and the height coordinate, h, and let f3 (0° < / < 360°) be the intersection angle between this positive direction and the direction the particles are leaving in, then we have... 

This is the model for the overall residence time distribution of the particles in the impinging stream contactor under consideration. The model contains several parameters related to equipment structure and operating conditions, i.e. the mean residence times in the four sub-spaces, 7ac, 7im, 7fai and cs. Among the four parameters, the mean residence time in the impingement zone, t m, and that in the collision-slipping region, fcs, are symmetrical parameters, which have the same influence on the overall residence time distribution. It can be seen from Eq. (3.27) or... 

Back-mixing in the impingement zone, the major active region for heat and mass transfer, is critical. This may be favorable for some processes while it is harmful for others since back-mixing usually results in a decreased mean driving force for the processes involved ... 

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