Inner vortex

As illustrated in Fig. 5, the outer downwardly spiralling gas velocity decays as gas peels off into the inner upwardly spiralling exiting vortex. The length of this inner vortex, the natural vortex length, L, (Alexander, 1949) then represents the distance below the edge of the gas outlet tube below which no feed gas remains to peel off into the inner vortex. If the... 

The inner vortex (often called the core of the vortex) rotates at a much higher velocity than the outer vortex. In the absence of solids, the radius of this inner vortex has been measured to be 0.4 to 0.8 r. With axial inlet cyclones, the inner core vortex is aligned with the axis of the gas outlet tube. With tangential or volute cyclone inlets, however, the vortex is not exactly aligned with the axis. The non-symmetric entry of the tangential or volute inlet causes the axis of the vortex to be slightly eccentric from the axis of the cyclone. This means that the bottom of the vortex is displaced some distance from the axis and can "pluck off and reentrain dust from the solids... 

Air classification is perhaps the simplest fly ash processing option and is normally employed to improve the fineness of the ash (i.e., remove coarse particles). A typical cyclone classifier uses centrifugal force to separate fine particles from an air stream. The particles enter tangentially into a cylindrical chamber dispersed in an air stream and centrifugal force forces the coarser particles to the wall of the cylinder while the air stream and finer particles spiral to an inner vortex. The air exits from the inner core via an outlet port while the particles slide down the chamber walls and exit the bottom. 

When air classification is employed for ash beneficiation purposes, the mechanism is similar, but a high-performance cyclone is used. An example is shown in Fig. 8. Devices vary considerably in the feed arrangement used, but most employ some mechanism to effectively distribute the ash particles across the profile of the cyclone, such as a rotating cage or distribution plate. The velocity of the feed is controlled to produce the desired size separation whereby fine particles and most of the air migrate to the inner vortex while coarse ash exits the bottom. Air classifiers have been used for many years to control pozzolan fineness simply by removing coarse ash particles, particularly when LOI is not a problem. Air classification is usually not effective for reducing LOI, particularly if the carbon is fine. Some coarse carbon particles may be rejected with the coarse ash, but since the density of the carbon particles is lower than... 

For the phase determination the same ECMWF analyses were used. Maps of EPV with temperature isolines were drawn. The classification of the vortex phase was based on the occurrence and shape of the EPV region characterising the inner vortex as well as the occurrence of the lowest temperatures. 

Figure l Variability of different Arctic vertical profiles of N2O during winter 1996/1997 (open symbols). Kiruna, in comparison with the flight Bll-34, 6. Feb. 1999 (solid symbols), Kiruna. As a reference, a mean mid latitude profile (dots) is presented, which was obtained from flights since 1987. A mean Arctic profile (bold) with its minimum and maximum values is also shown. The data of the mean Arctic profile were obtainedfrom Arctic inner vortex flights since 1987. 

Figure 4 Mid latitude vertical profiles of NiO (solidsquares, flight BII-32, 23.6.1997, Gap, open circles, flight Bl-7. 31.3.1985, Aire, open diamonds, flight A-10, 7.3.1993, Gap) and as reference a mean mid latitude (bold) and a mean Arctic profile (dots), obtained from mid latitude and inner vortex flights in early winter since 1987.

This means that the separating ability of the inner vortex is 8 times that of the outer one. 

If Po is the radial distance of the inner vortex, and Ri that of the outer one, then according to Lissman we may put Po = V2P1 (approx.) so that... 

Using STM, inner vortex structures of the differential conductance were successfully visualized for Bi2212 and Y123 crystals. The inner vortex excitation spectra are found to be quite different from those expected from a simple d-wave mechanism. 

As illustrated in Figure 10.7, a cyclone consists of a vertical cylinder with a conical bottom, a tangential inlet near the top, and outlets at the top and the bottom, respectively. The top outlet pipe protrudes into the conical part of the cyclone in order to produce a vortex when a dust-laden gas (normally air) is pumped tangentially into the cyclone body. Such a vortex develops centrifugal force and, because the particles are much denser than the gas, they are projected outward to the wall flowing downward in a thin layer along this in a helical path. They are eventually collected at the bottom of the cyclone and separated. The inlet gas stream flows downward in an annular vortex, reverses itself as it finds a reduction in the rotation space due to the conical shape, creates an upward inner vortex in the center of the cyclone, and then exits through the top of the cyclone. In an ideal operation in the upward flow... 

Figure 17. Stagnation graph of CO2. The stagnation graph shown is compatible with the induced current density shown in Figure 14. The primary vortex (0), as well as vortices (2) and (20, are diamagnetic the inner vortex (1) corresponds to the paramagnetic circulation near the center of symmetry. Vortices (3) and (30 are the other paramagnetic circulations near the oxygen atoms.

Muschelknautz et al. (1996) also proposed a mechanistic model of cyclone operation. In this model, the gas can carry only a maximum amount of solids (called the critical loading). At any solids loading in excess of this critical loading, the solids are immediately separated from the gas at the inlet to the cyclone, as indicated in Fig. 5. The solids remaining in the gas are then separated in the cyclone barrel and in the inner vortex below the gas outlet tube as if the cyclone were operating at a lower solids loading. 

Since the outer and the inner layers move in opposite vertical directions (i.e., the flow in the outer vortex moving down and the inner vortex moving up), there is a well-defined locus of zero vertical velocity between the two vortices. This locus forms an invisible boundary, which plays an important role in particle separa-... 

The cyclone is a mechanically simple, reliable device for the separation of PM from an air stream by the action of centrifugal forces. The centrifugal forces, resulting from the tangential velocity given to the dust-laden gas at the top of the cyclone, eject the particles in a circular, vortex motion toward the cyclone wall. These particles, because of their inertia forces, attempt to move toward the outside wall, from which they are led to a receiver or hopper. The clarified gas exits as an axial inner vortex through the top by way of the gas exit duct. 

Vortex coolers operate by injecting compressed air tangentially into a specially designed tube. The air forms a vortex, rotating at speeds approaching 1,000,000 rpm. The portion of the vortex closest to the outer wall of the tube moves axially upward, where the inner part of the vortex moves in the opposite direction (Fig. 35). In this design, energy (heat) is transferred from the inner vortex to the outer. Valves are positioned at the ends of the tube to bleed off hot air from the outer vortex (which is vented outside the enclosure) and cool air from the inner vortex (which is directed into the enclosure). 

Fig. 4.4.4. Profile plots from CFD simulations of the radial velocity distribution in a cylindrical swirl tube and a cylinder-on-cone cyclone. The main difference between the two is that the radial flow from the outer to the inner vortex is more uniformly distributed axially in the cyclone than in the swirl tube...

Fig. 6.1.1). This boundary layer flow can vary from about 4% to 16% of Q but a good, average value for calculation purposes is 10%. As a consequence, approximately 90% of the incoming flow Q directly participates in the flow along the walls and in the formation of the inner vortex. This is the reason for the factor 0.9 in Eq. (6.1.5) and in Eqs. (6.2.3) and (6.4.2) below. As we will see below, the inner vortex flow has a major influence on the cut-point diameter, X50.

In order to compute certain key cyclone characteristics, such as the internal spin velocity, vocs, or the particle cut size in the inner vortex core, X50, it is necessary to first compute the gas-phase and total gas-plus-solids wall friction factors, fair and /, respectively. Gas-phase wall friction factors for both cylindrical and conical cyclones as a function of body Reynolds number and relative wall roughness are presented in Fig. 6.1.3. Muschelknautz and Trefz define the cyclone body Reynolds number (compare with Eq. 4.2.8) as ... 

A very fundamental characteristic of any lightly-loaded cyclone is its cut-point diameter or cut size, X50, produced by the spin of the inner vortex. This is the particle diameter that has a 50% probability of capture. As discussed elsewhere in this book, the cut size is analogous to the screen openings of an ordinary sieve or screen although, with a cyclone, the separation is not as sharp as that of a sieve. 

Knowing Ar we are now in a position to compute vqcs from Eq. (6.2.1), which is needed in the computation of the cut-point diameter of the inner vortex ... 

Next we determine whether the mass loading effect (saltation) will occur. According to the MM, the amount of solids that the gas phase can hold in turbulent suspension upon its entrance into a cyclone depends on the mass average (the median) particle size of the feed, the cut-point of the inner vortex, X50, and, to a lesser extent, on the inlet loading itself, Cq. This limiting or limit-loading is ... 

Here, we will determine the overall separation efficiency for saltation conditions, i.e. when Cg > Col- This efficiency includes the efficiency due to saltation in the inlet and the efficiency due to classification in the inner vortex. A portion of the incoming solids that is not collected by the former is collected by the latter, so that the total efficiency becomes (see also Chap. 9) ... 

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