Cyclone Vortex flow pattern

Figure 1.115 Top photographs of vortex-flow pattern formation at various flow rates when contacting water and dyed water (acid blue) solutions in the tangential-flow cyclone micro mixer. Bottom comparison of the experimentally derived image of one vortex pattern with the predicted image by CFD simulation [131] (source IMM).

Flow Pattern In a cyclone the gas path involves a double vortex with the gas spiraling downward at the outside and upward at the inside. When the gas enters the cyclone, its velocity undergoes a redistribution so that me tangential component of velocity increases with decreasing radius as expressed by The spiral velocity in a... 

The complex three-dimensional flow pattern within the cyclone is dominated by the radial (Fr) and tangential (V0) velocity components. The vertical component is also significant but plays only an indirect role in the separation. The tangential velocity in the vortex varies with the distance from the axis in a complex manner, which can be described by the equation... 

Flow Pattern In a cyclone the gas path involves a double vortex with the gas spiraling downward at the outside and upward at the inside. When the gas enters the cyclone, its velocity undergoes a redistribution so that the tangential component of velocity increases with decreasing radius as expressed by V - rt". The spiral velocity in a cyclone may reach a value several times the average inlet-gas velocity. Theoretical considerations indicate that n should be equal to 1.0 in the absence of wall friction. Actual measurements [Shepherd and Lmple, Ind. Eng. Chem., 31, 972 (1939) 32, 1246 (1940)], however, indicate that n may range from 0.5 to 0.7 over a large portion of the cyclone... 

In addition to the main flow pattern there exists a secondary flow pattern, short circuit flow, at the top of the hydrocyclone. The short circuit flow is a flow pattern that moves across the cover of the cylindrical section to the base of the vortex finder. It flows along the outer wall of the vortex finder until it combines with the fluid in the overflow created by the main flow pattern. This short circuit flow pattern is due to the wall effect of the cyclone top cover and the outer wall of the vortex finder. The quantity of the short circuit flow can be as much as 15% of the total feed flow. 

The flow pattern of the vortex motion of the gas in reverse-flow cyclone is quite complex. First, it is three-dimensional second, the flow is turbulent An exact analysis is therefore difficult Soo (1989) has summarized a fundamental analysis of velocity profiles and pressure drops in such a cyclone. He has also analyzed the governing particle diffusion equation in the presence of electrostatic, gravitational and centrifugal forces. He has then provided an analytical expression for partide collection efficiency under a number of limiting conditions. We wiU, however, opt here for a much simpler model of particle separation in a cyclone developed by Clift et id. (1991). This approach is based on a modification of the original model by Leith and Licht (1972). The model will be... 

We note that this is an idealized flow pattern, if the radial velocity in a cyclone were zero, the cyclone would not function since, then none of the entering fluid could make its way to the inner core, and, hence, out the vortex finder. 

In some geometries the tangential gas velocity at the wall, and in the entire space between the wall and the vortex finder, can be significantly higher than the inlet velocity due to constriction of the inlet jet. In Fig. 4.2.2, the inlet flow pattern in a cyclone with a slot type of rectangular inlet is compared with one with a 360 wrap-around or full scroll inlet. 

As a further argument supporting what went before, we also remind the reader that, as shown in Fig. 7.3.3, the X50, and therefore the Stk o predicted by the models of Barth and of Mothes and Loffler, both described in Chap. 5, agree quite well with that determined by Derksen. This means that in the idealized flow patterns envisaged by Barth and by Mothes and Loffler, which did not take into account turbulence at all, particles smaller than the cut size determined by the simulations of Derksen will be carried into the inner vortex and lost from the cyclone. This ends our discussion of this issue. 

The decision to use or not use such sophisticated pressure-recovery types of vortex tube assemblies hinges on the projected savings in operating cost it provides versus the added expense of construction and the impact that such a device may have on access for routine inspection and maintenance. It is not shown beyond doubt whether or not the installation of vanes for pressure recovery always impacts negatively on the flow pattern in the cyclone body, and therefore the separation efficiency. 

Most cyclones are designed with flat roofs. Under high pressure or high vacuum conditions, however, it is sometimes necessary to fabricate a cyclone with a domed roof. Typically, such a roof is either elliptical or hemispherical— depending on such factors as the differential pressure across the roof, wall thickness, the size of the cyclone, and the relative vortex finder-to-barrel diameter. In such instances, it is recommended that a fiat false or inner roof be installed (and properly vented if necessary) so that the flow pattern is the same as that of a conventional flat-headed cyclone. 

Cyclone mixers give a rotational flow field [109], The corresponding formation of vortex patterns is another way of laminating and focusing streams. It is hoped that by folding of the vortices, thinning of the lamellae can be achieved, with an increase of residence time in the mixer [131]. A full rotation should halve the lamellae width. Hence the optimization parameter may be to have as many rotations as possible. 

The pattern of fluid flow within the hydrocyclone body is best described as a spiral within a spiral with circular symmetry. A schematic view of the spiral flow inside a hydrocyclone is shown in Fig. 23b. The entering fluid flows down the outer regions of the hydrocyclone body. This combined with the rotational motion creates the outer spiral. At the same time, because of the wall effect, some of the downward moving fluid begins to feed across toward the center. The amount of inward motion of fluid increases as the fluid approaches the cone apex, and fluid that flows in this inward stream ultimately reverses its direction and flows upward to the cyclone overflow outlet via the vortex finder. This reversal applies only to the vertical component of velocity, and the spirals still rotate in the same circular direction. In the meantime, the downward flow near the wall carries solid particles to the apex opening (bottom outlet). 

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