Vortex motion

The rotational operation of a CFB leads to a vortex motion in the freeboard which tends to inhibit particle loss by elutriation. Because of the relatively compact nature of the CFB and the operating flexibility provided by the rotational motion, the CFB has been proposed for a variety of applications including coal combustion, flue gas desulfurization, gas combustion, coal liquefaction and food drying. 

Wirbel, m. whirl, vortex, eddy whirlwind whorl spiral vertebra Tech.) spigot, button, collar, swivel, sheave, etc. vertigo intoxication crown (of the head) warbling. Wirbel-. whirl-, vortical vertebral, vertebrate, -bein, n. vertebra, -bewegung, /. vortex motion, eddying. 

Wirbel-sdule, /. vertebral column, -strom, m. whirlpool Elec.) eddy current, -stromimg, /. vortex motion, turbulent flow, -stuim, m. tornado cyclone, -tier, n. vertebrate. Wirbelung, /. whirling, etc. (see wirbeln) vortex motion. 

Rotational or vortex motion in a fluid 50 Rough pipes 67, 707... 

It is also interesting to note that the angular momentum conservation is assumed in predictions 4 and 9 however, the viscosity increases owing to temperature rise in the burnt gas, and the vortex motion diminishes rapidly behind the flame. The pressure behind the flame is raised up and becomes nearly equal to the ambient pressure. This may explain why the hot, stagnant gas model by Asato et al., line 5a, can considerably predict the results. 

This is most easily achieved by rotating the inner cylinder and keeping the outer fixed in the laboratory frame. Note, however, that this geometry leads to the formation of Taylor vortex motion if inertial effects become important (Reynolds number Re 1). Most rheo-NMR experiments are actually performed at low Re. In the cylindrical Couette, the natural coordinates are cylindrical polar (q, <(>, z) so the shear stress is denoted and is radially dependent as q 2. The strain rate across the gap is given by [2]... 

This will be found almost exclusively in the rough vacuum range. The character of this type of flow is determined by the interaction of the molecules. Consequently Internal friction, the viscosity of the flowing substance. Is a major factor. If vortex motion appears In the streaming process, one speaks of turbulent flow. If various layers of the flowing medium slide one over the other, then the term laminar flow or layer flux may be applied. 

Internal circulation measurements are very difficult to obtain for gas bubbles (D8). Some results have been obtained for large liquid skirted drops using tracer particles (W2), and provide a qualitative picture of the internal motion as shown in Fig. 8.5. It is not clear whether there is a reverse vortex motion in the interior of a large fluid particle (as indicated by the dotted lines). Such a secondary vortex would appear to be necessary to satisfy velocity and stress continuity, but experimental evidence is inconclusive. 

A certain minimum flow rate is necessary to set up the vortex motion and to establish centrifugal separation forces that grow in intensity as the flow rate increases and improve the separation efficiency. A point will be reached for a given set of conditions, however, beyond which further increases in flow rate will cause performance deterioration. This is caused principally by the following. 

On the lower end of the flow range, efficiency falls off when the flow rate is reduced below 318 m3/d water [2,000 BWPD]. As discussed, this results because insufficient flow is available to set up the vortex motion and to produce the strong centrifugal separation forces required for optimum performance. These two points define the lower and upper flow-rate limits for acceptable performance. 

Row-rate trials have been carried out from 111 to 684 m3/d water (700 to 4,300 BWPD] for a single 60-mm [2 4-in ] unit with about a 1200-kPa [174-psi] driving force. Efficiency starts to fall off at flow rates less than 159 m3/d water [1,000 BWPD] on the low end of the flow rate curve, again because there is insufficient flow lo support the vortex motion. It is also worth noting that the minimum flow rale threshold for the 60-mm [2.4-in.] cyclone is... 

The stable flux pattern in Figure 55(a) forms due to the penetration of a magnetic flux front of pinned vortices from the sample surface. The joule heating arising from vortex motion can release global flux jumps and thermal quench instabilities under certain conditions which have to be avoided for stable operation of current-carrying superconductors (Mints and Rakhmanov, 1981). Dendritic flux patterns which have been observed in Nb disks (Goodman and Wertheimer,... 

Preventing vortex motion by pinning is also critical to the development of the HTS magnets discussed below. 

The irreversibility field (Hm), which has to be measured experimentally, is an important parameter since it determines the size of the final M developed. As expected Hm depends upon temperature, and irreversibility field v. temperature curves are shown in Fig. 4.57. It is apparent that at liquid nitrogen temperature YBCO is suited to permanent magnet applications whereas Bi-2223 is not. Because of the energy dissipation accompanying vortex motion and referred to earlier, vortex pinning also raises /c. 

H. Aref. Integrable, chaotic and turbulent vortex motion in two-dimensional flows. Ann. Rev. Fluid Mech., 15 345-389, 1983. 

Labconco RapidVap Ni various blocks available, up to, e. g., 8 450 mb vessels or 48 12 mm tubes (model RapidVap N2/48) uses vortex motion in combination with heat and nitrogen blowdown... 

It follows that strong localized vortex motion may be generated by even slightly nonuniform fields, and the convective component of the convective diffusion equation (Eq. 20) becomes predominant, hi fact, a convincing argument may be put forward in favor of replacing Eq. 20 by the general vector equation... 

Although the formation of surface patterns via the Benard cell may occasionally be useful to form special finishes, usually it is desirable to eliminate the situation. Use of higher boiling solvents will retard evaporation rate and the cooling effect that changes surface tension and propels the vortex action. Increase in paint viscosity will inhibit the action, as will decrease in film thickness. Addition of a surfactant will provide a more uniform value of surface tension and also retard evaporation and thereby help to inhibit the vortex motion in cells. 

Friction loss from sodden expansion of cross section. If the cross section of the conduit is suddenly enlarged, the fluid stream separates from the wall and issues as a jet into the enlarged section. The jet then expands to fill the entire cross section of the larger conduit. The space between the expanding jet and the conduit wall is filled with fluid in vortex motion characteristic of boundary-layer separation, and considerable friction is generated within this space. This effect is shown in Fig. 5.13. 

It is commonly observed that increases in average heat transfer occur at a sound pressure level of about 134 to 140 dB (well above the normal human tolerance of 120 dB), and that these increases are associated with the formation of an acoustically induced flow (acoustic or thermoacoustic streaming) near the heated surface. Large circumferential variations in heat transfer coefficient are present [298], and it has been observed that local improvements in heat transfer occur at intensities well below those that affect the average heat transfer [299]. Correlations have been proposed for individual experiments however, an accurate correlation covering the limits of free convection and fully developed vortex motion has not been developed. 

---