Spiral Vortex Flow

FIGURE 7.12 Unidirectional flow system with air supply through diffusers located above the occupied zone.  

CHAPTER 7 PRINCIPLES OE AIR AND CONTAMINANT MOVEMENT INSIDE AND AROUND BUILDINGS 

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Normally the vortex finder should extend down into the conical portion of the cyclone. It is thought that the vortex finder plays an important role in the maintenance of a stable spiraling fluid flow in the cyclone, and this makes it more difficult for the particles to leak through the boundary layer on the roof of the lid of the cyclone to the overflow tube.- Without a vortex finder, the efficiency may be reduced by 4-5%. However, an excessive long vortex finder may hinder the high spin velocity in the fluid flow and thus reduce the efficiency of the cyclone. 

TFF module types include plate-and-frame (or cassettes), hollow fibers, tubes, monoliths, spirals, and vortex flow. Figures 20-52 and 20-53 show several common module types and the flow paths within each. Hollow fiber or tubular modules are made by potting the cast membrane fibers or tubes into end caps and enclosing the assembly in a shell. Similar to fibers or tubes, monoliths have their retentive layer coated on the inside of tubular flow channels or lumens with a high-permeability porous structure on the shell side. 

M 49] [P 46] The formation of vortex flow patterns was confirmed both by simulation and experimentally [109] (see also [132]). While the simulation suggests spirally wound fluid flow, the first experiment yields only a direct straight flow into the center outlet However, this difference might be merely due to the fact that very initial results are presented in [109],... 

Spiral vortex. So far the discussion has been confined to the rotation of all particles in concentric circles. Suppose there is now superimposed a flow with a velocity having radial components, either outward or inward. If the height of the walls of the open vessel were less than that of a liquid surface spread out by some means of centrifugal force, and if liquid were supplied to the center at the proper rate by some means, then it is obvious that liquid would flow outward, over the vessel walls. If, on the other hand, liquid flowed into the tank over the rim from some source at a higher elevation and were drawn out at the center, the flow would be inward. The combination of this approximately radial flow with the circular flow will result in path lines that are some form of spirals. 

Spiral vortex. If a radial flow is superimposed upon the concentric flow previously described, the path lines will then be spirals. If the flow goes out through a circular hole in the bottom of a shallow vessel, the surface of liquid takes the form of an empty hole, with an air core sucked down the hole. If an outlet symmetrical with the axis is provided, as in a pump impeller, we might have a flow either radially inward or radially outward. If the two plates are a constant distance B apart, the radial flow with a velocity Vr is then across a series of concentric cylindrical surfaces whose area is 0.2nrB. Thus Q = 2nrBVr is a constant, from which it is seen that rVr is a constant. Thus the radial velocity varies in the same way with r that the circumferential velocity did in the preceding discussion. Hence the pressure variation with the radial velocity is just the same as for pure rotation. Therefore the pressure gradient of flow applies exactly to the case of spiral flow, as well as to pure rotation. 

Many polymers exhibit neither a measurable stick-slip transition nor flow oscillation. For example, commercial polystyrene (PS), polypropylene (PP), and low density polyethylene (LDPE) usually do not undergo a flow discontinuity transition nor oscillating flow. This does not mean that their extrudate would remain smooth. The often observed spiral-like extrudate distortion of PS, LDPE and PP, among other polymer melts, normally arises from a secondary (vortex) flow in the barrel due to a sharp die entry and is unrelated to interfacial slip. Section 11 discusses this type of extrudate distortion in some detail. Here we focus on the question of why polymers such as PS often do not exhibit interfacial flow instabilities and flow discontinuity. The answer is contained in the celebrated formula Eqs. (3) or (5). For a polymer to show an observable wall slip on a length scale of 1 mm requires a viscosity ratio q/q equal to 105 or larger. In other words, there should be a sufficient level of bulk chain entanglement at the critical stress for an interfacial breakdown (i.e., disentanglement transition between adsorbed and unbound chains). The above-mentioned commercial polymers do not meet this criterion. 

Chung et al. ADI scheme Spiral tube Dean vortex flow promotes rapid mixing and inhibits the growth of the solute concentration boundary layer... 

Non-decaying patterns in a similar stirred oscillatory system were also found numerically by Perez-Munuzuri (2006) in the weakly chaotic flow regime of the blinking vortex flow, i.e. for small /x. When the distance between the vortices is large, the flow has little effect on the spatial structure and a pattern of spiral waves forms as in the... 

Figure 10-2. Reverse vortex flow system for gliding arc discharge stabilization (a) eonflgu-ration with a movable ring electrode (b) configuration with a spiral electrode. In the figures, (1) quartz tube (2) cylindrical reactor volume (3) swirl generator with tangential inlet holes (4) additional axial gas flow inlet (5) gas flow exit ...

With other short-time dryers, the product motion is in the form of a vortex flow driven by the hot gas which increases the residence time. This can be achieved with hot gas jets tangentially entering the drying area (vortex flow dryers such as helical flow tube with nozzles and annular flow dryer [5.77]), with displacement internals including gas guide vanes (spiral tube pneumatic dryer [5.78, 5.79]), or with tapered inclined perforated screen (cyclone dryer [5.80]). The convex dryer [5.81, 5.82] combines the functions of drying and classifying. With a... 

The impeller imparts a vortex flow pattern to the feed material, and the centrifugal acceleration forces the particles to the screen surface and up the cone (360°) in a spiraling path (13) (Figs. 3A and B). 

In a tangential-inlet reverse-flow cyclone, the cyclone inlet translates the linear inlet gas flow into a rotating vortex flow. As shown in Fig. 1, the gas solids mixture enters an annulus region between the outer wall of the cyclone and the outer wall of the gas outlet tube. As the gas solids mixture spirals downwards, it sets up a vortex with an axial direction downward toward the solids outlet. 

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... 

For a forced vortex with spiral flow, energy is put into the fluid in the case of a pump and extracted from it in the case of a turbine. In the limiting case of zero flow, when all path lines become concentric circles, energy input from some external source is still necessary for any real fluid in order to maintain the rotation. Thus a forced vortex is characterized by a transfer of mechanical energy from an external source and a consequent variation of H as a function of the radius from the axis of rotation. 

The existence of spiral flow is observed near the short radius of the bend. The water surface is superelevated at the outside wall for the cylindrical free vortex. The element EF is subjected to a centrifugal force mV2/r, which is balanced by an increased hydrostatic force on the left side due to the superelevation of the water surface at C above that at D. The element GH has exactly the same hydrostatic force inward, but the centrifugal force outward is much less because the velocity is decreased by friction near the bottom. This results in a cross flow inward along the bottom of the channel, which is balanced by an outward flow near the water surface, hence the spiral. This spiral flow is largely responsible for the commonly observed erosion of the outside bank of a river bend, with consequent deposition and building of a sand bar near the inside bank. 

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