Flow pattern turbulent vortex

The flow pattern in Fig. 10.55 has a violent turbulent region, characterized by a vortex street and two free vortices rotating in opposite directions... 

The vibration induced by the fluid flowing over the tube bundle is caused principally by vortex shedding and turbulent buffeting. As fluid flows over a tube vortices are shed from the down-stream side which cause disturbances in the flow pattern and pressure distribution round the tube. Turbulent buffeting of tubes occurs at high flow-rates due to the intense turbulence at high Reynolds numbers. 

An impeller in a tank functions as a pump that delivers a certain volumetric rate at each rotational speed and corresponding power input. The power input is influenced also by the geometry of the equipment and the properties of the fluid. The flow pattern and the degree of turbulence are key aspects of the quality of mixing. Basic impeller actions are either axial or radial, but, as Figure 10.4 shows, radial action results in some axial movement by reason of deflection from the vessel walls and baffles. Baffles contribute to turbulence by preventing swirl of the contents as a whole and elimination of vortexes offset location of the impeller has similar effects but on a reduced scale. 

Figure 15 Photograph of flow pattern at different Reynolds number, (a) Taylor vortex flow (Re = 177), (b) wavy vortex flow (Re = 505), (c) weakly turbulent vortex flow (Re = 3027), and (d) turbulent vortex flow (Re = 8072) (Dutta and Ray, 2004).

To allow the phases to settle and remain calm, any form of turbulence or vortexing inside the decanter should be avoided. Introduction of the feed stream into the decanter should be located close to the interface to facilitate phase separation. Turbulence can arise from the inlet liquid entering the vessel at too high a velocity, forming a jet that disturbs the liquid layers. To counter these flow patterns, the feed into the gravity settler should enter the vessel at a velocity of less than... 

In Fig. 7 some photographs of flow patterns are illustrated the first shows the flow patterns in the device without the valve and the second the flow patterns of a bioprosthesis while the last two show the flow patterns of a HK and a Sorin tilting disc valves. Without the valve, the flow patterns are rectilinear and parallel to each other and there is no turbulence. With the bioprosthesis the zone of rectilinear flow is smaller, but central the turbulent flow appears only close to the aortic wall. The two mechanical valves show a dissymmetrical flow with a great zone of turbulence over the disc hence their hemodynamics is worse than that of the bioprosthesis. It is interesting to note the presence of vortexes inside the sinuses of Valsalva in all the photographs. Such vortexes are important for the closing mechanics of the natural leaflets ... 

A flow, or a part of it, is said to be laminar if it is not perturbed by turbulent motions. The particularity of a laminar flow is to appear regular and ordered whereas a turbulent flow is intermittent and disordered. Laminar flows usually exhibit vortex-ffee patterns that can be made visible by optical interference methods or, more easily, by placing particles of visible size in the liquid. 

The presence of baffles can improve the flow pattern in certain conditions elimination of vortex, enhancement of turbulence, and so forth. The impeller position in the tank can modify the flow pattern The off-center position can avoid vortex generation. Agitator shafts can be mounted through the wall in very large tanks (>20 tons) to avoid a vortex when there is no baffle. 

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... 

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