Liquid tangential flow

The forces applied by an impeller to the material contained in a vessel produce characteristic flow patterns that depend on the Impeller geometry, properties of the fluid, and the relative sizes and proportions of the tank, baffles and impeller. There are three principal types of flow patterns tangential, radial and axial. Tangential flow is observed when the liquid flows parallel to the path described by the mixer as illustrated in Figure 7. 

Filtration separates components according to their size. Efficiency depends on the shape and compressibility of the particles, the viscosity of the liquid phase and the driving force, which is the pressure created by overpressure or by vacuum. Filtration can be performed either as dead-end filtration, where the feed stream flows perpendicular to the filter surface (Lee, 1989) or as tangential flow filtration, where the feed stream flows parallel to the filter and the filtrate diffuses across it. Examples of the former are the continuous rotaiy vacuum dram filter, where a rotaiy vacuum filter has a filter medium covering the surface of a rotating drum and the filtrate is drawn through the dram by an... 

Whenever the analyte of interest is soluble in the liquid phase or part of the gas phase, sample removal via a filtering device is the most reasonable solution. Filters mounted in situ are ideal provided they do not foul within an unreasonably short period. If this is the case, a filter operating in bypass must be used because this can be repeatedly exchanged with a freshly prepared one. In our experience, bypass filters should be operated with a high tangential flow, say > 2 m s 1 of superficial liquid velocity. Then, a useful lifetime of a few weeks can be achieved even in cultures of filamentous organisms. 

Cross-flow filtration is also referred to as tangential flow filtration or microfiltration, but all three terms refer to a process by which membranes are used to separate components in a liquid solution (or suspension) on the basis of their size. The development of robust membranes in polymeric and ceramic materials has provided a powerful new technology for bioseparations, which is already widespread in the process industries as well as for water treatment processes. 

Tangential flow, in which the liquid follows a circular path around the shaft. 

Figure 3.35. Creation of cin interfacial tension gradient by an externally applied tangential flow of the adjacent liquid in the x-direction, (a) Schematic picture of the phenomenon (b) creation of a gradient in the interfacial tension (c) the resulting v z) profile somewhere in this gradient.

Of the stirrer types which set the liquid in a radial motion - or into a tangential flow in the case of high viscosities - only the turbine stirrer ) (so-called Rushton turbine , a disk 2d/3 in diameter supporting 6 blades each d/5 high and d/4 wide [474]) belongs to the high speed stirrers. It can be sensibly utilized only with low viscosity liquids and in baffled tanks. Its diameter ratio D/d is 3-5. The turbine stirrer causes high levels of shear and hence is well suited for dispersion processes. 

The flow model propounded by Bittins and Zehner [33] for a baffled tank equipped with radial-flow stirrers is based on the fluid-dynamic interaction between the stirrer and the stationary vessel wall as well as the fittings such as baffles, coils etc. In the case of the blade stirrer, the radial liquid discharge towards the vessel walls is produced by the centrifugal forces, which has increased to qb by the time it reaches the baffles as a result of the inclusion of surroimding liquid. There the tangential flow velocity, which has left the stirrer with a value of Ms2, is decelerated from M51 to Ms2. The flow is turned back and flows above and underneath the stirrer plane back to the stirrer, where it arrives with a value of Wjj. 

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