Turbulent flow presence

Presence of dead-ends , loops, crevices, obstructions or other conditions which may produce turbulent flow causing erosion or stagnant flow which will allow debris or corrosive media to accumulate and set up corrosion cells. 

In turbulent motion, the presence of circulating or eddy currents brings about a much-increased exchange of momentum in all three directions of the stream flow, and these eddies are responsible for the random fluctuations in velocity The high rate of transfer in turbulent flow is accompanied by a much higher shear stress for a given velocity gradient. 

Herman J.L., 2002. Generic method for online extraction of drug substances in the presence of biological matrices using turbulent flow chromatography. Rapid Commun Mass Spectrom 16 421. 

For a passive scalar, the turbulent flow will be unaffected by the presence of the scalar. This implies that for wavenumbers above the scalar dissipation range, the characteristic time scale for scalar spectral transport should be equal to that for velocity spectral transport tst defined by (2.67), p. 42. Thus, by equating the scalar and velocity spectral transport time scales, we have23 t)... 

The presence of small amounts of certain polymers can produce spectacular reduction in the frictional losses of fluids in turbulent flow through conduits. Drag reduction has an immense field of applications, both currently and potentially. The list of exploitable situations as described in Sect. 2 could be extended, but a big snag exists drag reduction decreases with flow time. This is believed to be due to mechanical degradation of added polymer (Brostow 1983). In Fig. 32 and Fig. 33 the influence of Mw on drag reduction is displayed. 

However, the flow regime of a film cannot be defined uniquely as laminar or turbulent, as in the case of pipe flow, due to the presence of the free surface. Depending on the values of AFr and JVw , the free surface may be smooth, or covered with gravity waves or capillary or mixed capillary-gravity waves of various types. Thus, under suitable conditions, it is possible to have smooth laminar flow, wavy laminar or turbulent flow, where the wavy flows may be subdivided into gravity or capillary... 

Although the bulk of the flow may be turbulent, the presence of an interface or solid boundary causes boundary layers to form. The... 

Comparing these equations with the x- and y- Navier-Stokes equations for two-dimensional laminar flow shows that in turbulent flow extra terms arise due to the presence of the fluctuating velocity components. These extra terms, which arise because the Navier-Stokes equations contain nonlinear terms, are the result of the momentum transfer caused by the velocity fluctuating components and are often termed the turbulent or Reynolds stress terms because of their similarity to the viscous stress terms which arise due to momentum transfer on a molecular scale. This similarity can be clearly seen by noting that the x-wise momentum equation, for example, for laminar flow can be written as ... 

This chapter has been concerned with flows in wb ch the buoyancy forces that arise due to the temperature difference have an influence on the flow and heat transfer values despite the presence of a forced velocity. In extemai flows it was shown that the deviation of the heat transfer rate from that which would exist in purely forced convection was dependent on the ratio of the Grashof number to the square of the Reynolds number. It was also shown that in such flows the Nusselt number can often be expressed in terms of the Nusselt numbers that would exist under the same conditions in purely forced and purely free convective flows. It was also shown that in turbulent flows, the buoyancy forces can affect the turbulence structure as well as the momentum balance and that in turbulent flows the heat transfer rate can be decreased by the buoyancy forces in assisting flows whereas in laminar flows the buoyancy forces essentially always increase the heat transfer rate in assisting flow. Some consideration was also given to the effect of buoyancy forces on internal flows. 

These analogies are also applicable approximately for turbulent flow over a surface, even in the presence of pressure gradients. 

Experimental evidence has demonstrated that Dean vortices can be effective for enhancement of membrane performance under laminar conditions [18]. As flow conditions approach the transition and turbulent flow regimes, straight membranes have a better mass transfer and higher wall shear rate than in flows with curved membrane channels. The effects of Dean vortices on the performance of membrane filtration have been studied experimentally and theoretically by Belfort and coworkers [19-22]. Mallubhotla and Belfort [21] assessed the filtration of suspensions of polydispersed polystyrene particles (mean diameter 25 pm) and silica particles (mean diameter 20 pm) with and without the presence of Dean flow using an 180° U-bend channel... 

Laminar flow conditions are typically used for tablets, hard gelatin capsules, powders, and granules. Suppositories and soft gelatin capsules are placed in the cell without beads for turbulent flow. Nicolaides, Hempenstall, and Reppas have reported differences in the dissolution rate of a poorly soluble drug, tiaglitazone, from an immediate-release (IR) tablet formulation based on the presence or absence of a tablet holder and/or beads in the flow-through cell. 

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