Flooding point characteristic

The concepts of shp velocity and characteristic velocity are useful in defining the Flooding point and operational regions of different types of column contactors. The shp (or relative) velocity is given by the equation ... 

Flooding-point data may be correlated by equations 13.34 and 13.35 using the droplet characteristic velocity concept as discussed by Thornton and Pratt(34), since coalescence is absent. 

To use the flooding point diagram, first it is necessary to decide whether the drops produced in the extractor are circulating or oscillating. The mean diameter di,2 (see Eq. 9.1) is used for the characteristic drop size. If the flow rate ratio is known from the thermodynamic design, the superficial velocities of both phases can be determined at the flooding point. The minimum column cross-sectional area and diameter necessarily follows directly from the superficial velocity at the flooding point with Eq. 9.19. 

It is a characteristic of process equipment, that the best operation is reached, at neither a very high nor a very low loading. The intermediate equipment load that results in the most efficient operation is called the the best efficiency point. For distillation trays, the incipient flood point corresponds to the best efficiency point. We have correlated this best efficiency point, for valve and sieve trays, as compared to the measured pressure drops in many chemical plant and refinery distillation towers. We have derived the following formula ... 

Usually, practical design correlations for and or the characteristic velocity v are directly derived from experimental data. For example, in an Rotating Disc Contactor (RDC), in the operating range of interest, the velocity limit of the dispersed phase at the flooding point is according to Strobel and Salzer [6.30]... 

Figure 4-12 also includes the phase flow ratios for the respective liquid hold-ups at the flooding point hL,Fl- As the phase flow ratio increases Xq, the ratio between hL,Fl and the liquid hold-up hL, which is on the line hL ul for ul = ul,f1) and which is characteristic of the range below the loading line, decreases. 

With regard to the last point, [62] rightly point out that the storage capacity of the soil and subsoil is not exhausted everywhere, even in the case of extreme precipitation It is therefore important to determine the limit beyond which a catchment is virtually incapable of storing any more water. However, steep mountainous catchments are only capable of storing low volumes of water and generally react rapidly. The authors [62] then use case studies to demonstrate that in many alpine catchments the response can also be slower, which ultimately results in major spatial variability in the flood characteristics of alpine catchments. 

The point at which, supposedly, 50% of the acid species is transformed in salt corresponds to the half-neutrahzation, i.e., when half the alkahne required to reach the equivalence point has been added. This position corresponds to a buffer zone in which the variation of pH is small with respect to the amoimt of added neutralization solution (Fig. 14 left plot). Hence, in this region a very slight variation of pH can produce a very large variation of neutralization (Fig. 14 right plot), i.e., a considerable alteration of the relative proportion of AH and A . Far away from this pH, the opposite occurs. Consequently, the pH could be used to carry out a formulation scan, but the scale is far from hnear and the variation of pH does not render the variation of the characteristic parameter of the actual surfactant mixture that is at interface [77,78]. The appropriate understanding of the behavior of this kind of acid-salt mixture is particularly important in enhanced oil recovery by alkaline flooding [79,80] and emulsification processes that make use of the acids contained in the crude oils [81-83]. 

The characteristic velocity k is a function of droplet size, density difference, viscosity, etc. Thus, the holdup tends to increase either as the superficial flow velocities Uc and Ud are increased or as the characteristic velocity is reduced (e.g., by increasing agitation). A point is eventually reached where the increase in holdup becomes unstable (typically when = 0.3-0.4). This phenomenon is known as flooding, and it imposes a limit on the flow rates and agitation levels that can be used in countercurrent extraction processes. 

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