Flow regime flooding

The regulation of the Ebro River in the 1960s completed an irreversible change of the discharge pattern. The dams substantially altered flood timing, particularly of the flood peaks [26, 27]. Batalla et al. [28] analyzed flow records from 22 rivers to determine the effects of reservoirs on flow regime (flood frequency, flow duration of mean daily flows, monthly regime, and annual runoff) before and after dam construction. This research shows that variability of the mean daily flows was... 

Particular conditions may occur for two-phase downflows in vertical or inclined channels (ducts) that are not completely described by the flow regime maps. Flooding occurs as the rising vapor completely blocks descending liquid. With lowering velocities of the vapor phase, this condition is preceded by the phenome-... 

Dams and reservoirs have been built in the last 100 years in vast numbers throughout many mountain areas. They serve different purposes, mainly irrigation, hydropower, water supply or flood control, or they aim at pursuing multipurpose functions. Effects on flow regime, for example shifts in summer and winter patterns, on sediment dynamics, and on other features of the aquatic ecosystems can be dramatic (cf. Sects. 2.2 in [11], this volume, 2 in [15], this volume). 

Fig. 4.17. Flow regimes in three-phase fixed-bed reactors, (a) Gas and liquid in co-current downwards flow (trickle-bed operation). (b) Gas and liquid in co-current upwards flow (liquid floods bed), (c) Gas and liquid in countercurrent flow (not often used for catalytic reactors)...

Recommendations The information given in Chap. 6 can be used for an approximate estimation of the flow regime. The flooding conditions can be estimated from Fig. 8-1. 

When the data abruptly departs from the drift flux curve, a change in the flow regime is assumed to occur flooding, according to Wallis (3). It was visually observed that increased coalescence and slugging occurred when the experimental data diverged from the drift flux curve. 

Ideally, it should be possible to reach the maximum and still remain in the bubbly flow regime. Thereafter, any further increase in the gas flow rate results in a continuity limitation on the gas. Flooding occurs, resulting in the formation of large bubbles and transition. Thus, eqc may be considered as the transition gas hold-up. 

Physical stressors can be modified by the ecosystem as well. For example, siltation in streams depends not only on sediment volume, but on flow regime and physical stream characteristics. Similarly, nearby wetlands and levees influence water behavior during flood events. 

For a given gas flow rate, the dispersion pattern of gas bubbles in the working media depends on the interplay between the isothermal expansion energy of the gas and the hydraulic power of the impeller. One of three bubble dispersion scenarios is typically expected, i.e., flooding, dispersion in the upper region only, or complete dispersion. Fig. 7 illustrates each of these flow regimes. 

Under turbulent flow conditions, power dissipation is the controlling factor for mass transfer and phase dispersion. The power drawn by a single impeller in a liquid-gas system is typically lower than that drawn by the same impeller in liquid alone. The presence of the gas reduces the average density of the mixture, and the gas flow regime (e.g., flooding) may cause the impeller blades to be locally surrounded by a higher... 

The advantage of downflow operation with respect to upflow lies in the fact that there is no limitation on the flow rates imposed by flooding limits. The flow rates are only limited by the available pressure head at the inlet. Furthermore, the liquid is much more evenly and thinly distributed then with upward flow. Depending on the respective flow rates of gas and liquid different flow regimes may be obtained, however. Figure 14.3.b-2 is a schematic representation of the different possibilities, derived from diagrams presented by Hofmann [42], by Sato et al. [20], and by Charpentier and Favier [73]. The trickle flow regime... 

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