Drop regime

Spray regime (or drop regime, Fig. 14-20c). At high gas velocities and low liquid loads, the liquid pool on the tray floor is shallow and easily atomized by the high-velocity gas. The dispersion becomes a turbulent cloud of liquid droplets of various sizes that reside at high elevations above the tray and follow free trajectories. Some droplets are entrained to the tray above, while others fall back into the liquid pools and become reatomized. In contrast to the liquid-continuous froth and emulsion regimes, the phases are reversed in the spray regime here the gas is the continuous phase, while the liquid is the dispersed phase. 

Spray (Flge. 6.25d, 6.260, and 6.276 sometimes referred to as the drop" regime). As vapor load is increased at relatively low liquid rates, the spray regime is reached. While in the previous three regimes (and also... 

They also reported that satellite drops are produced with each main drop and that the mass fraction of satellite drops in single drop regime can be expressed as follows (Equation 6.18) ... 

Drop regime-. The gas forms the continuous phase and the liquid is dispersed into fine droplets. 

Froth regime -. This regime represents the intermediate state between bubble and drop regime. The two-phase layer is intensively agitated and no definitely dispersed phase exists. 

The froth regime is the dominant regime at normal column operation. Only in vacunm services drop regime may sometimes exist on trays. 

Most contactors, in particular columns, can be operated in different modes. The heavy phase is fed into the column at the top and, in turn, the light phase at the bottom. The two-phase mixture is, in most cases, an univocal drop regime, i.e., one phase is dispersed into the other phase in the form of small droplets that move countercurrently against the continuous phase. The Ught phase is withdrawn at the top, the heavy phase at the bottom of the column (Fig. 6.3-5). 

In contrast to gas/liquid contactors the two-phase system in the mass transfer zone of solvent extractors has a well-defined structure, which is called drop regime. One phase, mostly the organic phase, is dispersed in droplets in the other (mostly aqueous) phase. Therefore, the dimensioning of solvent extractors should be less empirical than that of distillation and absorption colmnns. 

The area effeetive for interfacial mass transfer can be easily calculated in case of drop regime in the mass transfer zone ... 

A distinction has to be made between the bubble regime, where the gas rises as a bubble through the continuous liquid phase, and the drop regime, where the gas is continuous and the liquid is dispersed. According to Stichlmair [1978], the transition from the first to the second regime occurs when... 

Pressure Drop. The pressure drop across a two-phase suspension is composed of various terms, such as static head, acceleration, and friction losses for both gas and soflds. For most dense fluid-bed appHcations, outside of entrance or exit regimes where the acceleration pressure drop is appreciable, the pressure drop simply results from the static head of soflds. Therefore, the weight of soflds ia the bed divided by the height of soflds gives the apparent density of the fluidized bed, ie... 

Total pressure drop for horizontal gas/solid flow includes acceleration effects at the entrance to the pipe and fric tional effects beyond the entrance region. A great number of correlations for pressure gradient are available, none of which is applicable to all flow regimes. Govier and Aziz review many of these and provide recommendations on when to use them. 

Pressure Drop Some models regard trickle bed flow as analogous to gas/liquia flow in pipe lines. Various flow regimes may exist like those typified in Fig. 23-25/ but in a vertical direction. The two-phase APcl is related to the pressure drops of the individual phases on the assumptions that they are flowing alone. The relation proposed by Larkin et al. (AJChE Journal, 7, 231 [1961]) is APaj 5.0784... 

Pressure drop in catalyst beds is governed by the same principles as in any flow system. Consequently, at very low flow, pressure drop is directly proportional to velocity, and at very high flow, to the square of velocity. These conditions correspond to the laminar and turbulent regimes of the flow. 

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