Flow of Continuous Phase

As mentioned before, the concept of impinging streams (IS) was originally suggested for enhancing heat and mass transfer between a solid and a gas, and the development of the application of impinging streams were long focused mostly on multiphase systems. However, the problems involved in multiphase impinging streams are considerably complex so that it is necessary to study the behaviors of the individual phases separately. 

The discussions in this chapter relate to single phase impinging streams, the behavior of which may reflect part of those of multiphase impinging streams. Taking into account the similarities of liquid with gas, the discussions will also involve impinging streams of liquid alone while the differences between gas- and liquid-continuous impinging streams will be described in detail in the chapters of Part II. 

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The head required for flow of continuous phase he includes losses due to (1) friction in the down spout, which should be negligible, (2) contraction and expansion upon entering and leaving the down spout, and (3) two abrupt changes in direction. These total 4.5 velocity heads ... 

Equations (15-188) and (15-189) represent decanter performance for a given feed with constant properties, i.e., a constant composition and phase ratio. Note that the analysis can be done in terms oDotal flow Q or the flow of continuous phase or dispersed phase (Ij. Typically, the value of the exponent a is greater than 2.5 [Barnea and Mizrahi, Trans. Inst. Chem. Eng., 53, pp. 61-91 (1975) and Golob and Modic,... 

The dispersion in the mixer sections is swept under the dividing partitions into the adjacent transfer sections. If the dispersed phase is the less dense of the two its droplets rise up through the transfer sections against the down-coming flow of continuous phase after which they pass to the next mixer section where the process is repeated. Unlike a mixer-settler the ROF contactor does not depend for its operation on the coalescence of the dispersed phase in separating compartments and in its application to the nitration stage of the TNT process nitrobody separates out only at the product end where a smaller unstirred compartment operates as a true separator. 

Similarly in Fig. 10.29, where the data are plotted against rate of flow of continuous phase at constant dispersed-phase rate, the great influence of interfacial area is evident. For the large drops it was observed that their very rapid rate of rise was not influenced by the rate of the continuous phase hold-up and coefficients therefore remain constant. For the smaller drops the rate of rise was markedly reduced by increased flow of the continuous phase, hold-up increased, and interfacial area and coeflScients in-... 

Most column extraction processes operate with a solvent of lower density than the aqueous phase and discrete solvent drops are usually allowed to ascend in the continuous aqueous medium, with an interface near the top of the column. Aqueous phase enters just below the interface and solvent phase is fed via the first distributor at the base of the column. Flooding of the column takes place at certain critical flow rates. This phenomenon arises when, for example, the flow rate of the dispersed phase is unduly increased with a constant flow of continuous phase. The additional column hold-up of dispersed phase leaves less space for continuous phase and therefore the linear velocity of the continuous phase is increased. A tendency to drag the dispersed phase droplets in the direction of the continuous phase thus arises. When the flooding point is reached, the dispersed phase is discharged along with the continuous phase and counter-current flow ceases. 

A few devices have been proposed that resemble cross-flow membrane emulsification, where a phase is induced to disperse through the small openings of a membrane in a flow of continuous phase [3]. Such processes are more energy efficient than conventional approaches such as colloid mills and homogenizers [142]. A microstructured analogue of membrane emulsification was presented by de... 

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