Mixing multiphase

Phase average models apply to well mixed multiphase flows, i.e. when the exact shape of the interfaces is not known, or not relevant e.g. bubbly flows. The principle could be applied under the two-fluid, six-equation model, where separate eonservation equations are required for each phase with appropriate exehange forces, or the homogeneous. Algebraic Slip model. Under sithermal, incompressible flow conditions, the equations of laminar motion for phase A are expressed in the two-fluid formalism as follows ... 

Tubular reactors, as previously stated, are also advantageous for high-pressure reactions where smaller-diameter cylindrical vessels can be used to allow thinner vessel walls. Tubular reactors should be avoided when carrying out multiphase reactions, since it is often difficult to achieve good mixing between phases. 

Pumping of liquids. Compression of gases Mixing (solids, liquids, gases possibly multiphase) Atomization, dispersion... 

Other important aspects include the effect of temperature (via activation energy) and mixing, particularly for multiphase reactions. Both of these can impact on selectivity and thus can be improved in operating continuously using the inherent benefits of heat transfer area and mixing strategies discussed previously. 

There are many nonintrusive experimental tools available that can help scientists to develop a good picture of fluid dynamics and transport in chemical reactors. Laser Doppler velocimetry (LDV), particle image velocimetry (PIV) and sonar Doppler for velocity measurement, planar laser induced fluorescence (PLIF) for mixing studies, and high-speed cameras and tomography are very useful for multiphase studies. These experimental methods combined with computational fluid dynamics (CFDs) provide very good tools to understand what is happening in chemical reactors. 

In a certain range of process conditions, column reactors for multiphase processes behave as a tubular reactor with respect to gaseous reactants and as an ideally mixed tank reactor with respect to condensed phases. 

Mixing by mechanical agitation is almost always necessary in multiphase reactors... 

The role of mixing in heterogeneous reactions is obvious. In multiphase processes mixing imposed by a stirrer or an external pump is necessary to increase the interface through which reactants pass to meet their partner in the other phase and/or to intensify mass transfer between phases. Mixing can also play a significant role in the case of homogeneous reactions. Chemical reactions occur at the molecular level. Reactant molecules introduced into a reactor encounter the environment in the vicinity of the inlet. The composition of the mixture there is obviously... 

Optimizing the formulation of micellar surfactant solutions used for enhanced oil recovery consists of obtaining interfacial tensions as low as possible in multiphase systems, which can be achieved by mixing the injected solution with formation fluids. The solubilization of hydrocarbons by the micellar phases of such systems is linked directly to the interfacial efficiency of surfactants. Numerous research projects have shown that the amount of hydrocarbons solubilized by the surfactant is generally as great as the interfacial tension between the micellar phase and the hydrocarbons. The solubilization of crude oils depends strongly on their chemical composition [155]. 

K. L. McCarthy, Y. Lee, J. Green, M. J. McCarthy 2002, (Magnetic resonance imaging as a sensor system for multiphase mixing), Appl. Mag. Reson. 22, 213. 

Figure 14.3 A temporal superstructure for a multiphase well-mixed batch reactor.

However, it should be noted that there are many practical issues that need to be considered when choosing mixing equipment and mixing patterns, in addition to those for maximizing yield, selectivity or conversion4. This is especially the case when dealing with multiphase reactions4. 

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