Fluid flow, multiphase systems patterns

The current progress of CFD enables computational experiments in a reactor apparatus to reveal the RTD. Typically, CFD is used for nonreactive fluid systems, but nowadays reactive systems can also be computed as discussed in Ref [8]. The difficulties of CFD, however, increase considerably as multiphase systems with chemical reactions are examined. For this reason, a logical approach is to utilize CFD to catch the essential features of the flow pattern and to use this information in classical reactor models based on RTDs. 

The performance of a chemical reactor, i.e., the relation between output and input, is affected by the properties of the reactional system (kinetics, thermodynamics,...) and by the contacting pattern. The importance of this contacting pattern is quite obvious in the case of multiphase reactors like trickle-bed reactors. Reactants are indeed present in both fluid phases and reactions occur at the contact of the catalytic solid phase. Unfortunately the description of the fluid flow pattern is very difficult because of the high number of intricate mechanisms that can control this pattern. The situation is so complex that, in many cases, we do not even know the essential hydrodynamic parameters that may affect the performance of the reactor. 

An understanding of multiphase microflows is critical for the development and application of microstructured chemical systems in the chemical industry. As one of the most important meso-scientific issues, interfacial science could be a bridge connecting microscopic molecular components and macroscopic fluid behaviors in these systems. Working together with viscous and inertial forces, the interfacial force also dominates complicated multiphase flow patterns and well-controlled droplets and bubbles. In this review, the generation mechanisms of different flow patterns and the break-up rules for droplets and bubbles in microchannels are introduced first. The effects of the adjustable fluid/solid interfaces, or so-called wetting properties, of microchannels on multiphase flow patterns, as well as microchannel surface modification methods, are then discussed. The dynamic fluid/fluid interfaces in multiphase microflows with variable... 

The hydrodynamic diameters of microchannels usually range from 10 to 1000 rm. In such confined flowing spaces, the multiphase flow patterns of Newtonian fluids are more variable compared with the common bubbly or droplet flows in larger vessels and columns. The confined flowing channel first affects the shape of droplets therefore, the flow patterns of liquid/hquid dispersed systems are usually categorized as plug flow and droplet flow, as shown in Fig. 1A and B. Usually, the droplet flow has larger specific surface area, which is fit for the mass transfer enhancement process (Mary et al,... 

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