Stabilization methods, multiphase method

Aota, A., Mawatari, K., Kitamori, T. (2009). Parallel multiphase microflows Fundamental physics, stabilization methods and applications. Lab on a Chip, 9, 2470-2476. 

In gas-solid multiphase flows, the wave propagation method is commonly used to study the stability of stratified pipe flows, where an analogy to gas-liquid wave motion with a free surface is prominent. The perturbation method is commonly used to study the stability of a fluidized bed. In the following, both methods are introduced. 

The theory of linear stability has been used. Jackson (1963a) has pioneered this method for the analysis of multiphase dispersions. The pertinent details have been given by Shnip et al. (1992). 

Gupta, A.K. Bishnoi, P.R. Kalogerakis, N. A method for the simultaneous phase equilibria and stability calculations for multiphase reacting and nonreacting systems. Fluid Phase Equilibria 1991, 63, 65-89. 

To illustrate the principles of the finite volume method, as a first approach, the implicit upwind differencing scheme is used for a multi-dimensional problem. Although the upwind differencing scheme is very diffusive, this scheme is frequently recommended on the grounds of its stability as the preferred method for treatment of convection terms in multiphase flow and determines the basis for the implementation of many higher order upwinding schemes. 

Abstract Among the noncontinuum-based computational techniques, the lattice Boltzman method (LBM) has received considerable attention recently. In this chapter, we will briefly present the main elements of the LBM, which has evolved as a minimal kinetic method for fluid dynamics, focusing in particular, on multiphase flow modeling. We will then discuss some of its recent developments based on the multiple-relaxation-time formulation and consistent discretizatirai strategies for enhanced numerical stability, high viscosity contrasts, and density ratios for simulation of interfacial instabilities and multiphase flow problems. As examples, numerical investigations of drop collisions, jet break-up, and drop impact on walls will be presented. We will also outline some future directions for further development of the LBM for applications related to interfacial instabilities and sprays. 

Other new processes have involved modifications of the solvent evaporation method. To produce a more homogeneous emulsion and stabilize the protein, surfactants have been added to the protein phase. For example, researchers have claimed that the addition of hydrophobic ion pairs to the protein phase allows a more homogeneous mixture of the protein in the polymer phase and provides stabilization of the protein (M. C. Manning, personal communication, 1994). Reversed micelles (sucrose esters of fatty acids) stabilize ultrafine emulsions of the protein in the polymer phase and provide stabilization ofthe protein (Hayashi et al, 1994). In addition, the use of a multiphase encapsulation system may protect the protein from denaturation. One t q)e of multiphase system involves the suspension of... 

For ceramic materials that are not extremely hard (e.g., stabilized zirconium oxide or multiphase materials), surface relief can be created within a few minutes by means of final polishing with colloidal silica on a chemicaUy resistant, short-napped fiber cloth. Because removal is dependent on the grain orientation and the type of phase, it is possible to distinguish between grains of a single phase and between different phases during microscopic examination. Application of the DIC method makes it possible to use even poorly defined reUef to display microstructure under the optical microscope. A brief final polishing step with very fine alumina (0.05 pm) will help reveal the spinel phase in aluminum oxide materials, for example. 

Another category of enzymatic transformations in multiphase systems is enzymes immobilized on the reactor wall as presented in Table 10.4. Enzymes are advantageously used in immobilized form because this strategy allows for increased volumetric productivity and improves stability. Continuous mode of operation is employed in these systems. The approaches commonly used for immobilization in conventional multiphase biocatalysis can also be employed in microreactors such as covalent methods, cross-linked enzyme aggregates (CLEA), and adsorption methods. The experimental setups can either be chip-type reactors with activated charmel surface walls where enzyme binds, or enzyme immobilized monolith reactors, where a support is packed inside a capillary tube. 

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