Multi-Phase Mixtures

Multiphase mixtures, in contrast to homogeneous mixtures (solutions, mixtures of gases) are characterized by the presence of macroscopic heterogeneities or inclusions (solid particles, bubbles, drops, macromolecules). Multiphase mixtures are also named heterogeneous. Among these are mixtures of gas with particles (aerosols), of liquid with solid particles (suspensions), of gas with drops (gas-liquid mixtures), of liquid with bubbles (liquid-gas mixtures), and also mixtures of liquid with drops of another liquid (emulsions). Colloidal mixtures, which are frequently called colloids, and also micellar solutions, fill in an intermediate domain between heterogeneous and homogeneous mixtures. 

The listed types of multiphase mixtures form the class of disperse mediums consisting of two phases. Inclusions in a continuous or disperse phase are in the suspended state. The disperse phase consists of particles of various nature, in particular drops, solid particles, bubbles. 

In studying various processes in multiphase mixtures, the scientists usually assume that the size of inclusions in a mixture (particles, drops, bubbles, the pores in the porous mediums) is much greater than the size of the molecules. This assumption named the continuity hypothesis, allows us to use the mechanics of continuous mediums for description of processes occurring inside or near the separate inclusions. For description of physical properties of phases, such as viscosity, heat conductivity etc., it is possible to use equations and parameters of an appropriate single-phase medium. 

If the average distance between the inclusions is much less than the characteristic size of a continuous phase over which the macroscopic parameters (velocity, pressure, temperature etc.) change, then it is possible to describe the macroscopic processes in the mixture by the methods of mechanics of continuous mediums as well. To this end, the averaged or macroscopic parameters are introduced. At this point, the concept of multi-velocity continuum [6], representing a set of N continuums, can also be introduced. The number N is the number of considered phases, each of which corresponds to a certain constituent phase of the mixture and fills one and the same volume. For each of these constituent continuums we define in the usual manner the local density, which is called the reduced density 

In the same manner as for solutions, one can introduce the phase velocity relative to the mass center of the mixture or medium as a whole 

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A bench-scale settler was used in an experimental study to assess continuous biodesulfurization operation to separate oil and water + biocatalyst [260], The design was based on a viton tubing settler surface placed at an angle to allow separation of the multi phase mixture. The device was reported to operate with over 95% efficiency for first 24 hours after which the performance reduced drastically. 

As part of geologic C02 sequestration demonstration projects conducted at the Frio Site, Liberty County, TX, USA, and the Otway Project, Nirranda South, Victoria, Australia, U-tubes were deployed for sampling multi-phase mixtures of gas, water and supercritical C02. At both these sites, C02 was injected in the subsurface to understand the subsurface movement of the C02 plume and geochemical sampling was one of many technologies employed to understand the fate of the C02. 

The integrated intensity I of reflection hkl for phase a in a multi-phase mixture measured on a flat-plate sample of infinite thickness can be calculated from ... 

A liquefied gas is widely sprayed from the exit developing a multi-phase mixture. In the opening, a narrow, so-called flashing zone is formed in which a certain firaction of the liquid depending on its thermodynamic conditions is spontaneously (flash-) vaporized. Adjacent zones are the zone of flow establishment characterized by a dilution of the jet stream from its boundaries and the zone of established flow with the full development of the plume interacting with the ambient [84]. 

The media with which one has to deal when investigating preparation processes of hydrocarbon systems are invariably multi-phase and multi-component mixtures. Section II thus covers the aspects of the hydromechanics of physical and chemical processes necessary for an understanding of the more specialized material contained in following sections. Among these are transfer phenomena of momentum, heat, mass, and electrical charge conservation equations for isothermal and non-isothermal processes for multi-component and multi-phase mixtures equations of state, and basic phenomenological relationships. 

The first assumption allows application for calculations of classical ideas and mechanical equations of continuous honnogeneous mediums for description of processes in scales of heterogeneities themselves (drops, bubbles, etc.). The second assumption determines possibihty of description of macroscopic processes in multi-phase mixture by methods of continuous medium mechanics with the help of averaged or macroscopic parameters. 

New on-off valves closing speeds shall be reviewed and adjusted to prevent hydraulic shock waves or water hammer. Also, piping velocity shall be checked so that it is well within erosion velocity. The possibility of multi-phase mixtures inside pipes shall be evaluated carefully to apply proper hydraulic equations and estimate adequate pipe sizing. 

In non-reactive blending, a two- (or multi-)phase mixture is formed when the immiscible polymers are physically mixed with each other. The minor phase, rich in B, is dispersed as droplets into a major phase rich in A. Apart from low interfadal tension, high shear rates and similar viscosities of both polymers are important for the size of the dipersed phase and therefore for the product quality. The reactive route follows the synthesis of a minor component via polymerization into a major component that acts as a host polymer. An alternative route for reactive blending is in situ formation of block co-polymers during the mixing process to decrease the interfacial tension. An extruder is the most commonly applied apparatus for the continuous production of polymer blends. 

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