Multi-phase system

Since the kW developed by a 3-0 winding is 50% more than by a 2-0 winding for the same value of stator current /, the economics of this principle is employed in an induction motor for general and industrial use. As standard practice, therefore, in a multi-phase system, only 3-0 induction motors are manufactured and employed, except for household appliances and applications, where mostly single-phase motors are ttsed. 

There is also growing interest in multi-phase systems in which hard phase materials are dispersed in softer polyether diols. Such hard phase materials include polyureas, rigid polyurethanes and urea melamine formaldehyde condensates. Some of these materials yield high-resilience foams with load deflection characteristics claimed to be more satisfactory for cushioning as well as in some cases improving heat resistance and flame retardancy. 

Soil is a multi-phase system consisting of solids, liquids, and gases. In a typical soil, solids, liquids and gases compose about 50%, 20-30% and 20-30% respectively of the total soil volume (Brady and Weil, 1999). The solid phase can be broken down into two components inorganic and organic matter, with organic matter ranging from 1 to 5% of the soil. 

Whitaker, S, The Transport Equations for Multi-Phase Systems, Chemical Engineering Science 28, 139, 1973. 

Speed-up of mixing is known not only for mixing of miscible liquids, but also for multi-phase systems the mass-transfer efficiency can be improved. As an example, for a gas/liquid micro reactor, a mini packed-bed, values of the mass-transfer coefficient K a were determined to be 5-15 s [2]. This is two orders of magnitude larger than for typical conventional reactors having K a of 0.01-0.08 s . Using the same reactor filled with 50 pm catalyst particles for gas/Hquid/solid reactions, a 100-fold increase in the surface-to-volume ratio compared with the dimensions of laboratory trickle-bed catalyst particles (4-8 mm) is foimd. 

GL 27] [R 3] [P 29] By means of sulfite oxidation, the specific interfacial areas of the fluid system nitrogen/2-propanol were determined for different flow regimes [5]. For two types of micro bubble columns differing in micro-channel diameter, interfaces of 9800 and 14 800 m m , respectively, were determined (gas and liquid flow rates 270 and 22 ml h in both cases). Here, the smaller channels yield the multi-phase system with the largest interface. 

Typical scale-up ratios for the incremental approach are shown in Table 5.3-4. It is not surprising that single-phase systems are easier to scale up than multi-phase systems. The reason is that the contact between phases changes with scale. In particular, the presence of solids complicates scale-up. 

Mixing Calorimetry Instantaneous heat of mixing, AHMI)aNG Gas generation rates Isothermal, from ambient to 150°C Cannot test multi-phase systems... 

The use of SCCO2 either alone [135-137] or in multi-phase systems [138-140] offers interesting process alternatives to other methods of catalyst immobilization such as heterogenization on solid supports [126-128], aqueous... 

One of the benefits of SCCO2 for homogeneous catalysis is that rates or se-lectivities may be significantly higher than in other multi-phase systems or in conventional solvents, because mass transfer across interfaces is enhanced. An example is CO2 hydrogenation that simultaneously uses CO2 as both reaction medium and substrate [114]. 

Many of these compounds (MH ) show large deviations from ideal stoichiometry (n= 1, 2, 3) and can exist as multi-phase systems. The lattice structure is that of a typical metal with atoms of hydrogen on the interstitial sites for this reason, they are also called interstitial hydrides. This type of structure has the limiting compositions M H, M H2 and M H 3 the hydrogen atoms fit into octahedral or tetrahedral holes in the metal lattice or a combination of the two types (Figure 5.21). 

The term food colloids can be applied to all edible multi-phase systems such as foams, gels, dispersions and emulsions. Therefore, most manufactured foodstuffs can be classified as food colloids, and some natural ones also (notably milk). One of the key features of such systems is that they require the addition of a combination of surface-active molecules and thickeners for control of their texture and shelf-life. To achieve the requirements of consumers and food technologists, various combinations of proteins and polysaccharides are routinely used. The structures formed by these biopolymers in the bulk aqueous phase and at the surface of droplets and bubbles determine the long-term stability and rheological properties of food colloids. These structures are determined by the nature of the various kinds of biopolymer-biopolymer interactions, as well as by the interactions of the biopolymers with other food ingredients such as low-molecular-weight surfactants (emulsifiers). 

Besides the effect on the solubility in multi-phase systems, the pressure can also directly increase the reactant concentrations in gas-phase reactions through the compressibility of gases. The reaction-rate increases because of the increased concentrations. The compression... 

The contrast variation method gives the ability to highlight or blank out different phases of a multi-phase system and adds greatly to the power of SANS. 

Nanoparticles are frequently used as a suspension in some kind of solvent. This is a two phase mixture of suspended solid and liquid solvent and is thus an example of a colloid. The solid doesn t separate out as a precipitate partially because the nanoparticles are so small and partially because they are stabilised by coating groups that prevent their aggregation into a precipitate and enhance their solubility. Colloidal gold, which has a typical red colour for particles of less than 100 nm, has been known since ancient times as a means of staining glass. Colloid science is a mature discipline that is much wider than the relatively recent field of nanoparticle research. Strictly a colloid can be defined as a stable system of small particles dispersed in a different medium. It represents a multi-phase system in which one dimension of a dispersed phase is of colloidal size. Thus, for example, a foam is a gas dispersed in a liquid or solid. A liquid aerosol is a liquid dispersed in gas, whereas a solid aerosol (or smoke) is a solid dispersed in a gas. An emulsion is a liquid dispersed in a liquid, a gel is liquid dispersed in a solid and a soils a solid dispersed in a liquid or solid. We saw in Section 14.7 the distinction between sol and gel in the sol gel process. 

RHEOLOGICAL MEASUREMENT PROBLEMS IN MULTI-PHASE SYSTEMS... 

Applications of positron imaging, particularly PEPT, have been extensive and very diverse. In general, they vary from quick diagnostic studies for industrial users to fundamental work on multi-phase systems, such as "granular gases" (see, e.g., Wildman et al., 2005). Here, we concentrate on work aimed at industrial understanding. 

In applications, increased capability in PEPT will enable more work with liquids and with multi-phase systems, and product-oriented studies aimed at probing the formation of microstructure. At the other extreme lies large-scale pilot- or process-level study which must be carried out in situ, using the new mobile PEPT camera. In large-scale applications, it will not in general be possible to provide trajectory information for the entire process volume. The challenge here is to develop "minimal" PEPT, in which location information is provided at as coarse a level as possible, consistent with the objectives of the study. 

As mentioned earlier, work on validation of computational approaches to simulating multi-phase systems under realistic momentum and heat-transfer conditions is growing PEPT represents one of very few ways of doing this convincingly. 

A series of pyrrolidines was conveniently prepared in a microwave-assisted double alkylation of aniline derivatives with alkyl dihalides in water in the presence of K2CO3 as a base (Scheme 1) [12,13]. Although the reaction mixture could be regarded as a multi-phase system, as neither reactant was soluble in the mildly basic aqueous medium, the microwave-assisted reaction proceeded readily without the use of phase-transfer reagents. The amount of side-reactions such as hydrolysis of bromides to alcohols in an alkaline reaction medium was substantially suppressed compared to the conventional thermal conditions. The reaction conditions were sufficiently mild to tolerate a variety of functional groups in anilines such as hydroxyls, ketones and esters. Alkyl bromides and tosylates were equally efficient as alkylating agents. Notably, isolation and purification comprised simply of phase separations (filtration or decantation) of the desired product from the aqueous media. 

Significantly, these reactions were not homogeneous single-phase reaction systems as neither reactant was soluble in the aqueous alkaline reaction medium. The workers postulated that selective absorption of microwaves by polar molecules and intermediates in a multi-phase system could substitute as a phase transfer catalyst without using any phase transfer reagent, thereby providing the observed acceleration similar to ultrasound irradiation [92],... 

A property seemingly unique to microwave chemistry is that the individual phases in multi-phase systems can be heated at different rates owing to differences in the dielectric properties. In some cases, a sizeable temperature difference can be maintained for several minutes. This technique has been applied usefully to produce aryl vinyl ketones batchwise by Hofmann elimination in a two-phase system comprising water and chloroform [77]. Although reactions took place in the aqueous phase, the thermally unstable products simultaneously were extracted and diluted into the cooler organic phase, which could be recycled. Yields were nearly quantitative and twice those obtained by traditional pyrolysis-distillation under vacuum. 

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