MULTI PHASE

A. M. Nazar and T. W. Clyne in T. N. Vezkoglu, ed.. Proceedings Multi-Phase Flow and Heat Transfer Symposium Hemisphere, Washington, D.C., 1980. 

For additional information, see Simpson (Chem. Eng., 75(6), 192-214 [1968]). A critical Fronde number of 0.31 to ensure vented flow is widely cited. Recent results (Thorpe, 3d Jnt. Conf. Multi-phase Flow, The Hague, Netherlands, 18-20 May 1987, paper K2, and 4th Int. Conf. Multi-phase Flow, Nice, France, 19-21 June 1989, paper K4) show hysteresis, with different critical Fronde numbers for flooding and untlooding of drain pipes, and the influence of end effects. Wallis, Crowley, and Hagi (Trans. ASME J. Fluids Eng., 405 13 [June 1977]) examine the conditions for horizontal discharge pipes to run full. 

The minimum capacity of quench liquid can be estimated by a heat balance, knowing the final quench pool temperature. The following equation given by Fauske Intemational Symposium on Multi-Phase Transpoii and Paiiiculate Phenomena, December 15-17, I9S6) can be used to calculate the minimum amount of quench hquid ... 

Vapor Pressure The pressure exerted by a vapor above its own liquid. The higher the vapor pressure, the easier it is for a liquid to evaporate and fill the work area with vapors which can cause health or fire hazards. Venting Emergency flow of vessel contents out of a vessel. The pressure is controlled or reduced by venting, thus avoiding a failure of the vessel by overpressurization. The emergency flow can be one-phase or multi-phase, each of which results in different flow characteristics. 

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. 

Conventionally, wastes are eonsidered as being predominantly either solid, liquid or gaseous but as illustrated in Table 16.3, they may be multi-phase. Solid waste eompiises liquid slurries, sludges, thixotropie solids and solids of varying partiele sizes it may be heterogeneous. Typieal examples are given in Table 16.4. 

The effect of physical processes on reactor performance is more complex than for two-phase systems because both gas-liquid and liquid-solid interphase transport effects may be coupled with the intrinsic rate. The most common types of three-phase reactors are the slurry and trickle-bed reactors. These have found wide applications in the petroleum industry. A slurry reactor is a multi-phase flow reactor in which the reactant gas is bubbled through a solution containing solid catalyst particles. The reactor may operate continuously as a steady flow system with respect to both gas and liquid phases. Alternatively, a fixed charge of liquid is initially added to the stirred vessel, and the gas is continuously added such that the reactor is batch with respect to the liquid phase. This method is used in some hydrogenation reactions such as hydrogenation of oils in a slurry of nickel catalyst particles. Figure 4-15 shows a slurry-type reactor used for polymerization of ethylene in a sluiTy of solid catalyst particles in a solvent of cyclohexane. 

Recalling from Chapter 2, the general heat duty for multi-phase streams is expressed as ... 

Grolmes, M. A., A Simple Approach to Transient Two-Phase Level Swell, Multi-Phase Flow and Heat Transfer III. Part A Fundamentals. Proceedings of the Third Multi-Phase Flow and Heat Transfer Symposium—Workshop, Miami Beach, FL, April 18-20, 1983. 

Huff,J. E., Multi-phase Flashing Flow in Pressure Relief Systems, Plant/Operations Progress, 4 (4), 191-199, October 1985. 

Fauske, H. K., Turbulent and Laminar Flashing Flow Considerations, Paper Presented at the 4th International Symposium on Multi-phase Flow, Miami Beach, FL, December 15-17, 1986. 

Dissolution kinetics are influenced by pH, potential and the ions present in the test solution, and this forms the basis of selective metallographic etching techniques that have been used for some time . The potentiostat is often used to hold the potential of a multi-phase alloy constant at a level... 

When a bluff body is interspersed in a fluid stream, the flow is split into two parts. The boundary layer (see Chapter 11) which forms over the surface of the obstruction develops instabilities and vortices are formed and then shed successively from alternate sides of the body, giving rise to what is known as a von Karman vortex street. This process sets up regular pressure variations downstream from the obstruction whose frequency is proportional to the fluid velocity, as shown by Strouai. 9. Vortex flowmeters are very versatile and can be used with almost any fluid — gases, liquids and multi-phase fluids. The operation of the vortex meter, illustrated in Figure 6.27, is described in more detail in Volume 3, by Gjnesi(8) and in a publication by a commercial manufacturer, Endress and Hauser.10 ... 

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. 

Comprehensive physicochemical characterization of any raw material is a crucial and multi-phased requirement for the selection and validation of that matter as a constituent of a product or part of the product development process (Morris et al., 1998). Such demand is especially important in the pharmaceutical industry because of the presence of several compounds assembled in a formulation, such as active substances and excipients, which highlights the importance of compatibility among them. Besides, variations in raw materials due to different sources, periods of extraction and various environmental factors may lead to failures in production and/or in the dosage form performance (Morris et al., 1998). Additionally, economic issues are also related to the need for investigating the physicochemical characteristics of raw materials since those features may determine the most adequate and low-cost material for specific procedures and dosage forms. 

Ismail, 1. et al. (2003) Tomography for multi-phase flow measurement in the oil industry. 4th International Symposium on Measurement Techniques for Multiphase Flows, 2003, Fiangzhou. 

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

Another important challenge is to enhance the reliability of the design and scale up of multi-phase reactors, such as fluidized bed reactors and bubble-colunms. The design uncertainty caused by the complex flow in these reactors has often led to the choice of a reactor configuration that is more reliable but less efficient. An example is Mobil use a packed-bed reactor for the methanol to gasoline process in New Zealand, even though a... 

The XRD pattern of the catalyst. Fig. 3. can be understood as thermal treatment lead to the crystallization of the catalyst and mixture of a majority of nanocrystalline MosOu-type oxide with minor amounts of nanocrystalline M0O3 and Mo02-type material [5]. The crystallization of the catalyst takes place only in a small temperature range and above which decomposes. The FTIR pattern. Fig. 4. shows the peak at 711 cm suggests that there exits a multi phase component like Mo (or V or W)-0- Mo bond [6]. 

In the above equations, a is a coefficient with the value of 1.0 for single phase flow and 2.0 for multi-phase flow [6], and pis an adjustable coefficient and has a value of 2.1 by fitting the experimental results for the two phase flow. The flow resistant coefficient is determined by the Blasius equation. 

Favoring multi-phase processing, including powder making Favoring single-phase processing... 

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. 

Jensen gives several examples for his present highly integrated chip systems [101], including a gas-phase reactor, a liquid-phase reactor, a catalyst-testing reactor, and a packed-bed multi-phase reactor. In addition, he provides the vision of a multiple micro-reactor test station (see Section 1.5.5.2). 

Worz et al. stress a gain in reaction selectivity as one main chemical benefits of micro-reactor operation [110] (see also [5]). They define criteria that allow one to select particularly suitable reactions for this - fast, exothermic (endothermic), complex and especially multi-phase. They even state that by reaching regimes so far not accessible, maximum selectivity can be obtained [110], Although not explicitly said, maximum refers to the intrinsic possibilities provided by the elemental reactions of a process under conditions defined as ideal this means exhibiting isothermicity and high mass transport. 

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