Multiphase systems pressure

The foUowiag criterion of phase equUibrium can be developed from the first and second laws of thermodynamics the equUibrium state for a closed multiphase system of constant, uniform temperature and pressure is the state for which the total Gibbs energy is a minimum, whence... 

It is presumed ia this statement that equUibrium ia a multiphase system implies uniformity of T and P throughout aU phases. In certain situations, eg, osmotic equUibrium, pressure uniformity is not required, and equation 212 is then not a useful criterion. Here, however, it suffices. 

A multiphase system consisting of a hydrocarbon solvent, a strong alkaline solution, and a quaternary onium salt, in the presence of a Pd/C catalyst with hydrogen that was bubbled at atmospheric pressure through the organic phase, allows the rapid displacement of chlorine from polyhalogenated benzenes. The onium salt, insoluble in both phases, is localized in the interfaces, coats the Pd/C catalyst, and constitutes the phase in which the reaction takes... 

NAPL will migrate from the liquid phase into the vapor phase until the vapor pressure is reached for that liquid. NAPL will move from the liquid phase into the water phase until the solubility is reached. Also, NAPL will move from the gas phase into any water that is not saturated with respect to that NAPL. Because hydraulic conductivities can be so low under highly unsaturated conditions, the gas phase may move much more rapidly than either of the liquid phases, and NAPLs can be transported to wetter zones where the NAPL can then move from the gas phase to a previously uncontaminated water phase. To understand and model these multiphase systems, the characteristic behavior and the diffusion coefficients for each phase must be known for each sediment or type of porous media, leading to an incredible amount of information, much of which is at present lacking. 

The hydrodehalogenation reaction of haloaromatics involved the substitution of halide atoms bound to the ring, with hydrogen. For example, tetrachloroben-zene could be reduced to benzene in 30 minutes, at 50°C, by bubbling H2 at atmospheric pressure in the multiphasic system constituted by isooctane, 50% aqueous KOH, 0.2 molar A336, in the presence of Pd/C (0.02 molar) (Figure h.lS)." ... 

As discussed in previous chapters, the phase behavior with changing temperature and pressure may be strongly influenced by small concentration gradients in multi-component systems already. Therefore, experimental control should take this into account. It is a common practice to use reactors with glass or sapphire windows. The transition of an inhomogeneous multiphase system to a homogeneous one can be observed visually as cloud point (Sect. 2.2, with the pressure and temperature values being monitored. 

The other alternative for achieving single-phase conditions is to add a suitable solvent. The advantage of the supercritical single-phase technology is that the reaction temperature can remain unchanged. However, the pressure, the solvent and the composition of the reaction mixture have to be selected carefully to ensure single-phase conditions. If this is not the case, a multiphase system remains [28 - 30,32]. 

Figure 1731. Fluidized bed reactor processes for the conversion of petroleum fractions, (a) Exxon Model IV fluid catalytic cracking (FCC) unit sketch and operating parameters. (Hetsroni, Handbook of Multiphase Systems, McGraw-Hill, New York, 1982). (b) A modem FCC unit utilizing active zeolite catalysts the reaction occurs primarily in the riser which can be as high as 45 m. (c) Fluidized bed hydroformer in which straight chain molecules are converted into branched ones in the presence of hydrogen at a pressure of 1500 atm. The process has been largely superseded by fixed bed units employing precious metal catalysts (Hetsroni, loc. cit.). (d) A fluidized bed coking process units have been built with capacities of 400-12,000 tons/day.

The on-line measurement of viscosity under plant conditions poses particular difficulties. This is due to the wide range of viscosities that can occur within a process plant, to the difficulty of obtaining reliable measurements (particularly for non-Newtonian fluids) and to the accuracy that is often required (e.g. better than within 1 per cent for lubricating oils). Variables which can affect the measured viscosity are the temperature, pressure and rate of flow of the sampled stream— quite apart from the normal errors that can occur in any similar instrument (e.g. due to variations in supply voltage and frequency, sample contamination, sample not being representative of the bulk fluid, etc.). Automatic temperature compensation is always required and, in the case of multiphase systems, the difficulty of obtaining a representative sample is considerable (see Section 6.9). In this instance... 

Section 5.1 presents the fundamental method as the heart of the chapter— the statistical thermodynamics approach to hydrate phase equilibria. The basic statistical thermodynamic equations are developed, and relationships to measurable, macroscopic hydrate properties are given. The parameters for the method are determined from both macroscopic (e.g., temperature and pressure) and microscopic (spectroscopic, diffraction) measurements. A Gibbs free energy calculation algorithm is given for multicomponent, multiphase systems for comparison with the methods described in Chapter 4. Finally, Section 5.1 concludes with ab initio modifications to the method, along with an assessment of method accuracy. 

Several subjects that might be considered under the title of thermochemistry are discussed in previous chapters. Such subjects are the heat capacities of a single-phase system, the dependence of the enthalpy of a single-phase system on temperature and pressure, and the dependence of the enthalpy of a one-component, multiphase system on the temperature, volume, and mole numbers. Here we are concerned with heat capacities of multiphase systems, with changes of enthalpy for the formation of a solution and for a change of concentration of the solution, and with changes of enthalpy of systems in which chemical reactions occur. First the basic concepts of calorimetry are reviewed. 

As explained in Chapters 10 and 11, the existence of pressure fluctuation and the promotion of micromixing are the major features of liquid-continuous impinging streams. For processes occurring on the molecular scale in liquid or multiphase systems with a liquid as the continuous phase, these features have important implications. One of their valuable applications is the promotion of process kinetics. 

Equilibrium in a multiphase system implies thermal, mechanical, and material equilibrium. Thermal equilibrium requires uniformity of temperature throughout the system, and mechanical equilibrium requires uniformity of pressure. To find the criterion for material equilibrium, we treat a two-phase system and consider a transfer of dn moles from phase p to phase a. First, we regard each phase as a separate system. Because material enters or leaves these phases, they are open systems and we must use Eq. (4) to write their change in internal energy ... 

Jet impingement test protocol Can simulate high turbulence conditions at high temperatures, pressures for gas, and liquid, multiphase systems. Involves small volumes of test fluids [8,9]... 

In this equation the brackets indicate molar concentrations for liquid phase species. The concentration of (S02)g must be given as partial pressure and H S02 represents the effective Henry s law constant of S02 considering the dissolution equilibria reactions of S(IV)aq As to be seen from Equation 8 the transformation of (S02)g to S(VI)aq in a multiphase system must be measured as a function of (S02)g/ L, [H202]aq and [H+]aq in order to determine the constant k4 and the exponents, p, X and . 

Mixtures of water (main component), organic substances and gases such as O2 or CO2 are multiphase systems under normal conditions. Pressures above 221 bar and temperatures higher than 374 °C generally provide single-phase behaviour and facilitate very fast oxidation reactions. These advantages led to the attempt to turn SCWO into a commercially available industrial process for sewage disposal especially in the case of hazardous waste. 

How must the Gibbs phase rule be modified to take account of the following cases (a) A multiphase system is placed between two charged parallel condenser plates (b) One or more of the components is absent from one or more of the phases present (c) Several distinct regions of the system are maintained at different pressures by means of semipermeable membranes Document your answers fully. 

A recent example is the optical fiber monolith reactor, reported by Lin and Valsaraj (208). They used a monolith for photocatalytic wastewater treatment with the channels of the monolith completely filled with flowing liquid. The monolith structure was used merely as the distributor of the optical fibers, but the benefits of monolith, such as low-pressure drop and excellent mass transfer characteristics for multiphase systems, were not fully exploited. 

Homsy and co-workers and Gibilaro, Foscolo, and co-workers have proposed neat methods for the experimental measurement of transition. The techniques of measurement of dynamic pressure and dynamic measurement of bed heights will prove to be extremely useful in understanding the hydrodynamics of multiphase systems. The measurements will also be useful for understanding other transport phenomena. 

It suffices to know all the parameters (pressure, temperature and amounts of the components) but one to have a multiphase system fully defined (Sillen 1967), and this likewise holds for al the organs, the solution phases (cell sap, blood or xylem liquid, etc.) and one or two gas phases referring to an organism. Since and as long as all the phases coexist, the number of degrees of freedom F in a multiphase system consisting of K components and P phases will be... 

Especially for multiphase systems flow visualization (Wen-Jei Yang, 1989 Merzkirch, 1987) can provide valuable initial information on the prevailing flow patterns and should at least always be considered as a first step. Of course, in applications that involve extreme conditions such as high temperature and/or pressure it is very difficult if not impossible to apply flow visualization and other techniques should be considered. Here the use of cold flow models which permit visual observation might be considered as an alternative as an important first step to obtain (qualitative) information on the flow regime and associated flow pattern. Of course, multiphase flows exist such as dense gas-solid flows that do not permit visual observation and in such cases the application of idealized flow geometries should be considered. A well-known example in this respect is the application of so-called 2D gas fluidized beds to study gas bubble behavior (Rowe, 1971). 

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