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Mass Transfer Between Two Phases

The experimental determination of the film coefficients kL and kc is very difficult. When the equilibrium distribution between the two phases is linear, over-all coefficients, which are more easily determined by experiment, can be used. Over-all coefficients can be defined from the standpoint of either the liquid phase or gas phase. Each coefficient is based on a calculated over-all driving force Ac, defined as the difference between the bulk concentration of one phase (cL or cc) and the equilibrium concentration (cL or cc ) corresponding to the bulk concentration of the other phase. When the controlling resistance is in the liquid phase, the over-all mass transfer coefficient KLa is generally used  [Pg.83]

Cj = liquid concentration in equilibrium with the bulk gas concentration. [Pg.84]

This simplifies the calculation in that the concentration gradients in the film and the resulting concentrations at the interface (cu or cGj) need not be known. [Pg.84]


In conventional continuous-flow configurations [2,3], (bio)chemical reactions, separations based on mass transfer between two phases, and continuous detection occur at different places and hence sequentially. [Pg.49]

U. Influence of the Marangoni Effect on the Mass Transfer BETWEEN Two PHASES... [Pg.101]

In the case of mass transfer between two phases - for example, the absorption of a gas component into a liquid solvent, or the extraction of a liquid component by an immiscible solvent - we need to consider the overall as well as the individual phase coefficients of mass transfer. [Pg.73]

Many parameters affect the mass transfer between two phases. As we discussed above, the concentration gradient between the two phases is the driving force for the transfer and this, together with the over-all mass transfer coefficient, determines the mass transfer rate. The influence of process parameters (e. g. flow rates, energy input) and physical parameters (e. g. density, viscosity, surface tension) as well as reactor geometry are summed up in the mass transfer coefficient. The important parameters for Kta in stirred tank reactors are ... [Pg.88]

Normally mass transfer between two phases is modelled using a mass transfer coefficient (km). The flux (mol s-1 m. surf) of a component i is given by the formula... [Pg.34]

Table 1 is a compilation of the more common industrial separation operations based on inter-phase mass transfer between two phases, either created by an energy-separating agent or added as a mass-separating agent. A more comprehensive table is given by Seader and Henley.1 In the following, the operations listed in Table 1 will be outlined briefly. The first two methods, distillation and absorption, will be discussed in more detail later. [Pg.143]

N0 Molar flux for mass transfer between two phases, component i. stage/ Sec. 4.2.13. [Pg.204]

Net mass transfer between two phases can occur only when there is a driving force, such as a concentration difference, between the phases. When equilibrium conditions are attained, the driving force and, consequently, the net rate of mass transfer becomes zero. A state of equilibrium, therefore, represents a theoretical limit for mass-transfer operations. This theoretical limit is used extensively in mass-transfer calculations. [Pg.650]

Mass transfer, an important phenomenon in science and engineering, refers to the motion of molecules driven by some form of potential. In a majority of industrial applications, an activity or concentration gradient serves to drive the mass transfer between two phases across an interface. This is of particular importance in most separation processes and phase transfer catalyzed reactions. The flux equations are analogous to Ohm s law and the ratio of the chemical potential to the flux represents a resistance. Based on the stagnant-film model. Whitman and Lewis [25,26] first proposed the two-film theory, which stated that the overall resistance was the sum of the two individual resistances on the two sides. It was assumed in this theory that there was no resistance to transport at the actual interface, i.e., within the distance corresponding to molecular mean free paths in the two phases on either side of the interface. This argument was equivalent to assuming that two phases were in equilibrium at the actual points of contact at the interface. Two individual mass transfer coefficients (Ld and L(-n) and an overall mass transfer coefficient (k. ) could be defined by the steady-state flux equations ... [Pg.239]

Different approaches have been used to model mass transfer performance of reactors. They comprise two main parts the micromodel, describing the mass transfer between two phases, and the macromodel, describing the mixing pattern within the individual phase. The micromodels assume two types of interfacial behavior stagnant films or dynamic absorption in small elements at the contact surface. [Pg.285]

In Section 15.4. the engineering approach to mass transfer, the linear driving-force model introduced in Eq. fl-4T is explored in more detail, particularly for mass transfer between two phases. This third approach is applicable to any situation because correlations for the mass-transfer coefficients can be developed on the basis of dimensional analysis, and the constants in the correlations can be fit to experimental mass transfer data. In Section 15.5. a few correlations for the mass-transfer coefficient based on Fickian diffusivity are presented. Additional correlations are presented when needed in Chapters 16 to IS. If you have had a chemical engineering mass-transfer course. Sections 15.1 to 15.5 will contain familiar material. If you have not had a mass-transfer course. Sections 15.1 to 15.5 are the minimum material required to proceed to Chapter 16. [Pg.603]

The purpose of an MC is to induce mass transfer between two phases without dispersing one phase into the other (Gabelman and Hwang, 1999). Depending on the specific application, the liquid phase can be aqueous or organic, whereas the membrane can be hydrophobic or hydrophilic (Kosaraju and Sirkar, 2007). [Pg.56]

Modelling the three-phase distillation based on nonequilibrium contains some specific features compared to the normal two-phase distillation or the equilibrium model. In the equilibrium model of three-phase distillation only two of the three equilibrium equations are independent. In the nonequilibrium model every phase is balanced separately. Therefore all three equilibrium equations are used in the model for the interfaces. A further characteristic is, although a three-phase problem is existing, that only the mass transfer between two phases has to be calculated at every interfacial area. Additionally, the convective and conductive part of the heat transfer have to be taken into consideration, as the own investigations presented. Often the conductive part is neglected due to the small difference of the temperatures of the phase interface and the bulk phase. For the modelling of the three-phase distillation this simplification is inadmissible. [Pg.882]

For many chemical reactions we will also have to consider the effects of physical transport phenomena. This is the case when mixing rates are relevant, or when we have heterogeneous reactions (with two or more phases). For such situations it is better to skip Chapter 3 and move on to Chapter 4, where the problems of physical contacting of reactants (such as mixing and mass transfer between two phases) are discussed, as well as interphase heat transfer. For many chemical reactions the way of contacting the reactants will determine the reactor configuration, or indeed the type of reactor we will have to use. [Pg.22]

One lumps the resistances into a single empirical overall resistance. This is the empiricism used in Illustration 1.6. It will be seen time and again throughout the text whenever mass transfer between two phases is expressed in terms of a single overall mass transfer coefficient K. ... [Pg.19]


See other pages where Mass Transfer Between Two Phases is mentioned: [Pg.53]    [Pg.82]    [Pg.83]    [Pg.713]    [Pg.915]    [Pg.332]    [Pg.152]    [Pg.284]    [Pg.83]   


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