Model mixed-flow

In practice, it is often possible with stirred-tank reactors to come close to the idealized mixed-flow model, providing the fluid phase is not too viscous. For homogenous reactions, such reactors should be avoided for some types of parallel reaction systems (see Figure 5.6) and for all systems in which byproduct formation is via series reactions. 

Now, combining relations (3.66) and (3.61), we obtain the expression for the time distribution function of the perfect mixing flow model ... 

The first hydrodynamic model proposed for fluid-bed reactor design (see Davidson and Harrison, 1963) is simple but is the basis of most models developed since. A sketch of the model appears in Figure CS5.1a. Three main groups are involved U for fluidization, for reaction, and Y for mass transfer. Equations can be derived both for plug flow and mixed flow of emulsion gas. The simpler mixed-flow model is usually adequate (with predictions close to those of the plug-flow model) and is given by... 

For several different models of barrier structure, the constants a and b in Eq. (14.7) can be related to dimensions of holes in the barrier. For straight circular holes of uniform radius r occupying e fraction of a barrier of uniform thickness /, Present and de Bethune assign to the constant a the value it would have for molecular flow and to b the value it would have for viscous flow, so that for this mixed flow model. 

The limiting value of 7 as the pressures p" and p approach zero has simple physical significance. In the mixed flow model. 

Effect of nonseparating flow. The effect of nonseparating viscous flow on the barrier separation efficiency depends on the detailed structure of the barrier. Because the theoretical derivation of this effect for the viscous leak model can be worked out simply and completely, this model will be dealt with first. Then results for the mixed flow model derived by Present and de Bethune [P3] will be summarized and both models will be compared with empirical correlations of separation performance suggested by experimental investigators of barrier performance. 

Comparison of Eqs. (14.52) and (14.12) shows that for this mixed flow model,... 

Comparison with Eq. (14.42) shows that evaluated from the slope factor with the mixed flow model is only 9.17 percent the value of Pc evaluated from Are slope factor with the viscous leak model. Equation (14.56) comes closer to representing the characteristics of actual barriers. 

Aspen Plus allows you to have sections with equilibrium calculations as long as at least one section is done rate-based). Clicking on this box activates the menus below. Use the default values for Calculation Parameters. The Mixed flow model (called Mixed-Mixed in the report) assumes that vapor and liquid are well mixed so that the bulk properties are the same as the exit properties. This model is appropriate for trays (not packing) and was used in Section 16.6 to derive Eq. (16-77) for binary distillation. The effect of flow model will be looked at in item 10. Select film for both Liquid and Vapor in the Film Resistance section, and select No for both nonideality corrections. 

Mixing effects may be found experimentally, by measuring the residence time distribution of the phases. Mixing flow models are used to convert the results into half empirical correlations (see, for example, [0.4]) ... 

The idealized flow models and axial dispersion model are used extensively to predict the performance of three-phase slurry reactors. For example, mixed flow model and axial dispersion models are used to predict the reactant conversion and product distribution for conversion of synthesis gas to liquid fuels using FT synthesis [52-57], methanol synthesis... 

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