Interfacial overall effectiveness factor

The approximate overall effectiveness of Eq. 7.24 above can be used for reactor design for first-order reactions. For nonlinear kinetics, however, it is difficult to obtain an analytical expression for the overall effectiveness factor that is accurate for partially wetted pellets. Even when a relatively accurate effectiveness factor is available, the presence of different bulk and interfacial concentrations in both phases reduces the utility of the overall effectiveness factor except for limiting cases. Therefore, an internal effectiveness factor applicable to both wetted and nonwetted parts of the pellet is used here instead. For the low liquid velocities being considered, only dispersion in the liquid phase need be considered, and the gas phase may be treated as though it were in plug-flow (Levee and Smith 1976). 

A controls the overall rate of conversion, equation 3.81 could be used directly as the rate equation for design purposes. If, however, external mass transfer were important the partial pressures in equation 3.81 would be values at the interface and an equation (such as equation 3.66) for each component would be required to express interfacial partial pressures in terms of bulk partial pressures. If internal diffusion were also important, the overall rate equation would be multiplied by an effectiveness factor either estimated experimentally, or alternatively obtained by theoretical considerations similar to those discussed earlier. 

From the simulated results of foregoing sections, the interfacial effect is influenced by many factors, such as Marangoni convection, Rayleigh convection, heat transfer, interface deformation, physical properties of the process, and others. Each factor may be positive or negative the overall effect depends on their coupling result. For the flowing system, it is also in connection with the behaviors of fluid dynamics. 

Abstract Multicomponent materials based on synthetic polymers were designed and used in a wide variety of common and hi-tech applications, including the outdoor applications as well. Therefore, their response to the UV radiation and complex weathering conditions (temperature, seasonal or freeze—thaw cycles, humidity, pH, pollutants, ozone, microorganisms) is a matter of utmost importance in terms of operational reliability and lifetime, protection of the environment and health safety. This chapter offers an overview of this subject and a critical assessment of more particular topics related to this issue. Thus, various types of multicomponent systems based on thermoplastic and thermosetting polymer matrices were subjected to natural and/or simulated UV radiation and/or weathering conditions. Their behavior was evaluated in correlation with their complex formulation and taking into consideration that the overall effect is a sum of the individual responses and interactions between components. The nature and type of the matrix, the nature, type and size distribution of the filler, the formation of the interphase and its characteristics, the interfacial adhesion and specific interfacial interactions, they all were considered as factors that influenced the materials behavior, and, at the same time, were used as classification criteria for this review. 

One cannot quantitatively predict the effect of the various interfacial phenomena thus, these phenomena will not be covered in detail here. The following literature gives a good general review of the effects of interfacial phenomena on mass transfer Goodridge and Robb, Ind. Eng. Chem. Fund., 4, 49 (1965) Calderbank, Chem. Eng. (London), CE 205 (1967) Gal-Or et al., Ind. Eng. Chem., 61(2), 22 (1969) Kintner, Adv. Chem. Eng., 4 (1963) Resnick and Gal-Or, op. cit., p. 295 Valentin, loc. cit. and Elenkov, loc. cit., and Ind. Eng. Chem. Ann. Rev. Mass Transfer, 60(1), 67 (1968) 60(12), 53 (1968) 62(2), 41 (1970). In the following outhne, the effects of the various interfacial phenomena on the factors that influence overall mass transfer are given. Possible effects of interfacial phenomena are tabulated below ... 

Increased levels of agitation have been found to be a major factor in obtaining improved quality alkylates (1,3). Agitation clearly has an important effect on the physical steps of the overall process. The interfacial surface is one such variable that would be increased by increased agitation. Careful consideration needs to be given in any proposed mechanism as to the role of agitation. 

Reactants migrate between phases in order to react from gas phase to liquid, from fluid to solid, and between liquids when the reaction occurs in both phases. One of the liquids usually is aqueous. Resistance to mass transfer may have a strong effect on the overall rate of reaction. A principal factor is the interfacial area. Its magnitude is enhanced by agitation, spraying, sparging, use of trays or packing, and by size reduction or increase of the porosity of solids. These are the same operations that are used to effect physical mass transfer between... 

The effect of a dynamic interfacial tension will be to increase the probability of a moving oil blob being trapped. The overall kinetics of blob entrapment and mobilization which depend on the dynamics of interfacial tension variation will determine whether or not the blobs will aggregate this will be a key factor in formation and stabilization of an oil bank. In addition, any interfacial rheological resistance will reduce the probability of mobilization, and of drop coalescence during oil bank formation. The quantitative assessment of interfacial dynamic properties is therefore of major importance in the development and optimization of chemical FOR systems. 

Effective medium theory (EMT) is commonly used to describe the microstructure-property relationships in heterogeneous materials and predict the effective physical properties. It has recently been revised to predict the thermal conduction of nanocomposites. For nanocomposites with nanopartides on the order of or smaller than the phonon mean free path, the interface density of nanopartides is a primary factor in determining the thermal conductivity. In graphite nanosheet polymer composites, the interfacial thermal resistance still plays a role in the overall thermal transport. However, the thermal conductivity depends strongly on the aspect ratio and on the orientation of graphite nanosheets. 

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