Basic Principles and Derivation of Multi-Fluid Models

4 Basic Principles and Derivation of Multi-Fluid Models 

The variety of applications clearly demonstrate that the El method has the potential of resolving many problem aspects in reactor technology. However, it is noted that the El concept is not primarily intended for multicomponent reactive flow analyzes, but still interfacial heat- and mass transfer fluxes and variations in the surface tension have been considered [224]. Nevertheless, in most cases the bulk phases are considered incompressible. 

An introductory summary of the basic ideas underlying the conventional single phase modeling concepts is given to emphasize the inherent limitations reflected by the different continuum model formulations [173]. It is generally 

In general, the differential description is useful for processes where there is a wide separation of scales between the smallest macroscopic scales of interest and the microscopic scales associated with the internal structure of the fluid. If the micro-scales were always of molecular magnitude then questions of scale separation would seldom arise. But, in many of the models employed for engineering purposes, the characteristic scales of the internal structure being described are themselves macroscopic in nature. In such situations the desired separation between the calculated and modeled scales is much less clear cut, and one must be careful not to attribute quantitative significance to any predicted solution features with scales comparable to the internal micro-scale. When a continuum description is pushed to far, i.e. applied on scales too small, one can only hope that such inaccuracies are not catastrophic in nature. 

Based on the considerations presented above, it was found necessary to carry out a critical evaluation of the various model formulations available aiming to achieve a proper description of the multiphase flow regimes occurring in chemical reactors. 

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Basic Principles and Derivation of Multi-Fluid Models [231], Sect. 12.7) ... 

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