Due to varied flow behavior, the demarcation of hydrodynamic flow regimes is an important task in the design and scale-up of bubble column reactors. This article reviews most hydrodynamic studies performed for flow regime identification in bubble columns. It begins with a brief introduction to various flow regimes. The second section examines experimental methods for measurement of flow regime transition. A few experimental studies are presented in detail, followed by the effect of operating and design conditions on flow regime transition. A table summarizes the reported experimental studies, along with their operating and design conditions and significant conclusions. The next section deals with the current state of transition prediction, and includes purely empirical correlations, semi-empirical models, linear stability theory, and Computational Fluid Dynamics (CFD) based studies.
In
multiphase flow reaction systems, in general, an extrapolation of
small diameter behavior to larger ones is always an important and
challenging task. The critical issue in such an extrapolation remains
to be mixing and hydrodynamic characteristics. It needs reliable similarity
criteria that would result in similar mixing and hydrodynamics and
hence transport and performance in two different scales. Numerous
experimental and computational studies have been performed to investigate
the flow behavior of bubble column reactors for a proper design and
scale-up. Experimental techniques vary from simple visual observation
to more advanced noninvasive diagnostic techniques. On computational
front the progress has been made from simple reactor models to fundamentally
based Computational Fluid Dynamics (CFD). Such studies ultimately
provide a knowledge that help in understanding the hydrodynamic and
mixing characteristics of these reactors and would aid in its scale-up.
Based on these studies, various methodologies have been proposed in
literature for scale-up and/or to maintain their hydrodynamic and
mixing similarity. This article attempts to review the current state
of reported dynamic similarity and scale-up methods of bubble column
reactors. It mostly covers the methods reported in open literature.
The scale-up practices in industry appear to be proprietary for obvious
reasons.
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