PHASE DISTRIBUTION PHENOMENA AND WALL EFFECTS IN BUBBLY TWO-PHASE FLOWS

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Abstract
This paper summarizes the state-of-the-art in the understanding and modelling of phase distribution in bubbly flows, which is of fundamental importance for many industrial applications. The available experimental results are first discussed. The capability of the two-fluid model to predict two-phase bubbly flows in different geometries is examined. In particular, results obtained independently at Rensselaer Polytechnic Institute and Ecole Centrale de Lyon, using different numerical codes but similar closure laws are presented. The closure hypotheses adopted are based on analytical and experimental information on the dynamics of a single bubble, and on the assumption of linear superposition of shear-induced and bubble-induced turbulence. The test cases chosen here include the flow of a bubbly mixture in a vertical pipe, in a triangular duct, over a flat plate and through a sudden expansion. It is found that most of the experimental data can be reproduced with reasonable accuracy using a multidimensional two-fluid model. However, in spite of the success of such models, some important physical mechanisms are still not well understood, and are discussed in the last section.

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