Opaque multiphase flows: experiments and modeling

This brief review deals with the characterization of multiphase flows needed in reaction engineering and describes the techniques and methods available to accomplish it. It emphasizes the fact that most multiphase systems of industrial interest (e.g. stirred tanks, slurry bubble columns, gas-solid or liquid-solid risers and fluidized beds, pneumatic transport reactors, etc.) operate in churn turbulent flow at large volume fraction of the dispersed phase and are opaque. This inevitably leads to the use of the Euler-Euler, interpenetrating fluid model in describing their fluid dynamics, which raises issues of closure for the interfacial momentum terms and turbulence. Hence, computational fluid dynamic (CFD) models based on the Euler-Euler approach with selected closures require experimental validation. Due to the non-transparency of the systems involved, non-conventional experimental techniques are required. The paper briefly describes two such techniques which have been successfully implemented at the Chemical Reaction Engineering Laboratory for characterization of opaque, multiphase flows. One is the gamma ray computed tomography (CT), the other is the computer automated radioactive particle tracking (CARPT). Their use in characterizing diverse systems such as liquid-solid risers and bubble columns is illustrated as well as the utility of CARPT-CT data in validation of the Euler-Euler CFD models. The goal is to enable the reader to grasp the advantages and limitations of the described experimental techniques and computational fluid dynamic models. (C) 2002 Elsevier Science Inc. All rights reserved.