Chapter 4 - Flow of multi-phase mixtures in pipes

Abstract

This chapter focuses on the complex problem of the flow of multiphase systems in which the composition of the mixture may show spatial variation over the cross-section of the pipe or the channel. Furthermore, the two components may have different in-situ velocities as a result of which there is “slip” between the two phases and in-situ holdups, which are different from those in the feed or exit stream. Multiphase flow is encountered in many chemical and process engineering applications, and the behavior of the material is influenced by the properties of the components, such as their Newtonian or non-Newtonian characteristics, or the size, shape, concentration of particulates, the flowrate of the two components, and the geometry of the system. In general, the flow is so complex that theoretical treatments, which tend to apply to highly idealized situations, have proved to be of little practical utility. Consequently, design methods rely very much on the analysis of the behavior of such systems in practice. While the term “multiphase flows” embraces the complete spectrum of gas/liquid, liquid/liquid, gas/solid, liquid/solid gas/liquid/solid, and gas/liquid/liquid systems, it illustrates the role of non-Newtonian rheology of the liquid phase on the nature of the flow. This chapter emphasizes the effects of non-Newtonian rheology; it is useful in drawing analogies with simpler cases of Newtonian liquids, details of which are much more readily available.