Chapter 4 - Flow of Multi-phase Mixtures in Pipes

Abstract

This chapter focuses on the flow of multi-phase systems in which the composition of the mixture shows spatial variation over the cross-section of the pipe or channel. Multi-phase 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, and concentration of particulates, the flow rate of the two components, and the geometry of the system. The role of non-Newtonian rheology of the liquid phase on the nature of the flow and the simultaneous cocurrent flow of a gas and a non-Newtonian liquid and the transport of coarse solids in non-Newtonian liquids are also discussed. The overall hydrodynamic behavior, with particular reference to the flow patterns, average holdup of the individual phases, and the frictional pressure gradient are also discussed. The two phase flow of gas–liquid mixtures exhibits many common features, and their application in the chemical, food, and processing industries ranges from the flow of mixtures of crude oil and gas from oil well heads to that of vapor–liquid mixtures in boilers and evaporators. The three particular aspects of gas–liquid flow, which are of practical importance, include flow patterns or regimes, holdup, and frictional pressure gradient. An important application of solid–liquid flows in pipes is in the sterilizing of foods by heat treatment to enable them to be transported and stored safely. Despite the advantages of continuous processing of foodstuffs, the inadequate understanding of solid–liquid flows even in straight tubes has led to the unavailability of definitive information on sound process design and performance of the equipment used in the thermal treatment of foodstuffs.