Multiphase Reacting Flows: Modelling and Simulation

Abstract

PREFACEThis book entitled ''Multiphase reacting flows: modelling and simulation'' contains the lecture notes of the CISM (International Centre for Mechanical Sciences) course held in Udine, Italy, on July 3-7, 2006, and it describes various modelling approaches for dealing with polydisperse multiphase reacting flows. A multiphase reacting system is characterized by the presence of multiple phases and in this book we focus on disperse multiphase systems, where one phase can be considered as a continuum, whereas the additional phases are dispersed in the continuous one. In other words, in this book we deal with multiphase systems constituted by particles, droplets or bubbles (i.e., solid particles suspended in a continuous liquid phase, liquid droplets in a gaseous phase, or gas bubbles in liquid.)The other important characteristic elements of the systems discussed in this book are the presence of one or more chemical reactions and the turbulent nature of the flow. The chemical reactions usually involve all the phases present in the system and might be responsible for the formation or disappearance of the disperse and/or continuous phases. The evolution of the different phases is not only governed by chemical reactions, but also by other fluid-dynamical interactions between the continuous and the disperse phases, and by interactions among elements of the disperse phases, such as coalescence, aggregation, agglomeration and break-up.All these phenomena are closely linked together resulting in what is known as phase coupling. When the continuous phase influences the disperse phase, we usually refer to one-phase coupling, whereas when the continuous phase influences the disperse phase and vice versa, we talk about two-way coupling. When also interactions between elements of the disperse phases are important, we must describe the turbulent system in terms of so-called four-way coupling.The evolution of the disperse phase and its interactions with the continuous phase can be mathematically described at the mesoscopic level by the generalized population balance equation, also known as the Boltzmann-Williams equation. This book contains a detailed derivation of this equation, and presents several numerical approaches to solve it. In particular, the derivation ofEulerian classes methods (or multi-fluid approaches) is presented both for the solution of laminar and turbulent multiphase systems. Moreover the use of alternative Eulerian methods, such as moment methods coupled with quadrature approximations, is also presented. The book deals also with the use ofLagrangian approaches such as direct particle tracking methods and Lattice-Boltzmann methods. Moreover, reference to the general modelling framework for turbulent flows (i.e. Reynolds-Average Navier Stokes approach, Large-Eddy Simulation and Direct Numerical Simulation) is made, as well as to computational details and numerical issues.In the first chapter, Fox provides an overview of the basic formulation and conceptual ideas needed for modelling polydisperse multiphase s...

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