Dispersed flows with droplets and particles abound in nature from clouds, mist and fogs to the long-range transport of fine dust released in desert storms or in volcanic eruptions. They control the weather and influence the climate. They play key roles in many industrial energy processes – from spray drying, pneumatic conveying and fluidized beds, to coal gasification and mixing and combustion processes. They can have a profound effect on our health and quality of life, e.g. the inhalation of very fine air-borne particulate (PM10s) damages respiratory functions, and lead to increased cardio- pulmonary mortality rates and allergic disorders. Understanding the behavior of these flows, through modeling and experiment, is therefore important in our control of the environment, improving our health, and in the design and improvement of industrial processes.
There are essentially two ways of modeling dispersed flows, the Euler-Lagrange (E-L) approach where individual particle are tracked through an Eulerian flow field or an entirely Eulerian (E-E) approach where both the dispersed and continuous phases are described by a set of continuum equations that represent the conservation of mass moment and energy within an elemental volume of the mixture. This e-Book is about the E-L approach and exploits the recent advances in modeling complex flows in which LES has been used to describe the underlying large scale features of the continuous phase and stochastic equations based on the Generalized Langevin equations for the sub-filtered (SGS) motion of the fluid seen by the particle. The main advantage of this approach is that one can deal very successfully with particle dispersion and transport in complex industrial flows with complex geometries and boundary conditions, noting also that much success has been achieved using this approach in more generic flows like deposition of particles in a turbulent boundary. The author has been successful in presenting a thoroughly comprehensible and readable text that engineering researchers can use as a source of reference as well as for fundamental understanding. In order to achieve the dual objectives of understanding and simplicity, lengthy mathematical analysis has been avoided and emphasis has been placed on detailed applications. In view of the recent advances in LES and sub grid scale modeling and the application of stochastic methods, a e-Book of this nature is very timely and one that I would thoroughly recommend to all young researchers embarking on a study of industrial dispersed flows.
Michael W. Reeks
Professor of Multiphase Flows
This e-Book presents an introduction to the numerical simulation of turbulent dilute two-phase flows using the very promising mesoscale approach namely; Large Eddy simulation (LES). The text details the use of the stochastic diffusion process in conjunction with LES approach to simulate industrial applications dealing with very small, turbulence-responsive particles convected by high-Reynolds, non-homogeneous and anisotropic flows. This novel approach has been proven to increase the accuracy of two-phase LES while keeping the computing cost at an affordable level.
The goal is to present a text that engineering researchers can read and understand and from which they can attack a variety of industrial problems. It serves only as a preliminary exposure to the readers who are interested in developing the subject at more advanced level. In order to achieve the dual objectives of understanding and simplicity, lengthy mathematical analysis was avoided and emphasis was placed on detailed applications.
The material included in this book is organized to facilitate the understanding of the numerical approach in the context of dilute gas-particle systems. The context in which the stochastic LES-particle is developed is explained in Chapter 1. In Chapters 2 and 3, the most important aspects of LES of single- and two-phase turbulent flows are covered, respectively. A separate chapter (Chapter 4) details the stochastic model developed to track small inertial particles transported by the LES-predicted turbulent flows. For that purpose, the simplest mathematical approach is used, consistent with technical vigor. In the subsequent three chapters (Chapters 5, 6 and 7), three important flow applications are presented in almost every details. The aim is to show the promising potential which the stochastic LES-particle approach has in tackling dispersed industrial flows. Also, to use the stochastic LES-particle approach to explain many of the experimental findings on inertial particle transport by turbulent flows.
The e-Book is written with the necessary dose of both the physics and the numerics needed to quickly understand such a topic, and use it to tackle important industrial applications. It is brief and easy, yet to-the-point, description of an important topic written in a style and language often preferred by young graduate students and young researchers. It may be used in several ways at various stages of particulate flow modeling. It may help postgraduates and researchers interested in applying tractable yet powerful numerical tools to solve problems involving multiphase flows. Researchers in chemical, mechanical, petroleum and environmental engineering are the primary targets. Also, R&D people working for industries, such as the chemical and petrochemical industries should find this book very helpful in their continuing endeavor to adopt shorter design cycles through increased reliance on numerical prediction. Conventional models for turbulent dispersed flows do not appear capable of meeting the growing needs of these industries in this regard and the physical testing is prohibitive.
This e-Book is essentially the outcome of my last five years of association with this subject. I have received great deal of help from numerous persons over these years in formulating and revising my views on this numerical approach for particulate turbulent flows. I am particularly indebted to my teacher and mentor, Professor D. Laurence, who has been one of the leading practitioners of large eddy simulation technique for three decades at both Electricite de France and the University of Manchester. There are no adequate words to express his contributions to my understanding of the subject. I was fortunate to have an opportunity to work with Professor J.J. Riley at University of Washington-Seattle. Without his support and critics, it would not have been possible to develop the stochastic model. I would like to acknowledge the support provided by Emeritus Professor M.W. Reeks of University of Newcastle, Emeritus Professor D.E. Stock of Washington State University, and Professor Krishnanswamy Nandakumar of Louisiana State University. I would like to thank Dr. Alexander Douce of Electricite de France, Dr. Andy Lowe of the University of Manchester, and Dr. Chunliang Wu of Guangdong Ocean University, China for sharing knowledge about the subject.
I am grateful to one of my brilliant students, Mohamed Abu-Taqiya, at the Petroleum Institute- Abu Dhabi who helped me collect the required information, edit and proofread the book. Any remaining errors or shortcomings are the responsibility of the author. Finally, I wish to thank my wife, Karima, for her patience, understanding and enthusiastic support, which carried me through this long and arduous writing process.
Abdallah Sofiane Berrouk
Chemical Engineering Department
Abu Dhabi, January 2011
List of Contributors
Abdallah S. Berrouk
Chemical Engineering Department
United Arab Emirates