First published 2019 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.
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The rights of Abdelhanine Benallou to be identified as the author of this work have been asserted by him in accordance with the Copyright, Designs and Patents Act 1988.
Library of Congress Control Number: 2019943764
British Library Cataloguing-in-Publication Data
A CIP record for this book is available from the British Library
ISBN 978-1-78630-285-4
Preface
“A river cuts through rock, not because of its power, but because of its persistence”
Confucius (551–479 BC)
For several years, I have cherished the wish of devoting enough time to the writing of a series of books on energy engineering. The reason is simple: for having practiced for years teaching as well as consulting in different areas ranging from energy planning to rational use of energy and renewable energies, I have always noted the lack of formal documentation in these fields to constitute a complete and coherent source of reference, both as a tool for teaching to be used by engineering professors and as a source of information summarizing, for engineering students and practicing engineers, the basic principles and the founding mechanisms of energy and mass transfers leading to calculation methods and design techniques. But between the teaching and research tasks (first as a teaching assistant at the University of California and later as a professor at the École des mines in Rabat, Morocco) and the consulting and management endeavors conducted in the private and in the public sectors, this wish remained for more than twenty years in my long list of priorities, without having the possibility to make its way up to the top. Only providence was able to unleash the constraints and provide enough time to achieve a lifetime objective.
This led to a series consisting of nine volumes:
– Volume 1: Energy and Mass Transfers;
– Volume 2: Energy Transfers by Conduction;
– Volume 3: Energy Transfers by Convection;
– Volume 4: Energy Transfers by Radiation;
– Volume 5: Mass Transfers and Physical Data Estimation;
– Volume 6: Design and Calculation of Heat Exchangers;
– Volume 7: Solar Thermal Engineering;
– Volume 8: Solar Photovoltaic Energy Engineering;
– Volume 9: Rational Energy Use Engineering.
The present book is the fifth volume of this series. It concerns the study of mass transfer from one system to another or between different parts of the same system. This volume also features a substantial section on physical data estimation, in view of the importance of the availability of information on physical properties for the completion of calculations.
The usefulness of this book is clear considering that the subject of mass transfer has always been somewhat neglected in academic scientific literature. Indeed, there are very few textbooks dedicated to this subject.
The objective is thus to provide students with the founding principles and basic data enabling an understanding of the determinants of this transfer, which govern industrial equipment design and sizing equations.
Particular importance has been attached to the search for physical data, given that data availability is often one of the factors that can impede the realization of design calculations.
A series of exercises is presented at the end of this document, aimed at helping students to implement the calculation techniques specific to mass transfer as rapidly as possible. These exercises are designed to closely correspond to real-life situations occurring in industrial practice or everyday life.
Abdelhanine BENALLOU June 2019
Introduction
As we saw in Volume 1 of this series, most industrial manufacturing processes involve the elaboration of products using, in one stage or another, mass transfer. Indeed, the making of a desired end product is actually the outcome of a certain number of handling operations or stages in which raw materials are mixed and sometimes react to form a new mixture from which the desired product would need to be extracted.
The purpose of this volume is to examine the way mass transfer occurs and to present the laws which govern it, the ultimate objective being to establish design equations which enable calculations of the exchanged mass fluxes.
It should, however, be emphasized that for all of the calculations required for the quantification of transferred matter fluxes, access to reliable physicochemical data will be necessary. Indeed, the availability of physical data, such as viscosity or diffusion coefficients, is essential in order to be able to perform the calculations.
It is for this reason, and in order to facilitate access to such information, that a collection of physical data is presented in Appendix 1. Yet, it has to be acknowledged that no matter the extent of the data collection effort made, it would realistically never be possible to get a hold on all the properties of all the chemical compounds and materials. For this reason, data estimation tools are needed to enable the engineer to determine the missing physical data which could be required in a given situation. Chapter 1 of this book is dedicated to presenting data estimation methods. It groups together the correlations that can be used to calculate the physicochemical properties of materials from basic data with a certain degree of accuracy.
Subsequently, Chapter 2 of this book is dedicated to presenting parameters used in different situations where mass transfer occurs, including transfers in resting mixtures as well as matter exchanged in situations where the fluids considered are in motion. The characterization of a diffusion velocity, for example, becomes linked to the type of coordinates system (fixed or mobile) in which it will be expressed. The same applies for transfer fluxes.
These fluxes are expressed using Fick’s first law (see Chapter 3), similarly to the way in which Fournier’s law expresses the thermal flux exchanged in conduction (see Volumes 1 and 2). Fick’s law makes it possible to understand mass transfer at the microscopic level. It states that the flux of matter transferred is proportional to the driving force expressed by the concentration gradient.
But for the analysis of transfers in real systems, the development of macroscopic balances is required, enabling deduction of the fluxes exchanged. These balances are established in Chapter 4. They enable continuity equations to be developed for macroscopic systems with or without chemical reactions.
Application of these principles is presented in the form of exercises, with solutions, in Chapter 5.
