Page 5 - Advanced thermodynamics for engineers

xii PREFACE – FIRST EDITION

both of these approaches enable thermodynamics to be developed in a logical manner, and limit the
reliance on cyclic processes, their understanding benefits from years of experience – the one thing stu-
dents are lacking. I have structured this book on the conventional method of developing the subject.
The other dilemma in developing an advanced level text is whether to introduce a significant amount
of statistical thermodynamics; since this subject is related to the particulate nature of matter, and most
engineers deal with systems far from regions where molecular motion dominates the processes, the
majority of the book is based on equilibrium thermodynamics; which concentrates on the macroscopic
nature of systems. A few examples of statistical thermodynamics are introduced to demonstrate certain
forms of behaviour, but a full understanding of the subject is not a requirement of the text.
The book contains XX chapters and while this might seem an excessive number, these are of a size
where they can be readily incorporated into a degree course with a modular structure. Many such
courses will be based on 2 h lecturing per week, and this means that most of the chapters can be pre-
sented in a single week. Worked examples are included in most of the chapters to illustrate the con-
cepts being propounded, and the chapters are followed by exercises. Some of these have been
developed from texts which are now not available (e.g. Benson, Haywood) and others are based on
examination questions. Solutions are provided for all the questions. The properties of gases have
been derived from polynomial coefficients published by Benson: All the parameters quoted have
been evaluated by the author using these coefficients, and equations published in the text: this means
that all the values are self-consistent, which is not the case in all texts. Some of the combustion ques-
tions have been solved using computer programs developed at UMIST, and these are all based on these
gas property polynomials. If the reader uses other data, e.g. JANAF tables, the solutions obtained
might differ slightly from those quoted.
Engineering thermodynamics is basically equilibrium thermodynamics although for the first two
years of the conventional undergraduate course these words are used but not often defined. Much of
the thermodynamics done in the early years of a course also relies heavily on reversibility, without
explicit consideration of the effects of irreversibility. Yet, if the performance of thermodynamic de-
vices is to be improved, it is the irreversibility which must be tackled. This book introduces the effects
of irreversibility through considerations of availability (exergy), and the concept of the endoreversible
engine. The thermal efficiency is related to that of an ideal cycle by the rational efficiency – to demon-
strate how closely the performance of an engine approaches that of a reversible one. It is also shown
that the Carnot efficiency is a very artificial yardstick against which to compare real engines: the in-
ternal and external reversibilities imposed by the cycle mean that it produces zero power at the
maximum achievable efficiency. The approach by Curzon and Ahlborn to define the efficiency of
an endoreversible engine producing maximum power output is introduced: this shows the effect of
external irreversibility. This analysis also introduces the concept of entropy generation in a manner
readily understandable by the engineer; this concept is the cornerstone of the theories of irreversible
thermodynamics which are at the end of the text.
Whilst the laws of thermodynamics can be developed in isolation from consideration of the prop-
erty relationships of the system under consideration, it is these relationships which enable the equa-
tions to be closed. Most undergraduate texts are based on the evaluation of the fluid properties from
the simple perfect gas law, or from tables and charts. While this approach enables typical engineering
problems to be solved, it does not give much insight into some of the phenomena which can happen
under certain circumstances. For example, is the specific heat at constant volume a function of tem-
perature alone for gases in certain regions of the state diagram? Also, why is the assumption of