Page 5 - Advanced Thermodynamics for Engineers, Second Edition

PREFACE – FIRST EDITION xiii

constant stagnation, or even static, temperature valid for flow of a perfect gas through a throttle, but
never for steam? An understanding of these effects can be obtained by examination of the more com-
plex equations of state. This immediately enables methods of gas liquefaction to be introduced.
An important area of engineering thermodynamics is the combustion of hydrocarbon fuels. These
have formed the driving force for the improvement of living standards which has been seen over the
last century, but they are presumably finite, and are producing levels of pollution that are a constant
challenge to engineers. At present, there is the threat of global warming due to the build-up of carbon
dioxide in the atmosphere: this requires more efficient engines to be produced, or for the
carbon/hydrogen ratio in fuels to be reduced. Both of these are major challenges, and while California
can legislate for the zero emissions vehicle (ZEV) this might not be a worldwide solution. It is said that
the ZEV is an electric car running in Los Angeles on power produced in Arizona! – obviously a case of
exporting pollution rather than reducing it. The real challenge is not what is happening in the West,
although the energy consumption of the United States is prodigious, but how can the aspirations of
the East be met. The combustion technologies developed today will be necessary to enable the newly
industrialised countries (NICs) to approach the level of energy consumption which we enjoy. The sec-
tion on combustion goes further than many general textbooks in an attempt to show the underlying
general principles which affect combustion, and it introduces the interaction between thermodynamics
and fluid mechanics which is so important to achieving clean and efficient combustion. The final chap-
ter introduces the thermodynamic principles of fuel cells, which enable the direct conversion of the
Gibbs energy in the fuel to electrical power. Obviously the fuel cell could be a major contributor to
the production of ‘clean’ energy and is a goal for which it is worth aiming.
Finally, a section is included on irreversible thermodynamics. This is there partly as an intellectual
challenge to the reader, but also because it introduces concepts that might gain more importance in
assessing the performance of advanced forms of energy conversion. For example, although the fuel
cell is basically a device for converting the Gibbs free energy of the reactants into electrical energy,
is its efficiency compromised by the thermodynamics of the steady state that are taking place in the
cell? Also, will photovoltaic devices be limited by phenomena considered by irreversible
thermodynamics?
I have taken the generous advice of Dr Joe Lee, a colleague in the Department of Chemistry,
UMIST, and modified some of the wording of the original text to bring it in line with more modern
chemical phraseology. I have replaced the titles Gibbs free energy and Helmholtz free energy by
Gibbs and Helmholtz energy respectively: this should not cause any problems and is more logical
than including the word ‘free’. I have bowed, with some reservations, to using the internationally
agreed spelling sulfur, which again should not cause problems. Perhaps the most difficult concept
for engineers will be the replacement of the terms ‘mol’ and ‘kmol’ by the term ‘amount of sub-
stance’. This has been common practice in chemistry for many years, and separates the general
concept of a quantity of matter from the units of that quantity. For example, it is common to talk
of a mass of substance without defining whether it is in grams, kilograms, pounds, or whatever sys-
tem of units is appropriate. The use of the phrase ‘amount of substance’ has the same generalising
effect when dealing with quantities based on molecular equivalences. The term mol will still be
retained as the adjective and hence molal enthalpy is the enthalpy per unit amount of substance
in the appropriate units (e.g. kJ/mol, kJ/kmol, Btu/lb-mol, etc.).
The author would like to acknowledge all those who have helped and encouraged the writing of this
text. First, I would like to acknowledge the influence of all those who attempted to teach me