When we “conserve energy,” do we aim at maximum or minimum mechanical work?
Why is it necessary for even the best electric power plants to dissipate and waste more
than 50% of the energy in their fuels? What is the maximum amount of useful
mechanical work we can get from an energy resource? How can we produce and
transport liquefied natural gas with the minimum amount of energy-resource consumption?
Exergy – the measure of useful mechanical work that may be extracted from
energy resources – offers answers to these and several other questions on energy
conversion and utilization.
In the pages of this book we analyze the energy conversion processes starting with
two important realizations: first, that the vast majority of energy conversion processes
take place in the terrestrial environment, which is the only naturally occurring reservoir
of heat, work, and mass; second, that all energy conversion processes occur because
there are materials, the energy resources, that exist not in thermodynamic equilibrium
with the environment. These two realizations and the laws of thermodynamics, lead us
to the concept of exergy – the key to the understanding of all energy conversion and
conservation processes.
Using the exergy concept, this book provides a new, simple, comprehensive, rigorous,
and holistic approach for the analysis of energy conversion and conservation
processes. Following a simple and comprehensive exposition of exergy and its relationship
to energy resources, the book offers several practical engineering cases and
examples on the application of exergy to energy conversion systems that utilize our
naturally occurring energy resources – fossil fuels, nuclear fuels, solar, wind, and
geothermal. Among the engineering systems that are analyzed are: steam and gas
electricity generation units; jet engines; nuclear reactors; heat exchangers; cogeneration;
geothermal power plants, including Organic Ranking Cycles (ORCs); biomass as a fuel;
photovoltaics; solar thermal systems; wind turbines; and fuel cells.
What are colloquially called energy conservation systems are examined under a new
perspective, the maximum work principle, which emanates from the laws of thermodynamics
and is intricately connected to the exergy concept. The exergetic analysis
reveals practical methods to reduce the power supplied to engineering systems and
provides benchmarks for the consumption of the least amount of resources in actual
processes. Examples and cases on the application of the exergy methodology include:
natural gas compression and transport; refrigeration; liquefaction; pasteurization; drying of foodstuff; water desalination; lighting; heat, ventilation and air-conditioning; transportation
with internal combustion engine vehicles, electric vehicles and fuel-cell
vehicles; energy storage; and petroleum refining.
Chapters 1–4 of this book follow the conventional exposition of exergy as a thermodynamic
concept and its implications for the operation of engineering systems. These
chapters offer a succinct exposition of the basic concepts and the laws of thermodynamics;
the thermodynamically rigorous development of the exergy concept and its consequences
for the several primary energy sources currently used by the human society;
analyses of several power-producing systems including those utilizing renewable
energy sources; analyses of power-consuming systems including the establishment of
benchmarks for the optimum operation of systems; and analyses of the engineering
systems used for transportation. A unique aspect of this book is the inclusion of three
chapters on nontraditional thermodynamics subjects of current interest:
1. Biological systems (Chapter 5), a chapter that includes an exergy analysis of the
human body as a thermodynamic system and explains in detail and with several
examples the exergetic processes of metabolism, thermic effects, the conversion
of nutrients to energy, and the production of mechanical power by the muscles.
2. The effects of energy resource utilization on the environment and the ecosystems,
including the concept of eco-exergy. Chapter 6 explores the connections and implications
of the exergy concept for a cleaner environment and sustainable development.
3. The mathematical optimization of engineering systems and processes, based on
the exergy concept. A very important part of Chapter 7 is the uncertainty
quantification of the optimization variables and the propagation of uncertainty
in the optimum solution.
The inclusion of many cases and solved examples in every chapter further explains
the application of exergy to dozens of significant engineering systems and processes.
Problems at the end of every chapter offer a challenge and an opportunity for students
and professionals to hone their analytical skills and appraise their ability to apply the
exergy methodology to a variety of practical engineering systems and processes.
A number of individuals have helped in the writing of this book. First among them
are my students in the courses on Thermal Science, Thermodynamics, Sustainable
Energy, and Advanced Thermodynamics, which I have taught in five universities during
the last 40 years. I have learned from them more than they have learned from me. I am
very thankful to my colleagues at these universities as well as to other colleagues
I regularly meet during conferences for many fruitful and animated discussions on
thermodynamics, energy utilization, and the environment. The arrangements of the WA
“Tex” Moncrief Chair of Engineering at TCU have afforded me the opportunity to
devote a significant fraction of my time to this book. The Cambridge University Press
staff in New York, Steven Elliott and Julia Ford, patiently answered all my inquiries and
gave me guidance. I am also very much indebted to my own family, not only for their
constant support, but also for lending a hand when this was needed. My wife, Laura,
and our three children, Emmanuel, Dimitri, and Eleni, are a constant source of inspiration
and were always ready to help. I owe to all my sincere gratitude.