Preface

Science, like writing, technology, and the rule of law, is an evolutionary add-on that empowers humanity, from one book to the next.┼ Thermodynamics is no exception. Its contemporary evolution is in full view in the four editions of this book. What in the first edition began as a unification of thermodynamics with heat transfer, fluid mechanics, and thermal design has become thermodynamics endowed with two muscular chapters, entropy generation minimization and the constructal law of evolution as physics (bio, nonbio, geo, socio, techno), Fig. 1.

Figure 1 The evolution and spreading of thermodynamics during the past two centuries, as a continuation of Fig. 1 in the Preface to the second edition of this book.

The constructal law accounts for the human urge to innovate, invent, and create contrivances, which include science and new methods to invent even better and faster. Science is about us, after all. This new edition draws attention to this truth. The growth of the constructal law field, which is documented in this new edition, is an illustration of the much broader phenomenon of how and why science evolves and improves. Science is an evolutionary design in which what we know-what is true, what works-becomes simpler, more accessible, and easier to transmit in order to facilitate human movement, which is life and sustainability.

The constructal law is a new law of physics that broadens significantly the reach of thermodynamics. The merger of mechanics with caloric theory into thermodynamics in 1851 was not the end of this morphing by simplification and replacement. The caloric line continued to this day as thermometry, calorimetry, and heat transfer. Although mechanics and caloric theory were incorporated in thermodynamics, heat transfer developed into a self-standing discipline, with major impact on applied mathematics, fluid mechanics, and aerodynamics. Still, its proper place is in thermodynamics, along with all the other caloric teachings.

The merger of heat transfer with thermodynamics was predicted in 1982 in the preface to my book Entropy Generation through Heat and Fluid Flow, and the prediction came true in the two decades that followed. Heat transfer journals became journals of "thermal sciences" (which means heat transfer + thermodynamics), and in many leading universities the heat transfer and thermodynamics courses were combined into a single course on thermal sciences or thermal engineering.

Thermal sciences expanded in new directions, most vigorously now because of the constructal law, which does what a law of physics does: It unifies science (physics, biology, engineering, social sciences). Constructal thermodynamics places the concepts of life, organization, and evolution in physics. It constitutes a wide-open door to new advances, especially in areas where design evolution is key to performance, for example, in logistics, biological evolution, art, and business and economics.

The constructal law runs against reductionism and empowers the mind to see the whole, its organization, performance, and future. In modern times, physics grew on a course tailored to infinitesimal effects. The constructal law is a jolt the other way, against the march of the crowd, a means to rationalize macroscopic design, objective, and behavior.

This fourth edition also teaches what thermodynamics is. Thermodynamics is brief, simple, unambiguous, and improving. Yet, confusion reigns in the field. The word entropy is pasted on almost any new thing, without any respect for its proper definition in thermodynamics. Every author bows to his own maximum or minimum principle, even when it contradicts English, not just thermodynamics. Minimizing resistance cannot be the same as maximizing resistance. Minimizing entropy generation cannot be the same as maximizing entropy generation.

Because of the word entropy, many believe that entropy generation minimization and maximization are covered by the second law, which is incorrect, twice. Because for an isolated system (or an adiabatic closed system) the second law states that the system entropy inventory increases during changes inside the system, many believe that the second law accounts for organization, evolution, and the arrow of time. This too is incorrect. In this new edition I invite the reader to take a look at nature, at the physics, at the science of all the natural things that "happen."

Law is not theory. The human observation that certain things happen innumerable times the same way is one natural tendency (i.e., one phenomenon). To observe the phenomenon is empiricism. The law of physics is the compact statement (text, or formula) that summarizes the innumerable observations of the same kind. To rely on the law to experience a purely mental viewing of how some things should be (i.e., to predict future observations) is a theory.

The law is one, and the theories underpinned by the law are as numerous as the things that are contemplated.

The phenomenon covered by the first law of thermodynamics is the "what goes up must come down." Today, we recognize this more generally as the conservation of energy, from kinetic to potential when a body is thrown upward to the energy flow (e.g., heat into work, or work into heat) through a thermodynamic system such as a power plant or a brake.

The phenomenon covered by the second law is the one-way flow, such as the flow of water under the bridge. Today, we recognize this natural tendency as irreversibility. Every flow, by itself, proceeds from high to low. Fluid through a duct flows from high pressure to low pressure. Heat through an insulation leaks from high temperature to low temperature. If you do not know beforehand which is the high and which is the low, then the direction of the flow will tell you. Why, because it is the law, and all systems obey the law.

The phenomenon covered by the constructal law is natural organization, evolution, and life: the occurrence and evolution of freely morphing configurations in every thing that flows and moves more easily over time. Observations of this kind are everywhere: river basin evolution, lung architecture evolution, city traffic evolution, aircraft evolution. These observations reveal the arrow of time┼ of evolution in nature, which points from existing flow configurations to new configurations through which the flowing is easier. Not the other way around. Why, because it is the law, and all systems obey the law.

Thermodynamics before 1996 is the thin book comprising the first law and the second law. It is an all-encompassing science story written in very few words. The two laws apply to "any system" imaginable. Their few words are system, boundary, environment, state, properties, equilibrium, and nonequilibrium. The any system is the most general system with flows in it, the nonequilibrium system, the flow system. This most general system can have nonuniformities internally (pressure, temperature, concentration) that drive currents through its various subsystems. It can have any configuration (organization, design), which is not specified.

The first law and the second law have equal standing. Each is a "first principle." The permanence and extreme generality of the two laws are consequences of the fact that in thermodynamics the any system is a black box. It is a region of space or a collection of matter without specified shape and structure. The two laws are global statements about the balance or imbalance of the flows (mass, heat, work, entropy) into and out of the black box. They say absolutely nothing about design, organization, and evolution.

Nature is full of organization and evolution, and science is not far behind. Science began with principle-based rationalizations of the images (designs) that humans perceive all around. It began with geometry and mechanics, which are about configurations, their principles, and the contrivances made based on configurations and principles. Science has always been about the human urge to make sense out of what we discern: numerous observations that we tend to store compactly as phenomena and, later, even more compactly as laws that account for the phenomena.

Nature is not made of boxes without configuration. The systems that we identify in nature have shape, structure, and evolution. They are resoundingly macroscopic, finite size, and recognizable as lines drawn on a background. They have organization, construction, configuration, pattern, rhythm, and sound. The very fact that they have names (river basins, blood vessels, trees) indicates that they have unmistakable appearances and meanings.

In 1996┼ and in the book the following year╬ I pointed out that the laws of thermodynamics do not account completely for the systems of nature, even though scientists have built thermodynamics into thick books in which the two laws are just the introduction. The body of the doctrine is devoted to contriving, describing, and improving designs that seem to correspond to systems found in nature and can be used by humans to make life easier.

If physics was to account for the systems of nature completely, then thermodynamics had to be enlarged with an additional self-standing law-with another first principle-that covers all phenomena of design occurrence and evolution. To achieve this, the constructal law states briefly that "for a finite-size flow system to persist in time (to live), it must evolve in such a way that it provides easier access to the imposed (global) currents that flow...