Thermodynamic Stability

3 Key excerpts on "Thermodynamic Stability"

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  eBook - ePub

  Thermodynamics and Ecological Modelling

  • Sven E. Jorgensen(Author)
  • 2018(Publication Date)
  • CRC Press

    (Publisher)

  persistence) should possess intrinsic abilities to resist perturbations coming from the environment. This ability is usually called “stability.” Though the notion seems obvious, it is quite a problem to provide a precise and unambiguous definition for it. This heavily overloaded term has no established (stable) definition so far. For instance, the theory of stability, which can be considered as a branch of theoretical mechanics, uses about 30 different definitions of stability. So we can consider a definition of stability (and also entropy) as a “fuzzy” one. Paraphrasing von Neumann, we can say “… nobody knows what stability means in reality, that is why in the debate you will always have an advantage.”

  Among these definitions we can select two large classes which differ in respect to the requirements coming under the headline of “stability” The first group of requirements concerns preservation of the number of species in a community. A community is stable if the number of member-species remains constant over a sufficiently long time. This definition is the closest to various mathematical definitions of stability.

  The second group refers to populations rather than to community, which is considered to be stable when numbers of component populations do not undergo sharp fluctuations. This definition is closer to the thermodynamic (or more correctly, to the statistical physics) notion of system stability. In thermodynamics (statistical physics) a system is believed to be stable when large fluctuations, which can take the system far from the equilibrium or even destory it, are unlikely (see, for instance, Landau and Lifshitz, 1964). Evidently, the general thermodynamic concepts (for instance, the stability principle associated in the case of closed systems with the Second Law and, in the case of open systems, with the Prigogine theorem) should be applicable to biological (and, in particular, ecological) systems. As an illustration of such a phenomenon, I would like to consider a very well known problem of the relationship between the biological diversity of a community and its stability.

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  eBook - ePub

  Fundamentals of Engineering Thermodynamics

  • Michael J. Moran, Howard N. Shapiro, Daisie D. Boettner, Margaret B. Bailey(Authors)
  • 2018(Publication Date)
  • Wiley

    (Publisher)

  surroundings. To facilitate this, thermodynamics has been extended to the study of systems through which matter flows, including bioengineering and biomedical systems.

  The objective of this chapter is to introduce you to some of the fundamental concepts and definitions that are used in our study of engineering thermodynamics. In most instances this introduction is brief, and further elaboration is provided in subsequent chapters.

  LEARNING OUTCOMES

  When you complete your study of this chapter, you will be able to…

  • Explain several fundamental concepts used throughout the book, including closed system, control volume, boundary and surroundings, property, state, process, the distinction between extensive and intensive properties, and equilibrium.
  • Identify SI and English Engineering units, including units for specific volume, pressure, and temperature.
  • Describe the relationship among the Kelvin, Rankine, Celsius, and Fahrenheit temperature scales.
  • Apply appropriate unit conversion factors during calculations.
  • Apply the problem-solving methodology used in this book.

  1.1 Using Thermodynamics

  Engineers use principles drawn from thermodynamics and other engineering sciences, including fluid mechanics and heat and mass transfer, to analyze and design devices intended to meet human needs. Throughout the twentieth century, engineering applications of thermodynamics helped pave the way for significant improvements in our quality of life with advances in major areas such as surface transportation, air travel, space flight, electricity generation and transmission, building heating and cooling, and improved medical practices. The wide realm of these applications is suggested by Table 1.1

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  eBook - ePub

  Introduction to the Thermodynamics of Materials

  • David R. Gaskell, David E. Laughlin(Authors)
  • 2017(Publication Date)
  • CRC Press

    (Publisher)

  1 Introduction and Definition of Terms

  1.1INTRODUCTION

  The term thermodynamics is related to the two Greek words therme and dynamikos , which translate into English as “heat” and “power” (or “movement”), respectively. Thermodynamics is the physical science that focuses on the relationship between energy and work as well as the equilibrium states and variables of systems that are being investigated. Importantly, thermodynamics defines heat and identifies it as the process in which energy is transferred from one region to another down a temperature gradient. In this text, we will mainly use the phrase thermal energy to identify this form of energy transfer, but sometimes the word heat will be used. Thermodynamics deals with the conservation of energy as well as the conversion of the various forms of energy into each other or into work. Thermodynamics is concerned with the behavior of and interactions between portions of the universe denoted as systems and those portions of the universe called the surroundings or the environment . The system is that part of the universe we wish to investigate in detail, and the surroundings is that part of the universe outside the system which may interact with it by exchanging energy or matter. The system may perform work on the surroundings or have work performed on it by the surroundings. The boundary or wall between the system and the surroundings is what allows such interactions. In what we will call simple thermodynamic systems , the surroundings interacts with the system only via pressure and temperature changes. The composition remains constant in simple systems.

  It is convenient to characterize systems by the kinds of interactions that are allowed between them and their surroundings.

  1.Isolated systems

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