Entropy Generation

7 Key excerpts on "Entropy Generation"

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  Entropy Vector, The: Connecting Science And Business

  Connecting Science and Business

  • Robert D Handscombe, Eann A Patterson(Authors)
  • 2004(Publication Date)
  • World Scientific

    (Publisher)

  50 Energy and Entropy 5 scattering the seed • organic companies • exergy conservation • energy management The principles of thermodynamics make rather grand and far-reaching claims. We are told that energy is constant; entropy is increasing. Yet, in making those claims they leave a large amount of freedom to the actual path and the time schedule of any process or activity or event. We can try, as Nicholas Georgescu-Roegen suggested back in the early 1970s, to find exceptions. On the one hand, he suggested we look at some simple and primitive living creatures that appear now as they must have done many millions of years ago. Surely there is evidence here of keeping entropy constant? On the other hand, he invited us to look at our inventive genius and consider, for example, how we make steel from iron ore and coal. Or, we might add, clear transparent panes of glass from a mixture of sand and crushed mineral. Both processes seem to be ones where we have reversed entropy from high to low. So, how does this work? How can simple organisms keep their entropy constant and how can clever ones like us actually invent processes that appear to reverse it? And how can energy remain constant when we plainly use it up each time we take a ride in our cars? We are moving too quickly! We need to look at what exactly we mean by energy and entropy. As ever, we must look carefully at our definitions. Law and disorder The first law of thermodynamics demands the conservation of energy. The corollary of the second law is that entropy cannot be destroyed. Entropy is about the quality of energy, or its ability to do useful work. The higher the entropy, the less the value. We could say that lightning is high entropy. Compared with the output from a power station it is not very useful energy except for burning down trees that are past their sell-by date. From nature’s viewpoint this might be more useful than a power station, but not from society’s.

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  Entropy Crisis, The

  • Guy Deutscher(Author)
  • 2008(Publication Date)
  • World Scientific

    (Publisher)

  53 Chapter 4 Entropy in Thermodynamics and Our Energy Needs As the name indicates, thermodynamics deals with heat and motion. This branch of physics developed after the invention of the steam engine which transforms the heat of the steam coming from the boiler into mechanical energy. This transformation from heat into mechanical energy occurs via the pressure that steam exercises on a piston which it gets moving inside a cylinder. After it does its work the steam is released and condenses back into water. In the process, heat has been transferred from the hot boiler into the colder environment, and work has been performed by the moving piston This immediately poses the question of the equivalence between these two forms of energy, heat and mechanical energy, and of the efficiency of the engine in converting the first into the second. Here entropy plays a decisive role, which we will discuss in the first part of this chapter. In particular, we shall see how the increase of entropy in the course of the conversion process must be compensated by an input of energy, a notion that we introduced already, qualitatively, in Chapter 1. 4.1. Entropy in thermodynamics 4.1.1. Heat and mechanical work as two forms of energy: the first law of thermodynamics While the transformation of heat into mechanical energy is a relatively recent invention with the discovery of the heat engine (and later the internal combustion engine), it has been known to mankind since the dawn of civilization that mechanical work can be transformed into heat. Today we light a match by rubbing it against a rough surface, the heat produced by friction raising 54 The Entropy Crisis sufficiently the temperature of the tip of the match to put it on fire. Life was more difficult for our ancestors, but they used the same physical principle apparently by rotating rapidly a sharpened tip of hard wood against another piece of wood.

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  The Mechanical Universe

  Mechanics and Heat, Advanced Edition

  • Steven C. Frautschi, Richard P. Olenick, Tom M. Apostol, David L. Goodstein(Authors)
  • 2008(Publication Date)
  • Cambridge University Press

    (Publisher)

  21.5 A FINAL WORD Entropy is a measure not only of uselessness, but also of disorder. As time goes on, entropy increases. Energy is degraded to more useless forms, and matter into less-oriented states. Of course, a given bit of matter might temporarily decrease its entropy, but this always means that something else nearby is increasing its entropy by at least as much, and usually more. Strictly speaking, the principle of increasing entropy only applies to systems of conserved total energy. The universe itself is such a system, so the universe appears to be headed for a state of thermal equilibrium, after which nothing else will happen. This cheerfully optimistic view of the future is generally referred to as the heat death of the universe, There is another equally extravagant extrapolation of the entropy principle which turns around the sentence, As time goes on, entropy increases to read As entropy increases, time goes on. In other words, the increase in entropy is the very arrow of time; almost all other physical laws would work equally well if time ran backward instead of forward.* We have seen that all systems, including the universe, tend to evolve in an irreversible way. Despite the action of men and women, the inexorable law of nature is for energy to become less useful and the universe more disorganized. This tendency of the flow of time was pointed out by an eleventh-century Persian poet-mathematician, Omar Khayyam, who wrote: The Moving Finger writes; and having writ, Moves on: not all thy Piety nor Wit Shall lure it back to cancel half a line, Nor all thy Tears Wash out a Word of it. There have been many other statements of the second law of thermodynamics, but none so elegant. Problems Entropy Changes 1. What is the change in entropy of a ball that is strictly obeying the law of inertia? 2. Can you think of a process for which the entropy decreases? 3. Construct an argument explaining why a gas by itself never freely contracts.

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  Towards an Environment Research Agenda

  A Third Selection of Papers

  • A. Winnett(Author)
  • 2004(Publication Date)
  • Palgrave Macmillan

    (Publisher)

  This underpins the notion of ‘capital’ and ‘income’ energy resources for the planet (such as fossil fuels and solar energy respectively), and is behind the first of the TNS system conditions. Outside the realm of energy systems, thermodynamic concepts are typically employed in terms of an analogy with, or resem- blance to, physical processes. Alternatively, their use may be regarded, as colleagues at the University of Bath have suggested (Stephen Gough and William Scott, Centre for Research in Education and the Environment (CREE), private communication, 2003), as metaphorical – being applicable imaginatively but not literally. Entropy is not an easy concept to grasp, particularly when it has been so widely used and abused. It was originally developed by Rudolf Clausius (circa, 1864) from a consideration of the Carnot cycle for an ideal heat engine. This original ‘energetic’ (Clausius) entropy reflects the fact that, although heat can flow down a temperature gradient unaided, shaft 200 Engineering Sustainability work or an electrical energy input is required in order to induce heat transfer to take place from a cold to a hot reservoir: this is Clausius’s inequality. However, the idea of entropy has fascinated writers in discip- lines far removed from engineering and the physical sciences. Many analogous properties have been proposed. Stephen Kline (1999) identifies five microscopic ‘entropies’ (including Gibbs’s statistical entropy), two information functions (Shannon’s and Brillouin’s so-called ‘entropies’), and what he amusingly denotes the ‘vulgar’ entropy. He uses the latter term to describe the generic, but vague or ill-defined, application of entropy to various kinds of disorder. Kline interprets Gibbs’s statistical entropy as a useful measure of the ‘spread-outness’ of random molecular fluctuations among various microstates within the constraints of the physical boundaries of a system.

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  Advanced Engineering Thermodynamics

  • Adrian Bejan(Author)
  • 2016(Publication Date)
  • Wiley

    (Publisher)

  The link between heat and fluid flow and the generation of entropy was first established in Ref. 1 and is now an active field of research. For example, the fundamentals of combined heat and fluid flow irreversibilities are examined in Refs. 24 and 25. The local generation of entropy in turbulent shear flows and the incorporation of this local calculation in computational fluid dynamics (CFD) numerical codes are the focus of Ref. 26. Use of the Entropy Generation rate as a criterion for flow regime selection is applied to Bénard convection in Ref. 27 and to boundary layer flow in Ref. 28. This criterion is related to the constructal law of the maximization of flow access in time, which was also invoked to predict the laminar–turbulent transition and all the features of large-scale structure in turbulent flow.

  3.6 Entropy Generation MINIMIZATION

  3.6.1 The Method

  Entropy Generation minimization is now recognized as a method of modeling and optimization of real devices that owe their thermodynamic imperfection to heat transfer, mass transfer, and fluid flow and other transport processes. It is also known as thermodynamic optimization in engineering, where it was developed. In the physics literature it appeared later under the name finite-time thermodynamics. The method combines from the start the most basic principles of thermodynamics, heat transfer, and fluid mechanics, and it covers the domain between these very important disciplines [1–3].

  The objectives of the optimization may differ from one application to the next: for example, minimization of Entropy Generation in heat exchangers, maximization of power output in power plants, and minimization of power input in a refrigeration plant. Common in these applications is the use of models that feature rate processes (heat transfer, mass transfer, fluid flow), the finite sizes of actual devices, and the finite times or finite speeds of real processes. The optimization is then carried out subject to physical (palpable, visible) constraints that are in fact responsible for the irreversible operation of the device. The combined heat transfer and thermodynamics model “visualizes” for the analyst the irreversible nature of the device. From an educational standpoint, the optimization of such a model gives us a feel for the concept of Entropy Generation—specifically, where and how much entropy is being generated, how it flows, and how it degrades thermodynamics performance.

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  Fundamentals of Physics

  • David Halliday, Robert Resnick, Jearl Walker(Authors)
  • 2021(Publication Date)
  • Wiley

    (Publisher)

  613 Entropy and the Second Law of Thermodynamics 20.1 ENTROPY Learning Objectives After reading this module, you should be able to . . . 20.1.1 Identify the second law of thermodynamics: If a process occurs in a closed system, the entropy of the system increases for irreversible processes and remains constant for reversible processes; it never decreases. 20.1.2 Identify that entropy is a state function (the value for a particular state of the system does not depend on how that state is reached). 20.1.3 Calculate the change in entropy for a process by integrating the inverse of the temperature (in kelvins) with respect to the heat Q transferred during the process. 20.1.4 For a phase change with a constant-temperature process, apply the relationship between the entropy change ΔS, the total transferred heat Q, and the temperature T (in kelvins). 20.1.5 For a temperature change ΔT that is small relative to the temperature T, apply the relationship between the entropy change ΔS, the transferred heat Q, and the average temperature T avg (in kelvins). 20.1.6 For an ideal gas, apply the relationship between the entropy change ΔS and the initial and final values of the pressure and volume. 20.1.7 Identify that if a process is an irreversible one, the integration for the entropy change must be done for a reversible process that takes the system between the same initial and final states as the irreversible process. 20.1.8 For stretched rubber, relate the elastic force to the rate at which the rubber’s entropy changes with the change in the stretching distance. Key Ideas ● An irreversible process is one that cannot be reversed by means of small changes in the environ- ment. The direction in which an irreversible process proceeds is set by the change in entropy ΔS of the sys- tem undergoing the process. Entropy S is a state prop- erty (or state function) of the system; that is, it depends only on the state of the system and not on the way in which the system reached that state.

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  Physical Principles of Chemical Engineering

  International Series of Monographs in Chemical Engineering

  • Peter Grassmann, H. Sawistowski(Authors)
  • 2013(Publication Date)
  • Pergamon

    (Publisher)

  % This section does not describe the derivation of the second law, which can be found in the textbooks of thermodynamics (cf. also § 8.7), but attempts to aid the reader in under-standing the concept of entropy. J. D. Fast, Entropy {Entropie), Philips Technische Bibliothek, Eindhoven, 1960 (the significance of the concept of entropy and its use in science and engineer-ing). 53 54 Concept and Use of Entropy [§2.1 could be entirely converted into work. If, for example, the molecules of a gas obeyed a dictator and he ordered that, in accordance with Fig. 1 b : (1) the energy should be distributed uniformly among all molecules; (2) only motion vertically upwards and downwards was permissible; (3) no energy should be used for rotation round any axis of the molecule or for any oscillations; then the energy of this ordered pile of molecules could be turned entirely into mechanical work, but we should then have to deal with the kinetic energy of two groups of molecules moving in opposite directions to each other which, like the kinetic energy of two solid bodies, have to be considered no longer as heat but as mechanical energy. In general, whenever work is to be produced from energy—by work we denote all completely ordered energy—a certain state of order must be reached which is higher than the state of maximum disorder consistent with the given external conditions. Usually it is said that for heat to be turned into work there must be a temperature difference. A temperature difference always presupposes a certain state of order. However, the molecules with the—on the average— greater kinetic energy are located in the area of higher temperatures, while those with the lower kinetic energy are in the area of lower temperatures. Corresponding to this partial order, part of the heat content of the two bodies in question can be turned into work. So far as we know at present, this also applies to the world as a whole. Its brisk movement, life, and passage of time is only possible when at the begin-ning a state of order is present and when light and darkness, heat and cold are separated from each other in the first act of creation. It is these opposites which maintain the passage of time. In fact, in a chaotic world without contrasts it makes no sense to

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