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Encyclopedia > Exergy

Exergy is defined differently in different fields of study. In thermodynamics, exergy is defined as a measure of the actual potential of a system to do work. In systems energetics, exergy has been defined as entropy-free energy. The latter definition is also related to the negentropy concept which aims to measure the work performed by biological systems. It is unclear whether these definitions are equivalent. Measure can mean: To perform a measurement. ... System (from Latin systēma, in turn from Greek systēma) is a set of entities, real or abstract, comprising a whole where each component interacts with or is related to at least one other component and they all serve a common objective. ... In thermodynamics, thermodynamic work is the quantity of energy transferred from one system to another. ... Energetics is the scientific study of energy flows under transformation. ... Ice melting - classic example of entropy increasing[1] described in 1862 by Rudolf Clausius as an increase in the disgregation of the molecules of the body of ice. ... To meet Wikipedias quality standards, this article or section may require cleanup. ...

Contents

Exergy (thermodynamics)

In thermodynamics, the exergy B of a system with respect to a reservoir is the maximum work done by the system during a transformation which brings it into equilibrium with the reservoir.[1] ("Reservoir" in practice is the surrounding with high capacity for receiving heat). Energy that has a high convertibility potential is said to contain a high share of exergy. Electricity and mechanical work are perfectly convertible and for these forms exergy contents equals the energy content. For nuclear and fossil fuels theoretical conversion potential is close to perfect, but severely limited by available technical processes. Reversely, heat at temperature close to the reservoir has low convertibility potential, the exergy content of such heat is much lower than its energy content[2]. Exergy analysis is used in the field of industrial ecology as a tool to both decrease the amount of exergy required for a process, and use available exergy more efficiently. The term was coined by Zoran Rant in 1956[3], but the concept was developed by J. Willard Gibbs in 1873.[4] Z. Rant introduced also the concept of anergy, which is the complementary part of the (heat) energy that can not be converted into work. Thermodynamics (from the Greek θερμη, therme, meaning heat and δυναμις, dunamis, meaning power) is a branch of physics that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analyzing the collective motion of their particles using statistics. ... In physics, mechanical work is the amount of energy transferred by a force. ... In thermodynamics, a thermodynamic system is defined as that part of the universe that is under consideration. ... Industrial ecology is the shifting of industrial process from open loop systems, in which resource and capital investments move through the system to become waste, to a closed loop system where wastes become inputs for new processes. ... Zoran Rant (September 14, 1904 - February 12, 1972) was a Slovene mechanical engineer, scientist and professor, associate member of SAZU. He invented terms known today as exergy and anergy. Categories: | | | ... Josiah Willard Gibbs (February 11, 1839 New Haven – April 28, 1903 New Haven) was one of the very first American theoretical physicists and chemists. ...


A body contains exergy also if its temperature is higher than the temperature of the reservoir (the surrounding). Exergy is actually a property of the wider system: the "system" as used above plus the "reservoir".


Using the concept of exergy, technical processes such as cogeneration and heat pump are readily described. In cogeneration, part of the energy is converted to work or electricity with high exergy content, and the remaining heat is used for purposes where moderate temperature (lower exergy content) is useful, such as food processing, drying and space heating. A heat pump takes pure anergy, energy without exergy, from the surrounding (reservoir), adds exergy provided by mechanical work or electricity, and delivers heat at a useful temperature level, that is, at an appropriate exergy content. In a similar way, an absorption heat pump combines two streams of heat: the driving heat with high exergy content and the pumped heat with low exergy content (temperature). The result is heat with an intermediate temperature, that is, with the exergy content better matching our needs, such as space heating. The output heat quantity will be much higher than the energy spent for driving the pump. Cogeneration (also combined heat and power or CHP) is the use of a heat engine or a power station to simultaneously generate both electricity and useful heat. ... A diagram of a simple heat pumps vapor-compression refrigeration cycle: 1) condenser, 2) expansion valve, 3) evaporator, 4) compressor. ... It has been suggested that this article or section be merged with Absorptive refrigeration The absorption refrigerator is a refrigerator that utilizes a heat source to provide the energy needed to drive the cooling system rather than being dependent on electricity to run a compressor. ...


The term exergy is also used, by analogy with its physical definition, in information theory related to reversible computing. Exergy is also synonymous with: availability, available energy, exergic energy, essergy (considered archaic), utilizable energy, available useful work, maximum (or minimum) work, maximum (or minimum) work content, reversible work, and ideal work. A bundle of optical fiber. ... The term reversible computing refers to any computational process that is (at least to some close approximation) reversible, i. ... In thermodynamics, a reversible process (or reversible cycle if the process is cyclic) is a process that can be reversed by means of infinitesimal changes in some property of the system. ...


History

Carnot

In 1824, Sadi Carnot studied the improvements developed for steam engines by James Watt and others. Carnot utilized a purely theoretical perspective for these engines and developed new ideas. He wrote: Sadi Carnot Nicolas Léonard Sadi Carnot (June 1, 1796 - August 24, 1832) was a French mathematician and engineer who gave the first successful theoretical account of heat engines, the Carnot cycle, and laid the foundations of the second law of thermodynamics. ... A steam engine is a heat engine that makes use of the thermal energy that exists in steam, converting it to mechanical work. ... James Watt James Watt (19 January 1736 – 19 August 1819) was a Scottish inventor and engineer whose improvements to the steam engine were fundamental to the changes wrought by the Industrial Revolution. ...


"The question has often been raised whether the motive power of heat is unbounded, whether the possible improvements in steam engines have an assignable limit—a limit by which the nature of things will not allow to be passed by any means whatever... In order to consider in the most general way the principle of the production of motion by heat, it must be considered independently of any mechanism or any particular agent. It is necessary to establish principles applicable not only to steam-engines but to all imaginable heat-engines... The production of motion in steam-engines is always accompanied by a circumstance on which we should fix our attention. This circumstance is the re-establishing of equilibrium... Imagine two bodies A and B, kept each at a constant temperature, that of A being higher than that of B. These two bodies, to which we can give or from which we can remove the heat without causing their temperatures to vary, exercise the functions of two unlimited reservoirs..."[5] In physics, mechanical work is the amount of energy transferred by a force. ... For other uses, see Heat (disambiguation) In physics, heat, symbolized by Q, is energy transferred from one body or system to another as a result of a difference in temperature. ... In mathematics, a function f defined on some set X with real or complex values is called bounded, if the set of its values is bounded. ... This article or section is in need of attention from an expert on the subject. ... A heat engine is a physical or theoretical device that converts thermal energy to mechanical output. ... In thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, and chemical equilibrium. ... In philosophy, physics, and other fields, a thought experiment (from the German Gedankenexperiment) is an attempt to solve a problem using the power of human imagination. ... This article includes a list of works cited or a list of external links, but its sources remain unclear because it lacks in-text citations. ... In thermodynamics a heat reservoir is considered as a constant temperature source. ...


Carnot next described what is now called the Carnot engine, and proved by a thought experiment that any heat engine performing better than this engine would be a perpetual motion machine. Even in the 1820s, there was a long history of science forbidding such devices. According to Carnot, "Such a creation is entirely contrary to ideas now accepted, to the laws of mechanics and of sound physics. It is inadmissible."[4] A Carnot heat engine is a hypothetical engine that operates on the reversible Carnot cycle. ... In philosophy, physics, and other fields, a thought experiment (from the German Gedankenexperiment) is an attempt to solve a problem using the power of human imagination. ... This article or section should include material from Parallel Path See also Perpetuum mobile as a musical term Perpetual motion machines (the Latin term perpetuum mobile is not uncommon) are a class of hypothetical machines which would produce useful energy in a way science cannot explain (yet). ... Classical mechanics is used for describing the motion of macroscopic objects, from projectiles to parts of machinery, as well as astronomical objects, such as spacecraft, planets, stars, and galaxies. ... A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ...


This description of an upper bound to the work that may be done by an engine was the earliest modern formulation of the second law of thermodynamics. Because it involves no mathematics, it still often serves as the entry point for a modern understanding of both the second law and entropy. Carnot's focus on heat engines, equilibrium, and heat reservoirs is also the best entry point for understanding the closely related concept of exergy. The second law of thermodynamics is an expression of the universal law of increasing entropy. ... Ice melting - classic example of entropy increasing[1] described in 1862 by Rudolf Clausius as an increase in the disgregation of the molecules of the body of ice. ... A heat engine is a physical or theoretical device that converts thermal energy to mechanical output. ... In thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, and chemical equilibrium. ... In thermodynamics a heat reservoir is considered as a constant temperature source. ...


Carnot believed in the incorrect caloric theory of heat that was popular during his time, but his thought experiment nevertheless described a fundamental limit of nature. As kinetic theory replaced caloric theory through the early and mid-1800s (see timeline), several scientists added mathematical precision to the first and second laws of thermodynamics and developed the concept of entropy. Carnot's focus on processes at the human scale (above the thermodynamic limit) led to the most universally applicable concepts in physics. Entropy and the second-law are applied today in fields ranging from quantum mechanics to physical cosmology. The caloric theory is an obsolete scientific theory that heat consists of a fluid called caloric that flows from hotter to colder bodies. ... Kinetic theory attempts to explain macroscopic properties of gases, such as pressure, temperature, or volume, by considering their molecular composition and motion. ... A timeline of events related to thermodynamics, statistical mechanics, and random processes. ... The laws of thermodynamics, in principle, describe the specifics for the transport of heat and work in thermodynamic processes. ... Ice melting - classic example of entropy increasing[1] described in 1862 by Rudolf Clausius as an increase in the disgregation of the molecules of the body of ice. ... In physics and physical chemistry, the thermodynamic limit is reached as the number of particles (atoms or molecules) in a system N approaches infinity — or in practical terms, one mole or Avogadros number ≈ 6 x 1023. ... A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... Fig. ... Physical cosmology, as a branch of astrophysics, is the study of the large-scale structure of the universe and is concerned with fundamental questions about its formation and evolution. ...


Gibbs

In the 1870s, Josiah Willard Gibbs unified a large quantity of 19th century thermochemistry into one compact theory. Gibbs's theory incorporated the new concept of a chemical potential to cause change when distant from a chemical equilibrium into the older work begun by Carnot in describing thermal and mechanical equilibrium and their potentials for change. Gibbs's unifying theory resulted in the thermodynamic potential state functions describing differences from thermodynamic equilibrium. Josiah Willard Gibbs (February 11, 1839 New Haven – April 28, 1903 New Haven) was one of the very first American theoretical physicists and chemists. ... The world’s first ice-calorimeter, used in the winter of 1782-83, by Antoine Lavoisier and Pierre-Simon Laplace, to determine the heat evolved in various chemical changes; calculations which were based on Joseph Black’s prior discovery of latent heat. ... In thermodynamics and chemistry, chemical potential, symbolized by μ, is a term introduced in 1876 by the American mathematical physicist Willard Gibbs, which he defined as follows: Gibbs noted also that for the purposes of this definition, any chemical element or combination of elements in given proportions may be considered a... Chemical equilibrium is the state in which the concentrations of the reactants and products have no net change over time. ... A standard definition of mechanical equilibrium is: A system is in mechanical equilibrium when the sum of the forces, and torque, on each particle of the system is zero. ... In thermodynamics, four quantities, measured in units of energy, are called thermodynamic potentials: where T = temperature, S = entropy, p = pressure, V = volume Differential definitions The following differential relations hold for the four potentials: If we write the above four equations generally as Then it is seen that yielding expressions for... In thermodynamics, a state function, or state quantity, is a property of a system that depends only on the current state of the system, not on the way in which the system got to that state. ... In thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, and chemical equilibrium. ...


In 1873, Gibbs derived the mathematics of "available energy of the body and medium" into the form it has today.[3] (See the equations below). The physics describing exergy has changed little since that time. The term exergy was suggested in 1956 by Zoran Rant (1904-1972) by using the Greek ex and ergon meaning "from work."[2] Zoran Rant (September 14, 1904 - February 12, 1972) was a Slovene mechanical engineer, scientist and professor, associate member of SAZU. He invented terms known today as exergy and anergy. Categories: | | | ... In thermodynamics, thermodynamic work is the quantity of energy transferred from one system to another. ...


Overview

Exergy is a measure of the potential of a system to cause a change as it achieves equilibrium with its surroundings. The surroundings are often also called a reference environment or reservoir. After the system and surroundings reach equilibrium, the system won't change or be changed. This is known as the system dead state, and it has an exergy of zero. This article does not cite any references or sources. ... In a thermodynamics problem, the surroundings, or environment, are anything not part of the system. ...


Unlike energy which is always conserved for a cyclic process, an irreversible cycle reduces exergy. This decrease is proportional to the entropy increase of the system together with its surroundings. Exergy is a co-property of a system and a reservoir. Because of this, exergy is neither a thermodynamic property of matter nor a thermodynamic potential of a system. It is, however, the most useful application of these values, and is derivable from them mathematically. Determining exergy was also the first goal of thermodynamics. Exergy and energy both have units of joules. Both are also state functions even though work itself is not. In physics, a conservation law states that a particular measurable property of an isolated physical system does not change as the system evolves. ... A cyclic process is a thermodynamic process which begins from and finishes at the same thermostatic state. ... In thermodynamics, a reversible process (or reversible cycle if the process is cyclic) is a process that can be reversed by means of infinitesimal changes in some property of the system. ... Ice melting - classic example of entropy increasing[1] described in 1862 by Rudolf Clausius as an increase in the disgregation of the molecules of the body of ice. ... Here is a partial list of thermodynamic properties of fluids: temperature [K] density [kg/m3] specific heat at constant pressure [J/kg·K] specific heat at constant volume [J/kg·K] dynamic viscosity [N/m²s] kinematic viscosity [m²/s] thermal conductivity [W/m·K] thermal diffusivity [m²/s] volumetric... In thermodynamics, four quantities, measured in units of energy, are called thermodynamic potentials: where T = temperature, S = entropy, p = pressure, V = volume Differential definitions The following differential relations hold for the four potentials: If we write the above four equations generally as Then it is seen that yielding expressions for... Thermodynamics (from the Greek θερμη, therme, meaning heat and δυναμις, dunamis, meaning power) is a branch of physics that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analyzing the collective motion of their particles using statistics. ... The joule (IPA pronunciation: or ) (symbol: J) is the SI unit of energy. ... In thermodynamics, a state function, or state quantity, is a property of a system that depends only on the current state of the system, not on the way in which the system got to that state. ...


Mathematical description

An application of the second law of thermodynamics

See Also: Second law of thermodynamics

Exergy uses system boundaries in a way that is unfamiliar to many. We imagine the presence of a Carnot engine between the system and its reference environment even though this engine does not exist in the real world. Its only purpose is to measure the results of a "what-if" scenario to represent the most efficient work interaction possible between the system and its surroundings. The second law of thermodynamics is an expression of the universal law of increasing entropy. ... In thermodynamics, a thermodynamic system is defined as that part of the universe that is under consideration. ... A Carnot heat engine is a hypothetical engine that operates on the reversible Carnot cycle. ...


If a real-world reference environment is chosen that behaves like an unlimited reservoir that remains unaltered by the system, then Carnot's speculation about the consequences of a system heading towards equilibrium with time is addressed by two equivalent mathematical statements. B, the exergy or available work, will decrease with time, and Stotal, the entropy of the system and its reference environment enclosed together in a larger isolated system, will increase with time: In thermodynamics, an isolated system, as contrasted with a closed system, is a physical system that does not interact with its surroundings. ...

 frac{dB}{dt} le 0 mbox{ is equivalent to } frac {dS_{total}}{dt} ge 0 qquad mbox{(1)}

For macroscopic systems (above the thermodynamic limit), these statements are both expressions of the second law of thermodynamics if the following expression is used for exergy: In physics and physical chemistry, the thermodynamic limit is reached as the number of particles (atoms or molecules) in a system N approaches infinity — or in practical terms, one mole or Avogadros number ≈ 6 x 1023. ... The second law of thermodynamics is an expression of the universal law of increasing entropy. ...

 B=U +P_RV -T_RS-sum_imu_{i,R}N_i qquad mbox{(2)}

where the extensive quantities for the system are U = Internal energy, V = Volume, and Ni = Moles of component i. The intensive quantities for the surroundings are PR = Pressure and μi,R = Chemical potential of component i. Individual terms also often have names attached to them: PRV is called "available PV work", TRS is called "entropic loss" or "heat loss" and the final term is called "available chemical energy." In physics and chemistry, an extensive quantity (also referred to as an extensive variable) is a physical quantity whose value is proportional to the size of the system it describes. ... In thermodynamics, the internal energy of a thermodynamic system, or a body with well-defined boundaries, denoted by U, or sometimes E, is the total of the kinetic energy due to the motion of molecules (translational, rotational, vibrational) and the potential energy associated with the vibrational and electric energy of... The volume of a solid object is the three-dimensional concept of how much space it occupies, often quantified numerically. ... The mole (symbol: mol) is the SI base unit that measures an amount of substance. ... It has been suggested that this article or section be merged into intensive and extensive properties. ... The use of water pressure - the Captain Cook Memorial Jet in Lake Burley Griffin in Canberra, Australia. ... In thermodynamics and chemistry, chemical potential, symbolized by μ, is a term introduced in 1876 by the American mathematical physicist Willard Gibbs, which he defined as follows: Gibbs noted also that for the purposes of this definition, any chemical element or combination of elements in given proportions may be considered a...


Other thermodynamic potentials may be used to replace internal energy so long as proper care is taken in recognizing which natural variables correspond to which potential. For the recommended nomenclature of these potentials, see (Alberty, 2001)[6]. Equation (2) is useful for processes where system volume, entropy, and number of moles of various components change because internal energy is also a function of these variables and no others. In thermodynamics, four quantities, measured in units of energy, are called thermodynamic potentials: where T = temperature, S = entropy, p = pressure, V = volume Differential definitions The following differential relations hold for the four potentials: If we write the above four equations generally as Then it is seen that yielding expressions for...


An alternative definition of internal energy does not separate available chemical potential from U. This expression is useful (when substituted into equation (1)) for processes where system volume and entropy change, but no chemical reaction occurs:

 B=U[mu_1, mu_2, ... mu_n] +P_RV -T_RS=U[boldsymbol{mu}] +P_RV -T_RS qquad mbox{(3)}

In this case a given set of chemicals at a given entropy and volume will have a single numerical value for this thermodynamic potential. A multi-state system may complicate or simplify the problem because the Gibbs phase rule predicts that intensive quantities will no longer be completely independent from each other. In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i. ... It has been suggested that this article or section be merged with Gibbs phase rule. ...


A historical and cultural tangent

In 1848, William Thomson, 1st Baron Kelvin asked (and immediately answered) the question: William Thomson, 1st Baron Kelvin, OM, GCVO, PC, PRS, FRSE, (26 June 1824 – 17 December 1907) was a mathematical physicist, engineer, and outstanding leader in the physical sciences of the 19th century. ...

Is there any principle on which an absolute thermometric scale can be founded? It appears to me that Carnot’s theory of the motive power of heat enables us to give an affirmative answer.[7]

With the benefit of the hindsight contained equation (3), we are able to understand the historical impact of Kelvin's idea on physics. Kelvin suggested that the best temperature scale would describe a constant ability for a unit of temperature in the surroundings to alter the available work from Carnot's engine. From equation (3):

 frac{dB}{dT_R}=-S qquad mbox{(4)}

Rudolf Clausius recognized the presence of a proportionality constant in Kelvin's analysis and gave it the name entropy in 1865 from the Greek for "transformation" because it describes the available energy lost during transformation from heat to work. The available work from a Carnot engine is at its maximum when the surroundings are at a temperature of absolute zero. Rudolf Clausius - physicist and mathematician Rudolf Julius Emanuel Clausius (January 2, 1822 – August 24, 1888), was a German physicist and mathematician. ... In mathematics, two quantities are called proportional if they vary in such a way that one of the quantities is a constant multiple of the other, or equivalently if they have a constant ratio. ... Ice melting - classic example of entropy increasing[1] described in 1862 by Rudolf Clausius as an increase in the disgregation of the molecules of the body of ice. ... Absolute zero is the lowest possible temperature where nothing could be colder, and no heat energy remains in a substance. ...


Physicists then, as now, often look at a property with the word "available" or "utilizable" in its name with a certain unease. The idea of what is available begs the question of "available to what?" and raises a concern about whether such a property is anthropocentric. Laws derived using such a property may not describe the universe but instead describe what people wish to see. Anthropocentrism (Greek άνθρωπος, anthropos, human, κέντρον, kentron, center), or the human-centered principle, refers to the idea that humanity must always remain the central concern for humans. ...


The field of statistical mechanics (beginning with the work of Ludwig Boltzmann in developing the Boltzmann equation) relieved many physicists of this concern. From this discipline, we now know that microscopic kinetic fluctuations among particles cause entropic loss, and this energy is unavailable for work because these fluctuations occur randomly in all directions. The anthropocentric act is taken, in the eyes of some physicists and engineers today, when one draws a hypothetical boundary and in effect says, "This is my system. What occurs beyond it is surroundings." In this context, exergy is sometimes described as an anthropocentric property, both by those who use it and those who don't. Entropy is viewed as a more fundamental property of matter. Statistical mechanics is the application of probability theory, which includes mathematical tools for dealing with large populations, to the field of mechanics, which is concerned with the motion of particles or objects when subjected to a force. ... Ludwig Eduard Boltzmann (Vienna, Austrian Empire, February 20, 1844 – Duino near Trieste, September 5, 1906) was an Austrian physicist famous for his founding contributions in the fields of statistical mechanics and statistical thermodynamics. ... The Boltzmann equation describes the statistical distribution of particles in a fluid. ...


In the field of ecology, the interactions among systems (mostly ecosystems) and their manipulation of exergy resources is of primary concern. With this perspective, the answer to, "available to what?" is simply, "available to the system" because ecosystems appear to exist in the real world. With the viewpoint of systems ecology, a property of matter like absolute entropy is seen as anthropocentric because it is defined relative to an unobtainable hypothetical reference system in isolation at absolute zero temperature. With this emphasis on systems rather than matter, exergy is viewed as a more fundamental property of a system, and it is entropy that may be viewed as a co-property of a system with an idealized reference system. This article or section does not cite any references or sources. ... A coral reef near the Hawaiian islands is an example of a complex marine ecosystem. ... Systems Ecology is a transdiscipline which studies ecological systems, or ecosystems. ...


A potential for every thermodynamic situation

In addition to U and  U[boldsymbol{mu}], the other thermodynamic potentials are frequently used to determine exergy. For a given set of chemicals at a given entropy and pressure, enthalpy H is used in the expression: In thermodynamics, four quantities, measured in units of energy, are called thermodynamic potentials: where T = temperature, S = entropy, p = pressure, V = volume Differential definitions The following differential relations hold for the four potentials: If we write the above four equations generally as Then it is seen that yielding expressions for... t In thermodynamics and molecular chemistry, the enthalpy or heat content (denoted as H or ΔH, or rarely as χ) is a quotient or description of thermodynamic potential of a system, which can be used to calculate the useful work obtainable from a closed thermodynamic system under constant pressure. ...

 B=H-T_RS qquad mbox{(5)}

For a given set of chemicals at a given temperature and volume, Helmholtz free energy A is used in the expression: In thermodynamics, the Helmholtz free energy is a thermodynamic potential which measures the “useful” work obtainable from a closed thermodynamic system at a constant temperature. ...

 B=A qquad mbox{(6)}

For a given set of chemicals at a given temperature and pressure, Gibbs free energy G is used in the expression: In thermodynamics, the Gibbs free energy is a thermodynamic potential which measures the useful work obtainable from a closed thermodynamic system at a constant temperature and pressure. ...

 B=G qquad mbox{(7)}

The potentials A and G are utilized for a constant temperature process. In these cases, all energy is free to perform useful work because there is no entropic loss. A chemical reaction that generates electricity with no associated change in temperature will also experience no entropic loss. (See fuel cell.) This is true of every isothermal process. Examples are gravitational potential energy, kinetic energy (on a macroscopic scale), solar energy, electrical energy, and many others. If friction, absorption, electrical resistance or a similar energy conversion takes place that releases heat, the impact of that heat on thermodynamic potentials must be considered, and it is this impact that decreases the available energy. A fuel cell is an electrochemical device similar to a battery, but differing from the latter in that it is designed for continuous replenishment of the reactants consumed; i. ... {{Portal|Energy}Potential energy is the energy available within a physical system due to an objects position in conjunction with a conservative force which acts upon it (such as the gravitational force or Coulomb force). ... The kinetic energy of an object is the extra energy which it possesses due to its motion. ... Solar power describes a number of methods of harnessing energy from the light of the sun. ... Electrical energy can refer to several closely related things. ... friction is the force that opposes the relative motion or tendency toward such motion of two surfaces in contact. ... Absorption, in optics, is the process by which the energy of a photon is taken up by another entity, for example, by an atom whose valence electrons make a transition between two electronic energy levels. ... Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ...


Applications

From equation (1),

 mbox{If } frac {dB}{dt} begin{cases} >0, & frac {dB}{dt}=mbox{ maximum power generated}  <0, & frac {dB}{dt}=mbox{ minimum power required} end{cases} qquad mbox{(8)}

This expression applies equally well for theoretical ideals in a wide variety of applications: electrolysis (G<0), galvanic cells and fuel cells (G>0), explosives (A>0), heating and refrigeration (exchange of H), motors (U<0) and generators (U>0). This article is about the chemical process. ... The Galvanic cell, named after Luigi Galvani, consists of two different metals connected by a salt bridge or a porous disk between the individual half-cells. ... A fuel cell is an electrochemical device similar to a battery, but differing from the latter in that it is designed for continuous replenishment of the reactants consumed; i. ... This article is concerned solely with chemical explosives. ... HVAC systems use ventilation air ducts installed throughout a building that supply conditioned air to a room through rectangular or round outlet vents, called diffusers; and ducts that remove air from return-air grills Fire-resistance rated mechanical shaft with HVAC sheet metal ducting and copper piping, as well as... A heat engine is a physical or theoretical device that converts thermal energy to mechanical output. ... “Dynamo” redirects here. ...


Utilization of the exergy concept often requires careful consideration of the choice of reference environment because, as Carnot knew, unlimited reservoirs do not exist in the real world. A system may be maintained at a constant temperature to simulate an unlimited reservoir in the lab or in a factory, but those systems cannot then be isolated from a larger surrounding environment. However, with a proper choice of system boundaries, a reasonable constant reservoir can be imagined. A process sometimes must be compared to "the most realistic impossibility," and this invariably involves a certain amount of guesswork.


We also now know that, on a microscopic scale, entropy is more "real" than temperature itself (see thermodynamic temperature), and macroscopic properties may all be determined from properties on a microscopic scale. Thermodynamic temperature is the absolute measure of temperature and is one of the principal parameters of thermodynamics. ...


Engineering applications

Application of exergy to unit operations in chemical plants was partially responsible for the huge growth of the chemical industry during the 1900s. During this time it was usually called availability or available work. Ore Extraction unit operations at Quincy Mine, Hancock, MI ca. ... A Chemical plant is an industrial process plant that manufactures chemicals, usually on a large scale. ... Chemical tanks in Lillebonne, France Chemical industry includes those industries involved in the production of petrochemicals, agrochemicals, pharmaceuticals, polymers, paints, oleochemicals etc. ...


As a simple example of exergy, air at atmospheric conditions of temperature, pressure, and composition contains energy but no exergy when it is chosen as the thermodynamic reference state known as ambient. Individual processes on Earth like combustion in a power plant often eventually result in products that are incorporated into a large atmosphere, so defining this reference state for exergy is useful even though the atmosphere itself is not at equilibrium and is full of long and short term variations. In chemistry and other sciences, STP or standard temperature and pressure is a standard set of conditions for experimental measurements, to enable comparisons to be made between sets of data. ...


If standard ambient conditions are used for calculations during plant operation when the actual weather is very cold or hot, then certain parts of a chemical plant might seem to have an exergy efficiency of greater than 100% and appear on paper to be a perpetual motion machine! Using actual conditions will give actual values, but standard ambient conditions are useful for initial design calculations.


One goal of energy and exergy methods in engineering is to compute balances between what comes into and out of several possible designs before a factory is built. After the balances are completed, the engineer will often want to select the most efficient process. An energy efficiency or first law efficiency will determine the most efficient process based on losing as little energy as possible relative to energy inputs. An exergy efficiency or second-law efficiency will determine the most efficient process based on losing and destroying as little available work as possible from a given input of available work. For meanings of the word balance, see: Look up balance in Wiktionary, the free dictionary. ... In physics and engineering, including mechanical and electrical engineering, energy efficiency is a dimensionless number, with a value between 0 and 1 or with times 100 given in percent. ... Exergy efficiency is also called second-law efficiency because it computes the efficiency of a process taking the second law of thermodynamics into account. ...


Design engineers have recognized that a higher exergy efficiency involves building a more expensive plant, and a balance between capital investment and operating efficiency must be determined in the context of economic competition. This article or section does not cite its references or sources. ...


Applications in natural resource utilization

In recent decades, utilization of exergy has spread outside of physics and engineering to the fields of ecological economics, systems ecology, and energetics. Defining where one field ends and the next begins is a matter of semantics, but applications of exergy can be placed into rigid categories. Ecological economics is a transdisciplinary field of academic research that addresses the dynamic and spatial interdependence between human economies and natural ecosystems. ... Systems Ecology is a transdiscipline which studies ecological systems, or ecosystems. ... Energetics is the scientific study of energy flows under transformation. ...


Researchers in ecological economics and environmental accounting perform exergy-cost analyses in order to evaluate the impact of human activity on the current natural environment. As with ambient air, this often requires the unrealistic substitution of properties from a natural environment in place of the reference state environment of Carnot. For example, ecologists and others have developed reference conditions for the ocean and for the Earth's crust. Exergy values for human activity using this information can be useful for comparing policy alternatives based on the efficiency of utilizing natural resources to perform work. Typical questions that may be answered are: Environmental accounting can be considered either a subset or superset of accounting proper, because it aims to incorporate both economic and environmental information. ... This article does not cite any references or sources. ... In thermodynamics a heat reservoir is considered as a constant temperature source. ... Animated map exhibiting the worlds oceanic waters. ... Earth cutaway from core to exosphere. ...

Does the human production of one unit of an economic good by method A utilize more of a resource's exergy than by method B?
Does the human production of economic good A utilize more of a resource's exergy than the producution of good B?
Does the human production of economic good A utilize a resource's exergy more efficiently than the production of good B?

There has been some progress in standardizing and applying these methods. A good in economics is anything that increases utility. ...


Applications in sustainability

In systems ecology, researchers sometimes consider the exergy of the current formation of natural resources from a small number of exergy inputs (usually solar radiation, tidal forces, and geothermal heat). This application not only requires assumptions about reference states, but it also requires assumptions about the real environments of the past that might have been close to those reference states. Can we decide which is the most "realistic impossibility" over such a long period of time when we are only speculating about the reality? Systems Ecology is a transdiscipline which studies ecological systems, or ecosystems. ... Solar irradiance spectrum at top of atmosphere. ... Comet Shoemaker-Levy 9 after breaking up under the influence of Jupiters tidal forces. ... Earth cutaway from core to exosphere. ...


For instance, comparing oil exergy to coal exergy using a common reference state would require geothermal exergy inputs to describe the transition from biological material to fossil fuels during millions of years in the Earth's crust, and solar radiation exergy inputs to describe the material's history before then when it was part of the biosphere. This would need to be carried out mathematically backwards through time, to a presumed era when the oil and coal could be assumed to be receiving the same exergy inputs from these sources. A speculation about a past environment is different from assigning a reference state with respect to known environments today. Reasonable guesses about real ancient environments may be made, but they are untestable guesses, and so some regard this application as pseudoscience or pseudo-engineering. Phrenology is regarded today as a classic example of pseudoscience. ...


The field describes this accumulated exergy in a natural resource over time as embodied energy with units of the "embodied joule" or "emjoule". There appear to be a number of different understandings of the term embodied energy. ...


The important application of this research is to address sustainability issues in a quantitative fashion through a sustainability metric: Sustainability is an attempt to provide the best outcomes for the human and natural environments both now and into the indefinite future. ... Sustainability is an attempt to provide the best outcomes for the human and natural environments both now and into the indefinite future. ...

Does the human production of an economic good deplete the exergy of Earth's natural resources more quickly than those resources are able to receive exergy?
If so, how does this compare to the depletion caused by producing the same good (or a different one) using a different set of natural resources?

Assigning one thermodynamically obtained value to an economic good

A technique proposed by systems ecologists is to consolidate the three exergy inputs described in the last section into the single exergy input of solar radiation, and to express the total input of exergy into an economic good as a solar embodied joule or sej. (See emergy) Exergy inputs from solar, tidal, and geothermal forces all at one time had their origins at the beginning of the solar system under conditions which could be chosen as an initial reference state, and other speculative reference states could in theory be traced back to that time. With this tool we would be able to answer: The neutrality of this article is disputed. ...

What fraction of the total human depletion of the Earth's exergy is caused by the production of a particular economic good?
What fraction of the total human and non-human depletion of the Earth's exergy is caused by the production of a particular economic good?

No additional thermodynamic laws are required for this idea, and the principles of energetics may confuse many issues for those outside the field. The combination of untestable hypotheses, unfamiliar jargon that contradicts accepted jargon, intense advocacy among its supporters, and some degree of isolation from other disciplines have contributed to this protoscience being regarded by many as a pseudoscience. However, its basic tenets are only a further utilization of the exergy concept. Energetics is the scientific study of energy flows under transformation. ... This article or section does not cite its references or sources. ... Phrenology is regarded today as a classic example of pseudoscience. ...


Implications in the development of complex physical systems

A common hypothesis in systems ecology is that the design engineer's observation that a greater capital investment is needed to create a process with increased exergy efficiency is actually the economic result of a fundamental law of nature. By this view, exergy is the analogue of economic currency in the natural world. The analogy to capital investment is the accumulation of exergy into a system over long periods of time resulting in embodied energy. The analogy of capital investment resulting in a factory with high exergy efficiency is an increase in natural organizational structures with high exergy efficiency. (See maximum power). Researchers in these fields describe biological evolution in terms of increases in organism complexity due to the requirement for increased exergy efficiency because of competition for limited sources of exergy. There appear to be a number of different understandings of the term embodied energy. ... The concpet of maximum power has been proposed as the fourth principle of energetics. ... This article is about evolution in biology. ...


Some biologists have a similar hypothesis. A biological system (or a chemical plant) with a number of intermediate compartments and intermediate reactions is more efficient because the process is divided up into many small substeps, and this is closer to the reversible ideal of an infinite number of infinitesimal substeps. Of course, an excessively large number of intermediate compartments comes at a capital cost that may be too high. In thermodynamics, a reversible process (or reversible cycle if the process is cyclic) is a process that can be reversed by means of infinitesimal changes in some property of the system. ... In mathematics, an infinitesimal, or infinitely small number, is a number that is smaller in absolute value than any positive real number. ...


Testing this idea in living organisms or ecosystems is impossible for all practical purposes because of the large time scales and small exergy inputs involved for changes to take place. However, if this idea is correct, it would not be a new fundamental law of nature. It would simply be living systems and ecosystems maximizing their exergy efficiency by utilizing laws of thermodynamics developed in the 19th century.


Philosophical and cosmological implications

Some proponents of utilizing exergy concepts describe them as a biocentric or ecocentric alternative for terms like quality and value. The "deep ecology" movement views economic usage of these terms as an anthropocentric philosophy which should be discarded. A possible universal thermodynamic concept of value or utility appeals to those with an interest in monism. Biocentrism is the belief that all life, or even the whole universe living or otherwise taken as a whole, is equally valid and humanity is not the center of existence. ... Ecocentrism or physiocentrism is a synonym for biocentrism, but differs in that it does not principally distinguish between living and non living forms of nature. ... For the Talib Kweli album Quality (album) Quality can refer to a. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Deep ecology is a recent branch of ecological philosophy (ecosophy) that considers humankind as an integral part of its environment. ... Economics (deriving from the Greek words οίκω [okos], house, and νέμω [nemo], rules hence household management) is the social science that studies the allocation of scarce resources to satisfy unlimited wants. ... Anthropocentrism (Greek &#940;&#957;&#952;&#961;&#969;&#960;&#959;&#962;, anthropos, man, human being, &#954;&#941;&#957;&#964;&#961;&#959;&#957;, kentron, center) is the practice, conscious or otherwise, of regarding the existence and/or concerns of human beings as the central fact of the universe. ... The philosopher Socrates about to take poison hemlock as ordered by the court. ... The Monad was a symbol referred by the Greek philosophers as The First, The Seed, The Essence, The Builder, and The Foundation Monism is the metaphysical and theological view that all is one, that there are no fundamental divisions, and a unified set of laws underlie nature. ...


For some, the end result of this line of thinking about tracking exergy into the deep past is a restatement of the cosmological argument that the universe was once at equilibrium and an input of exergy from some First Cause created a universe full of available work. Current science is unable to describe the first 10–43 seconds of the universe (See Timeline of the Big Bang). An external reference state is not able to be defined for such an event, and (regardless of its merits), such an arguments may be better expressed in terms of entropy. The cosmological argument is a metaphysical argument for the existence of God, traditionally known as an argument from universal causation, an argument from first cause, and also as an uncaused cause argument. ... In thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, and chemical equilibrium. ... This article does not cite any references or sources. ... Ice melting - classic example of entropy increasing[1] described in 1862 by Rudolf Clausius as an increase in the disgregation of the molecules of the body of ice. ...


Comparison of energy and exergy

Based on [8].

The energy change of a process is... The exergy change of a process is...
its ability to produce motion its ability to produce work
conserved by the first law of thermodynamics only conserved for reversible processes and destroyed by irreversible processes
different from zero (E=mc²) equal to zero when at equilibrium with the environment
independent of environment parameters dependent on environment parameters
limited by the second law of thermodynamics for all processes unlimited for reversible processes due to the second law
a measure of quantity only a measure of quantity and efficiency of utilization

Exergy is a measurable value that is decreased during the conversion of useful energy to useless energy. Therefore, exergy measures the actual potential of a system to do work. The exergy consumed to create something, a product or service, is more than the work done to create it. Exergy is the work that can no longer be done elsewhere because the economic good was made. Exergy has been described as a measure of energy quality because of these traits. This article or section is in need of attention from an expert on the subject. ... In physics, mechanical work is the amount of energy transferred by a force. ... In physics, a conservation law states that a particular measurable property of an isolated physical system does not change as the system evolves. ... The first law of thermodynamics, a generalized expression of the law of the conservation of energy, states: // Description Essentially, the First Law of Thermodynamics declares that energy is conserved for a closed system, with heat and work being the forms of energy transfer. ... A reversible process (or reversible cycle if the process is cyclic) , in thermodynamics, is a process that can be reversed by means of infinitesimal changes in some property of the system (Sears and Salinger, 1986). ... It has been suggested that this article or section be merged with Mass-energy equivalence. ... The second law of thermodynamics is an expression of the universal law of increasing entropy. ... A good in economics is anything that increases utility. ... Energy quality the contrast between different forms of energy, the different trophic levels in ecological systems and the propensity of energy to convert from one form to another. ...


Exergy is highly multidisciplinary

(This section will probably be shortened and added to the "Utilization" section as a table if possible) The cumulative exergy consumption of a good is a sum of the exergy decreases that occurred in order to create it. An initial state for an analysis might consist of exergy contributions from: Addition is one of the basic operations of arithmetic. ...

1) the material entering individual reactors or other unit
2) the material delivered to the industry and used for all the units in the industrial process.
3) the material purchased from other industries and all the associated indirect exergy decreases involved in transport and administration to get the material and process it.
4) all the initial natural resources used directly or indirectly to make the good.
5) all the initial ecological inputs (such as solar radiation, tidal forces, and geothermal heat) that created the natural resources.
6) These multiple inputs related to a single reference input (such as solar radiation).
7) This reference input is related to a single input of exergy to the universe from some external source at a time in the past when the entire universe was at equilibrium.

Choice 1 (if there are few components) is a tricky undergraduate homework problem in chemical engineering if a chemical reaction occurs in an open system. The worked example above utilizes choice 1 for a closed system with no reaction. Unit operation is the basic principle of chemical engineering. ... Solar irradiance spectrum at top of atmosphere. ... Comet Shoemaker-Levy 9 after breaking up under the influence of Jupiters tidal forces. ... Earth cutaway from core to exosphere. ... Solar irradiance spectrum at top of atmosphere. ... In thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, and chemical equilibrium. ...


Choice 2 would require an in-house exergy accounting analogous to a process mass balance or energy balance. If there are a reasonable number of unit operations, a professional chemical engineer could do this in a short period of time with a good software package to determine exergy flows in the plant. A mass balance (also called a material balance) is an accounting of material entering and leaving a system. ... Energy balance has the following meanings in several fields: In physics, energy balance is a systematic presentation of energy flows and transformations in a system. ...


Choice 3 would require all of choice 2 and converting multiple items usually thought of as economic overhead into terms of exergy. This could be a challenging task requiring considerable thought, but with several assumptions here and there (and more software to keep track of the accounting), it could be done. Business process overhead is the amount of resources used by an organization just to maintain existence. ...


Choice 4 would require a repetition of choice 3 for multiple industries, governmental agencies, and all other human activity to convert raw materials to the product. It seems unlikely that many producers would take the time to determine the complete exergy history of their product, but if we ever live in a world where producers were required to perform choice 3, we might be able to get a reasonable estimate of choice 4.


Choice 5 in combination with choice 4 is the only option that is relevant to environmental sustainability. Choice 5 requires exergy information from the field of systems ecology and many additional assumptions. However, with this information, we may address the questions: Sustainability is an attempt to provide the best outcomes for the human and natural environments both now and into the indefinite future. ... Systems Ecology is a transdiscipline which studies ecological systems, or ecosystems. ...

Does the human production of this item deplete the Earth's natural resources more quickly than those resources are able to regenerate themselves?
If so, how does this numerically compare to the depletion caused by producing an entirely different item using an entirely different set of natural resources?

Choice 6 represents all exergy changes on Earth in terms of one "currency" that may be used to estimate the relative value of different natural resources, but this value appraisal would not be on a time scale relevant to human activity. Choice 6 is useful for systems ecologists to consider exergy concepts as a driving force for the emergence structures in nature using a concept like emergy. Relative value is the attractiveness measured in terms of risk, liquidity, and return of one instrument relative to another, or for a given instrument, of one maturity relative to another. ... A termite cathedral mound produced by a termite colony: a classic example of emergence in nature. ... The neutrality of this article is disputed. ...


Choice 7 is the consequence of this line of thinking carried out to its fullest extent. It is a thought experiment to restate the cosmological argument. In philosophy, physics, and other fields, a thought experiment (from the German Gedankenexperiment) is an attempt to solve a problem using the power of human imagination. ... The cosmological argument is a metaphysical argument for the existence of God, traditionally known as an argument from universal causation, an argument from first cause, and also as an uncaused cause argument. ...


Quality of energy types

(exergy-to-energy ratio will be in this article. exergy-to-exergy will be moved to Exergy efficiency. Some will be removed.) Exergy efficiency is also called second-law efficiency because it computes the efficiency of a process taking the second law of thermodynamics into account. ...


The ratio of exergy to energy in a substance can be considered a measure of energy quality. Forms of energy such as macroscopic kinetic energy, electrical energy, and chemical Gibbs free energy are 100% recoverable as work, and therefore have an exergy equal to their energy. However, forms of energy such as radiation and thermal energy can not be converted completely to work, and have exergy content less than their energy content. The exact proportion of exergy in a substance depends on the amount of entropy relative to the surrounding environment as determined by the Second Law of Thermodynamics. Energy quality the contrast between different forms of energy, the different trophic levels in ecological systems and the propensity of energy to convert from one form to another. ... In thermodynamics, the Gibbs free energy is a thermodynamic potential which measures the useful work obtainable from a closed thermodynamic system at a constant temperature and pressure. ... Thermodynamics (from the Greek θερμη, therme, meaning heat and δυναμις, dunamis, meaning power) is a branch of physics that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analyzing the collective motion of their particles using statistics. ...


Exergy is useful when measuring the efficiency of an energy conversion process. The exergetic, or 2nd Law efficiency, is a ratio of the exergy output divided by the exergy input. This formulation takes into account the quality of the energy, often offering a more accurate and useful analysis than efficiency estimates only using the First Law of Thermodynamics. Thermodynamics (from the Greek θερμη, therme, meaning heat and δυναμις, dunamis, meaning power) is a branch of physics that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analyzing the collective motion of their particles using statistics. ...


Work can be extracted also from bodies colder than the surroundings. When the flow of energy is coming into the body, work is performed by this energy obtained from the large reservoir, the surrounding. A quantitative treatment of the notion of energy quality rests on the definition of energy. According to the standard definition, Energy is a measure of the ability to do work. Work can involve the movement of a mass by a force that results from a transformation of energy. If there is an energy transformation, the second principle of energy flow transformations says that this process must involve the dissipation of some energy as heat. Measuring the amount of heat released is one way of quantifying the energy, or ability to do work and apply a force over a distance. Ice melting - classic example of entropy increasing[1] described in 1862 by Rudolf Clausius as an increase in the disgregation of the molecules of the body of ice. ...


However, it appears that the ability to do work is relative to the energy transforming mechanism that applies a force. This is to say that some forms of energy perform no work with respects to some mechanisms, but perform work with respects to others. For example, water does not have a propensity to combust in an internal combustion engine, whereas gasoline does. Relative to the internal combustion engine, water has little ability to do work that provides a motive force. If “energy” is defined as the ability to do work then a consequence of this simple example is that water has no energy - according to this definition. Nevertheless, water, raised to a height, does have the ability to do work like driving a turbine, and so does have energy. Lightning is the electric breakdown of air by strong electric fields, which causes an energy transfer from the electric field to heat, mechanical energy (the random motion of air molecules caused by the heat), and light. ...


This example means to demonstrate that the ability to do work can be considered relative to the mechanism that transforms energy, and through such a conversion applies a force. From this observation we might wish to use the word “quality”, and the term “energy quality” to characterise the energetic differences between substances and their propensities to perform work given a specific mechanism. That is the abilities of different energy forms to flow and be transformed in certain mechanisms. With this lexicon, we can say that energy quality is mechanism-relative, and the energy efficiency of a mechanism is energy quality-relative – an internal combustion engine running on water has nearly 0% efficiency since it has the propensity to transform little or no water-energy into thermal-energy. In order to clarify things here we might think of this as the “water-efficiency”. The mechanism of interest is also our system of reference, such that the choice of energy quality specifies a certain system of reference. Thus with respects to the internal combustion system of reference, it has a low “water-efficiency”


Exergy of heat available at a temperature

(some of this will be moved up to mathematics section) Maximal possible conversion of heat to work, or exergy content of heat, depends on the temperature at which heat is available and the temperature level at which the reject heat can be disposed, that is the temperature of the surrounding. The upper limit for conversion is known as Carnot efficiency and was discovered by Nicolas Léonard Sadi Carnot in 1824. See also Carnot heat engine. This article includes a list of works cited or a list of external links, but its sources remain unclear because it lacks in-text citations. ... The Carnot heat engine uses a particular thermodynamic cycle studied by Nicolas Léonard Sadi Carnot in the 1820s and expanded upon by Thomas Benoit in the 1840s and 50s. ... Sadi Carnot Nicolas Léonard Sadi Carnot (June 1, 1796 - August 24, 1832) was a French mathematician and engineer who gave the first successful theoretical account of heat engines, the Carnot cycle, and laid the foundations of the second law of thermodynamics. ... 1824 was a leap year starting on Thursday (see link for calendar). ... A Carnot heat engine is a hypothetical engine that operates on the reversible Carnot cycle. ...


Carnot efficiency is

eta = 1 - frac{T_C}{T_H} qquad mbox{(1)}

where TH is the higher temperature and TC is the lower temperature, both as absolute temperature. From Equation 1 it is clear that in order to maximize efficiency one should maximize TH and minimize TC. Absolute zero is the lowest temperature that can be obtained in any macroscopic system. ...


For calculation of exergy of heat available at a temperature there are two cases: the body releasing heat is higher than the surrounding, or, the temperature of the body is lower than the surrounding.


Exergy fraction of heat available at a temperature higher than the surrounding is:

frac{E}{Q}  = 1 - frac{T_o}{T_h} qquad mbox{(2)}

where Th is the temperature of the heat source, and To is the temperature of the surrounding.


Exergy of cold is though:

frac{E}{Q}  = 1 - frac{T_c}{T_o} qquad mbox{(3)}

where Tc is the temperature of the cold body that is receiving heat from the surroundings.


See also

energy Portal
  • Energy: world resources and consumption
  • Emergy
  • Exergoecology

Image File history File links Portal. ... The neutrality of this article is disputed. ...

References

  1. ^  Perrot, Pierre (1998). A to Z of Thermodynamics. Oxford University Press. ISBN 0-19-856552-6. 
  2. ^  lowexnet.
  3. ^ a  Z. Rant (1956). "Exergie, ein neues Wort fur "Technische Arbeitsfahigkeit" (Exergy, a new word for "technical available work")". Forschung auf dem Gebiete des Ingenieurwesens 22: 36–37. 
  4. ^ a  J.W. Gibbs (1873). "A method of geometrical representation of thermodynamic properties of substances by means of surfaces: repreinted in Gibbs, Collected Works, ed. W. R. Longley and R. G. Van Name (New York: Longmans, Green, 1931)". Transactions of the Connecticut Academy of Arts and Sciences 2: 382–404. 
  5. ^ a  S. Carnot (1824). Réflexions sur la puissance motrice du feu sur les machines propres a developper cette puissance. (Reflections on the Motive Power of Fire and on Machines Fitted to Develop That Power. Translated and edited by R.H. Thurston 1890). Paris: Bachelier. 
  6. ^ Alberty, R. A. (2001). "Use of Legendre transforms in chemical thermodynamics". Pure Appl. Chem. 73 (8): 1349–1380. 
  7. ^ Lord Kelvin (William Thomson) (1848). "On an Absolute Thermometric Scale founded on Carnot's Theory of the Motive Power of Heat, and calculated from Regnault's Observations". Philosophical Magazine [from Sir William Thomson, Mathematical and Physical Papers, vol. 1 (Cambridge University Press, 1882), pp. 100-106.]. 
  8. ^  a  I. Dincer, Y.A. Cengel (2001). "Energy, entropy, and exergy concepts and their roles in thermal engineering". Entropy 3: 116–149. 
  9. S.E.Jorgensen, H.T.Odum, M.T.Brown (2004) 'Emergy and exergy stored in genetic information', Ecological Modelling, Vol. 178, pp. 11-16.
  1. San, J. Y., Lavan, Z., Worek, W. M., Jean-Baptiste Monnier, Franta, G. E., Haggard, K., Glenn, B. H., Kolar, W. A., Howell, J. R./1982/Exergy analysis of solar powered deiccant cooling system/In Proc. of the American Section of the Intern. Solar Energy Society, Houston, TX, pp. 567-572
  • S.Bastianoni, A. Facchini, L. Susani, E. Tiezzi (2007) 'Emergy as a function of exergy', Energy 32, 1158-1162.

External links

Exergy and Rankine cycle - http://twt.mpei.ac.ru/MAS/Worksheets/Rankine3D.mcd


  Results from FactBites:
 
Exergy - Wikipedia, the free encyclopedia (5221 words)
Exergy is a measure of the potential of a system to cause a change as it achieves equilibrium with its surroundings.
Exergy is a measurable value that is decreased during the conversion of useful energy to useless energy.
Exergy is the work that can no longer be done elsewhere because the economic good was made.
  More results at FactBites »

 
 

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