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Research Papers

On the Evolution of the Definition of Entropy From Clausius to Today*

[+] Author and Article Information
Elias P. Gyftopoulos

Departments of Mechanical Engineering
and of Nuclear Engineering
Massachusetts Institute of Technology,
Cambridge, MA 02139

All correct statements of the laws of thermodynamics that appear in the literature are proven to be special cases of the statements given by Gyftopoulos and Beretta [4].

*Proceedings of the Winter Annual Meeting of the American Society of Mechanical Engineers, Atlanta, GA, November 17–22, 1996, in Thermodynamics and the Design, Analysis, and Improvement of Energy Systems, editor A. B. Duncan et al., ASME book G01022, AES-Vol. 36, pp. 199–204 (1996).

J. Energy Resour. Technol 137(2), 021010 (Mar 01, 2015) (5 pages) Paper No: 10-Gyftopoulos-ASME-AES3; doi: 10.1115/1.4026386 History: Online November 18, 2014

Carnot analyzed an engine operating between two reservoirs. Through a peculiar mode of reasoning, he found the correct optimum shaft work performed during a cyclic change of state of the engine. Clausius justified Carnot's result by enunciating two laws of thermodynamics, and introducing the concept of entropy as a ratio of heat and temperature of a thermodynamic equilibrium state. By appropriate algebraic manipulations, in this paper we express Carnot's optimum shaft work in terms of available energies or exergies of the end states of the reservoirs, and Clausius' entropy in terms of energy and available energy. Next, we consider the optimum shaft work performed during a cyclic change of state of an engine operating between a reservoir, and a system with fixed-amounts of constituents, and fixed-volume but variable temperature. We express the optimum shaft work in terms of the available energies of the end states, and Clausius' entropy in terms of energy and available energy. Formally, the entropy expression is identical to that found for the Carnot engine except for the difference in end states. Finally, we consider the optimum shaft work performed during a cyclic change of state of an engine operating between system A initially in any state A1 (thermodynamic equilibrium or not) and reservoir R. We call this optimum generalized available energy with respect to R, and use it together with energy to define an entropy of any state A1. Again we observe that the expression for entropy is formally identical to the two given earlier except for the difference in end states.

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Figures

Grahic Jump Location
Fig. 1

Schematic of a Carnot Engine

Grahic Jump Location
Fig. 2

Schematic of a cyclic change of state of a Carnot engine: (a) initial states of the reservoirs; and (b) final states of the reservoirs

Grahic Jump Location
Fig. 3

Schematic of a cyclic change of state of an engine: (a) initial state of A at temperature T1; and (b) final state of A at temperature T0 = TR

Grahic Jump Location
Fig. 4

Schematic of a cyclic change of state of an engine: (a) initial state of A is not thermodynamic equilibrium; and (b) final state of A is thermodynamic equilibrium so that A and R are in mutual stable equilibrium

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