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The Elusive Nature of Entropy and Its Physical Meaning
Entropy 2014, 16(2), 1089-1100; doi:10.3390/e16021089

Entropy and Its Correlations with Other Related Quantities

1,*  and 2
1 School of Energy and Power Engineering, Huazhong University of Science & Technology, Wuhan 430074, China 2 Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China
* Author to whom correspondence should be addressed.
Received: 8 November 2013 / Revised: 21 January 2014 / Accepted: 27 January 2014 / Published: 19 February 2014
(This article belongs to the Special Issue Entropy and the Second Law of Thermodynamics)
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In order to find more correlations between entropy and other related quantities, an analogical analysis is conducted between thermal science and other branches of physics. Potential energy in various forms is the product of a conserved extensive quantity (for example, mass or electric charge) and an intensive quantity which is its potential (for example, gravitational potential or electrical voltage), while energy in specific form is a dissipative quantity during irreversible transfer process (for example mechanical or electrical energy will be dissipated as thermal energy). However, it has been shown that heat or thermal energy, like mass or electric charge, is conserved during heat transfer processes. When a heat transfer process is for object heating or cooling, the potential of internal energy U is the temperature T and its potential “energy” is UT/2 (called entransy and it is the simplified expression of thermomass potential energy); when a heat transfer process is for heat-work conversion, the potential of internal energy U is (1 − T0/T), and the available potential energy of a system in reversible heat interaction with the environment is U U0 T0(S S0), then T0/T and T0(S S0) are the unavailable potential and the unavailable potential energy of a system respectively. Hence, entropy is related to the unavailable potential energy per unit environmental temperature for heat-work conversion during reversible heat interaction between the system and its environment. Entropy transfer, like other forms of potential energy transfer, is the product of the heat and its potential, the reciprocal of temperature, although it is in form of the quotient of the heat and the temperature. Thus, the physical essence of entropy transfer is the unavailable potential energy transfer per unit environmental temperature. Entropy is a non-conserved, extensive, state quantity of a system, and entropy generation in an irreversible heat transfer process is proportional to the destruction of available potential energy.
Keywords: potential energy; entransy; entropy; unavailable energy; thermomass potential energy; entransy; entropy; unavailable energy; thermomass
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Wu, J.; Guo, Z. Entropy and Its Correlations with Other Related Quantities. Entropy 2014, 16, 1089-1100.

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