Maximum thermal efficiency is commonly assumed to correspond to minimum entropy generation. However, previous work has disproven this assumption for various power generation systems. In order to reconcile these two optimization approaches, second law analysis is performed here in terms of specific entropy generation (SEG), defined as the total entropy generation per mole of fuel. An inverse relationship between thermal efficiency and SEG is derived here, and it is shown that maximum thermal efficiency always corresponds to minimum SEG for lean fuel/air mixtures. Furthermore, the maximum efficiency limit of conventional power plants is shown to differ from the Carnot efficiency. Finally, a modified second law efficiency is introduced, and it is shown that the exhaust combustion products are bounded by a theoretical minimum temperature.
Issue Section:
Technical Brief
References
References
1.
Leff
, H. S.
Jones
, G. L.
1975
, “Irreversibility, Entropy Production, and Thermal Efficiency
,” Am. J. Phys.
, 43
(11
), pp. 973
–980
.2.
Salamon
, P.
Nitzan
, A.
Andresen
, B.
Berry
, R. S.
1980
, “Minimum Entropy Production and the Optimization of Heat Engines
,” Phys. Rev. A
, 21
(6
), pp. 2115
–2129
.3.
Salamon
, P.
Nitzan
, A.
1981
, “Finite Time Optimizations of a Newton's Law Carnot Cycle
,” J. Chem. Phys.
, 74
(6
), pp. 3546
–3560
.4.
Salamon
, P.
Hoffmann
, K. H.
Schubert
, S.
Berry
, R. S.
Andresen
, B.
2001
, “What Conditions Make Minimum Entropy Production Equivalent to Maximum Power Production
,” J. Nonequilib. Thermodyn.
, 26
(1), pp. 73
–83
.5.
Haseli
, Y.
2013
, “Optimization of Regenerative Brayton Cycle by Maximization of a Newly Defined Second Law Efficiency
,” Energy Convers. Manage.
, 68
, pp. 133
–140
.6.
Haseli
, Y.
2013
, “Performance of Irreversible Heat Engines at Minimum Entropy Generation
,” Appl. Math. Model.
, 37
(23
), pp. 9810
–9817
.7.
Haseli
, Y.
2016
, “Efficiency of Irreversible Brayton Cycles at Minimum Entropy Generation
,” Appl. Math. Model.
, 40
(19–20
), pp. 8366
–8376
.8.
Feidt
, M.
Costea
, M.
Petrescu
, S.
Stanciu
, C.
2016
, “Nonlinear Thermodynamic Analysis and Optimization of a Carnot Engine Cycle
,” Entropy
, 18
(7
), p. 243
.9.
Haseli
, Y.
2018
, “Specific Entropy Generation in a Gas Turbine Cycle
,” ASME J. Energy Resour. Technol.
, 140
(3
), p. 032002
.10.
Haseli
, Y.
2018
, “Efficiency Improvement of Thermal Power Plants Through Specific Entropy Generation
,” Energy Convers. Manage.
, 159
, pp. 109
–120
.11.
H.
, Teng
C. M.
, Kinoshita
S. M.
, Masutani
L.
Zhou
, J.
1998
, “Entropy Generation in Multicomponent Reacting Flows
,” ASME J. Energy Resour. Technol.
, 120
(3
), pp. 226
–232
.12.
Beretta
, G. P.
Keck
, J. C.
1983
, “Energy and Entropy Balances in a Combustion Chamber. Analytical Solution, Combust
,” Sci. Technol.
, 30
(1–6
), pp. 19
–29
.13.
Bejan
, A.
1996
, “Models of Power Plants That Generate Minimum Entropy While Operating at Maximum Power
,” Am. J. Phys.
, 64
(8
), pp. 1054
–1059
.14.
Bejan
, A.
1996
, “The Equivalence of Maximum Power and Minimum Entropy Generation Rate in the Optimization of Power Plants
,” ASME J. Energy Resour. Technol.
, 118
(2
), pp. 98
–101
.15.
Klein
, S.
Nellis
, G.
Thermodynamics
, 1st ed.
, Cambridge University Press
, New York, Chap. 13.16.
Gyftopoulos
, E. P.
Beretta
, G. P.
2010
, Thermodynamics: Foundations and Applications
, Dover Publications
, Mineola, NY
, Chap. 31.17.
Cengel
, Y.
Boles
, M. A.
Thermodynamics: An Engineering Approach
, 5th ed.
, McGraw-Hills
, New York
, Chap. 15.18.
Li
, T.
Fu
, W.
Zhu
, J.
2014
, “An Integrated Optimization for Organic Rankine Cycle Based on Entransy Theory and Thermodynamics
,” Energy
, 72
, pp. 561
–573
.19.
Adams
, T.
Mac Dowell
, N.
2016
, “Off-Design Point Modelling of a 420 MW CCGT Power Plant Integrated With an Amine-Based Post-Combustion CO2 Capture and Compression Process
,” Appl. Energy
, 178
, pp. 681
–702
.20.
Mac Dowell
, N.
Shah
, N.
2015
, “The Multi-Period Optimisation of an Amine-Based CO2 Capture Process Integrated With a Super-Critical Coal-Fired Power Station for Flexible Operation
,” Comput. Chem. Eng.
, 74
, pp. 169
–183
.21.
Mansour
, M. S.
Chen
, Y. C.
Peters
, N.
1999
, “Highly Strained Turbulent Rich Methane Flames Stabilized by Hot Combustion Products
,” Combust. Flame
, 116
(1–2
), pp. 136
–153
.22.
Leff
, H. S.
1987
, “Thermal Efficiency at Maximum Work Output: New Results for Old Heat Engines
,” Am. J. Phys.
, 55
, pp. 602
–609
.Copyright © 2019 by ASME
You do not currently have access to this content.
