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Technical Brief

Demonstration of an Inverse Relationship Between Thermal Efficiency and Specific Entropy Generation for Combustion Systems

[+] Author and Article Information
Yousef Haseli

School of Engineering and Technology, Central Michigan University Mount Pleasant, MI, USA
hasel1y@cmich.edu

Katherine Hornbostel

Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA, USA
hornbostel@pitt.edu

1Corresponding author.

ASME doi:10.1115/1.4040793 History: Received May 07, 2018; Revised July 02, 2018

Abstract

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, 2nd 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.

Copyright (c) 2018 by ASME
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