Two Principles of Differential Second Law Heat Exchanger Design

[+] Author and Article Information
R. B. Evans

Georgia Institute of Technology, The George W. Woodruff School of Mechanical Engineering, Atlanta, GA 30332

M. R. von Spakovsky

École Polytechnique Fédérale de Lausanne, Départment de mécanique, Laboratoire d’énergétique industrielle, Lausanne, Switzerland

J. Heat Transfer 113(2), 329-336 (May 01, 1991) (8 pages) doi:10.1115/1.2910565 History: Received April 26, 1989; Revised August 31, 1990; Online May 23, 2008


In this paper, two fundamental principles of differential Second Law analysis are set forth for heat exchanger design. The first principle defines a Second Law temperature, while the second principle defines a Second Law temperature difference. The square of the ratio of the Second Law temperature difference to the Second Law temperature is shown always to be equal to the negative of the partial derivative of the rate of entropy generation (for heat transfer) with respect to the overall conductance of the heat exchanger. For the basic design of elementary heat exchangers, each of these two Second Law quantities is shown to take the form of a simple geometric average. Nonelementary considerations result in corrected geometric averages, which relate directly to the corrected log-mean temperature difference. Both the corrected log-mean temperature difference (nonelementary considerations) and the uncorrected or just log-mean temperature difference (elementary considerations) are widely used in heat exchanger analysis. The importance of these two principles in both exergy and essergy analysis is illustrated by a unified basic treatment of the optimum design of elementary heat exchangers. This results in a single optimization expression for all flow arrangements (i.e., counterflow, parallel flow, and certain crossflow cases).

Copyright © 1991 by The American Society of Mechanical Engineers
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