Page 192 - Entrophy Analysis in Thermal Engineering Systems

Appendices

Appendix A: Efficiency at maximum power
An interesting characteristic of most endo-reversible engines is the
maximum power efficiency; i.e.,

r ffiffiffiffiffiffiffi
η ¼ 1 T L (A.1)
T H
For many years after Eq. (A.1) appeared in Curzon and Ahlborn (1975)’s
paper, the efficiency in Eq. (A.1) carried the subscripts “CA” denoting
the initials of the authors last names. Later, it turned out that Eq. (A.1)
had been presented about two decades earlier by Chambadal and Novikov.
There is however evidence [1] that the expression for the efficiency at max-
imum power had already been derived by James Henry Cotterill, Professor
of Applied Mechanics in the Royal Naval College, in the late 19th century.
The maximum power efficiency can be found in the second edition of the
Cotterill’s textbook [1], Chapter IV, pages 100–102. The author was unsuc-
cessful in locating the first edition of the book published in 1877 to confirm
whether Eq. (A.1) was first given in the earliest edition. Nevertheless,
important to remember is that it would be inappropriate to refer
Eq. (A.1) as Chambadal-Novikov-Curzon-Ahlborn efficiency.

Appendix B: Effect of fuel type on SEG

To examine the effect of the fuel type on SEG, the efficiency and the
specific entropy generation are calculated and compared for the gas turbine
cycle studied in Chapter 8 operating on hydrogen, propane, methanol, and
ethanol. At a given pressure ratio and TIT, the specific entropy generation is
quantitatively different depending on the type of the fuel burnt. The highest
and lowest values of SEG (measured in J/molK) are obtained for propane
(C 3 H 8 ) and hydrogen, respectively. A fuel with a greater heating value
would yield a higher SEG. The heating values of the fuels and the minimum
specific entropy generation of the cycle at TIT¼1100K are compared in
Table B.1. Note that if the calculations are performed on mass basis the
minimum SEG would still correlate with the heating value. In this case,

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