Page 34 - Advanced Gas Turbine Cycles

Chapter 1. A brief review of power genemfion fhetmo&namics 11

increase in 6 leads to higher thermal efficiency. Reheat alone (without a heat exchanger)
between two stages of turbine expansion, has the effect of increasing & but it also
increases so that 6 decreases and thermal efficiency drops. Similarly, intercooling alone
(without a heat exchanger) lowers the mean temperature of heat rejected (decreasing tA)
and it also decreases & so that 6 decreases and thermal efficiency drops. However, when
reheating and intercooling are coupled with the use of a heat exchanger then & is
increased and ,$A decreased, so 6 is increased and thermal efficiency increased markedly.
Indeed, for many stages of reheat and intercooling, a Carnot cycle efficiency can in theory
be attained, with all the heat supplied near the top temperature TB and all the heat rejected
near the lowest temperature, TA.
Reheat and intercooling also increase the specific work of the cycle, the amount of work
done by unit quantity of gas in passing round the plant. This is illustrated by the increase in
the area enclosed by the cycle on the T, s diagram.
More details are discussed in Chapter 3, where the criteria for the performance of the
components within gas turbine plants are also considered.

References
[l] Horlock, J.H. (1987). Cc-generation: Combined Heat and Power, Pergamon Press, Oxford, See also 2nd edn,
Krieger, Melbourne, FL, 1996.
[2] Horlock, J.H. (1992), Combined Power Plants, Pergamon Press, Oxford, See also 2nd edn, Krieger,
Melbourne, FL, 2002.
[3] Haywm R.W. (1991). Analysis of Engineering Cycles 4th edn, Pergamon Press, Oxford.
[4] Caputa, C. (1%7), Una Cifra di Merito Dei Cicli Termcdinamici Directti, Il Calore 7, 291-300.