The equivalence of minimum specific entropy generation and maximum thermal efficiency in a gas turbine cycle

In ECOS Conference 2010, I presented an article and discussed that minimizing entropy generation in simple and regenerative Brayton cycles would not lead to maximum thermal efficiency or maximum power output. Several articles have been published since then by others showing that minimization of entropy generation does not always lead to an optimum performance in energy conversion systems. A key element overlooked when applying an entropy-based analysis to irreversible power cycle is the amount of fuel burnt as the source of energy input to power plant. This article introduces specific entropy generation defined as the total entropy generated due to the operation of a power cycle per unit consumption of fuel. It is shown that the specific entropy generation correlates with the thermal efficiency of the cycle. The maximum thermal efficiency coincides with the minimum specific entropy generation. The results are presented for five different fuels including methane, hydrogen, propane, methanol and ethanol. The specific entropy generation describes the efficiency losses in a real power plant better than the entropy generation rate.