Maximum Specific Work for Power Optimized Endoreversible Gas Turbine Cycles

Abstract

As a Carnot-like cycle the continuous Ericsson cycle represents the upper efficiency limit of multistage gas turbine operations using intercooling, reheating and regeneration. When considering linear external heat transfer modes, the theory of irreversible thermodynamics for continuous endoreversible Carnot-like cycles gives rise to an optimum efficiency at maximum power output of β= 1 — ( T L/ T H)0.5 in contrast to the upper limit of β = 1 — ( T L/ T H) obtained from classical thermodynamics for ideal Carnot-like cycles. It is shown here that, additionally, for continuous (gas turbine) endoreversible cycles like Carnot and Ericsson, the optimum specific work output at maximum power ( wopt), is exactly half of that obtained for externally reversible cycles (Carnot work, wrev ) operating between the same temperature limits (i.e. wopt = 1/2 wrev). Moreover, this optimum specific work output is the same expression for these and a family of other continuous cycles. The formulation used in the analysis makes use of the ideal gas model with constant specific heats, though the results are shown to be universal for cycles using linear heat transfer laws and using vapours and real gases having specific heats that vary only as a function of temperature. Also given for the first time for this general family of cycles are expressions for power optimized mass flow rates and the cycle operating temperatures which yield optimum power. These results quantify the absolute upper power limit for power optimized gas turbine operations where the external heat transfer is by linear modes.