ERICSSON AND STIRLING CYCLES
Significant increases in the thermal efficiency of gas turbine power plants can be achieved through intercooling, reheat, and regeneration. There is an economic limit to the number of stages that can be employed, and normally there would be no more than two or three. Nonetheless, it is instructive to consider the situation where the number of stages of both intercooling and reheat becomes indefinitely large. An ideal closed regenerative gas turbine cycle has several stages of compression and expansion and a regenerator whose effectiveness is 100%. Each intercooler is assumed to return the working fluid to the temperature at the inlet to the first compression stage and each reheater restores the working fluid to the temperature at the inlet to the first turbine stage. Very often, the temperature at which energy rejection occurs in the cyclic process is much higher than the temperature of the air. A considerable amount of energy which could be gainfully utilized is being rejected to the sink. High cycle efficiency can be expected only if the energy rejection occurs at the lowest possible temperature. If the high temperature gases are used to provide part of the energy input at state, the energy rejected to the sink is reduced, and the temperature at which such rejection occurs is also reduced. A considerable gain in cycle efficiency can thus be achieved. This idea is used in Stirling and Ericsson cycles, where devices called regenerators are used to heat the air after compression. The regenerator is merely a part of the heat engine where energy transfer as heat occurs between the outgoing hot gases and the gas in the cycle that is to undergo expansion.
The Stirling and Ericsson cycles are by themselves of no practical interest as heat engine cycles, since devices working on these cycles do not exist. Nonetheless, they are of interest since they have theoretical efficiencies equal to that of the Carnot cycle, and can be...
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