constant pressure. J. H. Potter of Stevens Institute of Technology researched the origin of this cycle and found an early patent (1791) in Great Britain by John Barber that described the basic gas turbine [1]. About 1851, Joule, also of Great Britain, proposed an indirect-fired gas turbine. The man for whom the Brayton cycle is named, George Brayton, was a New England inventor who, in 1872, produced the first successful internal combustion engine in the United States. Although there is no evidence that he ever formally proposed the cycle that now bears his name, Brayton obtained several patents and produced many variants of his constant-pressure combustion cycle reciprocating piston engine. A Brayton engine was even specified in the famous Selden automobile patent. However, the large volume flow of gas required by the cycle resulted in Brayton piston engines being very large and inefficient when compared to the Otto and diesel cycle engines. As a result George Brayton's engines did not survive his death in 1892 [2]. The development of efficient rotating compressors and turbines provided the means to effectively flow the large volumes of working fluid required to produce a practical constant-pressure combustion cycle power plant, the gas turbine. Early texts on aircraft gas turbines attached the Brayton name to the gas turbine cycle and through perpetuation, like Topsy, it grew into our lexicon. Thus, although George Brayton's engines did not survive, except in museums, his name has been perpetuated by the success of the modern gas turbine power plant. Historically, the closed Brayton gas turbine cycle was conceived and patented in Switzerland during 1935 by Drs Ackeret and Keller of Escher Wyss. Escher Wyss constructed a 2 MW closed Brayton demonstration plant in 1939 which operated with a 32% efficiency at a turbine inlet temperature of 973K (1292F). Over 6000 hours of operation were achieved with this unit [3]. When compared to the steam Rankine or open cycle gas turbine, the closed Brayton cycle had a combination of features which neither could match: • High efficiency at modest power levels. • Ability to operate using a very wide range of fuels (coal, gas, oil, mine gas, blast furnace gas, and combinations of these). • High heat rejection temperatures which were ideal for cogeneration. Due to these attractive features and the experience gained from that first unit, closed Brayton cycle systems were chosen for installation at commercial sites where indigene- ous fuels could be used and the waste heat utilized for the heating of homes, factories, and mines. About 20 units were constructed in Europe and Japan during the 1950s and early 1960s [3, 4]. Over 700000 hours of successful operation have been logged by these units. However, as the technology of open cycle gas turbines progressed due to the development conducted by the aircraft industry and the cost of oil in Europe dropped below that of coal, the lower cost of open cycle systems resulted in these closed Brayton systems being supplanted by the open cycle systems in the small cogeneration market. Since the early 1950s the closed Brayton cycle has been investigated and tests conducted for a wide range of applications including marine, undersea, portable military power, cryogenic refrigeration, cogeneration, large utility power, and space power. These applications utilized a myriad of heat sources including chemical, nuclear reactors, radioisotopes, solar energy, and sensible heat (thermal storage) [5, 6, 7]. Based on this heritage of successful performance and the continuance of aircraft
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