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The Cheng cycle is a thermodynamic cycle which uses a combination of two working fluids, one gas and one steam. It can therefore be considered a combination of the Brayton cycle and the Rankine cycle. It was named for Dr. Dah Yu Cheng.
The company founded by Dr. Cheng has developed systems in partnership with both GM and GE turbine manufacturers to take advantage of the Cheng cycle by modification of existing turbine designs before construction. The Cheng cycle involves the heated exhaust gas from the turbine being used to make steam in a heat recovery steam generator.Penning, F. M. and de Lange, F. M. (1995) Steam Injection: analysis of a typical application Applied Thermal Engineering Vol. 16, No. 2, pp. 115 125 The steam so produced is injected into the gas turbine's combustion chamber to increase power output.De Paepe, M. and E. Dick (2001) Technological and economical analysis of water recovery in steam injected gas turbines, Applied Thermal Engineering, Volume 21, Issue 2, January 2001, Pages 135–156 The process can be thought of as a parallel combination of the gas-turbine Brayton cycle and a steam-turbine Rankine cycle.Stadler, F. and U. Schneider, (1997) ELIN Cheng Cycle, Elin Energieversorgung GmbH, 1997Motz, D.A. (1987) The Cheng Cycle: principles and applications, Ass. Energy Engng, 8th World Energy Engng Conf., Atlanta, USA The cycle was invented by Prof. Dah Yu Cheng of the University of Santa Clara, who patented it in 1976. Cen, Ke-fa Yong Chi, Jianhua Yan (2007) Challenges of Power Engineering and Environment: Proceedings of the International Conference on Power Engineering, Springer (Accessed August 2012)Cheng, D.Y. and A.L.C. Nelson (2002) Chronological development of the Cheng cycle steam injected gas turbine during the past 25 years. in: Anon (Ed.), Proceedings of ASME Turbo Expo 2002, Amsterdam, ASME Paper No. GT-2002-30119 (2002), pp. 421–428
A fully Cheng-cycle gas/steam two-fluid turbine can achieve a theoretical thermal efficiency of 60%, matching or even exceeding many traditional combined-cycle gas turbines that keep the steam Rankine Cycle and gas Brayton Cycle as separate loops.
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