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Problem 6-2 - Example 6-2 One of the most efficient types...

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Example 6-2 One of the most efficient types of power plant in service today is a Combined Cycle Power Plant, which includes both a high temperature gas turbine and a low temperature steam turbine. In one such plant, 480 MW of net power is produced. The cooling water that removes heat from the cycle enters at 45°F, leaves at 65°F, and flows at a rate of 1.52 x10 4 lbm/s. The firing temperature in the gas turbine is 2600°F. Compare the efficiency of this cycle to the efficiency of a theoretical maximum power cycle operating between these temperature limits. Also compute the efficiency of the Carnot cycle for the same temperature limits. Solution: Heat is rejected from the cycle in the cooling water at the rate: L p Q mc T = ± ± Btu cp(water, 55, 14.7) 1.00 lbm R p c T P = = = = ( ) 4 o lbm Btu 1.52 10 1.00 65 45 F s lbm R L Q ⎞⎛ = × ⎟⎜ ⎠⎝ ± 5 Btu 3.04 10 s L Q = × ± The first law for a cycle is H net L Q W Q = + ± ± ± ( ) 5 1000 kw Btu 1.055 kw 480MW 3.04 10 Btu 1 MW s 1 s H

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