ME300Lecture41

ME300Lecture41 - Lecture 41: Continue Brayton Cycle...

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41.1 Lecture 41: Continue Brayton Cycle Irreversibilities of Brayton cycles: Deviation of actual gas-turbine cycles from idealized ones: s 2s 1 C a 2a 1 a 3 4a T s 3 4s w h h w h h w h h w h h Note: T 2 > T 2s if p 2 = p 2s T 4 > T 4s if p 4 = p 4s irreversibilities change mechanical energy to thermal energy through friction.
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41.2 Continue Brayton Cycle Continue irreversibilities of Brayton cycles: Example: T 1 = 22 o C, p 1 = 0.95 bars, r p = p 2 /p 1 = 6, T 3 = 1100 K w C /w T Ideal 0.38 0.44 C = 0.82 and T = 0.85 0.23 0.62 Notes: » The overall efficiency is reduced by 40%! » Gas turbine performance is very sensitive to turbine and compressor efficiencies!
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41.3 Continue Brayton Cycle Introduce “regeneration” to boost overall efficiency : » Idea: reclaim “waste” heat normally exhausted to ambient. Regenerative open Brayton cycle: 4 1 fuel q R air 3 5 2 x Exhaust gases Regenerative heat exchanger Combustor w net
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41.4 Continue Brayton Cycle Continue regenerative Brayton cycle: s T 1 2 4 3 x 5 Reduction in q in Reduction in q out q in = q x 3 q out = q 5 1
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41.5
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ME300Lecture41 - Lecture 41: Continue Brayton Cycle...

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