GATE 2016 ME (ME2) – Question 29

Thermal Engineering Applications · Power Engineering: vapour and gas power cycles, regeneration and reheat · 1 mark · Numerical answer

Consider a simple gas turbine (Brayton) cycle and a gas turbine cycle with perfect regeneration. In both the cycles, the pressure ratio is 6 and the ratio of the specific heats of the working medium is 1.4. The ratio of minimum to maximum temperatures is 0.3 (with temperatures expressed in K) in the regenerative cycle. The ratio of the thermal efficiency of the simple cycle to that of the regenerative cycle is _________

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Correct answer: 0.79 to 0.81

Explanation

Put a=rp^((γ−1)/γ)=6^(2/7). Ideal simple-cycle efficiency is1−1/a. With perfect regeneration, efficiency is1−(Tmin/Tmax)a=1−0.3a. The required ratio is(1−1/a)/(1−0.3a)=**0.8022**. The stated temperatures permit useful regeneration.