Exercise 3 Second law analysis of power cycles

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ENERGY CONVERSION A 2016-17 1 Exercises Second-law analysis of gas turbines in diverse configurations Exercise 1 Consider four different gas turbines operating with the following common conditions: • ambient temperature: 15°C ; • ambient pressure: 1.01325 bar; • compression pressure ratio: 40; • TIT: 1400°C; • breathed air mass flow rate: 100 kg/s. The gas turbine differ by a localized pressure drop of 0.1 bar alternatively located at: 1. compressor suction; 2. compressor discharge; 3. turbine suction; 4. turbine discharge. Please: i. plot a realistic cycle on the T -s diagram, for all alternative cases, highlighting the differences; ii. compute and compare the second-law efficiency losses due to only the pressure drop for all alternative cases; iii. comment without computing how all other losses change from case to case. Note: the exercise could be setup as a single gas turbine operating in four off-design conditions. Exercise 2 Consider an air-cooled single-level combined cycle that features the following parameters: • TOT in combined cycle configuration: 600°C; • exhaust gas mass flow rate: 200 kg/s; • steam cycle evaporation pressure: 35 bar (absolute); • evaporation enthalpy at 35 bar (absolute): 1750 kJ/kg; • evaporation temperature at 35 bar (absolute): 242°C. Moreover, consider two alternative cases: 1. ΔT of subcooling at ECO outlet of 40°C; 2. ΔT of subcooling at ECO outlet of 0°C, employing a valve downstream of EC O with a pressure loss, Δp, of 15 bar; Please: i. sketch the plant layouts; ii. plot the temperature -heat transfer (T -Q) diagram of the HRSG for the two cases on a single chart in order to highlight the difference between the cases; iii. compute and compare the wasted power due to the following irreversibilities: o heat exchange within the ECO,…