Exercise 3 Second law analysis of power cycles

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ENERGY CONVERSION A 2019-20 1 Exercises Second-law analysis of power cycles 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; • (total) turbine intel temperature (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, for all cases: i. plot a realistic cycle on the T-s diagram, for all alternative designs, highlighting the differences; ii. compute and compare the second-law efficiency losses due to only the pressure drop; 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 (see off-design exercises). Exercise 2 Consider an air-cooled single-level combined cycle that features the following parameters: • (total) turbine outlet temperature (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 extreme cases: 1. ΔT of subcooling between EVAP and ECO outlet of 20 °C; 2. ΔT of subcooling between EVAP and ECO outlet of 0 °C, employing a valve between them with a pressure loss, Δp, of 10 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; iii. compute and compare the wasted power due to the following irreversibilities: o…