20 02 17

Page 1

ENERGY CONVERSION A 2016-17 Name/Lastname:__________________________________________ Code n.___________ Exam 20/02/2017 Exercise 1 (10 points) Consider an intercooled gas turbine characterized at 15°C, 1 bar and 60% relative humidity in a clean-and-new condition without filter and silencer by:  overall compression ratio, 𝛽𝑇𝑂𝑇: 42,  low-pressure compression ratio, 𝛽𝐿𝑃: 𝛽𝐿𝑃 = √𝛽𝑇𝑂𝑇 3  turbine inlet temperature: 1350°C,  net electric power: 110 MW,  net electric specific work: 520 kJ/kg,  net electric efficiency: 45%. Moreover, the intercooler is operated with cooling water entering at 25°C and exiting at 35°C. Lastly, all air bleed- ings are from the high-pressure compressor. Neglecting the pressure drop in the intercooler and adopting justified simplifying assumptions, please: i. clearly motivate the solution procedure and highlight the assumptions (1 point); ii. sketch the plant layout, the T-s diagram of the cycle and the T-Q diagram of the intercooler (1.5 point); iii. calculate the thermal power of the intercooler and the stack temperature (3 points); iv. determine the pressure drop of a silencer that reduces the technical power of the expander by 0.5% (3 pts); v. justify without computing how this pressure drop influences all second-law efficiency losses (1.5 pts). Exercise 2 (12 points) A hot air flow (mair=200 kg/s, Tin,air=320°C) is available from an industrial process. This flow is to be used as a hot source for a highly superheated Rankine power cycle operating with a selected fluid (Tcrit=300°C, pcrit=100 bar, MM=150 kg/kmol, cp0=1333 J/kg K, rhoL=900 kg/m3). The cycle employs an internal recuperator, a water-cooled condenser (cooling water available at 15°C) as well as a single-stage expander (isentropic work of 100 kJ/kg) that is coupled to the…