2020 Past Paper EC by HT

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ENERGY CONVERSION A 2019-20 Note: you can keep this text for self-evaluation at the end of the exam; in case you withdraw, you shall return it. Exam 14/02/2020 Please, write your person code and surname-name on all sheets you hand in. Exercise 1 (10 points) A conventional micro gas turbine is modified to operate with concentrated solar power: the combustor is replaced with a solar collector on which solar irradiation is concentrated to attain the same turbine inlet temperature of 950 °C at peak conditions (direct irradiation of 800 W/m2). Considering pressure drops in turbine components, please: i. motivate clearly the solution procedure and highlight neatly the assumptions (1 point); ii. sketch clearly the process flow diagram and the cycle on the T-s diagram (1.5 points); iii. estimate the mass flow rate of breathed air to produce 100 kW of electric output assuming proper values for the design parameters (2.5 points); iv. compute the second-law efficiency loss due to energy introduction in the cycle under proper simplifying assumptions (2 points); v. assuming a shadow coefficient of 5, calculate the land extension of the heliostat field referring to peak conditions (3 points). Exercise 2 (12 points) Consider two air streams characterized as follows: • Stream A: temperature 300 °C, pressure 5 bar and mass flow rate 10 kg/s, • Stream B: temperature -100 °C, pressure 0.5 bar and mass flow rate 5 kg/s. Please: i. clearly motivate the solution procedure and highlight the assumptions (1 point); ii. compute the maximum mechanical power obtainable simultaneously from the two sources (2 points); iii. propose and sketch an optimal plant layout that exploits simultaneously the two streams and that does not employ heat exchangers (2 point); iv. sketch the cycle on the T-s…