Exam 20190827 Eng

Pagina 1

ENERGY CONVERSION A 2018-19 Note: you can keep this text for self -evaluation at the end of the exam; in case , though, you withdraw dur- ing the exam, you shall return it. Exam 27/08/2019 Exercise 1 (10 points) There two streams available for generating electrical power as described in the following. • Stream 1: 1 kg/s flow of compressed dry air at 4.5 bar and 50 °C; • Stream 2: 0.05 kg/s flow of water at 4.5 bar and 50 °C. Considering a dead state condition of 1 bar and 15 °C, please: i. motivate clearly the solution procedure and highlight neatly the assumptions (1 point); ii. determine the maximum obtainable power from the two streams (2 points); iii. exploiting only Stream 1, propose a realizable plant for generating electric power and sketch the process flow diagram as well as the thermodynamic cycle on the Ts diagram (2 points); iv. referring to the proposed plant, estimate the generated electric power (2 points); v. explain accurately how the process varies in case Stream 2 is mixed with Stream 1 prior to entering the proposed plant (3 points). Exercise 2 (12 points) A cruise boat is propelled by 4 engines manufactured by Wärtsilä, each fueled with diesel (ρ=750 kg/m3, PCI=45 MJ/kg) and each rated at 5.8 MW. The total fuel consumption at nominal load is 5000 liters per hour. The thermal power output from the engines is released in the fraction of 50% to the stack as hot flue gas at 350 °C, and of 50% to the cooling circuit in which the cooling fluid heats from 60 °C to 120 °C. An ORC- based heat recovery plant shall be designed exploiting both sources. The recovered heat of one source is used in a preheating plate heat exchanger, while that of the other in a gas-tube evaporator. The ORC working fluid is nonane (MM=128.3 kg/kmol, Tcrit=321.5 °C, pcrit=22.8 bar,…