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ENERGY CONVERSION A 2016-17 Name/Lastname:__________________________________________ Code n.___________ Exam 03/02/2017 Exercise 1 (10 points) A thermal power source of constant heat capacity equal to 200 kW/°C at a temperature of 600°C can be cooled down as much as possible to ambient. Such a source is exploited by an open-loop air cycle employing a two-time intercooled compression. The two intercoolers use cooling water available at 15°C. Ambient air is instead at 20°C. Neglecting all pressure drops, but the pressure drop on th e air side of the heat exchanger for the heat input to the cycle equal to 5%, and considering non-ideal machines (i.e. assume efficiencies), please: i. highlight clearly throughout the text all assumed parameters and their values (1 point); ii. sketch a plant layout (1 point); iii. calculate the expansion ratio such that the expander outlet temperature is 250°C (1 point); iv. draw the T-s diagram of the cycle and the T-Q diagram of the heat input (hot source-air) exchanger (2 points); v. compute the second-law efficiency of the air plant (3 point); vi. estimate the number of stages required to assure a high-efficiency expander and estimate the rotational speed such that the specific rotation speed (Ns) is close to 0.1 (2 points). Exercise 2 (12 points) Consider a biomass-fired steam Rankine cycle in cogenerative architecture. The plant heats up a flow of diathermic oil exploiting the condensation of steam in two diverse heat exchangers, HX1 and HX2. The oil enters the plant at 15°C, and flows first in HX1 and then in HX2 (Voil=2700 m3/h, ρoil=800 kg/m3, cpoil=2100 J/kgK). The high pressure steam produced in the boiler (T=450°C, p=30 bar, Tsat(30 bar)=230°C) is expanded in a high-pressure turbine, operating with a pressure expansion ratio of 5,…