Exercise 2 Exergy

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ENERGY CONVERSION A 2019-20 1 Exercises Exergy Exercise 1 Consider the following energy source: an air stream of constant mass flow rate (100 kg/s) at the temper- ature of 300 °C and at the pressure of 0.8 bar (absolute, not gauge). Please: i. determine the maximum mechanical power obtainable from that source; ii. draw a realistic plant layout capable of producing mechanical power from the source; iii. compute the electrical power realistically obtainable from the system; iv. calculate the power losses related to all irreversibilities in the considered power plant; v. calculate the second-law efficiency losses and comment them; vi. verify the equality of the first-law and second-law results. Exercise 2 Consider a thermal power source of constant heat capacity equal to 1000 kW/°C at a temperature of 500 °C, which can be cooled down to the ambient temperature of 15 °C. Such a source is exploited by an open-loop air plant employing the following equipment:  intercooled air compressors (adiabatic efficiency = 90%),  three air-cooled intercoolers (pressurized air pressure losses=0%, compressed air end temp. 30 °C),  one hot air expander (adiabatic efficiency 93%),  one heat exchanger between thermal power source and compressed air (relative pressure loss for compressed air 5%, ∆𝑇𝑚𝑖𝑛= 20°C constantly during the heat transfer). Assuming a constant specific heat for air, please: i. determine the maximum mechanical power obtainable from that source; ii. sketch a possible plant layout; iii. calculate the expansion ratio such that the outlet temperature is 15 °C; iv. compute the useful electrical power obtainable from the air plant; v. compute the wasted power due to the fluid-dynamic irreversibility in the expander; vi. list and comment, without computing, the wasted power…