Exercise 2 Exergy

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ENERGY CONVERSION A 2016-17 1 Exercises Exergy Exercise 1 Consider the following energy source: an air stream of constant mass flow rate (100 kg/s) at temperature of 300°C and at pressure of 0.8 bar (absolute, not gauge). Please: 1. determine the maximum mechanical power obtainable from that energy source; 2. draw a realistic plant layout capable of producing mechanical power from the source; 3. calculate and comment on the power losses related to the most important irrever sibilities in the considered power plant. 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 air plant employing the following equipment:  four intercooled air compressors (adiabatic efficiency = 90%),  three air-cooled intercoolers (pressurized air-side pressure losses = 0%, compressed air end temperature 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: 1. sketch a plant layout; 2. calculate the expansion ratio such that the outlet temperature is 15°C, and then compute useful power obtainable by the air plant; 3. compute the wasted power due to the fluid-dynamic irreversibility in the expander; 4. list and comment, without computing, the wasted power due to all irreversibilities. Exercise 3 Consider two energy sources: a) a saturated steam stream of constant mass flow rate (100 kg/s) at 270°C (pressure 55 bar, saturated steam enthalpy = 2799 kJ/kg, saturated liquid enthalpy = 1185 kJ/kg), b) a water stream of constant…