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APPLIED ENGINEERING THERMODYNAMICS
MAE 115
1. Consider a steam power plant that operates on a simple ideal Rankine cycle and has a net power output of 45 MW. Steam enters the turbine at 7 MPa and 500°C and is cooled in the condense at a pressure of 10 kPa by running cooling water from a lake through the tubes of the condenser at a rate of 2000 kg/s. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) ther thermal efficiency of the cycle, (b) the mass flow rate of the steam, and (c) the temperature rise of the cooling water. Repeat the same calculations assuming an isentropic efficiency of 87% for both the turbine and the pump.
2. The schematic of a single-flash geothermal power plant with a bottoming binary cycle. Geothermal resource exists as saturated liquid at 230°C. The geothermal liquid is withdrawn from the production well at a rate of 230 kg/s and is flashed to a pressure of 500 kPa by an essentially isenthalpic flashing process where the resulting vapor is separated from the liquid in a separator and directed to the turbine.
The steam leaves the turbine at 10 kPa with a moisture content of 10% and enters the condense where it is condensed and routed to a reinjection well along with the liquid coming off the separator. Determine (a) the mass flow rate of steam through the turbine, (b) the isentropic efficiency of the turbine, (c) the power output of the turbine, and (d) the thermal efficiency of the plant (the ratio of the turbine work output to the energy of the geothermal fluid relative to standard ambient conditions). The separated liquid (point 6) is used as the heat source in a binary cycle with isobutane as the working fluid. Geothermal liquid water leaves the heat exchanger at 90°C while isobutane enters the turbine at 3.25 MPa and 145°C and leaves at 80°C and 400 kPa. Isobutane is condensed in an air-cooled condenser and then pumped to the heat exchanger pressure. Assuming an isentropic efficiency of 90% for the pump, determine (e) the mass flow rate of isobutane in the binary cycle, (f) the net power outputs of both the flashing and the binary sections of the plant, and (g) the thermal efficiencies of the binary cycle and the combined plant.
3. During a regeneration process, some steam is extracted from the turbine and is used to heat the liquid water leaving the pump. This does not seem like a smart thing to do since the extracted steam could produce some more work in the turbine. How do you justify this action?
4. The closed feedwater heater of a regenerative Ranking cycle is to heat 7000 kPa feedwater from 260°C to a saturated liquid. The turbine supplies bleed steam at 6000 kPa and 325°C to this unit. This steam is condensed to a saturated liquid before entering the pump. Calculate the amount of bleed steam required to heat 1 kg of feedwater in this unit.
5. A steam power plant operates on the reheat-regenerative Ranking cycle with a closed feedwater heater. Steam enters the turbine at 8 MPa and 500°C at a rate of 15 kg/s and is condensed in the condenser at a pressure of 20 kPa. Steam is reheated at 3 MPa to 500°C. Some steam is extracted from the low-pressure turbine at 1 MPa, is completely condensed in the closed feedwater heater, and pumped to 8 MPa before it mixes with the feedwater at the same pressure.
Assuming an isentropic efficiency of 88% for both the turbine and the pump, determine (a) the temperature of the steam at the inlet of the closed feedwater heater, (b) the mas flow rate of the steam extracted from the turbine for the closed feedwater heater, (c) the net power output, and (d) the thermal efficiency.