Thermodynamics

596 | Thermodynamics10–58 Reconsider Prob. 10–57. Using EES (or other)software, solve this problem by the diagramwindow data entry feature of EES. Include the effects of theturbine and pump efficiencies to evaluate the irreversibilitiesassociated with each of the processes. Plot the cycle on a T-sdiagram with respect to the saturation lines. Discuss theresults of your parametric studies.10–59 Determine the exergy destruction associated with theheat addition process and the expansion process in Prob.10–34. Assume a source temperature of 1600 K and a sinktemperature of 285 K. Also, determine the exergy of thesteam at the boiler exit. Take P 0 100 kPa. Answers: 1289kJ/kg, 247.9 kJ/kg, 1495 kJ/kg10–60 Determine the exergy destruction associated with theregenerative cycle described in Prob. 10–44. Assume a sourcetemperature of 1500 K and a sink temperature of 290 K.Answer: 1155 kJ/kg10–61 Determine the exergy destruction associated with thereheating and regeneration processes described in Prob.10–49. Assume a source temperature of 1800 K and a sinktemperature of 290 K.10–62 The schematic of a single-flash geothermal powerplant with state numbers is given in Fig. P10–62. Geothermalresource exists as saturated liquid at 230°C. The geothermalliquid is withdrawn from the production well at a rate of 230kg/s and is flashed to a pressure of 500 kPa by an essentiallyisenthalpic flashing process where the resulting vapor is separatedfrom the liquid in a separator and is directed to the turbine.The steam leaves the turbine at 10 kPa with a moisturecontent of 5 percent and enters the condenser where it iscondensed; it is routed to a reinjection well along with theliquid coming off the separator. Determine (a) the power outputof the turbine and the thermal efficiency of the plant,(b) the exergy of the geothermal liquid at the exit of the flashchamber, and the exergy destructions and the second-law(exergetic) efficiencies for (c) the flash chamber, (d) the turbine,and (e) the entire plant. Answers: (a) 10.8 MW, 0.053,(b) 17.3 MW, (c) 5.1 MW, 0.898, (d) 10.9 MW, 0.500,(e) 39.0 MW, 0.218Cogeneration10–63C How is the utilization factor P u for cogenerationplants defined? Could P u be unity for a cogeneration plantthat does not produce any power?10–64C Consider a cogeneration plant for which the utilizationfactor is 1. Is the irreversibility associated with thiscycle necessarily zero? Explain.10–65C Consider a cogeneration plant for which the utilizationfactor is 0.5. Can the exergy destruction associatedwith this plant be zero? If yes, under what conditions?10–66C What is the difference between cogeneration andregeneration?10–67 Steam enters the turbine of a cogeneration plant at7 MPa and 500°C. One-fourth of the steam is extracted fromthe turbine at 600-kPa pressure for process heating. Theremaining steam continues to expand to 10 kPa. Theextracted steam is then condensed and mixed with feedwaterat constant pressure and the mixture is pumped to the boilerpressure of 7 MPa. The mass flow rate of steam through theboiler is 30 kg/s. Disregarding any pressure drops and heatlosses in the piping, and assuming the turbine and the pumpto be isentropic, determine the net power produced and theutilization factor of the plant.62FlashchamberSeparator63Steamturbine4Condenser5Boiler5P II·Q processProcessheater34 27TurbineP IFIGURE P10–678Condenser11ProductionwellFIGURE P10–62Reinjectionwell10–68E A large food-processing plant requires 2 lbm/s ofsaturated or slightly superheated steam at 80 psia, which isextracted from the turbine of a cogeneration plant. The boilergenerates steam at 1000 psia and 1000°F at a rate of 5 lbm/s,