Thermodynamics

the kinetic energy change of the steam, determine (a) thetemperature at the turbine exit and (b) the power output ofthe turbine. Answers: (a) 69.1°C, (b) 3054 kW7–105 Reconsider Prob. 7–104. Using EES (or other)software, study the effect of varying the turbineisentropic efficiency from 0.75 to 1.0 on both the work doneand the exit temperature of the steam, and plot your results.7–106 Steam enters an adiabatic turbine at 7 MPa, 600°C,and 80 m/s and leaves at 50 kPa, 150°C, and 140 m/s. If thepower output of the turbine is 6 MW, determine (a) the massflow rate of the steam flowing through the turbine and (b) theisentropic efficiency of the turbine. Answers: (a) 6.95 kg/s,(b) 73.4 percent7–107 Argon gas enters an adiabatic turbine at 800°C and1.5 MPa at a rate of 80 kg/min and exhausts at 200 kPa. Ifthe power output of the turbine is 370 kW, determine theisentropic efficiency of the turbine.7–108E Combustion gases enter an adiabatic gas turbine at1540°F and 120 psia and leave at 60 psia with a low velocity.Treating the combustion gases as air and assuming an isentropicefficiency of 82 percent, determine the work output ofthe turbine. Answer: 71.7 Btu/lbm7–109 Refrigerant-134a enters an adiabatic compressoras saturated vapor at 120 kPa at a rate of0.3 m 3 /min and exits at 1-MPa pressure. If the isentropic efficiencyof the compressor is 80 percent, determine (a) thetemperature of the refrigerant at the exit of the compressorand (b) the power input, in kW. Also, show the process on aT-s diagram with respect to saturation lines.1 MPaChapter 7 | 409exit pressure of air and (b) the power required to drive thecompressor.7–112 Air is compressed by an adiabatic compressor from95 kPa and 27°C to 600 kPa and 277°C. Assuming variablespecific heats and neglecting the changes in kinetic and potentialenergies, determine (a) the isentropic efficiency of thecompressor and (b) the exit temperature of air if the processwere reversible. Answers: (a) 81.9 percent, (b) 505.5 K7–113E Argon gas enters an adiabatic compressor at 20psia and 90°F with a velocity of 60 ft/s, and it exits at 200psia and 240 ft/s. If the isentropic efficiency of the compressoris 80 percent, determine (a) the exit temperature of theargon and (b) the work input to the compressor.7–114 Carbon dioxide enters an adiabatic compressor at100 kPa and 300 K at a rate of 1.8 kg/s and exits at 600 kPaand 450 K. Neglecting the kinetic energy changes, determinethe isentropic efficiency of the compressor.7–115E Air enters an adiabatic nozzle at 60 psia and1020°F with low velocity and exits at 800 ft/s. If the isentropicefficiency of the nozzle is 90 percent, determine theexit temperature and pressure of the air.7–116E Reconsider Prob. 7–115E. Using EES (orother) software, study the effect of varyingthe nozzle isentropic efficiency from 0.8 to 1.0 on both theexit temperature and pressure of the air, and plot the results.7–117 Hot combustion gases enter the nozzle of a turbojetengine at 260 kPa, 747°C, and 80 m/s, and they exit at apressure of 85 kPa. Assuming an isentropic efficiency of92 percent and treating the combustion gases as air, determine(a) the exit velocity and (b) the exit temperature. Answers: (a)728.2 m/s, (b) 786.3 KR-134aCOMPRESSOR260 kPa747°C80 m/sNOZZLEη N = 92%85 kPa120 kPaSat. vaporFIGURE P7–117FIGURE P7–1097–110 Reconsider Prob. 7–109. Using EES (or other)software, redo the problem by including theeffects of the kinetic energy of the flow by assuming an inletto-exitarea ratio of 1.5 for the compressor when the compressorexit pipe inside diameter is 2 cm.7–111 Air enters an adiabatic compressor at 100 kPa and17°C at a rate of 2.4 m 3 /s, and it exits at 257°C. The compressorhas an isentropic efficiency of 84 percent. Neglectingthe changes in kinetic and potential energies, determine (a) theEntropy Balance7–118 Refrigerant-134a is throttled from 900 kPa and 35°Cto 200 kPa. Heat is lost from the refrigerant in the amount of0.8 kJ/kg to the surroundings at 25°C. Determine (a) the exitR-134a900 kPa35°CqFIGURE P7–118200 kPa