Thermodynamics

712 | ThermodynamicsThe mixture enters the turbine at 2.5 MPa and 1300 K andexpands isentropically to a pressure of 200 kPa. Determine thework output of the turbine per unit mass of the mixture.13–58E A mixture of 80 percent N 2 and 20 percentCO 2 gases (on a mass basis) enters the nozzleof a turbojet engine at 90 psia and 1800 R with a low velocity,and it expands to a pressure of 12 psia. If the isentropicefficiency of the nozzle is 92 percent, determine (a) the exittemperature and (b) the exit velocity of the mixture. Assumeconstant specific heats at room temperature.13–59E Reconsider Prob. 13–58E. Using EES (orother) software, first solve the stated problemand then, for all other conditions being the same, resolve theproblem to determine the composition of the nitrogen andcarbon dioxide that is required to have an exit velocity of2600 ft /s at the nozzle exit.13–60 A piston–cylinder device contains a mixture of0.5 kg of H 2 and 1.6 kg of N 2 at 100 kPa and 300 K. Heat isnow transferred to the mixture at constant pressure until thevolume is doubled. Assuming constant specific heats at theaverage temperature, determine (a) the heat transfer and(b) the entropy change of the mixture.13–61 An insulated tank that contains 1 kg of O 2 at 15°Cand 300 kPa is connected to a 2-m 3 uninsulated tank thatcontains N 2 at 50°C and 500 kPa. The valve connecting thetwo tanks is opened, and the two gases form a homogeneousmixture at 25°C. Determine (a) the final pressure in the tank,(b) the heat transfer, and (c) the entropy generated during thisprocess. Assume T 0 25°C.Answers: (a) 444.6 kPa, (b) 187.2 kJ, (c) 0.962 kJ/Kduring this process by treating the mixture (a) as an ideal gasand (b) as a nonideal gas and using Amagat’s law.Answers: (a) 4273 kJ, (b) 4745 kJHeat6 kg H 221 kg N 2160 K5 MPaFIGURE P13–6313–64 Determine the total entropy change and exergydestruction associated with the process described in Prob.13–63 by treating the mixture (a) as an ideal gas and (b) as anonideal gas and using Amagat’s law. Assume constant specificheats at room temperature and take T 0 30°C.13–65 Air, which may be considered as a mixture of 79 percentN 2 and 21 percent O 2 by mole numbers, is compressedisothermally at 200 K from 4 to 8 MPa in a steady-flowdevice. The compression process is internally reversible, andthe mass flow rate of air is 2.9 kg/s. Determine the powerinput to the compressor and the rate of heat rejection by treatingthe mixture (a) as an ideal gas and (b) as a nonideal gasand using Amagat’s law. Answers: (a) 115.3 kW, 115.3 kW,(b) 143.6 kW, 94.2 kWO 21 kg15°C300 kPaN 22 m 350°C500 kPa200 K8 MPaW·79% N 221% O 2FIGURE P13–6113–62 Reconsider Prob. 13–61. Using EES (or other)software, compare the results obtained assumingideal-gas behavior with constant specific heats at theaverage temperature, and using real-gas data obtained fromEES by assuming variable specific heats over the temperaturerange.13–63 A piston–cylinder device contains 6 kg of H 2 and21 kg of N 2 at 160 K and 5 MPa. Heat is now transferred tothe device, and the mixture expands at constant pressure untilthe temperature rises to 200 K. Determine the heat transfer200 K4 MPaFIGURE P13–6513–66 Reconsider Prob. 13–65. Using EES (or other)software, compare the results obtained byassuming ideal behavior, real gas behavior with Amagat’slaw, and real gas behavior with EES data.13–67 The combustion of a hydrocarbon fuel with air resultsin a mixture of products of combustion having the compositionon a volume basis as follows: 4.89 percent carbon dioxide,