Unformatted text preview: er) software, compare the exit velocity to the nozzle assuming ideal-gas behavior, the generalized chart data, and EES data for carbon dioxide. 12–78 A rigid tank contains 1.2 m3 of argon at 100°C and 1 MPa. Heat is now transferred to argon until the temperature in the tank rises to 0°C. Using the generalized charts, determine (a) the mass of the argon in the tank, (b) the final pressure, and (c) the heat transfer.
Answers: (a) 35.1 kg, (b) 1531 kPa, (c) 1251 kJ 12–79 Argon gas enters a turbine at 7 MPa and 600 K with a velocity of 100 m/s and leaves at 1 MPa and 280 K with a velocity of 150 m/s at a rate of 5 kg/s. Heat is being lost to the surroundings at 25°C at a rate of 60 kW. Using the generalized charts, determine (a) the power output of the turbine and (b) the exergy destruction associated with the process. 12–69 A 0.08-m3 well-insulated rigid tank contains oxygen at 220 K and 10 MPa. A paddle wheel placed in the tank is turned on, and the temperature of the oxygen rises to 250 K. Using the generalized charts, determine (a) the final pressure in the tank and (b) the paddle-wheel work done during this process. Answers: (a) 12,190 kPa, (b) 393 kJ 12–70 Carbon dioxide is contained in a constant-volume tank and is heated from 100°C and 1 MPa to 8 MPa. Determine the heat transfer and entropy change per unit mass of the carbon dioxide using (a) the ideal-gas assumption, (b) the generalized charts, and (c) real fluid data from EES or other sources. 7 MPa 600 K 100 m/s 60 kW · W Ar · m = 5 kg/s T0 = 25°C 1 MPa 280 K 150 m/s Review Problems
12–71 For b 0, prove that at every point of a singlephase region of an h-s diagram, the slope of a constantpressure (P constant) line is greater than the slope of a FIGURE P12–79 cen84959_ch12.qxd 4/5/05 3:58 PM Page 679 Chapter 12
12–80 Reconsider Prob. 12–79. Using EES (or other) software, solve the problem assuming steam is the working fluid by using the generalized chart method and EES data for steam. Plot the power output and the exergy destruction rate for these two calculation methods against the turbine exit pressure as it varies over the range 0.1 to 1 MPa when the turbine exit temperature is 455 K. | 679 12–85 The volume expansivity of water at 20°C is b 0.207 10 6 K 1. Treating this value as a constant, determine the change in volume of 1 m3 of water as it is heated from 10°C to 30°C at constant pressure. 12–86 The volume expansivity b values of copper at 300 K 10 6 K 1, and 500 K are 49.2 10 6 K 1 and 54.2 respectively, and b varies almost linearly in this temperature range. Determine the percent change in the volume of a copper block as it is heated from 300 K to 500 K at atmospheric pressure. 12–87 Starting with mJT (1/cp) [T( v/ T )p v] and noting that Pv ZRT, where Z Z(P, T ) is the compressibility factor, show that the position of the Joule-Thomson coefficient inversion curve on the T-P plane is given by the equation ( Z/ T)P 0. 12–88 Consider an infinitesimal reversible adiabatic compression or expansion pr...
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