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CHAPTER12

55 kgs using the generalized charts determine the

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Unformatted text preview: 10 MPa if it is assumed to be an ideal gas? Answers: (a) 50%, (b) 49% 12–60 Determine the enthalpy change and the entropy change of nitrogen per unit mole as it undergoes a change of state from 225 K and 6 MPa to 320 K and 12 MPa, (a) by assuming ideal-gas behavior and (b) by accounting for the deviation from ideal-gas behavior through the use of generalized charts. 12–61 Determine the enthalpy change and the entropy change of CO2 per unit mass as it undergoes a change of state from 250 K and 7 MPa to 280 K and 12 MPa, (a) by assuming ideal-gas behavior and (b) by accounting for the deviation from ideal-gas behavior. 12–62 Methane is compressed adiabatically by a steady-flow compressor from 2 MPa and 10°C to 10 MPa and 110°C at a rate of 0.55 kg/s. Using the generalized charts, determine the required power input to the compressor. Answer: 133 kW cen84959_ch12.qxd 4/5/05 3:58 PM Page 678 678 | Thermodynamics 10 MPa 110°C CH4 constant-temperature (T constant) line, but less than the slope of a constant-volume (v constant) line. 12–72 Using the cyclic relation and the first Maxwell relation, derive the other three Maxwell relations. 12–73 Starting with the relation dh T ds + v dP, show that the slope of a constant-pressure line on an h-s diagram (a) is constant in the saturation region and (b) increases with temperature in the superheated region. 12–74 Derive relations for (a) u, (b) h, and (c) s of a gas that obeys the equation of state (P + a/v 2)v RT for an isothermal process. 12–75 cv Show that Ta 0v 0P ba b 0T s 0T v and cp Ta 0P 0v ba b 0T s 0T P · m = 0.55 kg/s 2 MPa –10°C FIGURE P12–62 12–63 Propane is compressed isothermally by a piston– cylinder device from 100°C and 1 MPa to 4 MPa. Using the generalized charts, determine the work done and the heat transfer per unit mass of propane. 12–64 Reconsider Prob. 12–63. Using EES (or other) software, extend the problem to compare the solutions based on the ideal-gas assumption, generalized chart data, and real fluid data. Also extend the solution to methane. 12–76 Estimate the cp of nitrogen at 300 kPa and 400 K, using (a) the relation in the above problem and (b) its definition. Compare your results to the value listed in Table A–2b. 12–77 Steam is throttled from 4.5 MPa and 300°C to 2.5 MPa. Estimate the temperature change of the steam during this process and the average Joule-Thomson coefficient. Answers: 26.3°C, 13.1°C/MPa 12–65E Propane is compressed isothermally by a piston– cylinder device from 200°F and 200 psia to 800 psia. Using the generalized charts, determine the work done and the heat transfer per unit mass of the propane. Answers: 45.3 Btu/lbm, 141 Btu/lbm 12–66 Determine the exergy destruction associated with the process described in Prob. 12–63. Assume T0 30°C. 12–67 Carbon dioxide enters an adiabatic nozzle at 8 MPa and 450 K with a low velocity and leaves at 2 MPa and 350 K. Using the generalized enthalpy departure chart, determine the exit velocity of the carbon dioxide. Answer: 384 m/s 12–68 Reconsider Prob. 12–67. Using EES (or oth...
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