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Unformatted text preview: and cp (c) an incompressible substance. 12–38 Estimate the specificheat difference cp cv for liquid water at 15 MPa and 80°C. Answer: 0.32 kJ/kg · K 12–39E Estimate the specificheat difference cp cv for liquid water at 1000 psia and 150°F. Answer: 0.057 Btu/lbm · R 12–40 Derive a relation for the volume expansivity b and the isothermal compressibility a (a) for an ideal gas and (b) for a gas whose equation of state is P(v a) RT. 12–41 Estimate the volume expansivity b and the isothermal compressibility a of refrigerant134a at 200 kPa and 30°C. 12–50E  677 Estimate the JouleThomson coefficient of nitrogen at (a) 200 psia and 500 R and (b) 2000 psia and 400 R. Use nitrogen properties from EES or other source. 12–51E Reconsider Prob. 12–50E. Using EES (or other) software, plot the JouleThomson coefficient for nitrogen over the pressure range 100 to 1500 psia at the enthalpy values 100, 175, and 225 Btu/lbm. Discuss the results. 12–52 Estimate the JouleThomson coefficient of refrigerant134a at 0.7 MPa and 50°C. 12–53 Steam is throttled slightly from 1 MPa and 300°C. Will the temperature of the steam increase, decrease, or remain the same during this process? The dh, du, and ds of Real Gases
12–54C What is the enthalpy departure? 12–55C On the generalized enthalpy departure chart, the normalized enthalpy departure values seem to approach zero as the reduced pressure PR approaches zero. How do you explain this behavior? 12–56C Why is the generalized enthalpy departure chart prepared by using PR and TR as the parameters instead of P and T ? 12–57 Determine the enthalpy of nitrogen, in kJ/kg, at 175 K and 8 MPa using (a) data from the idealgas nitrogen table and (b) the generalized enthalpy departure chart. Compare your results to the actual value of 125.5 kJ/kg. Answers:
(a) 181.5 kJ/kg, (b) 121.6 kJ/kg The JouleThomson Coefficient
12–42C What does the JouleThomson coefficient represent? 12–43C Describe the inversion line and the maximum inversion temperature. 12–44C The pressure of a fluid always decreases during an adiabatic throttling process. Is this also the case for the temperature? 12–45C Does the JouleThomson coefficient of a substance change with temperature at a fixed pressure? 12–46C Will the temperature of helium change if it is throttled adiabatically from 300 K and 600 kPa to 150 kPa? 12–47 Consider a gas whose equation of state is P(v a) RT, where a is a positive constant. Is it possible to cool this gas by throttling? 12–48 Derive a relation for the JouleThomson coefficient and the inversion temperature for a gas whose equation of state is (P a/v2)v RT. 12–49 Estimate the JouleThomson coefficient of steam at (a) 3 MPa and 300°C and (b) 6 MPa and 500°C. 12–58E Determine the enthalpy of nitrogen, in Btu/lbm, at 400 R and 2000 psia using (a) data from the idealgas nitrogen table and (b) the generalized enthalpy chart. Compare your results to the actual value of 177.8 Btu/lbm. 12–59 What is the error involved in the (a) enthalpy and (b) internal energy of CO2 at 350 K and...
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 Spring '09
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