Thermodynamics

cen84959_ch03.qxd 4/1/05 12:31 PM Page 147Chapter 3 | 147T, K20 MPa10 MPa4 MPa2 MPa1 MPa0.2 MPa0.1 MPa3004.7%0.2%0.2%4.2%0.1%0.2%1.9%0.1%0.1%1.0%0.1%0.1%0.5%0.0%0.0%0.1%0.0%0.0%0.0%0.0%0.0%Van der Waals (top)Beattie-Bridgeman (middle)Benedict-Webb-Rubin (bottom)3.7%0.1%0.4%5.3%0.1%0.1%2.3%0.1%0.0%1.1%0.1%0.0%0.5%0.1%0.0%0.1%0.0%0.0%0.0%0.0%0.0%2002.9%0.3%0.7%6.7%0.7%0.1%2.8%0.1%0.1%1.2%0.1%0.1%0.5%0.0%0.0%0.1%0.0%0.0%0.0%0.0%0.0%20.7%14.1%2.1%11.6%6.3%1.2%3.2%0.1%1.0%0.4%0.1%0.4%0.1%0.0%0.2%0.0%0.0%0.0%0.0%0.0%0.0%100>100%>100%>100%5.7%59.3%18.7%15.2%74.5%51.0%7.9%0.7%5.2%5.2%0.6%3.7%0.9%0.1%0.1%3.3%0.4%2.5% 1.6%0.2%1.3%0.4%0.1%0.1%0.8%0.4%0.1%0.1%0.8%0.3%0.0125 MPa00.010.1110100v, m 3 /kmolFIGURE 3–60Percentage of error involved in various equations of state for nitrogen (% error [(|v table v equation |)/v table ] 100).Beattie-Bridgeman, and Benedict-Webb-Rubin equations of state is illustratedin Fig. 3–60. It is apparent from this figure that the Benedict-Webb-Rubin equation of state is usually the most accurate.EXAMPLE 3–13Different Methods of Evaluating Gas PressurePredict the pressure of nitrogen gas at T 175 K and v 0.00375 m 3 /kgon the basis of (a) the ideal-gas equation of state, (b) the van der Waalsequation of state, (c) the Beattie-Bridgeman equation of state, and (d) theBenedict-Webb-Rubin equation of state. Compare the values obtained to theexperimentally determined value of 10,000 kPa.Solution The pressure of nitrogen gas is to be determined using four differentequations of state.