Truncation Error of PRSV Vapor Pressures Calculated by a Series Method

Equations of state (EOS) describe relationships among pressure, molar volume, and temperature. Cubic EOS can be solved for liquid and vapor volume as well as equilibrium properties such as vapor pressure. A specific cubic EOS, Peng-Robinson-Stryjek-Vera (PRSV), was studied in this work. An existing technique expressed vapor pressure as a polynomial series in temperature. The series coefficients depended upon two substance-specific parameters, the acentric factor ω and a parameter labeled κ₁. Vapor pressures were calculated when the series was truncated after the first, fifth, eighth, and tenth power in temperature and were compared to exact vapor pressures calculated by a fugacity algorithm. Results were determined for values of the acentric factor ω between -0.4 and +0.4 and values of the κ₁ parameter between -0.2 and +0.3. Plots of truncation error versus reduced temperature were made by fixing the value of one of the two parameters and allowing the other to vary. In some cases, varying one of the parameters caused the sign of the truncation error to change. Plots showing 10% error contours were also produced for a fixed value of one parameter while reduced temperature and the other parameter were varied.