Wagner Equation Predicting Entire Curve for Pure Fluids from Limited VLE Data: Error Dependency Upon Data Interval & Fully-Determined Case

Abstract

The predictive error in vapor pressure of limited-data Wagner constants relative to that of entire-curve constants is studied for eleven data intervals.  Good precision is assumed for data inputs, four digits in the mantissa of Ln P_v,r and five digits for T_r.  An algebraic solution for the fully-determined case based on only four data points is used to estimate Wagner constants.  Seventy-two species are used to assess the impact of the location of the two interior points and the location and width of the limited-data interval upon the error in predicted P_v,r due to data imprecision.  Hydrogen, helium, R152a, and water are used to assess error due to Wagner imperfection and compare predictive capability of the algebraic fully-determined and regressed over-determined approaches.  The results indicate that limited VLE data of good precision from reduced temperature intervals with a width ≥ 0.1 and a lower bound ≤ 0.6 can generally provide reasonable VLE predictions over the entire two-phase curve for pure substances, with average error of approximately 1%.  It is shown that the algebraic, fully-determined solution presented is a viable tool for investigating the extensibility of limited-data Wagner constants.

Keywords

• Wagner equation,vapor-liquid equilibrium,pure substances,t* test,least-squares regression,fully-determined solution,equation imperfection,data imprecision

References

1. Dr. Ahmed Bellagi U. R. Thermique et Thermodynamique des Procedes Industriels, Ecole Nationale d'ingenieurs de Monastir (E.N.I.M.), Avenue Ibn El Jazzar, 5060 Monastir, Tunisia E-mail address: [e-mail]
2. Dr. Santiago Velasco Departamento de Fisica Aplicada, Universidad de Salamanca, E-37008 Salamanca, Spain E-mail: [e-mail]
3. Dr. Joachim Gross Institute of Thermodynamics and Thermal Process Engineering, University of Stuttgart, Pfaffenwaldring 9, D-70569 Stuttgart, Germany E-mail: [e-mail]