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

Year 2018, Volume: 21 Issue: 1, 38 - 53, 01.03.2018

Todd Nichols , Vivek Utgikar

https://doi.org/10.5541/ijot.372148

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

• 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]
• Dr. Santiago Velasco Departamento de Fisica Aplicada, Universidad de Salamanca, E-37008 Salamanca, Spain E-mail: [e-mail]
• Dr. Joachim Gross Institute of Thermodynamics and Thermal Process Engineering, University of Stuttgart, Pfaffenwaldring 9, D-70569 Stuttgart, Germany E-mail: [e-mail]