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

Authors : Todd Nichols, Vivek Utgikar

Pages : 38-53

Doi:10.5541/ijot.372148

View : 14 | Download : 6

Publication Date : 2018-03-01

Article Type : Research Paper

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