- International Journal of Thermodynamics
- Vol: 21 Issue: 1
- Wagner Equation Predicting Entire Curve for Pure Fluids from Limited VLE Data: Error Dependency Upon...
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 : 5 | Download : 2
Publication Date : 2018-03-01
Article Type : Research
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