Hope College Engineering Department Research Experiences for Undergraduates Summer 2007 Project Summary

The objective was to minimize error in a previously derived vapor pressure function for the Soave-Redlich-Kwong (SRK) equation of state. This function had been designed to reproduce the low temperature vapor pressure limit correctly and it gave order of magnitude estimates at moderate to high temperatures. One approach was to fit the curves with a fourth order polynomial in reduced temperature having coefficients that were quadratic functions of the acentric factor. This approach worked well for acentric factors between -0.2 and +1.0 producing less than thirteen percent error. A second more general approach used a piecewise fit comprised of four functions of reduced temperature having coefficients dependent upon a polynomial function of the acentric factor. The piecewise fit was a better fit with less than eight percent error for reduced temperature from zero to one. Further study to determine the optimal range of reduced temperatures for each of the piecewise fits is recommended to improve the vapor pressure estimates.