Helmholtz Energy Transformations of Common Cubic Equations of State for Use with Pure Fluids and Mixtures

Ian H. Bell, Andreas Jäger
2016 Journal of Research of the National Institute of Standards and Technology  
Comprehensive sets of derivatives of Helmholtz energy transformations of several common cubic equations of state are presented. These derivatives can be used for implementing cubic equations of state into complex multi-fluid mixture models when no multiparameter equation of state is available for a mixture component. Thus, pure fluids (or mixtures) for which no accurate model exists in literature can be modeled with a relatively small set of fluid property data. Composition derivatives have
more » ... calculated for the cases where the last mole fraction is either an independent or dependent variable. Analytic derivatives are presented up to fourth order in the independent variables combined with composition derivatives up to third order; this set covers the common requirements for derivatives needed in the state-of-the-art thermophysical property libraries. A C++ implementation of the presented analyses, data for computer code validation, and information about the computer algebra tools used to calculate the intermediate derivatives are provided as supplementary information. Helmholtz-Energy-Explicit Models Thermodynamic properties of fluids can be calculated by means of different types of equations of state. This section describes those that are formulated in terms of the Helmholtz energy. They evolved from the virial equation of state and became common when pure fluids had been characterized over wide ranges of states and in multiple properties because all this information could be represented with high accuracy in a single formulation of the Helmholtz energy.
doi:10.6028/jres.121.011 fatcat:qt7lr25bpjggjbyu6hncvw5jjy