The use of dense gases in many technological fields requires modern fluid dynamic solvers capable of treating the thermodynamic regions where the ideal gas approximation does not apply. Moreover, in some high molecular fluids, nonclassical fluid dynamic effects appearing in those regions could be exploited to obtain more efficient processes. This work presents the procedures for obtaining nonconventional thermodynamic properties needed by up to date computer flow solvers. Complex equations of state for pure fluids and mixtures are treated. Validation of sound speed estimates and calculations of the fundamental derivative of gas dynamics Γ are shown for several fluids and particularly for Siloxanes, a class of fluids that can be used as working media in high-temperature organic Rankine cycles. Some of these fluids have negative Γ regions if thermodynamic properties are calculated with the implemented modified Peng-Robinson thermodynamic model. Results of flow simulations of one-dimensional channel and two-dimensional turbine cascades will be presented in upcoming publications.

*Proceedings of the 38th Aerospace Sciences Meeting and Exhibit*, Reno, NV, Jan. 10–13, AIAA, Reston, VA, pp. 1–8.

*PICAST’1—Pacific International Conference on Aerospace Science Technology*, Vol. 2, National Cheng Kung University, Publ., Taiwan, pp. 818–825.

*35th Intersociety Energy Conversion Engineering (IECEC)*, Las Vegas, NV July, AIAA, Reston, VA, pp. 69–75.

*Nonclassical Dynamics of Classical Gases*(Nonlinear Waves in Real Fluids) International Center for Mechanical Sciences, Courses and Lectures, Springer-Verlag, Berlin.

*Models for Thermodynamic and Phase Equilibria Calculations*, Marcel Dekker, New York.

*Steam Tables*, John Wiley and Sons, New York.

*Equation of State and Computer Prediction—Fluid Thermodynamic Properties for Light Petroleum Substances*Gulf Publishing, Houston.

*Numerical Recipes in Fortran 77: The Art of Scientific Computing*(Vol. 2, Numerical Analysis Series), 2nd Ed., Cambridge University Press, Cambridge, UK.

*Fluidi di Lavoro Multi Componenti Per Cicli Termodinamici di Potenza*,” Ph.D. thesis, Politecnico di Milano, Milano.

*Multiparameter Equations of State—An Accurate Source of Thermodynamic Property Data*, Springer-Verlag, Berlin.