This function computes the ideal gas helmholtz derivatives of the fundamental equation of Tillner-Roth and Baehr for R134a (1994) w.r.t. to reduced temperature (tau=T_crit/T) and reduced density (delta=rho/rho_crit).
function fid_R134a
extends Modelica.Icons.Function;
input Real delta "reduced density (delta=d/dcrit)";
input Real tau "reduced temperature (tau=Tcrit/T)";
output Common.HelmholtzDerivs fid "helmholtz derivatives of ideal part";
end fid_R134a;