This function computes the ideal gas helmholtz derivatives of the fundamental equation of Richter et al for R1234yf (2011) w.r.t. to reduced temperature (tau=T_crit/T) and reduced density (delta=rho/rho_crit).
function fid_R1234yf
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_R1234yf;