This function computes the residual 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). The function can be used for special properties depending just on the residual derivative parts.
function fres_R134a
extends Modelica.Icons.Function;
input Real delta "Reduced density (delta=d/dcrit)";
input Real tau "Reduced temperature (tau=Tcrit/T)";
output Modelica.Media.Common.HelmholtzDerivs f "Helmholtz derivatives";
end fres_R134a;