This function is based on eq. 9 from [Slattery1958].
function pDstar_polar input Q.TemperatureAbsolute Tstar = 1 "Ratio of temperature to the geometric mean of the critical temperatures" annotation( Dialog(__Dymola_label = "<html><i>T</i><sub>c AB</sub></html>")); output Q.NumberAbsolute pDstar "Reduced pressure-diffusivity product"; end pDstar_polar;