Universal Scaling Form of the Equation of State of a Critical Pure Fluid

Close to the liquid gas critical point, the linear treatment of the symmetrical onecomponent F4 model to observe the fluid-restricted universality of the subclass of pure fluids is reversed. The comparison with the fitting results obtained from the recent applications of the crossover description to CO2, CH4, C2H4, C2H6 , R134a, SF6 , and H2O confirms that the dimensionless characteristic two scale factors involved in this description are: (a) the critical compressibility factor and (b) the slope at the critical point of the reduced potential PT Tc Pc along the critical isochore. For the two-phase domain along the critical isochore, a precise formulation for the extension range of the fluid-restricted universality is given in terms of the reduced scaling size ag−=t − ac of the critical density fluctuations, expressed as a function of the dilated scaling field which measures the distance to the critical point below Tc . The explicit definition of the microscopic length scale ac=(kBTc Pc )13 , which characterizes the short-range of the microscopic iInteraction, gives a correlative estimation of the crossover domain when t− Ã ac .