Thermodynamic Property Model for Fluid-Phase n-Butane

A Helmholtz free energy equation of state for the fluid phase of n-butane (R-600) has been developed on the basis of the ITS-90 temperature scale. This model has been established on the basis of selected measurements of the pressure density temperature (P, \, T), isochoric heat capacity, speed of sound, and the saturation properties. The linear structural regression optimization and nonlinear fitting procedure were used to determine the functional form and the numerical parameters of the present equation of state. Based on a comparison with available experimental data, it is recognized that the developed model represents most of the reliable experimental data accurately in the range of validity covering temperatures from 134.87 K (the triple-point temperature) to 589 K, at pressures up to 69 MPa, and at densities up to 745 kg } m&3. The reasonable behaviors of the derived thermodynamic properties have also been confirmed over the entire fluid phase of n-butane.