A new apparatus for measurements of second virial coefficients of gases or gas mixtures at room temperature is described. It was used to determine virial coefficients of He, H2, N2, CO2, NH3, and the interaction virial coefficient of Ar/NH3. Furthermore, low temperature interaction virial coefficients of Ar/NH3 and H2/CO are reported and finally a critical revision of second virial coefficients of He, H2, Ar, N2, and CO at 77.3 K is presented. The virial coefficients are discussed in their relation to new intermolecular potentials.

Measurements of second interaction virial coefficients of mixtures He/O2, CO, NO, CH4, CF4, CO2, N2O, SF6, and NH3 are presented. Temperatures range from 300 K to temperatures as low as the boiling temperature of the molecular components. New experimental data of second virial coefficients for most of the pure components are presented also and are critically compared with literature data. Recently published anisotropic intermolecular potential energy surfaces and several combining rules were tested with the new data.

A phenomenological model is presented for predicting the thermodynamic conditions at the onset of flashing in liquid undergoing a static or flow depressurization transient. It is shown that at extremely high rates of decompression (pulse expansion), a liquid may reach the homogeneous nucleation limit of superheat before appreciable phase transition occurs. A criterion for pulse expansion is derived by an asymptotic solution of the mass and energy equations in conjunction with the equation for spontaneous bubble nucleation and growth near the flashing inception point. The effect of impurities and dissolved gases is considered by an empirically defined heterogeneous nucleation coefficient. The model predicts the minimum pressure at the flashing point with a probable error of less than 11 percent, using 83 experimental data points.

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The interaction second virial coefficients of the mixtures Ar/CO, Ar/N2, Ar/O2, Ne/CO, Ne/N2, and Ne/O2 were measured from 296 K to 463 K, utilizing the expansion method and the temperature changing method. Improvements in the previously described apparatuses reduced systematical errors and provided more accurate measurements of the coefficients. The experimental data were compared to calculations of interaction second virial coefficients based on modern potential energy surfaces. None of the previously reported potential energy surfaces was sufficient to account for the measured interaction second virial coefficients over our experimental temperature range from 296 K to 463 K.

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