Dielectric constants and Clausius-Mossotti functions (CM) have been determined for selected pure components, binary mixtures, and ternary mixtures at temperatures between 91 and 115 K and pressures near saturation. Excess Clausius-Mossotti functions (CME) have been calculated from the pure fluid and mixture values.Mixture CME values are found to be generally less than 0.1% of the mixture CM values for systems containing only nonpolar species. Thus, dielectric constant measurements can be conveniently used as substitute density measurements for simple liquid mixtures. Rodosevich and Miller, 1973, 1974;Mollerup and Rowlinson, 1974). However, compositions and temperatures are difficult to measure within the required tolerances. It would often be highly desirable to determine quickly or monitor continuously liquid mixture molar volumes by use of some relatively simple device.Dielectric constant measurements can be used to indirectly determine molar volumes. A particular combination of the dielectric constant and the molar volume, termed the Clausius-Mossotti function (CM), is found to undergo changes of only a few percent as a simple fluid is taken from the ideal gas at high temperatures to the saturated liquid near the triple point. For an ideal gas mixture the CM function is rigorously given by the mole fraction average of the pure component values. If this same relationship is sufficiently accurate for liquid mixtures, that is, if CM" is very nearly zero, then measurements of composition and dielectric constant can be readily used to obtain molar volumes. In addition, if pure component CM values are proportional to heating values for the components of a liquefied natural gas, it will be possible to use dielectric constant measurements alone to convert a total volume measurement directly into total heating value, the basis for sale of such commodities.To test the above conjectures, the present investigation was designed to provide a consistent set of low temperature dielectric constants and Clausius-Mossotti functions for some relatively simple liquids and liquid mixtures, including components and mixtures of interest relative to liquefied natural gas. Previous results are available in the same temperature range for some of the pure components (Ar, N2, and CHI). No previous results appear to be available for the mixtures. CONCLUSIONS AND SIGNIFICANCEThe mixture results indicate that the excess ClausiusMossotti function (CME) is less than 0.1% of the mixture CM value for saturated liquid mixtures composed of simple nonpolar species. For such mixtures a dielectric constant measurement may be used as a substitute for a density measurement, if the composition and pure component CM values are known. This experimental approach Correspondence concerning this paper should be addressed to R. C. Miller. could reduce the effort required to determine the PVT surface for a fluid mixture.Pure component results for propane and isobutane indicate that their small permanent dipole moments are of sufficient magnitude to effect t...
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