Determination of the Relative Permittivity, ε_r, of Octane at Temperatures between (303 and 393) K and Pressures below 25 MPa with a Concentric Cylinder Capacitor at a Frequency of 1 kHz

摘要

The relative permittivity, ε_r(T, p), of liquid octane has been determined with an estimated expanded relative uncertainty of ± 0.018 % from measurements of the complex capacitance of a concentric cylinder capacitor at temperatures between (293 and 393) K and pressures below 25 MPa. The measurements were corrected for the capacitor's isothermal compressibility that was determined by comparison of measurements of ε_r(He, 303 K and 393 K, p) with ab initio results from quantum mechanics. The measured ε_r(C8H_(18), T, p) were combined with the amount-of-substance density, p, which was obtained from the equation of state reported by Span and Wagner (Int. J. Thermophys. 2003, 24, 41-109), to calculate the molar polarizability, P, that was fit with an expanded (k = 2) relative uncertainty of ± 0.01 % to a correlation with three parameters. The ε_r(T, p) obtained from the literature were converted to P·p and compared with our correlation and found to differ by < ± 0.2 % at temperatures that overlap ours.