Isochoric heat capacity of near- and supercritical benzene and derived thermodynamic properties

摘要

As part of a continuing study of the critical and supercritical phenomena in fluids and fluid mixtures, one- (C-v1) and two-phase (C-v2) isochoric heat capacities, densities (rho(s)) and phase-transition temperatures (T-s) of benzene were measured in the critical and supercritical regions. Measurements were made in the immediate vicinity of the liquid-gas phase transition and the critical points in order to accurately determine of the phase transition properties (T-s, rho(s), C-v1, and C-v2). The measurements cover the temperature range from (347 to 616) K for 10 liquid and vapor isochores between (265 and 653) kg .m(-3) at pressure up to 7.5 MPa. The measurements were performed using a high-temperature, high-pressure, nearly constant-volume adiabatic calorimeter. The standard uncertainties of the density, temperature, and isochoric heat capacity, C-v, measurements are estimated to be 0.1%, 0.02 K, and 1.5%, respectively. The measured one- (C-v1) and two-phase (C-v2) isochoric heat capacities along the critical isochore and the saturated liquid (rho(s)') and vapor (rho(s)'') densities near the critical point were used to accurately estimate the theoretically meaningful asymptotic critical amplitudes (A(0)(+/-) and B-0) and related amplitudes for other properties (Gamma(+)(0), D-0, xi(0)), and their universal relations, A(0)(+)/A(0)(-), A(0)(+)Gamma B-+(0)0(2), alpha A(0)(+)Gamma B-+(0)0(-2), D-0 Gamma B-+(0)0(delta-1),. Saturated liquid and vapor densities (p(s)', p(s)'') together with measured two-phase C-v2 data were used to estimate the values of asymmetric parameters a(3) (complete scaling parameter) and b(2) of the coexistence curve singular diameter. Experimentally determined asymptotical critical amplitudes (A(0)(+)and B-0 fluid-specific parameters) were used to check and confirm the predictive capability of the universal correlation in terms of their dependence on the acentric factor omega based on the generalized corresponding states principle. The measured values of two-phase C-v2 as a function of the specific:volume Valong various isotherms were used to calculate second temperature derivatives of vapor pressure and chemical potential and to estimate the value of Yang-Yang anomaly strength parameter R-mu = - 0.683 for benzene. The contributions of the vapor pressure, and the chemical potential, to the measured total two-phase C-v2 were derived from the measurements. (C) 2020 Published by Elsevier B.V.