Experimental study of the one-, two-, and three-phase isochoric heat capacities of n-hexane + water mixtures near the lower critical line. Part I. Experimental results

摘要

The one-, two-, and three-phase isochoric heat capacities (C _(VX)) of n-hexane + water mixtures near the lower critical line, including UCEP, have been measured with a high-temperature and high-pressure nearly constant-volume adiabatic calorimeter. The measurements were made in the temperature range from 443 K to 501 K for 8 liquid and vapor isochores from 121.07 kg m ~(- 3) to 377.5 kg m ~(- 3). The isochoric heat capacity jump (quasi-static thermograms supplemented by the sensor of adiabatic control) technique has been used to accurately measure the liquid-liquid-vapor (L-L-V) and liquid-vapor (L-V) phase transition parameters (T _S, ρ _S). The expanded uncertainty of the heat-capacity measurements at 95% confidence level with a coverage factor of k = 2 is estimated to be 0.06% for density (ρ), 15 mK for temperature (T), and 2% to 3% for isochoric heat capacity (C _V). The liquid-gas critical temperatures,T _C(x), and the critical densities,ρ _C(x) (lower critical lines) for binary n-hexane + water mixtures were determined from the measured saturated properties (C _(VS),T _S, ρ _S) near the critical point. The temperature, density, and the pressure at the UCEP (T _(UCEP) = 496.13 ± 0.2 K, P _(UCEP) = 5.220 ± 0.10 MPa, ρ _(UCEP) = 263.92 ± 2 kg m ~(- 3)) were extracted from the measured critical line and three-phase experimental data. For the first time we reported the temperature dependent behavior of C VX near UCEP.