Thermodynamics Research Center / ThermoML | Fluid Phase Equilibria

ABSTRACT

The pressure, P, and their temperature derivative ( YP/ YT)V , of binary mixture 0.7393H2O+ 0.2607NH3 has been measured in the near- and supercritical regions. Measurements were made in the immediate vicinity of the liquid.gas coexistence curve (one- and two-phase regions) using a high-temperature, highpressure, nearly constant-volume adiabatic piezo-calorimeter. Measurements were made along 40 liquid and vapor isochores in the range from 120.03 kgm.3 to 671.23 kgm.3 and at temperatures from 403K to 633K and at pressures up to 28 MPa. Temperatures at the liquid.gas phase transition curve, TS( ), for each measured density (isochore) were obtained using the quasi-static thermograms technique. The expanded uncertainty of the pressure, P, and temperature derivative, ( YP/ YT)V , measurements at the 95% confidence level with a coverage factor of k = 2 is estimated to be 0.05% and 0.12.1.5% (depending on temperature and pressure), respectively. The direct measured pressures, P, and temperature derivatives, ( YP/ YT)V , has been used to calculate the internal pressure (or energy-volume coefficient) as ( YU/ YV)T = T( YP/ YT)V . P. We also measured the temperature derivatives of the internal energy ( YU/ YT)V = CV (isochoric heat capacity) using the same apparatus. The measurements were made at isochoric heating of the system at quasiequilibrium conditions. The effect of pressure, temperature, and concentration on the internal pressure was studied. The measured values of pressure (PS ), temperature derivative, ( YP/ YT)VS, temperature (TS) and density ( S) at the saturation curve together with isochoric heat capacity measurements were used to calculate other thermodynamic properties of the mixture at the bubble- and dew-pressure points curves. Some unusual gappendix type shape h behavior of the ( YP/ YT)V and internal pressure, Pint, near the critical and maxcondetherm points (in the retrograde region) was found.