Thermodynamics Research Center / ThermoML | International Journal of Thermophysics

Experimental Study of the Critical Behavior of the Isochoric Heat Capacity of Aqueous Ammonia Mixture

Polikhronidi, N. G., Abdulagatov, I. M., Batyrova, R. G., Stepanov, G. V.
Int. J. Thermophys. 2009, 30, 3, 737-781
ABSTRACT
The isochoric heat capacity of a NH3 + H2O (0.2607 mole fraction of ammonia) mixture has been measured in the near- and supercritical regions. Measurements were made in the single- and two-phase regions including the coexistence curve using a high-temperature, high-pressure, nearly constant-volume adiabatic calorimeter. Measurements were made along 38 liquid and vapor isochores in the range from 120.03 kg * m-3 to 671.23 kg * m-3 and at temperatures from 478 K to 634 K and at pressures up to 28 MPa. Temperatures at the liquid gas phase transition curve, T S(?), for each measured density (isochore) and the critical parameters (T C and ? C) for the 0.2607 NH3 + 0.7393 H2O mixture were obtained using the quasi-static thermograms technique. The expanded uncertainty of the heat-capacity measurements at the 95 % confidence level with a coverage factor of k = 2 is estimated to be 2 % to 3 % in the near-critical and supercritical regions, 1.0 % to 1.5 % in the liquid phase, and 3 % to 4 % in the vapor phase. Uncertainties of the density, temperature, and concentration measurements are estimated to be 0.06 %, 15mK, and 5*10-5 mole fraction, respectively. An unusual behavior of the isochoric heat capacity of the mixture was found near the maxcondetherm point (in the retrograde region). The value of the Krichevskii parameter was calculated using the critical properties data for the mixture and vapor-pressure data for the pure solvent (H2O). The derived value of the Krichevskii parameter was used to analyze the critical behavior of the strong (C P , K T ) and weakly (C V ) singular properties in terms of the principle of isomorphism of critical phenomena in binary mixtures. The values of the characteristic parameters (K 1, K 2), temperatures (t 1, t 2), and the characteristic density differences (?? 1, ?? 2) were calculated for the NH3 + H2O mixture by using the critical-curve data.
Compounds
# Formula Name
1 H3N ammonia
2 H2O water
Datasets
The table above is generated from the ThermoML associated json file (link above). POMD and RXND refer to PureOrMixture and Reaction Datasets. The compound numbers are included in properties, variables, and phases, if specificied; the numbers refer to the table of compounds on the left.
Type Compound-# Property Variable Constraint Phase Method #Points
  • POMD
  • 1
  • 2
  • Molar heat capacity at constant volume, J/K/mol ; Liquid
  • Temperature, K; Liquid
  • Mole fraction - 1; Liquid
  • Liquid
  • Gas
  • Isochoric heat capacity
  • 39
  • POMD
  • 1
  • 2
  • Mass density, kg/m3 ; Liquid
  • Temperature, K; Liquid
  • Mole fraction - 1; Liquid
  • Liquid
  • Gas
  • Other PVT measurement
  • 39
  • POMD
  • 1
  • 2
  • Molar heat capacity at constant volume, J/K/mol ; Fluid (supercritical or subcritical phases)
  • Temperature, K; Fluid (supercritical or subcritical phases)
  • Mass density, kg/m3; Fluid (supercritical or subcritical phases)
  • Mole fraction - 1; Fluid (supercritical or subcritical phases)
  • Fluid (supercritical or subcritical phases)
  • isochoric heat capacity
  • 620