Thermodynamic properties of ammonia-water mixtures for power cycles

Power cycles with ammonia-water mixtures as working fluids have been shown to reach higher thermal efficiencies than the traditional steam turbine (Rankine) cycle with water as the working fluid. Different correlations for the thermodynamic properties of ammonia-water mixtures have been used in studies of ammonia-water mixture cycles described in the literature. Four of these correlations are compared in this paper. The differences in thermal efficiencies for a bottoming Kalina cycle when these four property correlations are used are in the range 0.5 to 3.3 %. The properties for saturated liquid and vapor according to three of the correlations and available experimental data are also compared at high pressures and temperatures [up to 20 MPa and 337 degrees C (610 K)]. The difference in saturation temperature for the different correlations is up to 20 %, and the difference in saturation enthalpy is as high as 100 % when the pressure is 20 MPa.