Comparison of correlations for predicting thermodynamic properties of ammonia-water mixtures

Tillner-Roth and Friend have presented a new correlation for the thermodynamic properties of ammonia-water mixtures. In this study, the new correlation has been compared to other correlations used in simulations of power cycles using ammonia-water mixtures as working fluids. The saturation properties for mixtures, calculated with the different correlations, have been examined at different temperatures and pressures. Available experimental data have been included in the comparison. The variation of the enthalpy with temperature at different pressures for a mixture has also been compared. The correlations have been examined for use in power cycle simulations as well. The comparison reveals that the new correlation shows a more reasonable behavior when the critical point of the mixture is approached. At lower temperatures and pressures, the compared correlations give very similar results. The differences in the results from the cycle simulations, using different correlations, are small but they tend to increase with increasing maximum pressure in the cycle.