Description of the real gas isentropic changes for an ammonia-water vapor mixture

The NH sub(3)-H sub(2)O binary mixture is used extensively in industrial refrigeration or heat-pump applications while it is a candidate for future units working with resorption-compression [1]. In this paper, the thermodynamic changes of an ammonia-water mixture in the vapor phase, along an isentropic expansion, have been calculated numerically for a starting point with a temperature of 800 degree C and initial pressures of 20, 30, 40, and 50 bar. For this purpose, a special computer program, ISENEXPR, has been developed. The thermodynamic relations used were obtained in terms of the Gibbs free energy equation for the gas phase of pure components [1], [3], [6] and the entropy was held constant with an accuracy better than 0.000 001 kJ/kg K. The runs performed for isentropic expansions showed a dependence of the isentropic on the both exponents initial pressure and NH sub(3) mass fraction xi , while the other properties depend on varying degrees upon xi . Results are given in the form of diagrams, describing the isentropic change of the NH sub(3)-H sub(2)O gas phase mixture.