An equation of state for ammonia-water mixtures is presented. Separate equations of state for liquid and gas phases are provided for pure ammonia and pure water. In the gas phase, the mixture is assumed to behave as an ideal solution, while in the liquid phase, the Gibbs excess energy is used to allow departure from ideal solution behaviour. An existing correlation for the liquid Gibbs excess energy is modified to include experimental data at higher temperatures and pressures. The new correlation covers vapour-liquid equilibrium pressures of 0.2 110 bar and temperatures of 230 to 600 deg.K. Comparisons with reported experimental data show good agreement.

KEYWORDS: thermodynamics, water, ammonia, mixtures, refrigeration, liquids, gases, calculating, compression refrigeration.