Simple Functions for Predicting Thermodynamic Properties of Ammonia - Water Mixture (RESEARCH NOTE)

The engineering calculation and simulation of absorption refrigeration systems require the availability of simple and efficient functions for the determination of thermodynamic property values of the operating fluid. This work presents a set of five simple and explicit functions for the determination of the vapor - liquid equilibrium properties of the ammonia-water mixture. The functions are constructed by least square method for curve fitting using the valid available data in the literature. The presented functions are valid for - 20 ≤ T ≤ 140º C, 0.2 ≤ P ≤ 100 bar, and the entire composition range (i. e. 0 ≤ x ≤ 1) which cover the region within which absorption cycles commonly operate. Obtained results are compared in detail with other correlations in the literature in graphical and statistical forms and reasonable accuracy are observed. Standard deviation of presented functions are 3.44 kJ/kg for enthalpy of saturated liquid mixture, 14.06 kJ/kg for enthalpy of saturated vapor mixture, and 0.0123 kg - NH3/kg - mix for ammonia mass fraction in vapor phase.