Numerical Description of the Real Gas Isentropic Expansion for an Ammonia-Water Vapor Mixture

The present work involves the numerical calculation of the thermodynamic changes of an Ammonia-Water mixture in the vapor phase, along an isentropic expansion, considered as an ideal mixture of real components that has been followed numerically by a specially written computer program. Taking as input the NH3 Mass fraction ξ, the T and P values of the initial point, as well as the final temperature, the expansion was calculated for a temperature decrement of 1°C with the entropy held constant with an accuracy better than 0.000001 kJ/kgK. The method used (James et al., 1977), is iterative and the temperature step is variable and self adjusted to assure short time and accuracy. The properties calculated and presented in this paper are: P/Po = Reduced Pressure. T/To = Reduced Temperature. Vo/V = Reduced Volume. A*/A = Reduced Cross-Sectional Area. C/2C* = Reduced Velocity. pC2/2Po = Reduced Dynamic Pressure. J*/J = Reduced Impulse Function. The index o indicates the initial stagnation point and the superscript * indicates the critical point were Mach=1. The results obtained were in the form of diagrams showing a dependence of the isentropic exponents to both the initial pressure and NH3 mass fraction ξ while the other properties examined, depend on varying degrees upon ξ.