Studies On The Equation Of State Of N₂-O₂-Ar Fluid And The Model Of Gas Solubility In Aqueous Electrolyte Solutions

N2,O2 and Ar are the main components of air,and knowledge of the pressure-volume-temperature-composition(PVTx)and vapor-liquid equilibrium(VLE)properties of N2-O2-Ar fluid mixtures can help us better understand the exchange between air and natural fluids.The solubility of N2,O2 and Ar in common aqueous electrolyte solutions and the water content in vapor phase are very important in the studies of groundwater,limnology and oceanography.Because experimental data are limited,the predictive models have become more and more useful.In this study,relevant computational simulation work has been carried out,and results are as follows:(1)A new Helmholtz free energy equation of state was developed,which can not only calculate the PVT and VLE properties of pure N2,O2 and Ar fluids,but also predict the PVTx and VLE properties of N2-O2-Ar fluid mixtures at different temperatures and pressures.The parameters of the mixture equation are obtained by using experimental volumetric and phase-equilibrium data of the corresponding binary systems and the nonlinear least square method.The results show that the equation can reproduce most of the experimental data and can approximately predict the thermodynamic properties of air.(2)The above equation of state was adopted in the vapor phase and the activity coefficient theory of the Pitzer electrolyte was used in the liquid phase,a gas solubility model has been developed based on the fugacity-activity relationship at VLE.The solubility model can accurately calculate the solubility of N2,O2 and Ar in pure water and aqueous NaCl,KCl,MgCl2,CaCl2,Na2SO4,K2SO4 and MgSO4 solutions.The model can also predict the N2,O2 and Ar solubility in multi-component electrolyte solutions and seawater,as well as the solubility of air in pure water and aqueous NaCl solution.(3)By using reliable experimental data of water content in the vapor phase of H2O-N2,H2O-O2 and H2O-Ar systems,a semi-empirical thermodynamic equation was established,which can accurately calculate the water content in the vapor phase of corresponding binary systems under different temperatures and pressures.The equation can also be extended to predict the water content of H2O-air system.