Saturation vapor pressure and critical constants of H2O, D2O, T2O, and their isotopic mixtures

Reliable data on the vapor pressure and critical constants of H2O isotopes and their isotopic mixtures are required for the generation of thermophysical properties data over a wide range of temperatures and pressures. In this study, vapor pressure equations for D2O and T2O have been developed based on the latest experimental and theoretical information. Considering the similarity among H2O isotopes, the functional form of the Saul and Wagner equation, fully proven for H2O, has been employed. The present equation for D2O shows a lower trend by up to 0.09% than the widely used Hill and MacMillan equation at temperatures below 1500C. For the vapor pressure of the isotopic mixtures, the available experimental data have been examined for the validity of Raoult's law. Then it has been shown that the critical temperature and the critical pressure of the isotopic mixture can also be predicted as simple mole-fraction average values