Liquid-vapor relations in the critical region of the system NaCl-H₂O from 380 to 415°C: A refined determination of the critical point and two-phase boundary of seawater

Pressure-temperature-composition (P-T-x) relations for coexisting vapor and liquid phases in the system NaCl-H₂O were determined experimentally in the critical region from 380 to 415°C. The results provide much improved control on the P-T-x critical line in this region. The critical point of seawater (3.2 wt% NaCl solution), which is bracketed in the present study, is at 407°C and 298.5 bar. In addition, the P-T two-phase boundary of seawater was re-determined. These results provide increased precision and accuracy for theoretical models of critical phenomena in this important two-component system and of the limiting P- Tconditions of seawater in seafloor geothermal systems.