Equation of State of Water and Seawater

Abstract

Equations of state for both water and sea water have been evaluated making use of the recent highly accurate work by Kell and Whalley on pure water. It was found that fits of 5 ppm from 0°–150° and 1–1000 bar could be obtained using: (1) the Tumlirz equation (P+P0) (v—v0)=λ from 0° to 70° and the differential form of the Tait equation (dv/dP)=C/(B+P) from 40° to 150°. It is shown how Kell and Whalley data can be used to normalize other PVT data including sea water. The data of Wilson and Bradley on sea water can be represented with fits of 70 ppm by a modified Tumlirz equation, v=v0+k1S+λ(P0+k2S+P)−1, where the constants λ, P0 and v0 are the pure water values, S is salinity, and k1 and k2 are constants. The fact that the equation of state for pure water appears to change from one form to another around 50° is particularly interesting since this is the region of the compressibility minimum and suggests that if the two-state model of water is valid, then each state may have its own PVT equation. Evaluation of Vedam and Holton's data from 30°–80° on water to 10 000 bar reveals that the Tait differential equation provides three times better fits than the Tumlirz equation. [This paper represents results of research sponsored by the Office of Naval Research and the National Science Foundation.]