The compressibility of seawater from 0 to 95 °C at 1 atm

Measurements on the speed of sound (U) in seawater as a function of salinity at 1 atm (P = 0 bar applied pressure) have been measured from 25 to 95 °C. The new measurements have been combined with the earlier studies to determine the adiabatic compressibility (βS = −(1/ρ)(∂ρ/∂P)S) of seawater from 0 to 95 °CβS=1/(ρU2)βS=1/ρU2where ρ is the density and S is the entropy of seawater. The isothermal compressibility of seawater were determined fromβT=βSα2T/(ρCp)βT=βSα2T/ρCpwhere the thermal expansively, α = −(1/ρ)(∂ρ/∂T)P and heat capacity (Cp) were determine from earlier measurements. The values of the isothermal compressibility at 1 atm (βT0) have been used to estimate the effect of pressure on the secant bulk modulus of seawater (KP at applied pressure P)KP=v0P/(v0–vP)=K0+A P+B P2KP=v0P/v0–vP=K0+A P+B P2where the specific volume v = 1/ρ and K0 = 1/(βT0). The values of A and B at high pressures have been determined from literature high pressure measurements. This allows one to make reasonable estimates of the density of seawater as a function of pressure to 100 °C when seawater is used as a cooling agent and for desalination (Feistel, 2010).

Research Highlights
► This is the first study on measurements of the speed of sound in seawater at high temperatures.
► The results have been used to determine the isothermal compressibility of seawater.
► The results extend the equation of state to high temperatures and applied pressure.