The enthalpy of water in the liquid state has been calculated from 32°F. to temperatures approaching the critical and pressures ranging from saturated conditions to 160,000 lb./sq. in. abs. (approximately 11,000 atm). The results of this study are presented graphically and show that the influence of pressure on enthalpy is significant, particularly in the lower temperature region. At these conditions pressure is found to increase the enthalpy of liquid water by as much as 360 B.t.u./lb. above the corresponding enthalpy of the saturated liquid state.
A comprehensive literature search disclosed PVT data for water that permitted the construction of a density correlation. This correlation expressed in reduced coordinates extends from the normal freezing point of water to temperatures of 1,870°F. (TR = 2.0) and pressures ranging up to 10,915 atm. (PR = 50). The recent extensive PVT data of Kennedy reported in 1950 supplemented with the earlier data of Amagat and Bridgman allowed the calculation of enthalpies at these elevated temperatures and pressures. For these calculations basic thermodynamic relationships were adapted which utilized this reduced density correlation. This approach has made possible the extension of the thermodynamic properties of liquid water above the highest pressure reported by Keenan and Keys. Below this pressure of 6,000 lb./sq. in abs. good agreement was found to exist between the enthalpy values presented by Keenan and Keyes and those reported in this investigation.