The enthalpy of water in the liquid state

Abstract

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.

Water: Two Liquids Divided by a Common Hydrogen Bond

“…43 Yet another intriguing feature of the model is that when compressed at constant temperature the simulated water has lower potential energy than before compression, Table 2. The numbers here are qualitatively consistent with the estimated enthalpy of water under pressure, 44 which if anything would imply an even larger decrease in potential energy with pressure than simulated here. To see how this is, the enthalpy is given in terms of the internal energy and pressure and volume, ΔH = ΔU + Δ(PV ).…”

“…To see how this is, the enthalpy is given in terms of the internal energy and pressure and volume, ΔH = ΔU + Δ(PV ). According to 44 the excess enthalpy of water at 273K and 400MPa above ambient pressure is ≈ 2.4kJ/mole. The pressure-volume contribution to the enthalpy change is 6.3kJ/mole, so the net change in potential energy is -3.9kJ/mole.…”

Viscosity and Thermal Conductivity of Water: Gaseous and liquid States.

“…Density values were obtained from an enlarged plot of the reduced density correlations presented in Figures 3 and 4. The construction of these figures has been based on the experimental P-V-T data of water compiled by Byrne and Thodos (8). A total of 26 references (8) was used to establish reduced density values which were extended by plotting pressure versus temperature for lines of constant reduced density.…”

“…The residual viscosity relationship of Figure 3 in conjunction with a reduced density plot for water (8) have permitted the construction of a reduced state viscosity correlation for gaseous and liquid water. The critical viscosity, µc = 4300 x 10~°c p. and Figure 1 permitted the construction of the base isobar, PR ~0.…”