Vapor Pressure Formulation for Water in Range 0 to 100 °C. A Revision

Area of Science:

• Thermodynamics
• Physical Chemistry
• Metrology

Background:

• The 1971 Wexler and Greenspan formulation provided water vapor pressure data from 0 to 100 °C.
• Recent experimental determination of the water triple point pressure by Guildner, Johnson, and Jones necessitated a review.

Purpose of the Study:

• To revise the 1971 water vapor pressure formulation.
• To ensure consistency with the definitive experimental value at the water triple point.
• To provide an updated formulation for water vapor pressure across a defined temperature range.

Main Methods:

• Revision of an existing thermodynamic formulation.
• Comparison with recent experimental data, specifically the vapor pressure at the triple point of water.
• Generation of a comprehensive table of vapor pressure values and temperature derivatives.

Main Results:

• The revised formulation shows minimal deviation from the 1971 formulation between 25 and 100 °C.
• Below 25 °C, the new formulation predicts higher vapor pressures compared to the 1971 version.
• At the triple point (0.01 °C), the revised formulation yields 611.657 Pa, differing from the 1971 value of 611.196 Pa.

Conclusions:

• The updated formulation offers improved accuracy for water vapor pressure, especially at lower temperatures.
• The revised model is consistent with the latest high-precision experimental data.
• A detailed table of vapor pressure and its temperature derivative is provided for practical applications.