Goff and Gratch developed an accurate formula for calculating the saturation vapor pressure ( Goff and Gratch 1945), and modified this formula later ( Goff 1957). The saturation water vapor pressure, which is a function of air temperature, provides a basis for determining other thermodynamic properties of moist air (humidity ratio, specific enthalpy, specific entropy, specific volume, etc.). The latter condition is called saturation, a state of neutral equilibrium between moist air and the condensed water phase ( ASHRAE 2013, chapter 8). The amount of water vapor in moist air changes from zero to a maximum that relies on the temperature and pressure of atmospheric air. Moist air is a mixture of dry air and water vapor. The composition of dry air is relatively unvarying. ![]() Dry air exists when all water vapor has been removed from atmospheric air. Therefore, this new formula has significant advantages over the improved Magnus formula and can be used to calculate the saturation vapor pressure of water and of ice in a wide variety of disciplines.Ītmospheric air consists of a number of gaseous components (e.g., nitrogen, oxygen, carbon dioxide, inert gas, and water vapor). In addition, this new formula yields a mean relative error of 0.0005% within the commonly occurring temperature range (10°–40☌). In comparison with the International Association for the Properties of Water and Steam reference dataset, the mean relative errors from this new formula are only 0.001% and 0.006% for the saturation vapor pressure of water and of ice, respectively, within a wide range of temperatures from −100° to 100☌. This new formula is simple and easy to remember. In this study, a new formula has been developed by integrating the Clausius–Clapeyron equation. ![]() These formulas either are tedious or are not very accurate. A number of formulas are available for this calculation. It is necessary to calculate the saturation vapor pressure of water and of ice for some purposes in many disciplines.
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