A simple extremely accurate formula for calculating saturation vapor pressure of water and ice

What is it about?

It is necessary to calculate the saturation vapor pressure of water and of ice for some purposes in many disciplines. A number of formulas are available for this calculation. These formulas are either tedious, or not very accurate. In this study, a new formula has been developed by integrating the Clausius-Clapeyron equation. This new formula is simple and easy to remember. In comparison to the IAPWS reference data set, 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°C to 100°C. In addition, this new formula yields a mean relative error of 0.0005% within the commonly occurring temperature range (10°C to 40°C). 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.

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Why is it important?

Although those formulas are simple, the computed results are not very accurate within a wide temperature range (-100°C to 100°C). In addition, it is desirable to use a very accurate formula when extreme accuracy is required, e.g. accurate calculation of rainfall, precise prediction of the rising surface temperature of the earth due to global warming, accurate calculation of evapotranspiration in agriculture. None of those simple formulas is able to achieve this goal. This paper proposed a simple and extremely accurate formulation for calculating the saturation vapor pressure of water and of ice. The computed results are extremely accurate for a wide temperature range from -100°C to 100°C.

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