![]() ![]() As expected, Buck's equation for T > 0 ☌ is significantly more accurate than Tetens, and its superiority increases markedly above 50 ☌, though it is more complicated to use. Tetens' equations are generally much more accurate and arguably simpler for use at everyday temperatures (e.g., in meteorology). The unattributed formula must have zero error at around 26 ☌, but is of very poor accuracy outside a very narrow range. Tetens is much more accurate over the range from 0 to 50 ☌ and very competitive at 75 ☌, but Antoine's is superior at 75 ☌ and above. The analysis here shows the simple unattributed formula and the Antoine equation are reasonably accurate at 100 ☌, but quite poor for lower temperatures above freezing. Here is a comparison of the accuracies of these different explicit formulations, showing saturation vapour pressures for liquid water in kPa, calculated at six temperatures with their percentage error from the table values of Lide (2005):Ī more detailed discussion of accuracy and considerations of the inaccuracy in temperature measurements is presented in Alduchov and Eskridge (1996). P = exp ( 20.386 − 5132 T ) Īccuracy of different formulations Some of these are (in approximate order of increasing accuracy): There are many published approximations for calculating saturated vapour pressure over water and over ice. An understanding of vapour pressure is also relevant in explaining high altitude breathing and cavitation. This is relevant to both pressure cooking and cooking at high altitude. The temperature-vapour pressure relation inversely describes the relation between the boiling point of water and the pressure. The boiling point of water is the temperature at which the saturated vapour pressure equals the ambient pressure.Ĭalculations of the (saturation) vapour pressure of water are commonly used in meteorology. The saturation vapour pressure of water increases with increasing temperature and can be determined with the Clausius–Clapeyron relation. ![]() At pressures higher than vapour pressure, water would condense, whilst at lower pressures it would evaporate or sublimate. The saturation vapour pressure is the pressure at which water vapour is in thermodynamic equilibrium with its condensed state. The vapour pressure of water is the pressure exerted by molecules of water vapor in gaseous form (whether pure or in a mixture with other gases such as air). Pressure exerted by molecules of water vapour in gaseous form Vapour pressure of water (0–100 ☌) T, ☌ ![]()
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