Calculation of isobar, isothermal, isochoric, adiabatic (isentropic) and isenthalpic processes. Calculation of properties of states, processes and thermodynamic cycles of free design. Explanations of the main concepts, equations and thermodynamic laws.Quick and reliable calculations of steam tables of water, air, ideal gases, refrigerants and other substances.App to solve problems and exercises from Thermodynamics Engineering books.Type negative temperatures into the calculator and vapor pressure will be determined according to Buck and Tetens formulas. Two formulas have a version for vapor pressure of water over ice (so for temperatures below 0 ☌). Have a look at this handy vapor pressure for water table to find the pressure for different temperatures quickly: T If we raise the pressure and keep the temperature, the water will condense. The vapor pressure of water is the pressure at which water vapor is in thermodynamic equilibrium with its condensed state. The Antoine equation is sometimes simplified (omitting C coefficient) or extended by three additional terms, what can increase the flexibility of the equation. The second for the range from the normal boiling point to the critical point (100-374 ☌ - or 212°-705 ☏ - for water)Ī = 8.14019, B = 1810.94, C = 244.485, so the formula looks as follows: One for describing the vapor pressure curve up to the normal boiling point. There are usually two sets of parameters used for a single component:Īntoine_pressure = 10^(A - (B / (C + temperature))) ![]() It works for many substances, although you need to know the coefficients. It's a semi-empirical formula describing the relation between vapor pressure and temperature. The Antoine equation is derived from the Clausius–Clapeyron relation. For temperatures higher than 100 ☌, the values start to differ significantly and the Antoine equation is usually the most accurate one. The Tetens equation works well for 0-50 ☌ range, but Buck beats all of them, for every checked value. T (☌)Īs you can notice, the Antoine equation is reasonably accurate for higher temperatures, but the low ones are calculated with quite a big error. ![]() The reference values come from Lide table with vapor pressure of water (all pressures given in kPa). The table below shows the comparison of the accuracies between different formulas, for several temperatures from 0-100 ☌ range (32-212☏). ![]() You can also use another equation, called the Goff-Gratch formula, but as it's more complicated (and approximately as accurate as Buck formula), we didn't implement it in our vapor pressure of water calculator. Buck formula, also known as Arden Buck equationīuck_pressure = 0.61121 * e^.Magnus formula, also known as August-Roche-Magnus or Magnus-Tetens equation.Jump to the next section to read more about the constants in the Antoine formula. The temperature T is expressed in degrees Celsius and the vapor pressure P is in mmHg. Simple_pressure = e^(20.386 - (5132 / (temperature + 273)), where vapor pressure is expressed in mmHg and temperature in kelvins.Īntoine_pressure = 10^ In our calculator you'll find implemented: The most well known and established is the Antoine equation, but other methods also exist (and they perform better in typical conditions). There are many different formulas thanks to which you can calculate the vapor pressure of water.
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