This process converts large hydrocarbons into smaller ones and introduces unsaturated products. Ethylene is not toxic, but is a simple asphyxiant.Įthylene is used as an anesthetic, a refrigerant, and to make other chemicals as polymers and plastics.Įthylene is produced in petrochemical processes, as steam cracking where hydrocarbons and steam are heated to 750–950 ☌. Vapors arising from the boiling liquid are lighter than air. Under prolonged exposure to fire or heat the containers may rupture violently and rocket. It is easily ignited and a flame can easily flash back to the source of the leak. , C 2H 4, is a highly flammable, colorless and noncorrosive gas with a sweet odor. "Polynomial fits to saturation vapor pressure". Journal of Research of the National Bureau of Standards Section A. "Vapor pressure formulation for water in range 0 to 100☌. "An approximating polynomial for the computation of saturation vapor pressure". In Transactions of the American Society of Heating and Ventilating Engineers, pp 95–122, presented at the 52nd annual meeting of the American Society of Heating and Ventilating Engineers, New York, 1946. Low-pressure properties of water from −160 to 212 ☏. "Improved Magnus form approximation of saturation vapor pressure". CRC Handbook of Chemistry and Physics (85th ed.). Graphical pressure dependency on temperature The former is an extremely simple Antoine equation, while the latter is a polynomial. Įxamples of modern use of these formulae can additionally be found in NASA's GISS Model-E and Seinfeld and Pandis (2006). However, there are more recent reviews of possibly superior formulations, notably Wexler (1976, 1977), reported by Flatau et al. They are all very accurate (compared to Clausius-Clapeyron and the Goff-Gratch) but use nested polynomials for very efficient computation. The Buck equation is even superior to the more complex Goff-Gratch equation over the range needed for practical meteorology.įor serious computation, Lowe (1977) developed two pairs of equations for temperatures above and below freezing, with different levels of accuracy. 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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