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e * is the saturation water vapor pressure T is the absolute air temperature in kelvins T st is the steam-point (i.e. boiling point at 1 atm.) temperature (373.15 K) e * st is e * at the steam-point pressure (1 atm = 1013.25 hPa) Similarly, the correlation for the saturation water vapor pressure over ice is:
The reduced temperature of a fluid is its actual temperature, divided by its critical temperature: [1] = where the actual temperature and critical temperature are expressed in absolute temperature scales (either Kelvin or Rankine). Both the reduced temperature and the reduced pressure are often used in thermodynamical formulas like the Peng ...
where temperature T is in degrees Celsius (°C) and saturation vapor pressure P is in kilopascals (kPa). According to Monteith and Unsworth, "Values of saturation vapour pressure from Tetens' formula are within 1 Pa of exact values up to 35 °C." Murray (1967) provides Tetens' equation for temperatures below 0 °C: [3]
The boiling point of water is the temperature at which the saturated vapor pressure equals the ambient pressure. Water supercooled below its normal freezing point has a higher vapor pressure than that of ice at the same temperature and is, thus, unstable. Calculations of the (saturation) vapor pressure of water are commonly used in meteorology.
The correct result would be P = 101.325 kPa, the normal (atmospheric) pressure. The deviation is −1.63 kPa or −1.61 %. It is important to use the same absolute units for T and T c as well as for P and P c. The unit system used (K or R for T) is irrelevant because of the usage of the reduced values T r and P r.
Lee [4] developed a modified form of the Antoine equation that allows for calculating vapor pressure across the entire temperature range using the acentric factor (𝜔) of a substance. The fundamental structure of the equation is based on the van der Waals equation and builds upon the findings of Wall [ 5 ] and Gutmann et al. [ 6 ] , who ...
In gas dynamics we are interested in the local relations between pressure, density and temperature, rather than considering a fixed quantity of gas. By considering the density ρ = M / V {\displaystyle \rho =M/V} as the inverse of the volume for a unit mass, we can take ρ = 1 / V {\displaystyle \rho =1/V} in these relations.
here e[T] is vapor pressure as a function of temperature, T. T dew = the dewpoint temperature at which water condenses. T wet = the temperature of a wet thermometer bulb from which water can evaporate to air. T dry = the temperature of a dry thermometer bulb in air.