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The US Occupational Safety and Health Administration recommends indoor air be maintained at 20–24.5 °C (68–76 °F) with a 20–60% relative humidity, [13] equivalent to a dew point of approximately 4.0 to 16.5 °C (39 to 62 °F) (by Simple Rule calculation below).
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.
Up to 99.63 °C (the boiling point of water at 0.1 MPa), at this pressure water exists as a liquid. Above that, it exists as water vapor. Note that the boiling point of 100.0 °C is at a pressure of 0.101325 MPa (1 atm), which is the average atmospheric pressure.
The percentage of water vapor in surface air varies from 0.01% at -42 °C (-44 °F) [15] to 4.24% when the dew point is 30 °C (86 °F). [16] Over 99% of atmospheric water is in the form of vapour, rather than liquid water or ice, [17] and approximately 99.13% of the water vapour is contained in the troposphere.
The water in food has a tendency to evaporate, but the water vapor in the surrounding air has a tendency to condense into the food. When the two tendencies are in balance— and the air and food are stable—the air's relative humidity (expressed as a fraction instead of as a percentage) is taken to be the water activity, a w .
One pascal is one newton per square meter (N·m −2 or kg·m −1 ·s −2). Experimental measurement of vapor pressure is a simple procedure for common pressures between 1 and 200 kPa. [2] The most accurate results are obtained near the boiling point of the substance; measurements smaller than 1 kPa are subject to major errors. Procedures ...
His equation makes use of the relationship between the LCL and dew point temperature discussed above. In the Earth's atmosphere near the surface, the lapse rate for dry adiabatic lifting is about 9.8 K/km, and the lapse rate of the dew point is about 1.8 K/km (it varies from about 1.6-1.9 K/km). This gives the slopes of the curves shown in the ...
The saturation vapor density (SVD) is the maximum density of water vapor in air at a given temperature. [1] The concept is related to saturation vapor pressure (SVP). It can be used to calculate exact quantity of water vapor in the air from a relative humidity (RH = % local air humidity measured / local total air humidity possible ) Given an RH percentage, the density of water in the air is ...