1. vapor pressure and relative humidity
Although the water vapor content of the atmosphere is not much, but it is the atmosphere extremely active ingredient, it plays an important role in weather and climate. Atmospheric water vapor content There are many measurement methods, everyday people are most concerned about is the water vapor pressure, absolute humidity and relative humidity.
Water vapor pressure (e) is the atmospheric pressure in the partial pressure of water vapor, and atmospheric pressure as measured by hPa. Previous constant pressure and vapor pressure in millimeters of mercury to measure, 1 hPa = 0.75008 mm Hg. At a certain temperature to reach the partial pressure of water vapor in the air is saturated, called the saturation vapor pressure (E). Saturation vapor pressure increases as the temperature rises rapidly.
Absolute humidity (a) refers to the mass per unit volume of water vapor contained in the moist air, which is the density of water vapor in the air, in units of g / cm3 or kg / m 3. Absolute humidity is not easy to directly measure actual use is relatively small. If the vapor pressure in units of hPa, absolute humidity fetch unit kg / m 3, the relationship between the two is: where T is the temperature.
Relative humidity (f) refers to the air vapor pressure than the saturation vapor pressure of the e E the same temperature, expressed as a percentage is: Relative humidity size represents air close to saturation level. When f = 100%, it means the air has reached saturation; when not saturated, f <100%; when supersaturation f> 100%. The size relative humidity and atmospheric water vapor content is not only relevant but also with temperature increases.
2. Relative humidity
At the same temperature, the ratio of water vapor content and saturated water vapor content of the air between.
Detailed explanation: pressure P, temperature T, relative humidity of moist air is given a wet finger in the air, water vapor mole fraction mole fraction of saturation vapor pregnant under the same temperature T and pressure P ratio of water surface, with He expressed as a percentage.
Relative humidity is the ratio of the two pressure values:% RH = 100 xp / ps
Where p is the actual value of the partial pressure of water vapor in the surrounding environment; ps is the ambient pressure in the water saturation values, a relative humidity sensor is generally calibrated at standard conditions of room temperature (higher than 0 degrees), the corresponding, typically Such a sensor may indicate that the relative humidity at all temperature conditions (including in the case of less than 0 degrees), the vapor pressure of the ice will have a strong lower than liquid water. Thus, when liquid water appear in the form of ice, condensation will generate a relative humidity of less than 100% of the cases.
3. Relative humidity balance
Hygroscopic substance will strive to maintain a balance between humidity and ambient humidity of itself. Substance in water will produce vapor pressure (PM) on its surface, while the surrounding atmosphere will produce water vapor pressure (P). If the PM and P same words, the material on its environment to achieve the equilibrium relative humidity. PM and P will be any different generation moisture exchange, leading to changes in the moisture content of the material until it reaches the equilibrium relative humidity. Thus, the relative humidity is defined as the balancing substance does not result in the ambient atmosphere moisture exchange relative humidity. (Atmospheric humidity must be greater than the material humidity)
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