evaporation
evaporation is the process that changes a liquid into a gas it can occur at any temperature and is due to the movement of molecules in the liquid for example water left in a saucer will gradually evaporate the water molecules escape into the air as a gas water vapour
the warmer the air the more moisture it can hold in the form of vapour every second about 15 million tonne of moisture is evaporated from the earths surface by the heat of the sun water evaporated from the ocean often travels hundreds of kilometres before falling as rain
when air contains the maximum water vapour possible for its temperature it is said to be saturated below this temperature called the dew point for a particular mass of air the water vapour begins to condense into water droplets
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29-11-2010 | 02:37 AM
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29-11-2010 | 03:04 AM
Condensation
Condensation is the process whereby water vapour in the atmosphere is returned to its original liquid state. In the atmosphere, condensation may appear as clouds, fog, mist,
dew or frost, depending upon the physical conditions of the atmosphere. Condensation is not a matter of one particular temperature but of a difference between two. Condensation of water vapour occurs when the temperature of air is lowered to its dew point.
All air contains water vapour of varying quantities. The lower the air temperature, the smaller the maximum possible capacity for vapour. When air is cooled, relative humidity, the air becomes saturated. Further cooling below the dew point will induce condensation of the excess water vapour. increases, until at a particular temperature, called the dew point
The temperature of the dew point will depend upon the absolute content of water vapour, that is the absolute humidity, measured in g/m3 (grams per cubic metre). The dew point of humid air will be higher than the dew point of dry air. Both air temperature and absolute humidity will determine what type of condensation will occur when the air is cooled. If air in contact with the ground is cooled to its dew point, dew or frost will form, dew if the point is above 0°C, or frost if it is below 0°C. Cooling of a larger layer of air near to the ground may produce mist of fog, which freezes if the dew point is below 0°C. Air that is cooled to its dew point by rising and expansion will condense to form clouds. Above 0°C, small droplets of water are formed. Condensation may also result in ice crystals at temperature well below 0°C. When temperatures are near or a little below 0°C, supercooled water droplets can form.
Condensation is the process whereby water vapour in the atmosphere is returned to its original liquid state. In the atmosphere, condensation may appear as clouds, fog, mist,
dew or frost, depending upon the physical conditions of the atmosphere. Condensation is not a matter of one particular temperature but of a difference between two. Condensation of water vapour occurs when the temperature of air is lowered to its dew point.
All air contains water vapour of varying quantities. The lower the air temperature, the smaller the maximum possible capacity for vapour. When air is cooled, relative humidity, the air becomes saturated. Further cooling below the dew point will induce condensation of the excess water vapour. increases, until at a particular temperature, called the dew point
The temperature of the dew point will depend upon the absolute content of water vapour, that is the absolute humidity, measured in g/m3 (grams per cubic metre). The dew point of humid air will be higher than the dew point of dry air. Both air temperature and absolute humidity will determine what type of condensation will occur when the air is cooled. If air in contact with the ground is cooled to its dew point, dew or frost will form, dew if the point is above 0°C, or frost if it is below 0°C. Cooling of a larger layer of air near to the ground may produce mist of fog, which freezes if the dew point is below 0°C. Air that is cooled to its dew point by rising and expansion will condense to form clouds. Above 0°C, small droplets of water are formed. Condensation may also result in ice crystals at temperature well below 0°C. When temperatures are near or a little below 0°C, supercooled water droplets can form.