Formation of a liquid or solid from its vapour. Condensation usually occurs on a surface that is cooler than the adjacent gas. A substance condenses when the pressure exerted by its vapour exceeds the vapour pressure of its liquid or solid phase at the temperature of the surface where the condensation is to occur. The process causes the release of thermal energy. Condensation occurs on a glass of cold water on a warm, humid day when water vapour in the air condenses to form liquid water on the glass's colder surface. Condensation also accounts for the formation of dew, fog, rain, snow, and clouds.
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Condensation is the change of the physical state of aggregation (or simply state) of matter from gaseous phase into liquid phase. When the transition happens from the gaseous phase into the solid phase directly, bypassing the liquid phase the change is called deposition, which is the opposite of sublimation.
Condensation commonly occurs when a vapor is cooled to its dew point, but the dewpoint can also be reached through compression. The condensed vapour is called a condensate, the laboratory or the industrial equipment used for condensation is called a condenser.
The science of studying the thermodynamic properties of moist air and the interrelationships between these in order to analyze, and predict properties by changing in the conditions of moist air is called psychrometry. The interrelationship can be graphically represented, and prediction carried out graphically by the psychrometric chart Most people think the water is condensation, but condensation is only the process of change.
Water vapor that naturally condenses on cold surfaces into liquid water is called dew. Water vapor will only condense onto another surface when the temperature of that surface is cooler than the temperature of the water vapor. The water molecule brings a parcel of heat with it. The temperature of the atmosphere also rises very slightly. In order to have condensed, the molecule tends to be relatively low in kinetic energy. Since the atmosphere has lost a slow-moving particle, the average speed of the molecules in the atmosphere has increased. Therefore, its temperature has also rise.
Because condensation is a naturally occurring phenomenon, it can often be used to generate water in large quantities for human use: Many structures that are made solely for the purpose of collecting water from condensation, such as fog fences, air wells and dew ponds. Such systems can often be used to retain soil moisture in areas where active desertification is occurring—so much so that some organizations educate people living in affected areas about water condensers to help them deal effectively with the situation.