Condensation

Condensation is the change in matter of a substance to a denser phase, such as a gas (or vapor) to a liquid. Condensation commonly occurs when a vapor is cooled to a liquid, but can also occur if a vapor is compressed (i.e., pressure on it increased) into a liquid, or undergoes a combination of cooling and compression. Liquid which has been condensed from a vapor is called condensate. A device or unit used to condense vapors into liquid is called a condenser. Condensers are used in heat exchangers which have various designs, and come in many sizes ranging from rather small (hand-held) to very large.

The water seen on the outside of a cold glass on a hot day is an example of condensation.

Condensation of water in nature
Water vapor from air which naturally condenses on cold surfaces into liquid water is called dew. Water vapor will only condense onto another surface when that surface is cooler than the temperature of the water vapor, or when the water vapor equilibrium in air, i. e. saturation humidity, has been exceeded. When water vapor condenses onto a surface, a net warming occurs on that surface. 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 risen.

In the atmosphere, condensation of water vapor is what produces clouds. The dew point of an air parcel is the temperature to which it must cool before condensation in the air begins to form.

Also, a net condensation of water vapor occurs on surfaces when the temperature of the surface is at or below the dew point temperature of the atmosphere. Deposition, the direct formation of ice from water vapor, is a type of condensation. Frost and snow are examples of deposition.

Condensation in buildings
Condensation is the most common form of dampness encountered in buildings. In buildings the internal air can have a high level of relative humidity due to the activity of the occupants (e.g. cooking, drying clothes, breathing etc.). When this air comes into contact with cold surfaces such as windows and cold walls it can condense, causing dampness.

Applications of condensation
Condensation is a crucial component of distillation, an important application in laboratory and industrial chemistry application.

Because condensation is a naturally occurring phenomenon, it can often be used to generate water in large quantities for human use. In fact, there are many structures that are made solely for the purpose of collecting water from condensation, such as fog fences, air wells and dew ponds. Such system can often be used to retain soil moisture in areas where active desertification is occurring. In fact, certain organizations use education about water condensers in efforts to effectively aid such areas.