condensation

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condensation,

in physics, change of a substance from the gaseous (vapor) to the liquid state (see states of matterstates of matter,
forms of matter differing in several properties because of differences in the motions and forces of the molecules (or atoms, ions, or elementary particles) of which they are composed.
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). Condensation is the reverse of vaporizationvaporization,
change of a liquid or solid substance to a gas or vapor. There is fundamentally no difference between the terms gas and vapor, but gas is used commonly to describe a substance that appears in the gaseous state under standard conditions of pressure and
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, or change from liquid to gas. It can be brought about by cooling, as in distillationdistillation,
process used to separate the substances composing a mixture. It involves a change of state, as of liquid to gas, and subsequent condensation. The process was probably first used in the production of intoxicating beverages.
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, or by an increase in pressure resulting in a decrease in volume. Certain natural phenomena, such as dew, fog, mist, and clouds, are the result of the condensation of water vapor in the atmosphere; the formation of dewdew,
thin film of water that has condensed on the surface of objects near the ground. Dew forms when radiational cooling of these objects during the nighttime hours also cools the shallow layer of overlying air in contact with them, causing the condensation of some water vapor.
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 illustrates well the fundamental principles involved in such phenomena. The explanation of condensation can be found in the kinetic-molecular theory of gaseskinetic-molecular theory of gases,
physical theory that explains the behavior of gases on the basis of the following assumptions: (1) Any gas is composed of a very large number of very tiny particles called molecules; (2) The molecules are very far apart compared to their sizes,
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. As heat is removed from a gas, the molecules of the gas move more slowly, and as a result, the intermolecular forcesintermolecular forces,
forces that are exerted by molecules on each other and that, in general, affect the macroscopic properties of the material of which the molecules are a part. Such forces may be either attractive or repulsive in nature.
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 are strong enough to pull the molecules together to form droplets of liquid. Similarly, reducing the volume of the gas reduces the average distance between molecules and thus favors the intermolecular forces tending to pull them together.

Condensation

A phase-change process in which vapor converts into liquid when the temperature of the vapor is reduced below the saturation temperature corresponding to the pressure in the vapor. For a pure vapor this pressure is the total pressure, whereas in a mixture of a vapor and a noncondensable gas it is the partial pressure of the vapor. Sustaining the process of condensation on a cold surface in a steady state requires cooling of the surface by external means. Condensation is an efficient heat transfer process and is utilized in various industrial applications. Condensation of vapor on a cold surface can be classified as filmwise or dropwise. Direct-contact condensation refers to condensation of vapor (bubbles or a vapor stream) in a liquid or condensation on liquid droplets entrained in the vapor. If vapor temperature falls below its saturation temperature, condensation can occur in the bulk vapor. This phenomenon is called homogeneous condensation (formation of fog) and is facilitated by foreign particles such as dust. See Heat transfer

In film condensation, a thin film of liquid forms upon condensation of vapor on a cold surface that is well wetted by the condensate. The liquid film flows downward as a result of gravity.

In dropwise condensation, on surfaces that are not well wetted, vapor may condense in the form of droplets (see illustration). The droplets form on imperfections such as cavities, dents, and cracks on the surface. The droplets of 10–100 μm diameter contribute most to the heat transfer rate. As a droplet grows to a size that can roll down the surface because of gravity, it wipes the surface of the droplets in its path. In the wake behind the large droplet, numerous smaller droplets form and the process repeats. The heat transfer coefficients with dropwise condensation can be one to two orders of magnitude greater then that for film condensation.

Steam at atmospheric pressure condensing on a vertical copper surfaceenlarge picture
Steam at atmospheric pressure condensing on a vertical copper surface

Direct-condensation involves condensation of vapor bubbles in a host liquid and condensation on droplets entrained in vapor. Both are also very efficient heat transfer processes, especially when the vapor-liquid interface oscillates.

Condensation

The formation of water on a surface, caused by the air temperature falling below its dew point. Most likely to occur in cool weather, when the temperature drops.

Condensation

 

the transition of a substance from the gaseous state to the liquid or solid state as a result of cooling or compression.

The condensation of vapor is possible only at temperatures below the critical temperature of the given substance. Condensation, like its reverse process, evaporation, is an example of a phase transition of matter (first-order phase transition). The amount of heat released in condensation is the same amount that was spent on the evaporation of the condensed substance. Rain, snow, dew, and frost are all natural phenomena resulting from the condensation of water vapor in the atmosphere. Condensation is widely used in industry in such areas as power engineering (for example, in the condensers of steam turbines), chemical technology (for example, in the separation of substances by fractional condensation), refrigeration and cryogenic technology, and desalinization. The liquid formed as a result of condensation is termed the condensate.

In technology condensation is usually achieved on condensing surfaces (cooling surfaces). There are two mechanisms of surface condensation: filmwise condensation and dropwise condensation. The former is observed in condensation on a wettable surface and is characterized by the formation of an even film of condensate. The condensate forms as drops on nonwettable surfaces. In dropwise condensation the rate of heat transfer is much higher than in filmwise condensation because the uniform condensate film hinders the transfer of heat.

The lower the temperature of the surface relative to the vapor saturation temperature at a given pressure, the higher the rate of surface condensation. The presence of other gases decreases the rate of surface condensation since these gases hinder the approach of the vapor to the condensing surface. In the presence of noncondensable gases, condensation begins when the vapor at the condensing surface attains the partial pressure and temperature corresponding to the saturation state (dew point).

condensation may also occur within the vapor volume (vaporgas mixture). To initiate condensation in the volume, the vapor must be significantly supersaturated. A measure of supersaturation is the ratio of the vapor pressure p to the pressure of the saturated vapor ps that is in equilibrium with a liquid or solid phase possessing a flat surface. The vapor is supersaturated if P/PS > 1; when p/ps = 1, the vapor is saturated. The degree of supersaturation p/ps necessary for the onset of condensation depends on the content of tiny dust particles (aerosols) in the vapor, which serve as ready condensation nuclei. The cleaner the vapor, the higher the initial degree of supersaturation. Electrically charged particles, in particular ionized atoms, may also serve as condensation nuclei. This phenomenon serves as the basis of the action of a number of devices used in nuclear physics (for example, the Wilson cloud chamber).

REFERENCES

Kikoin, I. K., and A. K. Kikoin. Molekuliarnaia fizika. Moscow, 1963.
Isachenko, V. P., V. A. Osipova, and A. S. Sukomel. Teploperedacha, 2nd ed. Moscow, 1969.
Kutateladze, S. S. Teploperedacha pri kondensatsii i kipenii, 2nd ed. Moscow-Leningrad, 1952.

D. A. LABUNTSOV

Condensation

(dreams)

The notion that dreams provide an avenue for the expression of normally repressed desires while simultaneously disguising and censoring our real urges was systematically formulated by Sigmund Freud, the father of psychoanalysis. In Freud’s view, the purpose of dreams is to allow us to satisfy in fantasies the instinctual urges that society judges to be unacceptable in some way, such as the urge to seduce or to kill. If, however, we were to dream about an actual seduction or an actual assault, the emotions evoked by the dream would awaken us. So that our sleep is not continually disturbed by such dreams, the mind modifies and disguises their content so that strong emotions are not evoked. Freud referred to the process of censoring and transforming dream contents into less disturbing images as the dreamwork, and explicitly identified five processes through which dreams are censored: displacement, condensation, symbolization, projection, and secondary revision.

Condensation, as the word implies, is a process that disguises a particular thought, urge, or emotion by contracting it into a brief dream event or image, the deeper meaning of which is not readily evident. Condensation also refers to the tendency of the dreamwork to bring together two or more different experiences or concerns into a single dream narrative or image. In Freud’s words,

From every element in a dream’s content associative threads branch out in two or more directions; every situation in a dream seems to be put together out of two or more impressions or experiences.

The overlap of two or more distinct sets of associations in one dream situation effectively disguises the true meaning of the dream.

condensation

[‚kän·dən′sā·shən]
(acoustics)
A measure of the increase in the instantaneous density at a given point owing to a sound wave, namely (ρ-ρ0)/ρ0, where ρ is the density and ρ0 is the constant mean density at the point.
(chemistry)
Transformation from a gas to a liquid.
(electricity)
An increase of electric charge on a capacitor conductor.
(mechanics)
An increase in density.
(meteorology)
The process by which water vapor becomes a liquid such as dew, fog, or cloud or a solid like snow; condensation in the atmosphere is brought about by either of two processes: cooling of air to its dew point, or addition of enough water vapor to bring the mixture to the point of saturation (that is, the relative humidity is raised to 100).
(optics)
Focusing or collimation of light.

Condensation

A phase-change process in which vapor converts into liquid when the temperature of the vapor is reduced below the saturation temperature corresponding to the pressure in the vapor. For a pure vapor this pressure is the total pressure, whereas in a mixture of a vapor and a noncondensable gas it is the partial pressure of the vapor. Sustaining the process of condensation on a cold surface in a steady state requires cooling of the surface by external means. Condensation is an efficient heat transfer process and is utilized in various industrial applications. Condensation of vapor on a cold surface can be classified as filmwise or dropwise. Direct-contact condensation refers to condensation of vapor (bubbles or a vapor stream) in a liquid or condensation on liquid droplets entrained in the vapor. If vapor temperature falls below its saturation temperature, condensation can occur in the bulk vapor. This phenomenon is called homogeneous condensation (formation of fog) and is facilitated by foreign particles such as dust. See Heat transfer

In film condensation, a thin film of liquid forms upon condensation of vapor on a cold surface that is well wetted by the condensate. The liquid film flows downward as a result of gravity.

In dropwise condensation, on surfaces that are not well wetted, vapor may condense in the form of droplets (see illustration). The droplets form on imperfections such as cavities, dents, and cracks on the surface. The droplets of 10–100 μm diameter contribute most to the heat transfer rate. As a droplet grows to a size that can roll down the surface because of gravity, it wipes the surface of the droplets in its path. In the wake behind the large droplet, numerous smaller droplets form and the process repeats. The heat transfer coefficients with dropwise condensation can be one to two orders of magnitude greater then that for film condensation.

Direct-condensation involves condensation of vapor bubbles in a host liquid and condensation on droplets entrained in vapor. Both are also very efficient heat transfer processes, especially when the vapor-liquid interface oscillates.

condensation

1. In a refrigeration system, the process of changing the refrigerant into liquid by the extraction of heat.

condensation

1. anything that has condensed from a vapour, esp on a window
2. Chem a type of reaction in which two organic molecules combine to form a larger molecule as well as a simple molecule such as water, methanol, etc.
3. Psychoanal
a. the fusion of two or more ideas, etc., into one symbol, occurring esp in dreams
b. the reduction of many experiences into one word or action, as in a phobia
References in classic literature ?
But it must always be remembered that in such writing as Comedy and Romance the strict rules of motivation must be relaxed, and indeed in all literature, even in Tragedy, the idealization, condensation, and heightening which are the proper methods of Art require them to be slightly modified.
But I may state that we all kept the middle of the deck, lest the boat should unexpectedly tip over; and that the machinery, by some surprising process of condensation, worked between it and the keel: the whole forming a warm sandwich, about three feet thick.
Basic design of the oil refinery and gas condensations meet the latest international standards, said Bazmi, adding that the products of the refinery are superior to products of other refineries in terms of quality and environment standards.