Condensation

As the physical condensation is defined as the transfer of a substance from the gaseous to the liquid state. As a product of the condensate is formed. This process is carried out under certain pressure and temperature conditions which are known as condensation point. The opposite of the condensation is the evaporation. The applied during the evaporation heat of evaporation is released back into the environment during the condensation.

Fundamentals of Thermodynamics

Depending on the nature of the nucleation process, two basic types of condensation can be distinguished. Condition is in any case such that the gas phase is saturated with respect of the condensing component. Unite individual gas particles at their meeting within the gas, it is called a homogeneous condensation. For this it is necessary that sufficient slow particles without the participation of interfaces come together to form larger structures. This process is only possible at a high supersaturation of usually several hundred percent. In contrast, only very low supersaturation of you needs in the heterogeneous condensation often even below one percent. This type of condensation is carried out in pre-existing surface, so a rule of suspended solid particles in the gas phase, the condensation aerosol particles, or nuclei. These act in relation to the respective gas as a kind of particle catcher, wherein substantially the radius and the chemical properties of the particle to determine how well it adhere to the gas particles. This also applies analogously for surfaces not of a particulate body, then one speaks of a fitting.

Condensation processes in the atmosphere

The condensation occurs in the case of water, the atmosphere, together with the evaporation to a separate importance, because the phase transition between water vapor and liquid water is a fundamental process of the natural water cycle and the weather is at all. At the macro level, the physical sales volumes are here alone enormous because the atmospheric water with approximately 13.1015 kg has a mean residence time of only 10 days, so within this period is essentially implemented through the condensation. The condensation of the basic process is any form of liquid precipitation from water vapor and fog and cloud formation. Thereby also the heat balance of the earth is a decisive influence on the latent heat.

At the micro- physical level, however, the condensation processes are shown as very complex and elude the exact predictability. It comes in the atmosphere almost exclusively for heterogeneous nucleation, ie in this case the formation of water droplets out of the air. The required supersaturation of the air must be more or less according to the prevailing conditions, to cause condensation. They can be on the one hand, by increasing the absolute humidity in the course of evaporation or sublimation, and the other hand by a reduction in the air temperature. It dominates the cooling, especially the adiabatic, ie a reduction of the maximum moisture that is able to take the air. If the diameter of the aerosol particles over roughly 1 micron in size, so often ranging from supersaturations of a few tenths of a percent. Furthermore, it is important that the surface of the particles having hydrophilic or hydrophobic properties to facilitate or impede the attachment of Wasserdampfteilchen. Just as important, of course, is the concentration of the aerosol in the gas phase.

Thus, the meteorological and climatological aerosol research has a whole range of factors berücksichten, additionally already considered other factors such as the spatial and temporal occurrence of the aerosol particles in addition to those. All these factors have to be related to each other in order to come to a correct understanding of processes of precipitation and cloud formation, which in turn on the water and affect the radiation budget. While this is on a qualitative level, quite possible, the quantitative influence of these parameters, especially on a global scale is difficult to determine and forms an element of uncertainty in all climate models.

Technical Applications

Steam power plant

In steam power plants, the exhaust steam from the steam turbine at the capacitor is further cooled and condensed to water. This water is reused as supply water for the steam generator. This results in a closed circuit.

Heating networks

In chemical plants, the condensation of water vapor is an economically significant size, as the power supply for chemical processes carried out with water vapor. After release of the thermal energy is present, condensed water which is collected via manifolds. This normally "clean" water is fed back into the steam generator, a so-called feed water to generate steam for quality control and possible regeneration. Such a condensate drain, massive savings can be made.

Also heating networks in trains or buildings in use ( et ) s partially wet steam heat transport. The radiator temperature arises by itself to max. 100 ° C. ( the water at the low pressures used condensation temperature).

Flue gas condensation

Exhaust gases from the combustion of fossil fuels, biogenic materials and household waste contains high amounts of water vapor.

In modern furnaces, the exhaust gas is cooled in a condenser. Focus is on the use of the latent heat of the vapor content in the foreground. The separated condensate contains beside the water more impurities whose output is reduced in the environment through the flue gas condensation.

Cooling

In conservatories overheating or draft problems can be a so-called " Hypo exchanger " system are avoided, in which the warm air in the winter garden water evaporates and the Ascended moist air is exhausted at the highest point of the conservatory and is headed by hypocaust pipes on the cold ground, followed where the water vapor condenses, and the liberated heat of condensation is discharged to the ground. Much work also air conditioners, which use the heat of evaporation of water.

Dehumidification

For drying of construction moisture in new buildings and wall drainage and wet rooms, in that require large amounts of water vapor (swimming pools ) dehumidifiers are often used. These condense the water vapor out of sucked air that leaving the device dry air can absorb moisture again. Function in a similar condensation dryers are used for drying laundry.