Evaporation and Condensation
Evaporation is the process by which water transforms into a vapour. Condensation is the inverse process that converts water vapour to tiny droplets of water. Before reaching its boiling point, a liquid evaporates. Condensation is a phase change that occurs regardless of temperature. This article discusses Evaporation and Condensation which is useful for competitive exams such as the UPSC exam.
Evaporation is mostly caused by temperature. The process of evaporation turns water from a liquid to a gas. The temperature at which water vaporises is referred to as the latent heat of vaporisation. The concentration of air in the parcel and the absorption of water both increase as the temperature rises. The unsaturated layer replaces the saturated layer as a result of air movement. As a result, evaporation grows in direct proportion to air movement.
It is how liquid water changes into water vapour on heating. The amount and rate of evaporation at a particular place depend upon the aridity, temperature, and air movement. Evaporation is faster in dry air than in wet air. There is more evaporation from the ocean than from the land. The temperature at which the water starts evaporating is the latent heat of vaporization. A special case of evaporation is transpiration which entails the loss of water from the leaves and stems of the plants.
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Evaporation and Humidity
The air becomes more humid due to evaporation, particularly from the sea and the soil. Diffusion is investigated, but it is the process through which liquid water changes into a gaseous state. The difference between the pressure of the water vapour in the free air and the vapour near the saturated evaporative material directly correlates to the rate of spread or evaporation.
Evaporation is proportional to the saturation deficit when the liquid and the air are both at the same temperature. Between the evaporator and the outside air, the medium conductivity is also proportional. Conductivity increases with airflow in an open evaporator. The moving water will, however, travel through the silent air between the tiny pores between the interior of the water and the exterior of the dry air if the evaporator is a leaf. Porosity may have a greater impact on conductance in this situation than ventilation.
Condensation is the transformation of water vapour into water. If water vapour directly condenses into solid form, it is known as sublimation.
Condensation takes place due to the loss of heat and can occur in one of the following ways:
- Warm moist air rises upwards and expands.
- Warm and moist air comes in contact with the cold surface.
- Warm moist air mixes with the air coming from the colder regions.
Cloud drops and ice crystals, which are allergic to the Earth’s atmosphere, are linked to suspended aerosols produced by natural and human processes. In the absence of these aerosols, the relative humidity requirements for the spontaneous conversion of water vapour into liquid water or ice crystals would be well above 100% compared to the flat H2O surface.
Forms of Condensation
The transformation of water vapour into liquid is referred to as condensation. Condensation can occur in a variety of ways, including dew, frost, fog, mist, and clouds, depending on the temperature and location. Below are the forms of Condensation:
When moisture is deposited in the form of water droplets on cooler surfaces of solid objects, it is known as dew. Here, the deposition occurs on surface objects rather than nuclei in the air above the earth’s surface. A clear sky, calm air, high relative humidity, and cold and long nights are ideal conditions for its formation. The dew point should be above the freezing point for dew formation.
Frost is frozen dew. It is formed when the dew point temperature falls below the freezing point. Under such conditions, droplets of condensation near or on the ground are frozen. Generally, the conditions are similar for dew and frost formation. The only difference is that the temperature should fall below the freezing point for frost formation. It can be found on solid surfaces of the earth’s crust as ice or snow crystal.
It’s a cloud with a base on or near the ground. It is formed when the temperature of an air mass containing a large quantity of water vapour falls suddenly. The condensation of water vapour takes place around the dust and smoke particles that remain suspended in the air. It is formed under conditions such as low temperature and high relative humidity. The visibility is drastically reduced (less than one km).
Types of Fog
There are 3 types of Fog described below in detail:
|Types of Fog|
|Radiation Fog||It is also called ground fog. The fog is formed surface is cooled at night due to terrestrial radiation, and the air which comes into contact with it also gets cooled. There should be long winter nights and a cloudless sky for the formation of radiation fog. The thickness of radiation fog varies from 10 to 30 meters.|
|Advection Fog||It is formed when there is a fall in the temperature of warm moist air moving horizontally over a cold surface. It is cooled by contact and sometimes by mixing with cold air prevailing over cold surfaces.|
|Frontal or Precipitation Fog||The dividing line separating cold and warm air masses is known as a front. Warm and cold air converge at these fronts, and fog is formed. The warm air in the frontal area is light and rises above the cold air mass. It then begins to cool, and when the temperature reaches the dew point, frontal fog is formed.|
Impacts of Fog
- Fog hinders travel by land, air, and sea as visibility is greatly reduced.
- In urban and industrial areas, smoke and dust provide nuclei for fog formation. When fog is mixed with smoke, it forms smog. Smog is hazardous to human health.
- The agriculture sector is also affected since fog adversely hits late-sowing crops.
- Fog is beneficial to tea and coffee plants as it saves them from the scorching sunlight on the hill slopes.
It is also a type of fog but is relatively less dense. The difference between mist and fog is density and its effect on visibility. The fog reduces visibility to less than 1 km, whereas it’s called mist if the visibility range is between 1 and 2 km. Mists are frequent over mountains as the rising warm air up the slopes meets a cold surface. Fogs are drier than mist. Mist can occur as part of natural weather or volcanic activity or could be created artificially.
It is a phenomenon that occurs when dust, smoke, and dry particles reduce visibility. In case of haze, the visibility is reduced from 2 kilometres to 5 kilometres.
Condensation Related Concepts
1. Latent Heat
At the time of evaporation, heat is absorbed and conserved in water vapour. It is known as latent heat. It is this same heat that is released when water vapour again changes into the water through the process of condensation. Latent heat is essential for the development of typhoons (storms, cyclones).
2. Saturated Air
The air containing moisture to its full capacity at a given temperature is said to be saturated. This means that the air can no longer hold an additional amount of moisture. One hundred per cent humid air is called saturated air.
3. Hygroscopic Nuclei
Condensation always takes place around some particles present in the air. These may be dust particles, smoke, oceanic salts or carbon dioxide which act as nuclei to hold water. They are thus called condensation nuclei or hygroscopic nuclei.
4. Dew Point
The temperature at which saturation occurs in a given sample of air is known as the dew point. The nuclei for the condensation of the moisture in the atmosphere are provided by the smoke and the dust particles.
Once the condensation of water vapour in the atmosphere has taken place, the moisture present in the atmosphere may take one of the following forms— dew, frost, fog, mist, clouds, etc. This will be according to the conditions prevalent in the atmosphere.
Evaporation and Condensation UPSC
We all know that water is made up of molecules that are held together by some force. However, the molecules are free to move independently. Aside from this force, water molecules contain thermal energy generated by extremely fast vibrations. Thus, molecules at the surface move or vibrate with such force that they escape into the air and turn into vapour. This is known as evaporation. Simultaneously, the process is reversible, and molecules can rejoin to form liquids. This is referred to as condensation.
This article will also be useful for other competitive exams such as the UPSC exam. This article discusses evaporation and condensation.