March 16, 2014

What is Condensation? Different Types of Condensation: Clouds, Fog, Dew & Frost Explained

Condensation is the phase transformation of water vapour to liquid water. Water does not easily condense without a surface present. Vegetation, soil, buildings provide surface for dew and frost formation. Particles act as sites for cloud and fog drop formation.

Types of Condensation

1. Clouds — When the moist air moves upward it cools down. When the temperature of the air reaches the dew point, the water vapours condense in the form of small droplets of water or ice crystals. These droplets cling to the dust particles and hang in the air in the form of clouds. They move hither and thither along the wind in the sky. Clouds are of a great variety depending on their height.

2. Fog — Fog is formed in the same way as clouds with the only difference that fog is formed near the surface of the earth or water bodies. It is formed when the moist air cools down below its dew point in the lower layers of the atmosphere. Fog is formed over the water when a cold current meets the hot current. Fogs are clouds in contact with the ground.  Several types of fogs commonly form a) Radiation fog  b) Advection fog c) Up-slope fog  d) Evaporation (mixing) fog.

3. Dew — At night everything radiates heat which it had absorbed during the day. Grass, flowers and leaves of trees radiate heat more quickly than ;r things because they are good radiators. Thus, they become cold quite early. When the warm and moist air comes into contact with them its moisture condenses into small droplets of water on the grass and other things. These droplets arc- known as dew. It occurs only on calm, cold and clear nights. The dew point is the temperature at which the air is saturated with water vapour If a surface cools below the dew point, water condenses on the surface and dew drops are formed. Dew does not “fall”.

4. Frost — If the dew-drops get frozen due to fall in temperature, it is called the frost. It happens when the dew point is below the freezing point. On the other hand, in dew formation, the dew point is above the freezing point. If the temperature is below freezing, the dew point is called the frost point. If the surface temperature falls below the frost point water vapour is deposited directly as ice crystals called deposition.  When the dew-point temperature is less than 0C, then we call this the "frost point". Frost will form when the dew-point is less than 0 C because the temperature of the surface and near the surface can be at or below freezing (0 C) thus, if moist air comes in contact with that surface, we’ll get frost instead of dew! ( Difference between Dew & Frost)


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