In this article we will discuss the meaning of condensation.
The transformation of gaseous form of water (i.e., water vapour) into solid form (ice) and liquid form (water) is called condensation. In other words, the process of change of water vapour into liquid form is called condensation. It is evident that condensation is opposite to evaporation. The process and mechanism of condensation depends on the amount of relative humidity present in the air.
The air having 100 per cent relative humidity is called saturated air. An air may become saturated in two ways e.g., either:
(i) the absolute humidity at a given temperature is raised to equal the humidity retaining capacity of the air or
(ii) the temperature of the air is reduced to such an extent that the humidity capacity becomes equal to its absolute humidity.
For example, the humidity capacity and absolute humidity of an air with 60°F temperature are 5.7 grains and 4.1 grains per cubic foot respectively (relative humidity being 72 per cent), if the air is cooled to 50°F temperature, the humidity capacity decreases to 4.1 grains which is equal to absolute humidity of 4.1 grains per cubic foot, thus the air becomes saturated as relative humidity becomes 100 percent, and hence condensation begins.
The temperature at which an air becomes saturated is called dew point. It may be pointed out that condensation will begin only when the air is supersaturated i.e., if the relative humidity exceeds 100 per cent, and this can be achieved only when the air is further cooled. If dew point is above freezing point (32°F), condensation will occur in liquid form (e.g., dew, fog, rainfall etc.) but if dew point is below freezing point, condensation occurs in solid form (e.g., frost, ice, snow, hailstorm etc.).
It is apparent that condensation depends on:
(i) the percentage of relative humidity of the air and
(ii) the degree of cooling of the air.
The air becomes cool when it rises while it gets heated when it descends. Thus, the ascending air may bring moist weather while descending air causes dry condition.
Much cooling of the air is required in hot arid regions before dew point is reached. On the other hand, very little cooling causes condensation in humid regions. The heat released at the time of condensation is called latent heat of condensation.