Publisher's Synopsis
The number of gases and water vapour in atmosphere being present in different proportion at given temperature and pressure. Water vapour is produced from the evaporation of water and by the sublimation of ice. Under normal atmospheric conditions, water vapour is created regularly by evaporation and removed by condensation. Condensation is a process in which water vapour turns into the liquid.
On the earth water exists in three forms i.e. solid, liquid and gas. The solid phase of water is called ice. The liquid phase of water is called water and the gaseous phase of water is called vapour. Humidity is the measurement of water vapour present in air. There are three main measurements of humidity i.e. absolute, relative and specific. Absolute humidity range in atmosphere from 0 to 30 grams per cubic meter for saturated air at 30 degree C.
When the air is saturated by water vapour and it comes contact to another surface of lower temperature with respect to air. Then water vapour condenses on that surface. Nucleation is the process in which the formation of either a new thermodynamic phase in distinct region or a crystal from a solution, a liquid or a vapour via self-assembly. It is usually a random process, so even in two identical system it may occur at different times. In this process liquid droplets create in saturated vapour or gaseous bubble in a saturated liquid.
In atmosphere water vapour condenses on the liquid water droplets or dust and form embryo, this is the first stage of nucleation process. For example in cloud formation dust and pollutants provide nucleation sites for water vapour in atmosphere. Nucleation is affected by the impurity level in atmosphere. By the help of nucleation we can understand many natural and industrial process. It plays an important role in most of engineering process. Recently much work is done on nucleation phenomenon.
The appearance of the first crystal is also called primary nucleation and the time, creation for first crystal, is called primary nucleation time and the secondary nucleus produced from a pre-existing crystal called secondary nucleation.
