• Evaporation is the physical process of conversion of a liquid into its gaseous phase at a certain high temperature.
• It is usually below the boiling point of the liquid. The molecules in a liquid have different values for kinetic energy.
• When we provide energy from outside to the liquid (such as heat), the kinetic energy of these liquid molecules increases.
• When the energy is enough for the molecules on the surface to overcome the intermolecular forces between them, the molecules tend to escape the surface and convert into a gas state.

The benefits include:

• Relatively low residence times.
• Relatively high heat transfer rates.
• Relatively low cost.
• Large units can be manufactured.
• Low hold-up.
• Small floor space requirements.
• Good heat transfer over a wide range of services.