Drying usually refers to the removal of liquids from a subject via evaporation or vaporisation.
In drying processes that use convection, the vapour pressure of liquid that is to be expelled at a certain temperature or pressure is critical. If the vapour pressure is identical to or less than the liquid content in the atmosphere, no drying is possible.
If the vapour pressure is greater than the liquid content in the atmosphere, the velocity of the drying process is dependent on the gas exchange (convection surface, air flow).
Because vapour pressure usually increases at higher temperatures, thus promoting drying, the drying process of the product to be treated is designed using the parameters that are required for the type of liquid to be expelled.
In order to achieve rapid drying at low temperatures, including the drying of deep pores, in a way that does not damage the product, specialised drying technology – vacuum drying – must be used. In vacuum drying, the dried material is exposed to a vacuum, thus reducing the boiling point and leading to water evaporation even at low temperatures.
The material can be dried further to improve drying performance.