An air dryer is a mechanical equipment for obtaining a solid material with a specified moisture content by heating the wet vaporization (generally refers to water or other volatile liquid components).
The air dryer can be classified according to operating procedures, operating pressure, heating mode, wet material movement or structure. According to the operation procedures, the air dryer is divided into intermittent (batch operation) and continuous types.
According to the operation pressure, the air dryer is divided into two types: atmospheric air dryer and vacuum air dryer. Under vacuum operation, it can reduce the moisture content of space and accelerate the drying process. Besides, it can reduce the boiling point of moisture and the drying temperature of the material, and the steam is not easy to leak. Therefore, the vacuum air dryer is suitable for drying heat sensitive, oxidizable, explosive and toxic materials, and wet separation steam needs to be recycled. According to the heating mode, the air dryer is divided into the flow type, conduction type, radiation type and dielectric type.
The flow air dryer is also known as the direct air dryer. It uses the hot dry medium to contact with the wet material directly, passing the heat by convection, and taking the generated steam away; The conduction type air dryer is also called indirect air dryer. It uses conduction to transfer heat from a heat source through a metal partition to a wet material and the generated humidification steam can be removed by reducing suction, passing in a small amount of scavenging air or condensing on the surface of a low temperature condenser. This kind of air dryer does not use the drying medium, the thermal efficiency is higher, and the product is free from pollution. However, the drying capacity is limited by the heat transfer area of the metal wall, and the structure is also complex, which is often operated under vacuum. Radiant air dryer is a kind of electromagnetic wave that uses various radiators to emit a certain wavelength range of electromagnetic waves, which are selectively absorbed by the wet material surface and converted to heat for drying. Dielectric air dryer uses high frequency electric fields to dry the heat effect inside the wet material.