A dryer is a mechanical device that USES heat energy to reduce the moisture content of materials. The drier vaporizes and escapes the moisture content (usually water or other volatile liquid components) of the material by heating to obtain the solid material with specified moisture content. The purpose of drying is to meet the needs of materials for use or further processing. According to the operating pressure, the dryer is divided into two types: normal pressure dryer and vacuum dryer. According to the operating pressure, it can be divided into normal pressure and decompression dryer (also known as vacuum dryer). The adsorption dryer, freeze dryer and microwave dryer are also introduced in detail.