For example, the drying of wood before the production of wooden molds and woodware can prevent the deformation of the product. The drying of the ceramic blank before calcination can prevent the finished product from cracking. In addition, the dried material is also easy to transport and store, such as drying the harvested grain to a certain moisture content to prevent mildew. Since natural drying is far from meeting the needs of production development, various mechanized dryers are increasingly used.

The amount of water vapor in the compressed air is determined by the temperature of the compressed air: by keeping the pressure of the compressed air essentially constant, lowering the temperature of the compressed air can reduce the water vapor content in the compressed air, while the excess water vapor condenses. Become liquid. Freeze dryers use this principle to use refrigeration technology to dry compressed air. Therefore, the dryer has a refrigeration system. The refrigerating system of the freeze dryer belongs to the compression type refrigeration and consists of four basic components such as a refrigerating compressor, a condenser, an evaporator, and an expansion valve. They are connected by pipes in turn to form a closed system. The refrigerant continuously circulates in the system, undergoes a state change and exchanges heat with the compressed air and the cooling medium. Compressed air dryers also have an adsorption dryer and a dissolution dryer.