What is the working principle of a freeze dryer refrigeration system?

What is the working principle of a freeze dryer refrigeration system?
For example, the drying of wood before making wooden molds and woodware can prevent deformation of the product, and the drying of ceramic blanks before calcination can prevent cracking of the finished product. In addition, the dried material is also convenient for transportation and storage, such as drying the harvested grain below a certain moisture content to prevent mildew. As natural drying is far from meeting the needs of production development, various mechanized dryers are more and more widely used.
The amount of water vapor in the compressed air is determined by the temperature of the compressed air: under the condition that the pressure of the compressed air is kept basically constant, reducing the temperature of the compressed air can reduce the water vapor content in the compressed air, and the excess water vapor will condense Into a liquid. Freeze dryers use this principle to dry compressed air using refrigeration technology. Therefore, the dryer has a refrigeration system.
The refrigeration system of a freeze dryer is a compression type refrigeration, which is composed of four basic components: a refrigeration compressor, a condenser, an evaporator, and an expansion valve. They are connected in order by pipes to form a closed system. The refrigerant continuously circulates in the system, changes state, and exchanges heat with compressed air and cooling medium. Compressed air dryers also have adsorption dryers and dissolving dryers.
The refrigeration compressor draws the low-pressure (low-temperature) refrigerant in the evaporator into the compressor cylinder. After the refrigerant vapor is compressed, the pressure and temperature increase at the same time. The higher temperature refrigerant vapor exchanges heat with the lower temperature cooling water or air. The heat of the refrigerant is taken away and condensed by the water or air, and the refrigerant vapor becomes a liquid.