For example, drying wood before making molds and woodenware prevents deformation, and drying ceramic blanks before firing prevents cracking. Additionally, dried materials are easier to transport and store; for instance, drying harvested grain to a certain moisture content prevents mold growth. Since natural drying is far from meeting the needs of production development, various mechanized dryers are increasingly widely used.
The amount of water vapor in compressed air is determined by its temperature: while maintaining a relatively constant compressed air pressure, lowering the temperature reduces the water vapor content, and excess water vapor condenses into liquid. Refrigerated dryers utilize this principle, employing refrigeration technology to dry compressed air. Therefore, refrigerated dryers have a refrigeration system. The refrigeration system of a refrigerated dryer is a compression refrigeration system, consisting of four basic components: a refrigeration compressor, a condenser, an evaporator, and an expansion valve. These are connected sequentially by pipes, forming a closed system. The refrigerant continuously circulates within the system, undergoing state changes and exchanging heat with the compressed air and cooling medium. There are also adsorption dryers and dissolution dryers for compressed air.
There are also adsorption dryers and dissolution dryers. The refrigeration compressor draws low-pressure (low-temperature) refrigerant from the evaporator into its cylinder. The refrigerant vapor is compressed, increasing both its pressure and temperature. This high-pressure, high-temperature refrigerant vapor is then forced into the condenser. In the condenser, the higher-temperature refrigerant vapor exchanges heat with cooler cooling water or air, carrying away the heat and condensing the refrigerant vapor into a liquid. This liquid is then sent to the expansion valve, where it is throttled into a low-temperature, low-pressure liquid and enters the evaporator. In the evaporator, the low-temperature, low-pressure refrigerant liquid absorbs heat from the compressed air and vaporizes (commonly known as "evaporation"). The compressed air, cooled, condenses into a large amount of liquid water. The refrigerant vapor in the evaporator is then drawn back into the compressor. Thus, the refrigerant undergoes four processes in the system: compression, condensation, throttling, and evaporation, completing a cycle.
In the refrigeration system of a freeze dryer, the evaporator is the device that delivers cooling capacity. The refrigerant absorbs heat from the compressed air within it, achieving dehydration and drying. The compressor is the heart of the system, responsible for drawing in, compressing, and delivering the refrigerant vapor. The condenser is a heat-releasing device that transfers the heat absorbed in the evaporator, along with the heat converted from the compressor's input power, to the cooling medium (such as water or air) for removal. The expansion valve/throttle valve throttles and reduces the pressure of the refrigerant, while controlling and regulating the amount of liquid refrigerant flowing into the evaporator, and dividing the system into two main parts: the high-pressure side and the low-pressure side.
