For example, the drying of wood before making wooden molds and woodware can prevent the deformation of the product, and the drying of the ceramic blank before calcination can prevent the finished product from cracking. 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. Since 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: while keeping the pressure of the compressed air basically unchanged, lowering the temperature of the compressed air can reduce the water vapor content in the compressed air, and the excess water vapor will condense Into liquid. The freeze dryer uses this principle to use refrigeration technology to dry compressed air. Therefore, the dryer has a refrigeration system. The refrigeration system of the freeze dryer is a compression refrigeration, which is composed of four basic components such as a refrigeration compressor, a condenser, an evaporator, and an expansion valve. They are sequentially connected by pipes to form a closed system. The refrigerant circulates continuously in the system, changes state and exchanges heat with compressed air and cooling medium. Compressed air dryers also have adsorption dryers and dissolution dryers.
The refrigeration compressor draws the low-pressure (low-temperature) refrigerant in the evaporator into the compressor cylinder. The refrigerant vapor is compressed, and the pressure and temperature increase at the same time. The high-pressure and high-temperature refrigerant vapor is pressed to the condenser. In the condenser, The refrigerant vapor with a higher temperature exchanges heat with the cooling water or air with a lower temperature. The heat of the refrigerant is taken away by the water or air and condensed. The refrigerant vapor becomes a liquid. This part of the liquid is sent to the expansion valve, which is throttled by the expansion valve to become a low-temperature and low-pressure liquid and enters the evaporator; the low-temperature, low-pressure refrigerant liquid in the evaporator absorbs the heat of the compressed air and vaporizes (commonly known as "evaporation") After the compressed air is cooled, a large amount of liquid water is condensed; the refrigerant vapor in the evaporator is sucked away by the compressor, so that the refrigerant passes through the four processes of compression, condensation, throttling, and evaporation in the system, thereby Completed a cycle.
In the refrigeration system of the freeze dryer, the evaporator is a device that transports cold energy, in which the refrigerant absorbs the heat of the compressed air to achieve the purpose of dehydration and drying. The compressor is the heart and plays the role of sucking, compressing, and delivering refrigerant vapor. The condenser is a device that releases heat, and transfers the heat absorbed in the evaporator together with the heat converted by the input power of the compressor to the cooling medium (such as water or air) to take away. The expansion valve/throttle valve has a throttling and pressure-reducing effect on the refrigerant, and simultaneously controls and regulates the amount of refrigerant liquid flowing into the evaporator, and divides the system into two parts, the high-pressure side and the low-pressure side.
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