The structure of the freeze dryer is varied. According to the layout of the freeze-drying chamber and the cold trap, there are two types of built-in and external cold traps. The so-called built-in type means that the cold trap is placed under or on both sides of the shelf group in the freeze-drying box. The back of the drying box), the bottom type (the pit trap is below the freeze-drying box), the side-mounted type (the cold trap is on the side of the freeze-drying box), etc.
The built-in structure is simple, the water vapor flow resistance generated during drying is small, and the evaporation temperature of the refrigerator can be increased, so the refrigeration capacity of the refrigerator is large and the power consumption is low. However, if the hot shelf and the cold trap are placed in the same room, the cold and heat will be offset, the energy consumption will increase, and the radiation and convection between the cold surface of the cold trap and the hot surface of the product will cause the shelf to The temperature field between them is not uniform, resulting in unequal drying rates of the products.
Thus, the freeze-drying efficiency is reduced and the freeze-drying cycle is prolonged. The degree of drying of the product varies, which also reduces the quality of the medicine. At the same time, the defrosting of the cold trap and the loading and unloading of products on the shelf cannot be carried out at the same time, which prolongs the auxiliary time of freeze-drying.
The external type is the opposite of the built-in type. Therefore, most modern pharmaceutical freeze dryers adopt an external structure. In modern food freeze dryers, the shelf and the condenser tube of the cold trap are still placed in the same simplified structure, but in fact, some partitions are used to separate them into two chambers. , leaving only the water vapor channel in the middle, this structure should still be an external type.
