Vacuum freeze dryer is suitable for drying raw materials such as pharmaceuticals, traditional Chinese medicine decoction pieces, biological and wild vegetables, dehydrated vegetables, food, fruits, chemicals, pharmaceutical intermediates, etc. Freeze vacuum drying is a new type of box structure developed by combining the refrigeration system, vacuum system, thermal oil heating system, and dehumidification system in a vacuum freeze dryer, which greatly utilizes the storage space inside the box for freeze-drying.

When choosing a vacuum freeze dryer, you can mainly refer to the following aspects:

1. Freeze dried area

The number in the freeze-drying machine model represents the freeze-drying area of the model, for example, the freeze-drying area of the LGJ-18C freeze-drying machine is 0.18 square meters. Users should determine the required freeze-drying area based on their own needs through calculation. For example, if each batch of products requires a liquid volume of 1.8 kilograms (liters) to be freeze-dried, and materials are loaded onto material trays with a thickness of 10mm per tray, the load area of the freeze-drying plate layer can be calculated

A (area, ㎡)=V (volume, m)/H (height, m)=0.0018m/0.01m=0.18 ㎡

It is necessary to choose a freeze dryer with a load area of 0.18 square meters for the board layer.

2. Cold trap temperature

A cold trap is a device used in the freeze-drying process to capture water. In theory, the lower the temperature of the cold trap, the stronger its water capturing ability. However, a low temperature of the cold trap requires high refrigeration requirements, resulting in high machine and operating costs. The cold trap temperature of the experimental series freeze dryer mainly includes several levels such as -45 ℃, -60 ℃, and -80 ℃. Freeze drying with a cold trap temperature of -45 ℃ is suitable for some products that are easily freeze-dried, freeze drying machines with a cold trap temperature of around -60 ℃ are suitable for freeze-drying most products, and freeze drying with a cold trap temperature of -80 ℃ is suitable for freeze-drying some special products. The experiment on the effect of cold trap temperature on water capture capacity shows that when the cold trap temperature decreases from -35 ℃ to -55 ℃, the water capture capacity is significantly improved. When the cold trap temperature is below -55 ℃, the water capture capacity of the cold trap is not significantly improved. Therefore, in the absence of special requirements, choosing a cold trap temperature of around -60 ℃ is an ideal choice. The cold trap temperature of the LGJ-10D freeze dryer in the four ring freeze dryer is ≤ -55 ℃, and the cold trap temperature of the LGJ-18 series and LGJ-25 series freeze dryers is ≤ -60 ℃. The mixed working fluid refrigeration technology is used, and under the same refrigeration unit, the refrigeration temperature is low, the refrigeration capacity is large, the working stability is high, and the failure rate is low. The four ring freeze dryer also includes the LGJ-10 freeze dryer with a cold trap temperature of ≤ -45 ℃, which is suitable for freeze-drying some products that are easy to freeze dry. The cold trap temperature of LGJ-50C freeze dryer is ≤ -80 ℃, which is particularly suitable for freeze-drying of pharmaceuticals and special products.

3、 降温速率

The cooling rate reflects the refrigeration capacity of the refrigeration system. Under no-load conditions, the temperature of the cold trap should reach the specified low temperature within 1 hour. For example, for a freeze dryer with a cold trap temperature ≤ -60 ℃, the machine should start timing from the start of refrigeration, and the time for the cold trap temperature to reach -60 ℃ should not exceed 1 hour.

4. Ultimate vacuum degree

The ultimate vacuum degree reflects the leakage situation of the freeze dryer and the pumping efficiency of the vacuum pump. The vacuum degree of the freeze-drying box used to be believed to be better with a higher vacuum degree, while the industry believes that the vacuum degree should be within a reasonable range. The vacuum degree is too high, which is not conducive to heat transfer, and the drying speed actually decreases. However, the maximum vacuum degree of the freeze-drying box under no load should reach 15Pa or above.

5. Vacuum extraction time

The evacuation speed of the freeze-drying box without load should be reduced from atmospheric pressure to 15Pa within half an hour.

6. Uniformity and flatness of plate temperature:

The uniformity and flatness of the layer temperature have a significant impact on the uniformity of product quality. The better the temperature uniformity and flatness, the better the uniformity of freeze-dried product quality. The temperature control of the freeze-drying machine shelf includes heater type and intermediate fluid type. The freeze-drying machine shelf with intermediate fluid control plate layer has good temperature uniformity and flatness. This freeze-drying machine plate layer is a hollow sandwich structure, and the cooling and heating of the plate layer are achieved through the circulation of the intermediate fluid in the fluid channel inside the plate layer, so the temperature of the plate layer is uniform and consistent. The LGJ-50C freeze dryer in the four ring freeze dryer adopts the technology of using fluid in the middle of the shelf. The shelf temperature control of the bell jar type freeze dryer basically uses heaters, and the consistency of the plate temperature is slightly poor. However, overall, the temperature difference between the layers of pharmaceutical lyophilizers should be controlled within ± 1.5 ℃, and the temperature difference inside the plates should be ± 1 ℃. Food lyophilizers can be appropriately relaxed.

7. Control system

The control system types and functions of freeze-drying machines vary. For the experimental series of freeze-drying machines, they are mainly used for exploring the freeze-drying process of materials and small-scale trial production. Therefore, the control system should be able to display real-time freeze-drying process parameters and automatically record them; Set, modify, and effectively execute freeze-drying process procedures; Equipped with communication interfaces for easy data collection and storage.