There are roughly three types of refrigeration temperature ranges and condensing temperatures of freeze dryer shelves.
- The refrigeration system adopts a single-stage refrigeration compression cycle. The refrigeration temperature of layers of shelfis about – 35 ~ – 40 ℃, and the refrigeration temperature of the condenser is about – 50 ℃. This freeze dryer is suitable for the production of some products that are easy to freeze dry,such as food, meat, etc.
- The refrigeration system adopts a two-stage refrigeration compression cycle.The refrigerating temperature of the layers of shelf is about – 45 to – 50 ℃, and the refrigerating temperature of the condenser is about – 65 ℃. This freeze dryer is suitable for the freeze drying of most pharmaceutical products.
- The refrigeration system adopts a cascade refrigeration cycle, the refrigeration temperature of the layers of shelf is about -55 to -60 ℃, and the refrigeration temperature of the condenser is about -75 ℃. This freeze dryer is suitable for the freeze drying of some special products.
The selection of the above temperature range is determined by the eutectic point of the freeze-dried product. Products with a low eutectic point require that the cooling temperature of the shelf is low, and the temperature of the condenser is correspondingly lower.
Regarding the vacuum degree of the freeze-drying chamber, the past view believed that the higher the vacuum degree, the better, and the current view 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 decreases, but in any case, the no-load ultimate vacuum degree of the freeze-drying box should reach more than 1 × 10 – 2 mbar. If a high degree of vacuum is not required during use, the vacuum degree can be controlled by the vacuum degree adjustment device, so that the vacuum degree can be controlled within the required range. Therefore, the vacuum adjustment device should be selected.
The emptying speed of the lyophilization chamber should be evacuated from atmospheric pressure to 1 × 10 – 1 mbar within half an hour. 2 hours to a vacuum of more than 1 x 10 – 2 mbar.