What aspects should we consider when buying a freeze dryer?
I. Freeze-drying area
The number in a freeze dryer model represents the freeze-drying area of the freeze dryer of this model, and users should determine the size of freeze-drying area the freeze dryer should have by calculation according to their own needs.
II. Cold trap temperature
The cold trap is a device that captures moisture during the freeze-drying process. In theory, the lower the temperature of the cold trap, the stronger the water trapping capacity of the cold trap. However, the lower the temperature of the cold trap, the higher the requirement for refrigeration, the higher the machine operating cost. The cold trap temperature of the experimental series freeze dryers mainly has several grades such as -45℃, -60℃, and -80℃. A freeze dryer with a cold trap temperature of -45°C is suitable for some products that are easy to freeze-dry, a freeze dryer with a cold trap temperature of -60°C is suitable for most products, and a freeze dryer with a cold trap temperature of -80°C is suitable for freeze-drying of some special products. The effect of cold trap temperature on water trapping capacity experiments showed that the cold trap temperature dropped from -35℃ to -55℃, and the water trapping capacity improved significantly. The cold trap temperature was lower than -55℃, and the water trapping capacity of the cold trap was not significantly improved. Therefore, when there is no special requirement, it is an ideal choice to choose a cold trap temperature of -60℃.
III. Cooling rate
The cooling rate reflects the cooling capacity of the refrigeration system. Under no-load conditions, the temperature of the cold trap should reach the minimum temperature specified by the index within 1 hour. For example, for a freeze dryer with a cold trap temperature ≤ -60°C, the machine starts timing from turning on the refrigeration, and the time for the cold trap temperature to reach -60°C should be no more than 1 hour.
IV. Ultimate vacuum
The ultimate vacuum degree reflects the leakage of the freeze dryer and the pumping efficiency of the vacuum pump. About the vacuum degree of the freeze-drying box, the previous view is that the higher the vacuum degree, the better, while the current view is that the vacuum degree should be within a reasonable range. When the vacuum is too high, it is not conducive to heat transfer, and the drying speed drops instead, but in any case, the no-load ultimate vacuum of the freeze-drying box should reach more than 15Pa.
V. Vacuum time
The emptying speed of the freeze-drying box should be pumped from atmospheric pressure to 15Pa within half an hour.
VI. Temperature uniformity and flatness
The uniformity and flatness of the slab temperature have a great influence on the uniformity of product quality. The better the temperature uniformity and flatness, the better the uniformity of freeze-dried product quality. Freeze dryer shelf temperature control has heater type and intermediate fluid type. The freeze dryer shelf adopting the intermediate fluid control plate layer has good temperature uniformity and flatness, which 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 plate temperature is uniform.The freeze dryer uses the technology of the fluid in the middle of the shelf. The shelf temperature control of the bell-type freeze dryer basically uses heaters, and the temperature consistency of the plate layer is slightly poor. However, in general, the temperature difference between the layers of the medical freeze dryer should be controlled at ±1.5°C, and the temperature difference within the plate should be ±1°C. The food freeze dryer can be a little flexible.
VII. Control system
The control system types and functions of the freeze dryers are different. For the freeze dryers of the experimental series, it is mainly used for the exploration of the freeze drying process of materials and a small amount of trial production. Therefore, the control system should be able to display the freeze-drying process parameters in real time and automatically record, at the same time, it can set, modify and effectively execute the freeze-drying process procedures and has a communication interface for data collection and storage.