The use and maintenance of the laboratory freeze dryer must be strictly in accordance with the requirements, especially the inspection and replacement of lubricating grease. Grease change intervals
are affected by compression end temperature. When the temperature at the compression end is high, the replacement cycle of the lubricating oil is appropriately shortened.
In general, the lubricating oil should be checked every 10000h of continuous operation. When the compressor is running for the first time. It is recommended to change the lubricating oil and clean the oil filter after 2000h of operation. Check whether the system is clean, if the system is in good operating condition, change the lubricating oil every 20000h.
When checking and replacing the lubricating oil, avoid exposed air for a long time, because the freezer has water absorption.
After a fault occurs, the cause must be thoroughly investigated, and if necessary, please ask a professional company to find and eliminate it. If the motor burns out, impurities such as its patent skin
will spread all over the refrigeration system, and the system should be thoroughly cleaned during maintenance.
The filtration system of the entire system should be thoroughly inspected and replaced if necessary. Improper handling will have adverse effects on the long-term operation of the compressor, and may even cause irreversible consequences due to small losses.
Laboratory freeze dryer
The whole process of the laboratory freeze dryer is actually a process of heat transfer and mass transfer (water vapor) at the same time. The heat and mass transfer rates together affect the drying rate, thereby affecting the entire freeze-drying cycle. Both will affect the drying rate. The simple analysis is as follows:
1. Form and composition of materials
According to the form of freeze-dried materials, it is usually divided into solid and liquid. The morphology of the solid and the concentration of the liquid have a great influence on the freeze-drying rate.
2. Pre-freezing rate
The size of the crystals formed during freezing greatly affects the rate of drying and the dissolution rate of the dried product. The process of quick freezing and slow freezing has the following differences: the ice crystals produced by quick freezing are smaller, and the ice crystals produced by slow freezing are larger.
Large ice crystals are beneficial to sublimation, while small ice crystals are not conducive to sublimation. Fast freezing leads to low sublimation rate and fast desorption rate; slow freezing leads to fast sublimation rate and slow resolution rate.
3. Loading capacity
When the material is freeze-dried, there is a certain ratio of surface area to material thickness after being sub-packed into the container, that is, freeze-drying is related to the loading amount.
Small surface area and thickness are conducive to water sublimation, easy to freeze drying and ideal quality. When drying, the wet weight load per unit area of the tray is an important factor in determining the drying time.
Generally, the thinner the thickness of the material stack, the faster the heat and mass transfer speed, and the shorter the drying time. However, if the thickness of the material is thin, there will be less material to be dried per batch per unit freeze-drying area, which is unfavorable for improving the unit freeze-drying area and the output per unit time.
4. Drying indoor pressure
The pressure in the drying chamber affects the rate of heat transfer and mass transfer. For mass transfer, the lower the pressure, the better, and for heat transfer, the higher the pressure, the better. The size of the mass transfer rate is mainly determined by the temperature and pressure of the sublimation interface and the surface of the drying layer.
To increase the escape rate of water vapor in the drying layer, one is to increase the temperature of the sublimation interface to increase the interface water vapor pressure; two It is to improve the vacuum degree of the drying chamber and reduce the vapor pressure on the surface of the drying layer.
5. Heat transfer method Heat transfer method
According to the traditional classification, it can be divided into: conduction, convection, thermal radiation and medium heating (microwave heating).
Since the process of sublimation drying involves the transfer of heat and mass (steam), the drying rate is greatly affected by which heat transfer method is used to transfer the heat to the material more efficiently.
Application of freeze dryer machine
