The vacuum system consists of vacuum vessel, vacuum pump, vacuum valve, vacuum gauge, vacuum seal, condenser and pipeline.
I. Basic requirements for vacuum system
(1) according to the needs of freeze-drying materials, certain vacuum degree and working vacuum degree shall be achieved. The limiting vacuum is the lowest pressure that can be achieved without leaking the system; the working vacuum is the vacuum that can be maintained in a certain process.
(2) increase the effective pumping speed, shorten the pumping time and reduce the cost of freeze-dried products under as many conditions as possible.
(3) the system structure is simple, firm, easy to operate and easy to maintain.
II. Vacuum system sealing
There are two kinds of vacuum seal, one is metal or ceramic permanent seal or glass and metal welding; the other is removable static seal and dynamic seal. Static seals are connected by components and remain static after sealing; dynamic seals must ensure movement and sealing.
The detachable vacuum seal must be provided with sealing material in the middle of the joint flange of the component. The sealing can be realized by pressing and fastening. Different sealing materials can be selected according to the vacuum degree. Commonly used sealing materials are: rubber, polytetrafluoroethylene, soft metal aluminum, oxygen free copper, etc.
Vacuum grease is used for vacuum sealing and lubrication between two smooth surfaces. Vacuum sealing wax is used to fill small leaks in the vacuum system. Vacuum seal is divided into vacuum mud and vacuum wax.
III. drying oven
Drying oven is one of the important parts of vacuum system, its vacuum performance will affect the performance of the whole refrigerator. It is not only a vacuum chamber but also a container for freeze-drying materials.
IV. water collector
Water collector is one of the vessels of vacuum system, which can capture water vapor from material sublimation to protect vacuum pump. Traps are also known as traps, condensers, and cold traps.
V. vacuum pipe and valve
There is a vacuum pipe between the drying box and the water catcher, the water catcher and the vacuum pump, and a vacuum valve is provided to control the opening and closing, and the flow rate is minimum, etc.
According to the working strength of the valve, the vacuum valve can be divided into low vacuum valve, high vacuum valve and ultra-high vacuum valve. Therefore, the selection of vacuum valve mainly depends on its use and use conditions, its model size, it depends on the diameter of the pipeline.
Vi. vacuum measurement
Vacuum is usually expressed as pressure. Therefore, the vacuum cone is attributed to the pressure measurement in the vacuum environment. Vacuum measurement is also an important and closely related part of vacuum technology. The traditional vacuum measurement method is to measure the pressure directly. For example, a U-tube vacuum gauge (e.g., a McIntosh vacuum gauge) is used to measure the I vacuum. It is still applicable, but it is not applicable to the environment with condensable gas molecules and automatic control system. The vacuum degree is basically a small number of people with small molecular density. The density of gas molecules has its own physical properties, such as heat conduction and conduction. According to these properties, a variety of vacuum meters are designed.
In the freeze-drying vacuum system, the gas pressure range is generally 105-1pa, but it often contains water vapor, oil vapor and other condensable gases, which are often accompanied by temperature changes and uneven temperature in the equipment. In some process, there is also unsteady gas directional flow. So we should pay attention to the actual process condition and its influence on the measurement value when choosing the vacuum gauge and measurement.
The vacuum gauges suitable for freeze-drying process are McIntosh vacuum gauge, film vacuum gauge, resistance vacuum gauge, ionization vacuum gauge, etc.
Vacuum system for freeze drying process