Introduction to Intermittent Exhaust Technology of Vacuum Device:
Stopping the vacuum will not affect the material out-gassing process. The characteristic of material out-gassing is that once the material, structure and temperature are determined, within a certain pressure range, the reduction of material out-gassing rate mainly depends on the out-gassing time, and has nothing to do with the pumping speed and the degree of vacuum. Therefore, continuous evacuation cannot promote a faster reduction in the out-gassing rate. In the case of intermittent evacuation, the "certain pressure range" that does not affect the out-gassing of the material in the insulation layer of the vacuum device is maintained during the stop of the evacuation, and does not affect the out-gassing process, so the out-gassing rate can continue to decrease with time.
During the period when the vacuum is stopped, the gas diffusion and penetration vacuum still exist. When the vacuum is stopped, the out-gassing rate of the material in the insulation layer of the vacuum device is the highest, the volume between the layers is small, and the pressure rises the fastest. The volume of the interlayer space is large, the out-gassing rate of surrounding materials is low, and the pressure rises the slowest. As a result, there is always a pressure difference between the insulation layer of the vacuum device and the interlayer space. According to tests, this pressure difference can be as high as tens or even hundreds of times when vacuuming, and several times or even ten times when vacuuming is stopped. When the vacuum is stopped, the gas in the insulation layer of the vacuum device can continuously reach the interlayer space through diffusion and permeation under the action of the pressure difference. At this time, the space always has a certain vacuum effect on the gas in the insulation layer of the vacuum device.
Due to the influence of conductance during vacuuming, the out-gassing rate of the material in the insulation layer of the vacuum device is not uniformly reduced.
The mezzanine space has a large gas storage effect. The interlayer space has a large volume and the surrounding material has the lowest out-gassing rate, so it can store a large amount of gas released from the material in the insulation layer of the vacuum device.
The stored gas is pumped out faster. Therefore, when re-evacuating, the gas stored in the space can be quickly pumped away by the vacuum pump.
For the liquid nitrogen container, the gas heat flushing process is used first, and then the vacuum device intermittent exhaust process is used in the formal exhaust. As a result, the actual vacuuming time can be further shortened to 24h when the air volume is the same as the continuous evacuation 72h.
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