The degree of vacuum is an important indicator for judging the quality of a liquid nitrogen cryogenic tank!
Liquid nitrogen cryogenic tanks are manufactured to store liquid nitrogen, relying on Dewar’s vacuum jacket principle and the clever use of thermal insulation materials. It can store liquid nitrogen for a long time, and cryopreservation of biological samples also relies on vacuum. Vacuum can provide thermal insulation! Without vacuum, there is no thermal insulation. If the vacuum is not good, the thermal insulation effect will be greatly reduced!
Mainly the following two types:
1.A large amount of frost suddenly formed on the can body
If the vacuum structure of the liquid nitrogen cryogenic tank is intact, it must be insulated externally and insulated internally to prevent leakage of liquid nitrogen cold air internally and to prevent liquid nitrogen from being exposed to heat externally. If the vacuum is not good, some parts cannot be covered by the vacuum. The external heat will be transmitted to the liquid nitrogen in the inner tank through here. The low temperature of the liquid nitrogen will also be transmitted to the outer wall of the jar. The water vapor on the outer wall will become frost when it is cold. .
If a liquid nitrogen tank is used normally and suddenly a lot of frost forms, it can basically be judged that the vacuum is defective. It is best to suspend use and quickly transfer the sample to other cryogenic containers.
2.The thermal insulation effect is significantly reduced
This is not as intuitive as the previous frosting. Users need to have a certain understanding of how long their liquid nitrogen cryogenic tank will last once it is filled with liquid nitrogen, whether it is 100 days or 80 days. If the time for refilling with liquid nitrogen is much shorter than the normal time, and the frequency and duration of sample collection have not changed, for example, the original 100 days has become 50 days, then it can be concluded that the vacuum is defective.
These are the two major manifestations of poor vacuum in the liquid nitrogen cryogenic tank: one is frost and the other is a drop in insulation. But pay attention to the difference. The frost here refers to the sudden frost during normal use, not the frost that occurs when a new container is used without pre-cooling!
If frost appears in a new container without pre-cooling, it is normal for it to subside after a few hours!