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Will the dewar tank seal stay cold all the time?

2024-05-06 10:26:10

According to conventional thinking, if you want to maintain a certain temperature, you need to seal the temperature coverage area;

Such as thermos cups and thermos lunch boxes!

The design of the Dewar tank also evolved from this basis. The inner and outer tanks are combined with a top neck plug. A vacuum is drawn between the inner and outer tanks. The neck plug covers the mouth of the tank to isolate external heat transfer and form a nearly sealed environment. , note that it is close to rather than equal to.

This seems different from conventional insulation thinking!

If we follow conventional thinking and seal the dewar tank, will it remain cold all the time?

Answer: Not only no, there is also a risk of explosion!

The reason is that the dewar tank stores cryogenic liquid nitrogen instead of liquids like water!

Water will not vaporize, but liquid nitrogen will; even if water evaporates, the vapor pressure generated will be very limited and will not hurt people;

Liquid nitrogen is different. Its evaporation is converted into nitrogen gas. The expansion of the gas brings its own pressure. As the pressure accumulates day by day in the liquid nitrogen container, the pressure also accumulates. For the sake of safety, all dewar tanks, no matter which manufacturer they are from, will have the neck plug loosened, leaving a certain gap for the evaporated nitrogen to escape, so as not to accumulate in the container and create pressure.

If the dewar tank is completely sealed at this time, no matter what kind of sealing method is adopted, replacing the original neck plug or covering it with a plastic film, the naturally vaporized nitrogen will not be able to be discharged, and eventually pressure will build up. If the tank continues to accumulate, there is a risk of bursting. It may even threaten the safety of users!

Therefore, the sealing of the dewar tank cannot keep the container cold all the time, but may cause danger!

Will the dewar tank seal stay cold all the time