Cryogenic storage Dewar, that is, what we often call a liquid nitrogen tank, needs liquid nitrogen for its operation!
The cryogenic storage Dewar without liquid nitrogen is just a metal tank with a vacuum structure, similar to a large thermos cup, which cannot play the role of storing samples. Moreover, it does not mean that it can run normally with liquid nitrogen installed. It has a range value. If it is less, it will not work, and if it is too much, it will be troublesome.
90% of the total capacity is charged for the first time!
That is to leave 10% space for the reaction of the vaporized liquid nitrogen to prevent the nitrogen from topping off the neck plug!
During use, if liquid nitrogen is simply stored, it should not be less than 1/3 of the total capacity; if samples are stored, liquid nitrogen should be used to completely cover the samples.
Normally, as long as the sample is submerged in liquid nitrogen in the cryogenic storage dewar, it can run. It is only filled with liquid nitrogen for the first time. If it is not pre-cooled, the overall loss of liquid nitrogen will be high, because the tank itself is at room temperature, and the liquid nitrogen is lowered to a low temperature. This process will consume more.
Therefore, it is recommended to guarantee 90% liquid nitrogen filling for the first time in the new tank.
When refilling, ensure that the liquid nitrogen covers the sample and it can run normally!
Only in this way, with the natural loss of liquid nitrogen, there will be more temperature space above non-196°C, which will inevitably reduce the use time. According to personal habits, you can only cover the sample. Of course, it is recommended to replenish it to 90%. Use longer.
In addition, like some cryogenic storage Dewars with fewer models and larger calibers, whether they are used for simply storing liquid nitrogen or storing samples, such as 10 liters 125, 6 liters 80 liters, etc., the complete static storage time is only about 30 to 28 days. , in real use, the rehydration interval will be even smaller. Coupled with the low level of liquid addition, the interval should be further reduced, and frequent rehydration is also a troublesome matter.
Therefore, based on the above considerations, liquid nitrogen tank manufacturers still recommend that you ensure that the normal operating liquid level of the cryogenic storage Dewar is 90%, leaving 10% of the gas phase space, neither too much nor too little.