The outer wall of the liquid nitrogen container is evacuated between the outer wall and the inner wall and filled with the heat insulating material to insulate the heat exchange. After the liquid nitrogen is filled into the tank, the upper space in the tank is filled with low-temperature nitrogen gas.
After the tank is closed, there may still be some heat exchange between the liquid nitrogen container and the external environment. When the room temperature is relatively stable, as a system, the tank internal space forms a cryogenic system with a relatively stable temperature distribution.
Studies have shown that the liquid nitrogen container filled with a part of liquid nitrogen inside the container at a constant room temperature has a relatively stable temperature distribution in the upper space of liquid nitrogen, thereby achieving optimal preservation of the sample.