Liquid Nitrogen Tank Pressure Problem

We know that the critical temperature for nitrogen is -147 ° C and the critical pressure for critical temperature is 3.4 MPa. According to thermodynamic knowledge, nitrogen is above liquefied when it is above the critical temperature. However, when searching for nitrogen gas tank, we actually found that the working pressure of nitrogen gas tank on the market is not only not higher than 3.4 MPa, but much lower than 3.4 MPa. May I ask what is going on? Is it stored in a nitrogen tank liquid nitrogen temperature is very low?

Yes, the temperature is lower than the critical temperature, the general temperature of liquid nitrogen tank minus 190 or so, the pressure is generally about 0.3-0.8 This is a low pressure tank. There are also high-pressure tank, you can reach 2,88 Mpa liquid nitrogen tank, also known as the degree of Jue - low temperature insulated cylinders, has a very warm effect, but will also absorb heat to increase the pressure, after all, will not be absolutely warm. After the pressure is increased, the maximum design pressure of the tank is reached. The tank has a safety valve that automatically opens and releases the gasified part of the hot gas until the pressure has been reduced to the design pressure of the tank. The safety valve will automatically shut down.

The design temperature for liquid nitrogen storage tanks is -196 ° C. There are two conventional pressures for design, one 0.8 MPa and the other 1.6 MPa. Both design pressures are based on the use requirements. Nitrogen under pressure, when the temperature reaches -196 ° C, will become a dark blue liquid, that is, liquid nitrogen, liquid nitrogen storage can be pressure-free storage can also be stored.