When heating the liquefied air, although the boiling point of nitrogen is lower than that of oxygen, nitrogen should be evaporated first. However, due to the mutual influence of nitrogen and oxygen molecules, when nitrogen molecules evaporate from the liquid, it is also accompanied by the evaporation of oxygen molecules, but the evaporation of nitrogen molecules is relatively easier than that of oxygen molecules, that is, the nitrogen component in the steam is larger than that in the liquid. For example, when the liquid air with 79.1% N2 of nitrogen Mol is heated and evaporated at 0.1MPa, the nitrogen Moore in the vapour that begins to generate is 93.7% N2, and the rest is oxygen. When the liquid air evaporates for 50%, because more oxygen also evaporates, the Moore composition of nitrogen in the steam reduces to 89.8% N2, the Moore composition of oxygen in the liquid is 31.5% O2 (68.5% N2); when 90% of the liquid is evaporated, the mole composition of nitrogen in the vapor is 82% N2, the Moore composition of oxygen in the liquid is 475% O2 (53% N2 ). Although the oxygen concentration in the liquid increases with the increase of the oxygen content in the vapor, the maximum content of oxygen in the vapor can only reach 20.9% O2 (when the liquid is completely evaporated), therefore, the maximum content of oxygen in the finally evaporated liquid is only 51.5% O2 (48.5% N2 ).
