Regarding the main cooling temperature difference
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I hope to discuss with everyone the relationship between the pressure at the bottom of the upper column and the pressure at the top of the lower column, as well as the temperature difference with the main cooler!
Based on solution thermodynamics, we can see that there are only two factors that affect the boiling point of a substance: pressure and composition. The temperature difference in the main cooler is the difference between the liquid oxygen at the bottom of the upper column and the gaseous nitrogen at the top of the lower column. In terms of pressure, as the pressure increases, the temperature also increases; conversely, as pressure decreases, the temperature drops. As for composition, the higher the purity of the gaseous nitrogen, the lower the temperature, while the higher the purity of the liquid oxygen, the higher the temperature. We control the temperature difference in the main cooler by regulating pressure and composition.
The resistance of the heat exchangers and pipes, that is, the pressure at which the contaminated nitrogen is sent out, determines the pressure at the top of the upper column; thus, the pressures at the bottom of the upper column and at the top of the lower column can also be determined, as well as the temperature difference in the main cooler.