When the full low pressure oxygen generator begins to accumulate liquid oxygen, is it necessary to keep the liquid level? Why?

The start-up phase of the whole low-pressure oxygen generator is that liquid empty appears first in the lower tower, and then liquid oxygen appears in the upper tower. The cold energy needed to accumulate liquid in the tower mainly comes from the expansion machine, which uses the low temperature gas after expansion to make part of the air liquefaction in the liquid purifier. But the upper tower itself can not produce liquid, it mainly depends on the liquid from the lower tower into the upper tower. In the phase of hydrops, in order to accumulate the liquid level as soon as possible, the cooling volume should be transferred to the tower as much as possible, the phenomena of overcooling, temperature difference at the hot end and cold loss increase caused by excess cooling of switching heat exchanger should be avoided.
As for how to recycle and transfer the cold volume of the air expansion into the tower, whether it is by the liquid purifier to transfer the cold volume to the lower tower first, and then to the upper tower, it is OK to transfer directly to the upper tower through the supercooler. If the cold fluid channel of the liquid air cooler can be directly connected with the channel behind the expansion machine (for example, set the cooler and the liquid purifier together ), in other words, the liquid-air supercooler can be used to recover part of the cooling capacity of the expansion gas and directly give it to the upper tower, and the supercooler can act as a liquid purifier at the same time. That is to transfer the cooling volume to the tower by the liquid purifier and supercooler at the same time, which can accelerate the accumulation of liquid. In this case, the liquid level of the lower tower can be temporarily ignored and kept, and the air throttle valve can be opened to make as much gas included in the liquid air as possible pass through the supercooler to strengthen the heat exchange of the supercooler, to recycle more cold energy. Some oxygen generator does not even set a liquid purifier in the process design, but only uses it as a liquid purifier when the supercooler is started, and begins to accumulate liquid from the top tower.