During the start-up phase, when the liquid volume accumulates in the condensing evaporator, the gas and liquid mixture will pass through the liquid air and liquid nitrogen throttle valves. When the throttle valve begins to close, due to the large opening of the valve, when the amount of gas and liquid mixture from the lower column to the upper column changes little, and the pressure of the lower column does not increase significantly, it means that the temperature difference of the condensing evaporator has not increased. At this time, the condensing evaporator and the surrounding insulation have been cooled to the low temperature required by the liquid accumulation stage.
Due to a large amount of cold production and a large amount of gas liquefaction, the liquid evaporation in the condensing evaporator is also increased. The rising steam produced prevents the flow of liquid from the sieve plate hole, and gradually accumulates liquid on the tray, so the liquid level will drop. In addition, because the throttle valve opening is small, the return gas will temporarily decrease, and the temperature of the heat exchanger will increase, which will increase the medium pressure and cause the liquid level to decrease. When the valve is closed to the normal working position, the medium pressure and low pressure will no longer increase, and the temperature of the upper and lower columns will not change. Since the high pressure pressure does not decrease, the cooling capacity appears to be excessive and the liquid level will start to rise again. Therefore, measures must be taken to reduce the high pressure to ensure that the liquid level is stable at a certain height.