In the precooler, cold and hot compressed air exchange heat and mass, and the total heat exchanged is equal. However, the saturated hot air flow undergoes phase change during the cooling process, and the condensate will consume a part of the cooling capacity. However, the heat absorbed by the cold air flow in the heat exchange process is all used for temperature rise, so the temperature change amplitude of the cold air flow and the hot air flow is different. The rule is that the temperature drop amplitude of the hot air flow is smaller than the temperature rise amplitude of the cold air flow. For example, under certain working conditions, hot air can drop from 40 ℃ to 28 ℃, with a drop of 12 ℃, while cold air can rise from 5 ℃ to 24 ℃, with a rise of 19 ℃.