How does the cryogenic pump pump pump air?
the cryogenic pump is equipped with a cold plate cooled to a very low temperature by liquid helium or a refrigerator. It condenses the gas and keeps the steam pressure of the condensate below the limit pressure of the pump, so as to achieve the function of air extraction. The main functions of low-temperature extraction are low-temperature condensation, low-temperature adsorption and low-temperature capture. ① Low temperature condensation: gas molecules condense on the surface of the cold plate or on the condensed gas layer, and its equilibrium pressure is basically equal to the vapor pressure of the condensate. When pumping air, the temperature of the cold plate must be lower than 25K; During hydrogen extraction, the cold plate temperature is lower. The thickness of the condensing layer of low-temperature condensing extraction can reach about 10mm. ② Low temperature adsorption: gas molecules are adsorbed to the adsorbent surface coated on the cold plate with a single molecular layer thickness (centimeter order of magnitude). The equilibrium pressure of adsorption is much lower than the vapor pressure at the same temperature. If the vapor pressure of hydrogen is equal to the atmospheric pressure at 20K, the adsorption equilibrium pressure is lower than PA when hydrogen is absorbed by activated carbon at 20K. In this way, it is possible to extract gas through low-temperature adsorption at higher temperatures. ③ Low temperature capture: gas molecules that cannot condense at the extraction temperature are buried and adsorbed by the growing condensable gas layer
generally speaking, the limit pressure of the cryogenic pump is the vapor pressure of the condensed gas under the cold plate temperature. When the temperature is 120K, the vapor pressure of Shui Larsen is lower than 12 Fill the hydraulic oil in the oil source in strict accordance with the instructions. When the temperature is 20K, the vapor pressure of other gases except helium, neon and hydrogen is also lower than PA. However, due to the different temperatures of the pumped container and the low-temperature cold plate, the limit pressure of the low-temperature pump is higher than the vapor pressure of the condensate. For containers at room temperature, when the low temperature plate is 20K, the limit pressure of the pump is about 4 times the condensate vapor pressure