Study On Characteristic Of Water And Carbon Dioxide Impurity In Cryogenic Liquid

Cryogenic fluid has important application value in aerospace and other fields.The study of the solubility of impurities in cryogenic fluids and the characteristics of impurity particles plays a key role in guiding the optimization of pipeline filter blockage during rocket filling and refilling process.This thesis focuses on the properties of water and carbon dioxide impurities in liquid nitrogen and liquid oxygen.The solubility of carbon dioxide in liquid nitrogen（77K）and liquid oxygen（90K）is in the order of10^-5～10^-6,so a variety of methods can be used to measure it;and the solubility of water is predicted to be below 10^-8,beyond the accuracy range of conventional measurement methods.Therefore,the experimental data of carbon dioxide is relatively sufficient,and the experimental determination and theoretical calculation of the solubility of water impurities are much more difficult.This thesis analyzes the solubility of water impurities from the theoretical and experimental aspect,and designs a visualization experimental system to conduct qualitative and quantitative research on water and carbon dioxide impurities in liquid nitrogen and liquid oxygen.Main content of this thesis is as following:（1）Three theoretical solution models are used to calculate the solubility of water in liquid oxygen,and their advantages and disadvantages are analyzed.Further calculations based on the literature show that the solubility of water in liquid oxygen（90K）is lower than 10^-9.By summarizing the experiment apparatus in literature,the traditional measurement method of impurity solubility in cryogenic fluid is categorized into static method and quasi-static method,and their limitations in the determination of water-liquid oxygen/water-liquid nitrogen system are analyzed.After fully discussing the difficulties of the direct measurement of impurity solubility,the design of the microscopic visualization experiment system of impurity particle characteristics is introduced.（2）Static microscopic visualization experiments are carried out on the impurity characteristic of ice crystals and carbon dioxide in liquid nitrogen and liquid oxygen,with 0.001%,0.01%,and 0.1%water content conditions.The formation of water and carbon dioxide impurities in liquid nitrogen and liquid oxygen are studied.Under the condition of water pre-condensation,water forms ice crystals independently.The average size of ice crystals changes with water content,and no observable changes occur after their formation;carbon dioxide impurity forms flocculation independently.As the liquid nitrogen temperature decreases（77K～65K）,it gradually accumulates and grow,with the average size increasing by about80%.Under the conditions of co-condensation of water,carbon dioxide and liquid oxygen,part of the water forms fine ice crystal particles,which,together with carbon dioxide,form loose flocculent structure,and break down as temperature decreases.（3）Combining the classical filter theory,the impurity particles filtration model is established.The upper limit of the molar concentration of impurity particles passing through the filter is calculated.When the particles pass through the filter pore larger than the particle size,it is generally considered to cause no clogging.However,at a temperature of90K in the liquid oxygen working condition where the ice crystals are pre-condensed without moisture,the large particles with loose flocculent structure have a certain risk of clogging.When particles pass through a filter screen smaller than the particle size,it is generally considered to cause clogging.However,for conditions with loose flocculent carbon dioxide impurities,the particles may disintegrate and become smaller in size,smoothly passing by the pore.Proper filter size for each case is recommended.Through the work listed above,the solubility range of low-solubility impurities in liquid nitrogen/liquid oxygen was further clarified,and appropriate research methods for such impurities were analyzed.By the method of microscopic visualization,the characteristic of ice crystals and carbon dioxide impurity in liquid nitrogen/liquid oxygen under specific working conditions is studied,which provides theoretical guidance for the selection of rocket charging pipeline filter.