| High vacuum multilayer insulated cryogenic vessels（hereinafter referred to as cryogenic vessels）have been widely utilized in the storage and transportation of cryogenic liquids such as liquid hydrogen,liquid oxygen and liquid nitrogen because of its excellent thermal insulation performance.The deterioration of vacuum performance in annular space will give rise to the decline or even failure of the thermal insulation performance of cryogenic vessels.The outgassing of cryogenic insulation materials in vacuum is one of the primary reasons for the vacuum deterioration of cryogenic vessels.Therefore,the study on the outgassing characteristics of cryogenic insulation materials is of great significance for the long-term and efficient maintenance of vacuum level and the prediction of vacuum life.In this paper,the insulation materials like aluminum foil,glass fiber paper and epoxy glass fiber reinforced plastic（GFRP）,usually applied in the cryogenic vessels,are mainly regarded as research objects,and their outgassing characteristics in vacuum are studied by combining theories with experiments.Firstly,the outgassing mechanisms of insulation materials in vacuum are theoretically analyzed and the relevant theoretical outgassing models are proposed.Secondly,the outgassing experiments are carried out to explore the outgassing characteristics of the above materials under different working conditions.Thirdly,the relevant theoretical models are selected to study the outgassing mechanisms.The main work contents are as follows:（1）Applying molecular dynamics theory,this paper analyzes the outgassing mechanisms of insulation materials in vacuum,reveals the main difficulties faced in the theoretical study on material outgassing,summarizes and analyzes the related theoretical models of material outgassing,and introduces the research contents and application scopes of various theoretical models,which provides a theoretical basis for the fitting research on outgassing rate curves of insulation materials and the calculation of outgassing amount in the following paper.（2）The outgassing experiments of aluminum foil and glass fiber paper were performed.The variation law of outgassing rates and outgassing compositions of these two types of materials with static outgassing time,vacuum-pumping time,baking temperature was investigated.With the extension of static outgassing time,the outgassing rate of aluminum foil decreases gradually,and the outgassing rate of glass fiber paper remains basically unchanged;With the extension of vacuum-pumping time,the outgassing rates of these two kinds of materials reduce gradually.The outgassing rates of aluminum foil and glass fiber paper decreased to 38.78%and 15.17%respectively when the vacuum pumping time was prolonged for 3 hours;With the increase of baking temperature,the outgassing rates of these two types of materials mount up gradually.The outgassing components of aluminum foil and glass fiber paper are analyzed and obtained by using mass spectrometer.The outgassing components of these two materials are predominantly H2 and also contain a small amount of H2O,CO and N2.（3）Taking epoxy GFRP as the experimental sample,the outgassing experiments were conducted and the variation law of outgassing rate and outgassing composition with vacuum-pumping time and baking temperature was studied.With the extension of evacuation time,the outgassing rate of epoxy GFRP decreases exponentially.With the extension of evacuation for 3 hours,the outgassing rate of epoxy GFRP reduced to 45%;With the increase of temperature,the outgassing rate of epoxy GFRP goes up gradually.For every 20℃rising of temperature,the outgassing rate of epoxy GFRP increased by about 1.5 times.The outgassing composition of epoxy GFRP is mainly H2O.The effect of increasing temperature on the outgassing composition of epoxy GFRP is not obvious.（4）The general outgassing model is selected to perform nonlinear fitting on the outgassing rate curves of aluminum foil and glass fiber paper at different temperatures.The outgassing rate curves of epoxy GFRP at different temperatures are fitted by diffusion outgassing model.The calculation formulas of outgassing rates of insulation materials with practical significance are obtained,which can estimate the total outgassing amount of insulation materials within the minimum error range and serve as a theoretical underpinning for the prediction of vacuum life of cryogenic vessels.At the meanwhile,the outgassing mechanisms of aluminum foil and glass fiber paper are judged on the basis of the general outgassing model.Through the investigation on the outgassing characteristics of cryogenic insulation materials such as aluminum foil,glass fiber paper and epoxy GFRP in vacuum,this paper offers a theoretical reference for the prospective development and application of correlative materials employed in cryogenic vessels,the design and improvement of pretreatment process,the prediction and evaluation of vacuum life of cryogenic vessels. |
