Experimental Study On Pressure Rise Rate Of High Vacuum Multilayer Insulated Cryogenic Vessels Under Vacuum Failure

Due to unreasonable design and manufacture,nonstandard operations in use or some external impacts,the walls or pipelines of high vacuum multilayer insulated cryogenic vessels would break and leak,resulting in the vacuum deterioration or complete vacuum loss in the annular space of cryogenic vessels.After such an emergency occurs,the heat transfer process in the annular space would become complicated.The heat leakage of the annular space increases sharply,and a large amount of cryogen stored boils off,leading to the rapid pressure rise of the inner vessels,which poses a serious threat not only to the routine use of the cryogenic vessels,but to the safety of operating personnel.The past research on cryogenic vessels mainly focused on the conditions of good vacuum maintenance or complete vacuum loss of annular space,and the research objects are mostly concentrated in the fields of aerospace and high-energy physics.In order to fully understand the influence of vacuum deterioration on the heat transfer process of annular space and the storage process of cryogen in cryogenic vessels,this paper makes a more systematic study under different vacuum failure levels and various initial filling rates through the combination of theoretical analysis and experimental investigations,and the completed researches are mainly as follows:（1）The theoretical model for heat transfer calculation of annular space after vacuum failure of cryogenic vessels is constructed.The model is utilized to compute the heat flux variations of annular space under different vacuum degrees.The heat flux increases with the decrease of vacuum levels.When the vacuum degree of annular space is higher than 10^-2 Pa,the gas flow regime in annular space is the free molecular regime,and the heat flux of cryogenic vessels remains small;When the vacuum degree of annular space is between 10^-2 Pa and 10 Pa,the gas flow regime turns into slip flow regime and transition regime,and the heat flux of cryogenic vessels increases rapidly with the vacuum degrees decreasing;When the vacuum degree of annular space is lower than 10 Pa,the gas flow state becomes a continuous state,the heat flux increases rapidly and finally reaches the maximum value as the vacuum level of annular space goes up to 10³ Pa.With the continuous degradation of vacuum degrees,the heat flux changes little.（2）Based on the self-built experimental platform,after vacuum failure of the cryogenic vessel happens,the pressure rise rates and temperature variations of the inner vessel are experimentally studied under pressurized storage condition.The pressure rise rate of cryogenic vessel grows up with the increase of initial filling rate and the decrease of vacuum level.There is an obvious phenomenon of thermal stratification existing in the ullage space of cryogenic vessel.When the vacuum degree of annular space is 1 Pa,the pressure rise rate with the initial filling rate of 70%is 1.51 times and 1.95 times as large as those with the initial filling rates of 50%and 30%,respectively;When the initial filling rate is 50%,the pressure rise rate with the vacuum degree of 10³ Pa is 1.36 times,2.66 times and 5.27 times as large as those with the vacuum levels of 10² Pa,1 Pa and 10^-3 Pa,respectively.（3）After vacuum failure of cryogenic vessel,the variations of evaporation capacities and temperatures inside inner vessel are studied experimentally under the condition of atmospheric pressure storage.The evaporation capacity of cryogenic vessel mounts up with the increase of initial filling rate and the decrease of vacuum level.The variation of vacuum levels in the annular space has a significant effect on the evaporation capacity of cryogenic vessel.There is an evident thermal stratification in the ullage space of cryogenic vessel.According to the experimental results,the calculation results indicate that the theoretical values are in good agreement with the experimental ones,which can well mirror the variation of heat flux after vacuum failure of cryogenic vessel.（4）Based on the cryogenic vessel test-bed of vacuum failure,the effects of active cryocooling on the storage process of cryogen are studied.The results show that,under pressurized storage condition,the pressure rise rate of cryogenic vessel decreases with the operation of cryocooler and gradually stabilizes at a certain pressure value.Furthermore,the phenomenon of temperature stratification in the ullage space is effectively alleviated.In the process of atmospheric pressure storage,the evaporation capacity of cryogenic vessel decreases with the working of cryocooler,and the temperature stratification in ullage space is effectively restrained.