Thermal And Structure Analysis Of Cryogenic Vessels Adopting High Vacuum VD-MLI Technology

With the development of science and technology as well as the needs of industrial and agricultural production, the cryogenic technology has become an indispensable technology in national defense construction, national economy, scientific research and many other fields. Aerospace science and technology supported by the cryogenic technology, including ground rocket launching, satellite environment testing, space to earth observation, deep space exploration, even the space resources development, develops rapidly in the 21 st century.In the process of large capacity storage for cryogenic liquid with long time, the boiling point s of cryogenic liquids are far lower than the environment temperature, although the high-performance heat insulation measures have been taken for the vessel s used for storing and transporting cryogenic liquid s, the evaporation of cryogenic liquid s is still inevitable. The heat, which continuously passes into the inside of vessel through the vessel wall and the accessory pipes, causes the evaporation of cryogenic liquid s, the production of BOG, and the variations of components and thermodynamic properties of cryogenic liquids, moreover with the constant production of BOG, the pressure and temperature will rise and the adverse impact will occur on the vessel. Therefore, the heat insulation performance of cryogenic vessel s is the key problem of greatly limiting the development of cryogenic technology.In order to keep the stability of cryogenic vessel pressure and avoi d the damage of cryogenic vessels, the BOG needs to be expelled from the vessel, then it is adverse to the loss-free storage of cryogenic liquids and shortens the storage and transportation cycle of cryogenic liquid s as well as causes the resource waste an d the environment pollution. Aimed at the cryogenic propellant storage of spacecraft, the ZBO storage technology of cryogenic liquid s was put forward by the cryogenic researchers of NASA. The ZBO storage technology of cryogenic liquid s, that is, the heat insulation layer of cryogenic vessel adopts the combinational high-performance heat insulation structure of SOFI and VD-MLI, the strut adopts the PODS, the external heat leakage, which cannot be solved by the heat insulation layer and the strut, is removed from the vessel by the heat exchanger coupled with the small cryogenic refrigerator, and the cooling of cryogenic liquids and the condensation and reliquefaction of BOG will be realized finally. The ZBO storage technology of cryogenic liquids controls the evaporation of cryogenic liquids effectively, ensures the storage and transportation of cryogenic liquid s efficiently and safely, and realizes the long time ZBO loss-free storage of cryogenic liquids.According to the need of experimental research on BOG reliquefaction technology of ZBO storage for cryogenic liquids, A testing device of BOG reliquefaction system was designed and set up, and the VD-MLI was used for the heat insulation of cryogenic vessel in the testing device. The heat transfer and structure of the cryogenic vessel adopting the high vacuum VD-MLI technology will be studied.Firstly, the heat transfer of the cryogenic vessel was studied, and the influence of heat-leak rate of all the components on the heat insulation performance of cryogenic vessel was analyzed. The result shows that the heat-leak rate of the cryogenic vessel adopting the VD-MLI technology is small and meets the requirement of refrigeration system. Of the total heat-leak rate, the heat-leak rate of neck tube accounts for 51.8% and is the main factor of influencing the heat insulation performance of cryogenic vessel.Secondly, the thermal-structure coupling analysis of cryogenic vessel with the high vacuum VD-MLI technology was obtained based on the ANSYS finite element software, and the distribution rule of therm al stress under thermal load and strength load was discussed. The result shows that the maxmum thermal stress occurs in the joint, which is between the upper head of inner vessel and the neck tube, and the thermal stress decreases along the direction of the joint between the vessel straight and the head, then, the circumferential thermal stress remained unchanged. The maximum thermal stress section was classified and studied based on the equivalent linearization method, and it shows that the strength of maximum thermal stress section meets the requirement.Finally, the leak-outgassing rate of interspace and the evaporation rate of the cryogenic vessel with the high vacuum VD-MLI were tested and measured on the basis of the testing device of BOG reliquefaction system, and the function correlations of the outgassing rate of the interspace with time under room temperature condition was obtained through fitting analysis. In addition, the heat-leak rate of cryogenic vessel was calculated by the measured evaporation rate, and the result is in accordance with the theoretical calculated heat-leak rate, so the validity and the rationality of the theoretical heat transfer analysis was further verified.In conclusion, the research results can provide the theoretical foundation for the structure optimization of the testing device of BOG reliquefaction system for cryogenic liquid and the design of the r efrigeration system, and lay the theoretical foundation and the experimental condition for the follow-up development of the study on the BOG reliquefaction technology of cryogenic liquids, it is also significant to the study on the ZBO storage technology of cryogenic liquid s.