Study On Structural Optimization For Further Improvement In Thermal Insulation Property Of Cryogenic Insulated Cylinder

As special cryogenic liquid storage and transportation container, the cryogenic insulated cylinders are widely used in many fields, especially in the machinery, chemical industry, and national economy areas to replace the high pressure gas cylinders for supplying industrial gasses. The structure is more complicated compared with ordinary pressure vessel because of the pressured storage and transportant. The thermal insulating properties and security is an assurance of efficiency and operational reliability.The study onheat transfer mechanism, stress analysis and reasonable effective optimization method for thermal insulating construction is of theoretical significance and practical,andestablishing rational evaluation standards of thermal insulating properties have important significance on promoting the development and application of cryogenics technology.Therefore,the heat transfer models and thermal-mechanical coupling model established in this thesis by guidance of heat transfer theory, numerical analysis and theory of finite element anylysis, and the finite element analysis software of ANSYS has been utilized to analyzethe constructionoptimization forthermal insulating constructionof cryogenic cylinder. Further exploration for influence factors and correction relation of daily evaporation rate is also made in this thesis. Several studies of this thesis are summarized as follows:(1) As an important support structure between inner and outer vesselin cryogenicinsulated cylinders,the heat flux from the outside environment through the neck tube into the cryogenic liquid occupies a great proportion of the total heat leak and can be more than half of the total heat loads. By using the mothed of experimental combined the simulation, the steady-state conduction model and conjuage heat transfer model have been established, andthe performance deviation compared with experiment results is within8.91% and 5.66% respectively. The more cryongenic liquid filled, thehigher the accuracy.So considering the effect of practicality and computational efficiency, the accuracy of steady-state conduction model is high enough for heat transfer through necks. The necks of cryogenic cylinder with height-to-diameter ratio of 2.61 and 1.94 have been analyzed basing on that model.(2) The thermal-mechanical coupling modelhas been establishedbasing on structural properties of cryogenic cylinder. The thermal stresses of cryogenic cylinder with height-to-diameter ratio of 2.61 and 1.94 under the static load and impact load have been analyzed respectively.The position with the highest stress level has been confirmed which is along theedge of opening on head, and the root of neck tube becomes the weakest link. The tress classification of discontinuity stress in most dangerous section has been also analyzed byusing the method of equivalent linearization.(3) The optimization analysisof neck tube is based on the above two models ofsteady-state conduction model and thermal-mechanical coupling model.The effect of dimensionless parameters with h/H,d/D andδn/δon heat flux through the necks and the max thermal stress have been researched, so the optimization analysis of neck is reviewed from two aspects of heat transfer and strength to find out the optimaldimension parameter. And the importance of opening reinforcement has been discussed.The study result has guiding significance for design and application of cryogenic cylinders.(4) As an important technology parameter to evaluate the thermal insulating properties of cryogenic cylinders, daily evaporation rate which is attracting more attention can intitively reflect the thermal insulating properties of cryogenic cylinders, so the accurate measurement and calculation of daily evaporation rate for cryogenic cylinders is very important. This thesis researches the influencing factores of daily evaporation rate which includes environmental temperature, environmental pressure and liquid height by using numerical simulation mothed and experimental.And the more accurate more reasonable correction methods are put forward to calculate daily evaporation rate which can provid the data support for revision of national standard GB 18443《Testing method of performance for vacuum insulation cryogenic equipment-Part 5: Static evaporation rate measurement》The research method and conclusion of this thesis makes design of cryogenic cylinders more rational, and provides theoretical basis and engineering value for design and application of cryogenic cylinders.