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Study of Getter Absorbing Performance in High Vacuum Multilayer Insulation Cryogenic Vessel

Author: XieSiWei
Tutor: WangRongShun
School: Shanghai Jiaotong University
Course: Refrigeration and Cryogenic Engineering
Keywords: adsorbent adsorption isotherm equilibrium pressure adsorption capacity high vacuum multilayer insulation liquid nitrogen temperature
CLC: TB658
Type: Master's thesis
Year: 2013
Downloads: 92
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Abstract

With the continuous development of cryogenic technology, highvacuum multilayer insulation has been widely used in the field ofcryogenic storage and transportation because of its excellent heatinsulation performance. In order to achieve good insulation purpose, thesandwich vacuum must keep above10^-2Pa. However, leakage of inner andouter barrel and deflation of metal and insulation material would lead toreducing of sandwich vacuum, which would influence cryogenic vessel’sinsulation performance. Getter in the sandwich plays an important role ineffectively maintaining sandwich vacuum, and sandwich vacuum lifedepends largely on the characteristics and charging weight of getter andwhether the getter can give full play to its role and so on. A lot of researchshows that residual gas in high vacuum multilayer insulation vesselsandwich mainly are N₂and H₂and so on, therefore, It has an importantmeaning to study different getter’s N₂and H₂adsorption properties indifferent charging condition, which can help to choose getter reasonably、 calculate charging weight accurately and make getter play its full role.In this paper, activated carbon、carbon filled paper and5A molecularsieve’s suction performance are investigated, their N₂and H₂adsorptionperformance in the temperature of77K are stress tested and analyzed,adsorption isotherms at the range of10^-4-10Pa are obtained and fitted. Thispaper also test the influence of multilayer insulation on adsorbent’s suctionperformance. Results indicate that all of the three kinds of adsorbent havea good N₂adsorption capacity but a poor H₂adsorption capacity, andmultilayer insulation package or not has great influence on three kinds ofadsorbent’s suction performance.Because activated carbon、carbon filled paper and5A molecularsieve’s H₂adsorption capacity are all too small in77K, this paper testedPdO’s H₂adsorption performance which has a good H₂adsorption capacity,obtained PdO’s H₂adsorption isotherm and fitted curve at the range of10^-4¹0Pa. This paper also tested the influence of packing PdO on its H₂adsorption performance. Results show that PdO’s H₂adsorption capacity ismuch bigger than activated carbon、carbon filled paper and5A molecularsieve’s. At different equilibrium pressure, PdO’s H₂adsorption capacity isdozens of times as much as carbon filled paper’s, and hundreds of times asmuch as activated carbon and5A molecular sieve’s. PdO’s H₂adsorption capacity without package is about1.5times as much as that of PdO withpackage.PdO has a good H₂adsorption performance and can meet the H₂adsorption requirement in high vacuum multilayer insulation sandwich, butthe high price of PdO go against its large scale application and productioncost reduction. Hence, after a lot of experimental tests, author propose anew type H₂adsorbent—copper oxide powder, and design a external highefficiency hydrogen removal device which can be used in high vacuummultilayer insulation sandwich. After the testing of CuO’s H₂adsorptionperformance in high vacuum multilayer insulation sandwich, and thefollowing conclusions can be reached:（1）CuO is a brand new type of H₂adsorbent which can be used in high vacuum multilayer insulationsandwich. In the condition of about200℃, CuO can produce chemicalreaction with residual H₂in high vacuum multilayer insulation sandwich,then obtain the purpose of removing residual H₂, and the generated H₂Ocan be adsorbed by5A molecular sieve.（2）when used with5A molecularsieve, CuO has a excellent H₂adsorption capacity which can closelyachieve the theoretical value of chemical reaction, and CuO’s H₂adsorption capacity is far much larger than that of the other four kinds ofadsorbent. CuO’s H₂adsorption speed is very fast and can make sandwich’s pressure which has thousands of palmer H₂drop to10-3Pa in ashort time. CuO’s H₂adsorption capacity focuses on within10-3Pa whichcan meet high vacuum multilayer insulation sandwich’s vacuumrequirement adequately.（3）CuO’s H₂adsorption performance is muchmore excellent than that of activated carbon、carbon filled paper、5Amolecular and PdO，and CuO’s price is very cheap. Though CuO’s H₂adsorption must be under the condition of about200℃, a special hydrogenremoval device installed outside of high vacuum multilayer insulationvessel can solve this problem effectively.

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