基于火积分析的低温管线绝热支撑漏热输运过程控制和实验研究

Cryogenic transfer line is one of the key components of large scale hydrogen and helium refrigerator, and its support results in serious heat leak and heat penetration. First, the expression of "thermal insulation least entransy dissipation principle" for thermal insulation research is derived from the model of the maximum entransy dissipation principle which is an important component of the entransy dissipation extremum principle. Further, the bi-objective topology optimization is performed to investigate the heat leak of the supports, and the bi-objective is the consolidation of "thermal insulation least entransy dissipation principle" and realization of strength maximization. And the research puts emphasis on optimization of parameters such as support shape, hole shape, number and distribution. By obtaining the optimized support shape, passive governing on transport process of heat leak arising in the support is achieved. The method of measurement of the boil off rate of cryogenic liquid and thermal balance is engaged to validate the optimized support shape. Bi-objective design criteria of the heat leak process adaptive to liquid hydrogen and helium temperature region is expected. Last, the study not only improves the efficiency of large scale hydrogen and helium refrigerator, and paves the way for optimization of spacers between radiation shield layers, multilayer insulation in dewar and tank, but also provides cryogenic experimental data for the heat mass theory and thus extends its reaches.

低温管线是大型氢、氦低温系统的关键部件之一，其绝热支撑会造成严重的漏热损失和热穿透。将火积耗散极值原理中的最大火积耗散原理的表述改进为适合于绝热性能研究的"绝热最小火积耗散原理"。以该原理和强度最大化为双目标对绝热支撑的漏热过程进行拓扑优化，重点研究支撑的形状、开口形状、数量和空间分布等因素，得到优化的绝热支撑结构，从而实现对该输运过程的被动热控，减少漏热。运用低温液体蒸发法和热平衡法对优化结构进行实验验证。力争形成适用于液氢液氦温区的漏热过程双目标优化设计准则。研究成果不仅可以提高大型氢、氦低温制冷机的效率，对多层材料间隔物结构优化、杜瓦类和贮槽类真空多层绝热结构漏热优化等问题具有指导意义，而且可以为热质理论积累低温实验数据，拓展其适用范围。

深入研究了低温真空条件下，以“绝热最小火积耗散原理”和强度最大化为优化目标的低温管线绝热支撑的双目标拓扑优化问题，在不考虑辐射和等厚度假设下，以“绝热最小火积耗散原理”为优化目标，提出了绝热支撑的拓扑重构方法，提出了以六面体结构为主体而金字塔结构和四面体结构为补充的绝热支撑拓扑重构方法。进行了绝热支撑的拓扑优化，得到了包括开口形状、数量和空间分布等在内的双目标约束条件下的绝热支撑优化结构，当低温管线内径d/外径D<0.43时，绝热支撑的优化结构是带一些通孔的正三角体并且与外管接触处存在60度豁口；当低温管线d/D≥0.43时，绝热支撑的优化结构是带一些通孔的长着三个尖角的环形并且与外管接触处存在60度豁口。现场实测某4K装置绝热支撑的漏热量约为6W@4.5K/个，合8.2kW/个的功率损失。搭建了低温管线漏热过程测定试验平台，运用低温液体蒸发法进行了实验验证。得到了适用于液氢液氦温区的漏热过程双目标优化设计准则。. 提出了适用于氦气Brayton制冷循环的有限时间热力学模型。研究表明，与空气Brayton制冷循环区别：（1）最大热导分配（90.7%）出现在冷箱内的第一级和第二级换热器而不是高温热源换热器和低温热源换热器；（2）存在氦气旁路；（3）存在内纯化器；（4）氦气的比热等参数在循环过程中呈现强烈的非线性。得到了制冷量和性能系数（COP）解析解，解析解是分段函数。提出了“低温吸附温深”的概念。试验验证了该模型，误差不大于7.6%。分析了包括质流率、压机透平效率、低温吸附温深等参数对制冷量和制冷效率的影响。. 设计并搭建了试验台研究接触热阻，该试验台运用稳态法测定样件的接触热阻。对辐射的影响，得到了试验数据，计算表明真空多层绝热结构（MLI）的温度范围对应的热辐射波长范围，与“Saharan银蚁效应”提高电磁波的发射率的波长作用范围一致，即2-16µm。提出了基于“Saharan银蚁效应”的仿生被动热控技术的关键结构——仿生中空三棱体阵列，对仿生中空三棱体单体内部的散射输运过程进行了解析研究。