【作者】 周志雄；

【导师】 汪荣顺；

【作者基本信息】 上海交通大学 ， 制冷与低温工程， 2007， 硕士

【摘要】 被称为“超级绝热”的高真空多层绝热技术的研究热浪始于上个世纪六十年代。此后,由于层间固体接触导热及残余气体传热等问题难以得到满意的解决,研究步伐开始逐渐放慢。本文尝试着突破以上所提到的研究瓶颈,并在前人研究的基础之上,提出了多层材料中理想传热模型,用牛顿迭代法计算了国外和本文实验中测量的高真空多层绝热材料,数值计算出绝热层最小比热流,从而能够更好比较工程应用中不同高真空多层绝热层的绝热性能。文章首先简介了高真空多层绝热技术研究的历史和现状,然后讨论了高真空多层绝热计算中理论模型、接触导热的理论模型和高真空多层绝热层中的固体接触导热,进而针对层间固体接触导热计算这一难点,提出一个层间固体接触导热、残余气体传热和辐射传热三种传热途径相分离的逐层实际传热模型,通过将层间固体接触导热计算中众多不可精确测量的因素的影响归于接触面积比f的方法,间接的解决了层间固体接触导热计算的难题。利用所建立的模型,可以很方便的得到三种层间传热途径的传热量在总传热量中所占的比重,这对于生产实际无疑是十分有意义的。计算模型分析实验数据表明,模型计算的比热流和层间温度分布与实验测量结果相吻合,比热流计算误差可控制在10%以内。这表明本文提出的数值计算模型用于分析高真空多层材料中的传热是可行的。为探索改善工程应用中高真空多层绝热层绝热性能的方法,本文实验研究中首先测量了包扎在实际低温储罐上不同结构的高真空多层绝热层的绝热性能,并分析了环境温度、环境压力,层数、不同隔热材料的组合等因素对工程应用中的高真空多层材料绝热性能的影响;然后利用多层绝热层中的低温真空环境测量5层干法纸在不同温度区间内的表观导热系数,在有限实验数据的基础上用牛顿迭代数值拟和出计算5层干法纸表观导热系数的经验公式,对比经验公式计算值和实验测量值,发现二者的误差在10%以内,因此在工程应用中可用本文的经验公式计算干法纸在低温下的导热系数。最后在忽略5层干法纸间残余气体导热和单层薄干法纸本身固体导热基础上,计算和分析多层干法纸接触界面在低温真空下的接触热阻,其大小与国外实验测量值接近。更多还原

【Abstract】 The peak of R&D movement of multi-layer insulation (MLI), the so-called“super insulation”, began in 1960s. However, due to the hardness of solving questions of interlayer solid heat conduction and residual gas conduction, the pace of research has been slowed.This thesis tries to solve the two questions mentioned above, so the breakthrough in theoretical research could facilitate the utilization of MLI in practical engineering. Firstly, an ideal heat transfer model is proposed,(namely,in this model,only radiation heat transfer occurs in ideal multilayer insulation which the reflector is installed without spacerand contact)by using this model,the smallest limit of real multilayer insulation can be numerically calculated through Newton interative method,so the better comparison of insulating efficiency among different real multilayer insulation becomes feasible; Secondly a layer-by-layer heat transfer model based on separation of three ways of heat transfer inside layers (that is, solid contact conduction, residual gas conduction and radiation) is built. Through summing up all the unknown influences of diversified factors related with solid contact conduction to a coefficient of“f”, which stands for the ratio between actual contact area and nominal contact area between two contacting solids, the model gets the calculated total heat flux and corresponding heat flux of solid thermal contact conductance, radiation and residual gas conduction, the results indicate that the errors are within 10%, which undoubtedly proves the validity of this model. At the same time, the calculated temperature distribution of shields is coincided with the experimental results.Next focus is experimental study of different multilayer insulation and effective thermal conductivity of fiber sheets .First by testing the practical multilayer insulation in a cryogenic tanker, which is the carilometer in my paper,some affecting factors on multilayer insulation are analysed, then by using the low-temperature and vacuum environment caused by multilayer insulation, the effective thermal conductivity of multiple fiber paper with 5 layers is tested.Through Newton interativemethod,an empirical formula is deduced to computer the thermal conductivity of fiber paper,The errors between experimental thermal conductivity and the calculated conductivity by empirical formula are below10%,so the formula of fiber conductivity can be applied to practical enginnering. Finally, based on the assumption that the thermal contact resistance is much larger than other thermal resistance caused by gas conduction and bulk solid conduction among the fiber sheets, the thermal contact resistance at the interface of two layers of fiber paper is calculated, the results are comparable with other experimental results in the literature.更多还原