Abstract: Low thermal conductivity, small additional mass and good mechanical strength are basic requirements for the thermal insulation of liquid hydrogen and liquid oxygen tank on the rocket. Polyurethane (PU) foam is the most widely-used material in the insulation of the cryogenic tank in rocket due to its light mass, good thermal and mechanical performance. However, long-time exposure to large temperature gradient will incur additional mass due to moisture uptake, which also deteriorates the thermal performance. Thus it is important to determine the exact additional mass for the design of the rocket thrust. This paper designs an experimental apparatus for the test of PU foam specimen, one side of which is cooled to about 45 K and another is exposed to temperature controlled at 30°C and relative humidity of > 95%. Two home-made pulse tube coolers are used to provide the cooling power, which are installed on a vacuum room. Totally 4 groups with each 2 specimens are tested, and the data are compared to the test results at temperature of 78 K. The results reveal that the effects of cryogenic pump for 78 K and 45 K on one side have no effects on the moisture uptake and the butt-jointed structure.

Key words: foam, absorption, mass transfer, experimental validation, pulse tube cooler

摘要： 为减少火箭上液氢/液氧燃料蒸发损失，要求绝热材料热导率小，附加质量轻，并有好的抗应力强度。泡沫塑料因其密度低、绝热性能及机械强度好等优点，是国内外最广泛使用的火箭上深低温系统绝热材料。但泡沫塑料长时间存在大温度梯度时，将强化吸湿增重，从而增加火箭起飞附加质量，也恶化绝热效果。因此，获得可靠的泡沫塑料吸湿增重数据对大推力火箭推力设计有重要意义。报告了用脉管制冷机冷却的泡沫塑料吸湿增值实验装置及实验结果。利用两台自行研制的GM型单级脉管制冷机提供冷量，样本一面被冷却到约45 K温度，同时另一面暴露在30℃恒温及>95%的相对湿度环境。设计了一种波纹管结构来减少环境对真空低温系统的漏热。总共测试了4组8个样本，测试时间为7 h。测试结果与液氮温度的测试结果进行对比和分析，结果发现两者吸湿增重相同，即温度梯度降低引起的低温泵增强效应在该温区可忽略不计。同时发现样本搭接结构对吸湿增重没有影响。

关键词: 泡沫, 吸收, 传质, 实验验证, 脉管制冷机