Heat Loads Due To Small Penetrations In Multilayer Insulation Blankets

[摘要] The main penetrations (supports and piping) through multilayer insulation systems for cryogenic tanks have been previously addressed by heat flow measurements. Smaller penetrations due to fasteners and attachments are now experimentally investigated. The use of small pins or plastic garment tag fasteners to ease the handling and construction of multilayer insulation (MLI) blankets goes back many years. While it has long been understood that penetrations and other discontinuities degrade the performance of the MLI blanket, quantification of this degradation has generally been lumped into gross performance multipliers (often called degradation factors or scale factors). Small penetrations contribute both solid conduction and radiation heat transfer paths through the blanket. The conduction is down the stem of the structural element itself while the radiation is through the hole formed during installation of the pin or fastener. Analytical models were developed in conjunction with MLI perforation theory and Fourier's Law. Results of the analytical models are compared to experimental testing performed on a 10 layer MLI blanket with approximately 50 small plastic pins penetrating the test specimen. The pins were installed at ∼76-mm spacing inches in both directions to minimize the compounding of thermal effects due to localized compression or lateral heat transfer. The testing was performed using a liquid nitrogen boil-off calorimeter (Cryostat-100) with the standard boundary temperatures of 293 K and 78 K. Results show that the added radiation through the holes is much more significant than the conduction down the fastener. The results are shown to be in agreement with radiation theory for perforated films.

[发布机构] Glenn Research Center, Cleveland; OH; 44135, United States^1;Sierra Lobo, Cryogenics Test Laboratory, Kennedy Space Center, FL; 32899, United States^2;Cryogenics Test Laboratory, Kennedy Space Center, FL; 32899, United States^3

[效力级别] 物理学 [学科分类] 材料科学（综合）

[关键词] Boundary temperature;Cryogenic tanks;Degradation factor;Experimental testing;Lateral heat transfer;Multi-layer insulation;Solid conduction;Structural elements