Heat flux from 277 to 77 K through a few layers of multilayer insulation
✍ Scribed by Q.S. Shu; R.W. Fast; H.L. Hart
- Publisher
- Elsevier Science
- Year
- 1986
- Tongue
- English
- Weight
- 561 KB
- Volume
- 26
- Category
- Article
- ISSN
- 0011-2275
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✦ Synopsis
The insulating ability of a multilayer insulation (MLI) system, consisting of a few layers on an aluminium taped 77 K surface, was experimentally studied to understand quantitatively how thermal performance changes with the number of multilayers and vacuum level. This information can help to make design decisions trading-off the cost of material and installation manpower against liquid nitrogen consumption in many cryogenic applications. The ratios of the measured heat flux for different systems are: Q(painted) : Q(taped) : (2(5 layers) : Q(10 layers) : ~(20 layers) : Q(30 layers) = 1 : 0.19 : 0.06 : 0.037 : 0.027 : 0.022. The effective thermal conductivity also increases with the number of layers so only a marginal benefit can be gained in excess of 30 layers; for large liquid vessels 30-40 layers are recommended. The heat flux and temperature distribution in the MLI were also measured as functions of vacuum pressure. The temperature of the last layer is closer to the temperature of the warm box than that of the first layer is to the cold surface, even if the last layer is separated from the warm box and the first layer is in contact with the cold surface. The results and heat transfer mechanisms through MLI are analysed and discussed.