Aerogel-Based Cryogenic Superinsulation

Abstract

This paper presents the development of a flexible, easy-to-use superinsulation. The innovative material system employs ultralow density aerogels within a flexible fiber matrix for minimum heat transfer and maximum applicability and durability. The core of the system is aerogels formed at the fiber-fiber contacts of the matrix, forcing solid conduction to occur through the aerogels. This composite configuration improves both the ease of handling aerogels and the overall thermal resistance. The close-packed structure of the aerogels also eliminates the open spaces in the fiber matrix and thereby reduces gas conduction. Excellent thermal resistance was achieved for both evacuated and nonevacuated insulation systems while maintaining structural flexibility. The aerogels were also produced in an opacified fiber matrix. Testing of these composites indicated a significant inhibition of radiation in the infrared range. Thermal performance was measured by transient heat flux and liquid nitrogen boiloff methods. The apparent thermal conductivity of the silica-aerogel/fiber composite was lower than 1 milliwatt per meter-kelvin (mW/m-K) at a high vacuum level [below 1×10⁻⁵ millibars (mbar)] and below 10 mW/m-K in ambient pressure nitrogen (boundary temperatures were approximately 77 K and 280 K for all tests). Performance was found to be insensitive to residual gas pressure up to a vacuum level of about 1×10⁻¹ mbar. Aerogel-based superinsulation systems have been produced and tested in blanket, sheet, and clamshell forms for use on a variety of cryogenic equipment.