Thermal Conductivity and Compressive Strain of Aerogel Insulation Blankets Under Applied Hydrostatic Pressure

Abstract

Aerogel is among the best solid thermal insulators. Aerogel is a silica gel formed by supercritical extraction which results in a porous open cell solid insulation with a thermal conductivity as low as 0.013W∕mK. Aerogels have a wide range of uses such as insulation for windows, vehicles, refrigerators∕freezers, etc. Usage for aerogel can be extended for use where flexibility is needed, such as apparel, by embedding it into a polyester batting blanket. These aerogel blankets, although flexible, have little resistance to compression and experience a residual strain effect upon exposure to elevated pressures. It was suggested, by Aspen Aerogels Inc., that a prototype aerogel blanket would have increased resistance to compression and minimized residual strain upon exposure to elevated pressures. Samples of prototype and normal product-line aerogel insulating blankets were acquired. These materials were separately tested for thermal conductivity and compressive strain at incremental pressure stops up to 1.2MPa. The compressive strain of the prototype aerogel blanket reached a level of 0.25mm∕mm whereas the product-line aerogel blanket compressed to 0.48mm∕mm at 1.2MPa. Before compression, the thermal conductivity of the prototype aerogel blanket was slightly higher than the product-line aerogel blanket. During compression the thermal conductivity increased 46% for the product-line aerogel blanket whereas it increased only 13% for the prototype aerogel blanket at 1.2MPa. The total thermal resistance decreased 64% for the product-line aerogel blanket at 1.2MPa and remained at that value upon decompression to atmospheric pressure. The total thermal resistance of the prototype aerogel blanket decreased 33% at 1.2MPa and returned to within 1% of its initial value upon decompression to atmospheric pressure. It was found that the prototype aerogel blanket has approximately twice as much resistance to hydrostatic compression to a pressure of 1.2MPa and also recovers to its original state upon decompression. The thermal resistance of the prototype aerogel blanket remained 37% higher than the product-line aerogel blanket at 1.2MPa. This resistance to compression and the ability to recover to its original state upon decompression from elevated pressures makes the prototype aerogel blanket suitable for applications where high insulation, resistance to compression, and recovery after a compression cycle is needed.