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ISSN Online: 2377-424X

ISBN Print: 0-85295-345-3

International Heat Transfer Conference 10
August, 14-18, 1994, Brighton, UK

THERMAL TRANSPORT IN NANOSTRUCTURED POROUS MATERIALS AND THEIR OPTIMIZATION AS THERMAL SUPERINSULATORS

Get access (open in a dialog) DOI: 10.1615/IHTC10.1840
pages 223-232

摘要

The contributions from gaseous and solid thermal conduction as well as from radiative transport in highly porous nanostructured materials are quantified. We describe the correlation of these contributions with the structural features of aerogels: the gaseous conductivity can be decreased by reducing the pore size; the solid thermal conductivity can be influenced via the connectivity and the bond strength within the gel network and thus can be correlated with the sound velocity of the specimen; the radiative transport depends on the absorption of the building groups in the gel and the absorption/ scattering properties of added opacifiers. Detailed understanding of the heat transfer mechanisms has allowed us to make monolithic opacified Si02 aerogels with an extremely small total thermal conductivity of only 0.012 Wm−1 K−1 at 300 K in air; in this case the contribution from the gaseous thermal conduction is 0.007 Wm−1 K−1, from the solid thermal conduction 0.004 Wm−1 K−1 and from the radiative thermal conduction 0.001 Wm−1 K−1, Such aerogels can be considered highly effective and environmentally favorable substitutes for conventional insulants.