ISSN:
1432-0657
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mathematics
,
Natural Sciences in General
Notes:
Abstract We determined the flow properties of powders used as thermal insulative materials at different temperatures, pressures and moisture conditions. The powders used in this study, SiO2-aerogel, precipitated and fumed silica, have primary particle sizes ranging from a few nanometers to hundred micrometers. Due to the porosity of the particles and/or their large interparticular forces compared to their weight, the powders have very low densities (about 100 kg/m3). Therefore they display very small solid thermal conductivities in the order of 1 to 2 · 10−3 W/(m K) and thus are promising as evacuated thermal insulants. In addition these powders are resilent to external loads. A prerequisite for the use of these powders in technical applications is the determination of their flow properties. For this purpose the powder samples were filled into a stainless steel hopper and the flow rate through the bottom opening was measured using a balance. Simultaneously, the resulting angle of repose was determined. The hopper can be heated up to 200°C to remove adsorbed water and gases from the inner surface of the powder. The measuring device was mounted into a vacuum chamber in order to determine the influence of atmospheric humidity or gas pressure (pressure variation from 30 to 105 Pa).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s100350050031
