Development of Vacuum Super Insulations with Glass Cover and Powder Filling

Abstract

An evacuated thermal insulation panel has been developed consisting of glass panes as covers and a powder filling. Several powder materials and mixtures of powders have been tested regarding their thermal conductivity and the critical gas pressure for the onset of gas conductivity. With an opacified precipitated silica powder a thermal conductivity of less than 0.003 W/mK could be reached if evacuated below 0.1 mbar. A value of 0.004 W/mK has been measured at an internal gas pressure of 1 mbar. A crucial point of panel design is the rim seal which should provide a negligible gas permeation and a small thermal heat transfer coefficient. With very thin stainless steel foils these requirements could be met.