A study of the thermal conductivity of granular silica materials for VIPs at different levels of gaseous pressure and external loads
2014 (English)In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 85, 199-211 p.Article in journal (Refereed) Published
Fast and reliable methods for the determination of thermal properties of core materials for vacuum insu-lation panels (VIPs) are needed. It is of great importance to know the thermal performance of a VIP core atdifferent levels of vacuum and external loads. In this study a new self-designed device, consisting of twocylindrical cavities connected to a Transient Plane Source instrument, is used to determine the thermalconductivity of low-density nanoporous silica powders, from atmospheric pressure down to 0.1 mbarwhile applying different levels of external pressure up to 4 bars. The study includes a brief theoreticaldiscussion of methods. The TPS is validated through comparison with available data for commercial silicaas well as through independent stationary measurements with a hot plate apparatus and with a TransientHot Bridge method. The different materials illustrate clear but different trends for the thermal conductiv-ity as a function of the level of vacuum and external pressure. The analysis of experimental results showsthat the transient methods are less suitable for measuring the thermal conductivity of low-density sil-ica powders, especially for the cases when the density is less than a limit at which the heat transfer byradiation becomes dominant compared to pure conduction.
Place, publisher, year, edition, pages
2014. Vol. 85, 199-211 p.
Vacuum insulation panels, Core material, Nanoporous silica aerogel, Thermal conductivity measurements, Transient and stationary methods, Hot plate apparatus, Transient Hot Bridge (THB) method, Transient Plane Source (TPS) method
Research subject Physics; Energy Technology
IdentifiersURN: urn:nbn:se:kth:diva-154072DOI: 10.1016/j.enbuild.2014.09.038ISI: 000348880900020ScopusID: 2-s2.0-84908338898OAI: oai:DiVA.org:kth-154072DiVA: diva2:755125
QC 201503102014-10-132014-10-132015-11-09Bibliographically approved