Effect of pressure holding time of extraction process on thermal conductivity of glassfiber VIPs

Vacuum insulation panels (VIPs) are regarded as the most promising high-performance thermal insulation products on the market today. A high and stable vacuum state within VIP enclosure provides a durable service life for VIP. In this paper, multiple core material layers (CMLs) with thickness of 0.5 mm, 1 mm, 3 mm, and 7 mm were formed as the core of glassfiber VIPs. The microstructure of the core materials and thermal conductivity of as-prepared VIPs was investigated. The porosity of the core materials was about 90% while the mean pore diameter was about 10∼25 μm. At adopted pressure holding time of extraction process of 180 s, the initial total thermal conductivity of VIPs was lower than 4 mW/(m K) and slightly increased with total thickness of core material, but increased greatly with CMLs thickness. Mass transfer characteristics within core material during extraction process was analyzed based on the interlayer-microstructure model. Residual gases within VIPs were mainly extracted from the connected gas flow channel built by glass fibers. The optimum pressure holding time for VIPs with 0.5 mm-thickness, 1 mm-thickness, 3 mm-thickness, and 7 mm-thickness CMLs was 300 s, 240 s, 240 s, and 180 s, respectively.