The effect of drying condition of glassfibre core material on the thermal conductivity of vacuum insulation panel

Vacuum insulation panel (VIP) core materials were successfully fabricated by wet method. The density of VIP core material was 177 kg/m3, while the porosity was 92%. The average tensile strengths of glassfibre core material layer samples in longitudinal and transversal direction were 575 and 503 N/m, respectively. The phase composition, chemical composition, and microstructure of the core material and thermal conductivity of as-prepared VIPs were investigated. Convection drying characteristics of VIP core materials were determined using heated ambient air at temperatures from 30 °C to 110 °C, 130 °C, 150 °C, and 170 °C and hold the temperatures for 30 min and 60 min, respectively. The moisture and heat transfer characteristics within the VIP were analyzed based on the multiphase medium model. Drying at 150 °C for 60 min showed complete drying characteristics and the VIPs thereof showed a low and stable thermal conductivity. Reducing the drying temperature or lowering the drying time could greatly damage the thermal insulation ability of the VIPs. Overheating and longer heating time had little effect on shortening complete drying time but creating huge energy consumption. In order to get a better drying condition, the pores within the core material should be well distributed and the pore size ought to be uniform.