Experimental characterisation and evaluation of the thermo-physical properties of expanded perlite—Fumed silica composite for effective vacuum insulation panel (VIP) core

The thermo-physical properties of expanded perlite-fumed silica composites were experimentally investigated as an alternative lower cost material for vacuum insulation panel (VIP) core using expanded perlite as a cheaper substitute of fumed silica. Pore size analysis was carried out using nitrogen sorption technique, mercury intrusion porosimetry and transmission electron microscopy and average pore size was estimated to be in the range of 50–150 nm. VIP core board samples measuring 100 mm × 100 mm and consisting of varying proportions of expanded perlite, fumed silica, silicon carbide and polyester fibre in the composite were prepared. The centre of panel thermal conductivity of the core board containing expanded perlite mass proportion of 60% was measured as 53 mW m−1 K−1 at atmospheric pressure and 28 mW m−1 K−1 when expanded perlite content was reduced to 30%. The centre of panel thermal conductivity with 30% expanded perlite content was measured as 7.6 mW m−1 K−1 at 0.5 mbar pressure. Radiative conductivity of the composite with expanded perlite mass of 30% was measured to be 0.3–1 mW m−1 K−1 at 300 K and gaseous thermal conductivity 0.016 mW m−1 K−1 at 1 mbar, a reduction of 8.3 mW m−1 K−1 from the value of gaseous thermal conductivity at 1 atm pressure. Opacifying properties of expanded perlite were quantified and are reported. A VIP core cost reduction potential of 20% was calculated through the use of expanded perlite in VIP core.