Predicting the conductive heat transfer through evacuated perlite based vacuum insulation panels

Abstract

© 2021 The Authors. The core material contributes ≥40% of the total cost of a fumed silica based vacuum insulation panel (VIP). Expanded perlites, which come at approximately one-tenth of the current price of fumed silica, have been identified as potential core material candidates. Though, the characteristic vacuum insulation properties i.e. evacuated thermal conductivity and half pressure value of expanded perlites are not suitable for most applications, these can be improved by altering their structural properties like particle size, pore size, porosity etc. during manufacture. The knowledge of the relationship between structural properties and the thermal conductivity of perlite is key to develop improved thermal performance VIPs.

In the present work, it has been found that the thermal conductivity of the perlite cores lies between the thermal conductivities of two regular packing orders – simple cubic packing and the hexagonal close packing. Owing to the complex geometries involved, the thermal conductivity of particle beds arranged in these two packing structures was numerically calculated using finite element method. The dependence of the thermal conductivity on five parameters (particle size, intra-particle pore size, porosity, internal gas pressure and contact ratio) was observed and correlated with existing studies in literature. The model was also validated by experiments performed on expanded perlite. The developed framework can be employed to produce bespoke perlites for most cost-effective thermal insulation systems.