A coupled model of finite element method and Mie theory for heat transfer inside expanded perlite vacuum insulation panels (VIPs) at high temperatures

The present study introduces the first coupled model of the finite element method and Mie theory that predicts the heat transfer mechanism inside the expanded perlite vacuum insulation panels at a temperature range of 300-800 K. The finite element method is applied to discretise the governing equation of the steady state heat transfer and the three-dimensional Fourier's law is used. COMSOL Multiphysics is the finite element numerical solver which predicts solid and gaseous thermal conductivity inside the VIPs. Moreover, Mie theory predicts the radiative conductivity. Heat transfer radiation is superimposed on the heat transfer through conduction. The model is capable of predicting total thermal conductivity of VIPs at high temperatures >= 500 K, which makes it a unique model with clear advantage over previously developed numerical models. The numerical predictions of the developed coupled model are validated experimentally. The predictions of the coupled model are in good agreement with the experimental measurements, which indicate the capability of the developed model to predict the mechanisms of heat transfer at high temperatures. For instance, the values of total thermal conductivity for numerical prediction and experimental measurement, at 557 K, are 14.6 and 14.7 +/- 1.2 mW/m/K, respectively, excellently agreeing within +/- 8.9 %.