Modelling of the mechanisms of heat transfer in recycled glass foams

Abstract

Glass foams are highly sustainable materials with enormous potential to replace traditional thermal insulators. Current research on glass foams is focused on improving thermal insulation by reducing density, but this is somehow a limited approach. Selecting the best approach to reduce thermal conductivity relies on establishing a detailed knowledge on the heat transfer mechanisms playing the most significant role. We have studied the mechanisms of heat transfer in a set of cathode-ray-tube (CRT) panel glass foams. The influence of relative density, cellular structure, gas composition, glass distribution between cell walls and struts, and radiation on heat transfer is addressed. From a detailed characterisation and state-of-the-art models, we have created a new analytical model adapted to the peculiarities of the foams under analysis. Additionally, the thermal conductivity for varying temperature conditions has been predicted. The obtained results point out to a significant contribution of the heat transfer by radiation for foams with porosities higher than 0.96. The predicted values of thermal conductivity indicate the existence of a plateau region at high porosities. Temperature is proven to shift the contributions of heat transfer, increasing the weight of radiation and gas conduction. The predictions of the new analytical model have been contrasted with experimental measurements of the thermal conductivity at different densities and temperatures obtaining differences below 2%.