Coupled radiative and conductive thermal transfers across transparent honeycomb insulation materials

Combined radiative and conductive heat transfer across transparent, square-celled, honeycomb insulation is investigated. The governing equations for one-dimensional heat transfer are formulated using an exponential kernel approximation. The resulting non-linear equation is linearised by least-squares approximation and solved analytically. Computational results for conductive, radiative and total heat transfers through the transparent insulation material (TIM) of three bounding plate conditions: black-black, selective-black and selective-selective are presented. For the case of selective bounding plates, there is a strong coupling of conductive and radiative heat transfer because of the intermediate wall emissivity of the TIM. The effect of cell aspect ratio, wall emissivity and the absorber temperature on the total heat transfer is also studied and it is pointed out that the following configurations of TIM have the lowest heat loss coefficients: (1) TIM with black end plates and cellular walls of high emissivity; (2) TIM with selective end plates and cellular walls fully transparent to IR radiation.