Analytical model for the thermal conductance of compound honeycomb transparent insulation, with experimental validation

This article extends a first-principal analytical model for the heat transfer across a convection-suppressing honeycomb to the case where an air gap is left between one of the plates bounding the honeycomb and the honeycomb itself. The leaving of such an air gap (for example between the absorber plate and the honeycomb in a honeycomb solar collector) has been shown to dramatically increase the honeycomb's insulative effect, by helping to decouple the radiative and conductive heat transfer modes. The model is based on analyzing an isolated honeycomb cell, by invoking the exponential approximation to the relevant “ring-to-ring” specular view factor as well as linearizing of the 4th power temperature dependence of radiant heat transfer. This article gives the solution for the heat transfer in terms of the elements of an 8 × 8 matrix, which must be inverted to obtain the heat transfer. Comparison between the predictions of the model and 132 experimental measurements of the heat transfer show agreement to within a maximum error of 15% and a mean bias error of 6%.