CALCULATION PROCEDURE FOR COLLECTORS WITH A HONEYCOMB COVER OF RECTANGULAR CROSS-SECTION

For a highly efficient collector with honeycomb cover an optimisation procedure has to take into account a lot of parameters like material choice, geometric dimensions, cell wall thickness, and aspect ratios of the honeycomb. An approximate, but comprehensive theoretical description of the optical properties and the heat transport within a honeycomb absorber system is given and discussed in the paper. Selective absorbers and air gaps with convecting air can be treated within the model. Solar transmittance and heat transport are treated with a consistent model, which in principle needs only film data and the geometric parameters as input. Theoretical results compare quite favourably with experimental data from honeycomb structures. The main innovative features of the model are its use of an effective optical thickness, and the inclusion of both, convective boundary conditions and solar absorption, in a coupled mode analysis leading to an analytical solution.