Heat transfer characteristics of straw-core paper honeycomb plates (beetle elytron plates) I: Experimental study on horizontal placement with hot-above and cold-below conditions

To develop functional sandwich plates (FHPs) and identify new ways to use straw, straw-core paper honeycomb plates (SHPs) were prepared. The mechanisms of the influence of the spatial distribution of various filling systems on the heat transfer performance of SHPs were investigated, and the following results were obtained. 1) The equivalent thermal conductivity (λE) of the three FHPs were significantly lower than that of the honeycomb plate (HP), and the λE of all the FHPs met or approached the requirements of high-efficiency heat insulation materials for envelope structures. Moreover, the λE values of the three FHPs were closest to each other at the upper and lower limits of the tested thickness. 2) The spatial distribution characteristics of the spherical particle and slender filling systems under natural filling conditions, their corresponding simple heat transfer models and the concept of divisional local radiative (DLR) heat transfer were presented for the first time. 3) The fundamental factor determining the magnitudes of the λE of the HP and FHPs was the presence of DLR in the core layer structures, and the heat transfer characteristics of the FHPs were the result of the combined actions of the DLR and filling material properties.