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ABSTRACT
For the development of functional honeycomb plates (FHPs) and efficient resource utilization of straw, based on the measurement of the equivalent thermal conductivity (λE) of paper honeycomb plates (HPs) and FHPs, including straw-core paper honeycomb plates (SHPs), under cold-left and hot-right conditions, the influence mechanism of the system geometry parameters on the convective heat transfer of HPs and the heat insulation performance of FHPs by fillers are discussed. The results are as follows. 1) Compared with the case of hot-above and cold-below conditions, the convective heat transfer ratio of HP increases substantially under cold-left and hot-right conditions. 2) The main heat transfer modes of the FHPs are radiative heat transfer between the wall (including the panel and side) and filling material and solid heat conduction in the filling material, supplemented by a small amount of heat conduction through air or local convection heat transfer in the void. 3) The higher the temperature is, the greater the FHP equivalent thermal conductivity, with little influence from the heat transfer direction. 4) It is relatively conservative to use the heat transfer effect of HPs and FHPs to evaluate that of beetle elytron plates (BEPs) and functional beetle elytron plates (FBEPs). This study lays a foundation for the application of multifunctional BEPs and HPs in building envelopes.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (Grant No. 51875102).
Disclosure
The authors declare that they have no conflicts of interest to report.
Nomenclature
| A | = | total area of the HP, m2 |
| Aa | = | area of the honeycomb wall, m2 |
| As | = | area of the honeycomb wall, m2 |
| D | = | diameter of the inscribed circle of the constant temperature wall, m |
| g | = | gravity, m⋅s−2 |
| Gr | = | Grashof number |
| h | = | thickness of the HPs, m |
| Nμ | = | Nusselt number |
| Pr | = | Prandtl number |
| Ra | = | Rayleigh number |
| T | = | temperature (K) |
| qR | = | radiation heat flux, W⋅m−2 |
| Greek | = | |
| α | = | air expansion coefficient, K−1 |
| σ | = | Stefan-Boltzmann constant, W⋅m−2K−4 |
| λE | = | equivalent thermal conductivity, W⋅m−1K−1 |
| λCv | = | convective equivalent thermal conductivity, W⋅m−1K−1 |
| λR | = | radiant equivalent thermal conductivity, W⋅m−1K−1 |
| λS | = | thermal conductivity of the honeycomb wall, W⋅m−1K−1 |
| λ0 | = | air thermal conductivity, W⋅m−1K−1 |
| ε | = | emissivity of the rear surface |
| ν | = | kinematic viscosity, m2⋅s−1 |
| Abbreviations | = | |
| BEP | = | beetle elytron plate |
| HP | = | honeycomb plate |
| HPHC | = | HP under cold-above and hot-below conditions |
| HPHH | = | HP under hot-above and cold-below conditions |
| HPV | = | HP under cold-left and hot-right conditions |
| HP8 | = | HP with a side length of 8 mm |
| HP16 | = | HP with a side length of 16 mm |
| FBEP | = | functional BEPs |
| FHP | = | functional honeycomb plates |
| FHPHC | = | FHP under cold-above and hot-below conditions |
| FHPHH | = | FHP under hot-above and cold-below conditions |
| FHPV | = | FHP under cold-left and hot-right conditions |
| GHP | = | FHP filled with granular insulation materials |
| SHP | = | FHP filled with straw |