Effect analysis of edge layers on volumetric radiative properties of nickel foams

This study aims to analyze the effect of edge layers on the volumetric radiative properties of open-cell nickel foam based on a three-layer structure model composed of two edge layers and one complete layer. Pore-scale simulation was performed for five nickel foams with typical structural parameters, using their component optical properties and reconstructed digitalized foams. First, the ligament morphology of foam samples was rebuilt and the optical properties of rough ligament surfaces were predicted with the finite difference time domain method. Then, pore-scale radiative transfer models were established which absorption and scattering were computed using Monte Carlo Ray-Tracing (MCRT) method. Afterwards, the size of representative elementary volumes was determined, and it illustrates that at least three foam cells in the thickness of a foam structure are required to characterize volumetric radiative transfer. Moreover, the MCRT results show that accounting for the existence of edge layers, the extinction coefficients were underestimated by 7% for 20PPI nickel foam and 13% for 40PPI nickel foam by Beer's law in the studied wave band. When compared with the results by present simulation, the values of extinction coefficients by the double-thickness model in the reference are quite close within the wave band of 0.83–2.2 μm. While the scattering coefficients was overweighed for about 107 m−1 of sample 2 and 84 m−1 of sample 3 at the wavelength of 0.83 μm. Additionally, the extinction coefficients of five samples changed slightly in the wavelength from 0.75 μm to 12.5 μm. Scattering albedos approach to the reflectivity of the nickel component and scattering phase functions of all nickel foams show an obviously backward predominance.