Prediction of high-temperature radiative properties of copper, nickel, zirconia, and alumina foams

Abstract

High-temperature radiative properties of open-cell foams are relatively scarce due to measurement limitation. This study aims to numerically predict the volumetric radiative properties of irregular open-cell foams at high temperatures. The prediction is based on established relations which link the volumetric radiative properties to the structural parameters and/or component optical/radiative properties. Four typical foams are considered, including copper foams, nickel foams, zirconia foams and alumina foams. Former two are made of opaque metals, while latter two are made of semitransparent oxidized ceramics. For the four foams, the highest temperatures investigated are up to 1084 K, 1605 K, 1633 K and 2300 K, respectively. The variations of radiative properties with wavelength and temperature are analyzed. It was found that high temperature can strengthen radiation absorption inside metal and ceramic foams at most of wavebands. The temperature has almost no influence on the scattering phase function of metal and ceramic foams. Compared to copper foams, the nickel foams behave more absorbing at most of wavebands and temperatures. Alumina foams show an obviously forward predominance (asymmetry factor g > 0.4), and the fraction of forward scattering increases with increasing wavelength. Zirconia foams show a slight backward predominance (asymmetry factor g = -0.1) at short wavelengths, and a closely isotropic scattering was found at around wavelength λ = 7 μm. This study provides a feasible way to obtain the radiative properties of open-cell foams at high temperatures. Normal-normal transmittance and normal-hemispherical transmittance/reflectance of foams were measured at room temperature. The experimental results validate the numerical approach to obtaining radiative properties from analytical relations and bulk properties.