Tomography-based pore level analysis of combined conductive-radiative heat transfer in an open-cell metallic foam

Abstract

Open-cell metallic foams are increasingly used in various thermal systems. The temperature distributions are significant for the comprehensive understanding of the foam-based engineering applications. This study aims to numerically analyze combined conductive-radiative transfer in a tomography-based open-cell metallic foam. The method used to carry out the simulations consists of a Monte Carlo ray-tracing method based on mesh-agglomeration approach, which avoids the error caused by block-off treatment of porous media surfaces, while greatly minimizing the computation cost for solving the Radiative Transfer Equation. A validation test case has been considered for the distribution of wall heat flux against other benchmark available in the literature. The detailed absorbed radiative flux at local strut surface is analyzed for the real nickel foam, and great difference up to 100% between the front and the back of the strut is found. In addition, the effects of average temperature (i.e. the arithmetic mean temperature of the cold and hot boundary) on the distribution of temperature, the absorbed radiative flux and radiative heat flux are investigated. The results show great fluctuation of absorbed radiative flux and radiative heat flux distribution due to the irregular porous structure. On this basis, the effective thermal conductivity and radiative conductivity of nickel foam at different temperatures are also evaluated. Results show when the temperature increases from 800 K to 1100 K, the radiative conductivity increases from 0.18 W/m•K to 0.46 W/m•K, and the effective thermal conductivity decreases from 4.81 W/m•K to 4.76 W/m•K first and then increases to 4.92 W/m•K, which indicates though the value of radiative conductivity is relatively small, it still influences the variation trend of the effective thermal conductivity with the temperature. The results also show that radiative thermal conductivity and the effective thermal conductivity are strongly dependent upon porosity.