Discrete vs. continuum-scale simulation of coupled radiation and convection inside rectangular channel filled with metal foam

Open-cell metal foam has been increasingly applied in heat exchangers to enhance heat transfer. In this work, the coupled radiation-convection in a rectangular channel filled with metal foam under constant wall temperature is simulated numerically. Discrete-scale approach (DSA) and continuum-scale approach (CSA) are respectively developed for the simulation. In DSA, foam domain is constructed through numerous Kelvin structures, and pore scale field is obtained via CFD simulation with re-radiation flux calculated by surface to surface model; while in CSA, local thermal non-equilibrium model (LTNE) is employed with Monte Carlo method to solve radiative heat transfer, and volume-averaged correlations are determined based on Kelvin structure. The flow field and heat transfer at pore-level generated from DSA are analyzed. By means of a representative volume-averaged post-processing method, thermal behaviors from DSA and CSA are compared in terms of pertinent parameters. It shows that spatial fluctuation phenomenon is observed in pore-level temperature field. The overall heat transfer performance characterized by local Nusselt number is enhanced by inclusion of thermal radiation, and the effect is significant for lower pore density and higher porosity case. Increasing the inlet velocity, pore density or decreasing the porosity all can lead to heat transfer enhancement more or less. For all the cases studied, DSA and CSA can predict the temperature field consistently while the discrepancy between them is relatively larger in the local thermal non-equilibrium region. Additionally, it reveals that CSA is not applicable for accurately predicting energy transport in large gradient heat transfer region due to its volume-averaged characteristic.