Particle non-isothermality effect on the radiative thermal conductivity in dense particulate systems

Emerging high-temperature applications require a deeper understanding of radiative heat transfer in particulate systems, while existing theoretical tools are still limited in estimating the influence of the highly variable particle parameters (morphology, size, and optical properties) on heat transfer characteristics. In this work, a novel method is developed to determine radiative heat transfer in optically thick particulate media based on the radiation distribution factor. The important parameters of characterizing radiative heat transfer in particulate systems, i.e., transport coefficient and radiative thermal conductivity, are directly calculated by the Monte Carlo ray tracing method at particle scale. Two ideal cases of high and low thermal conductivity of solid particles, characterized by radiative Biot number Bi, are considered to investigate the effect of particle non-isothermality on the radiative thermal conductivity, which correspond to the cases of isothermal (Bi << 1) and non-isothermal particles (Bi >> 1), respectively. The results show that radiative transfer is more intensive in isothermal particles due to the additional contribution of internal heat transfer in highly conductive particles. The difference between the limits of isothermal particles and non-isothermal particles is significant at high values of solid fraction and surface emissivity. In addition, the results are used to estimate the applicability domain of the analytic multiphase approach. This work brings new insights to the understanding of radiative heat transfer in particulate media. (c) 2022 Elsevier Ltd. All rights reserved.