Thermal radiation effects on heat transfer in slender packed-bed reactors: Particle-resolved CFD simulations and 2D modeling

Abstract

Radial heat management is crucial for a safe and stable operation of fixed-bed reactors with small tube-to-particle diameter ratios (N). Under high temperature conditions, thermal radiation can contribute substantially to the overall heat transfer. In the present work, the influence of radiation is studied with particle resolved computational fluid dynamics (PRCFD) in a fixed-bed reactor consisting of 1000 spheres and rings with N = 5.1 over 300 < Rep< 2000 and for three different temperature levels (300–800 ∘C). Two heat transfer parameters, i.e., the wall Nusselt number Nuw and the effective radial thermal conductivity of the bed keff, r, are derived directly from PRCFD. While the radiation effect is minor in keff, r, it is substantial for Nuw, which is not captured adequately in the current correlations presented in literature. Depending on the temperature level and flow conditions, thermal radiation between the hot wall and the packed bed intensifies the radial heat transfer represented by an increase of up to 170 % in Nuw and 65% in keff, r. A 2D axisymmetric pseudo-homogeneous model including the derived heat transfer parameters can predict the radial temperature profile of the PRCFD with reasonable accuracy also with radiation except for the near-wall region.