In this work, the behavior of a 200-μm spherical carbon particle moving in a hot environment mainly consisting of O2 and CO2 was investigated numerically. The main goal of this work was to study the influence of the particle velocity, temperature, and composition of the surrounding gas on the carbon consumption rates. The particle investigated was placed in a uniform oxygen/carbon dioxide mixture at different Reynolds numbers corresponding to different laminar flow regimes. The ambient temperature was systematically varied in the range of 1000–3000 K, and the mass fraction of O2 was varied between 0.12 and 0.36. To solve the Navier–Stokes equations for the flow field coupled with the energy and species conservation equations, a finite volume solver was applied. In addition to the solid carbon, the model incorporates six gaseous chemical species (O2, CO, CO2, H2, H2O, and N2). The semiglobal reaction mechanism includes the forward and backward water–gas-shift reaction, one reaction for CO combustion, and four heterogeneous reactions. The ambient medium was assumed to be nearly dry (Y H2O = 0.001). The numerical results were carefully validated against experimental data published in the literature ( Bejarano Levendis Bejarano Levendis Combust. Flame2008153270287). In particular, it was shown that taking into account losses from radiation (gas–gas, gas–solid) brings the results closer to the experimental data. Additionally, the influence of the gas–gas radiation effect on the integral characteristics of the oxidizing particle was studied. In particular, the results are discussed with a focus on the systematic variation of the ambient-gas temperature and Reynolds number. We found out that increasing the Reynolds number enhances species transport to the particle surface and shifts particle oxidation from a diffusion-controlled to a kinetically controlled regime.

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. Trois réactions hétérogènes sont utilisées, ainsi que deux réactions semi-globales homogènes, à savoir l'oxydation du monoxyde de carbone et la réaction du gaz à l'eau. Les particularités distinctives du modèle de sous-maille se trouvent dans la prise en compte de l'influence des réactions homogènes sur les caractéristiques intégrales telles que les taux de combustion du carbone et la température de la particule. Le sous-modèle a été validé en comparant ses résultats avec un modèle complet basé sur la CFD résolvant les questions de flux volumique et de couche limite autour de la particule. Dans ce modèle, les équations de Navier-Stokes couplées aux équations de conservation de l'énergie et des espèces ont été utilisées pour résoudre le problème au moyen de l'approche en état pseudo-stationnaire. À la surface de la particule, l'équilibre de la masse, de l'énergie et de la concentration des espèces a été appliqué, y compris l'effet de l'écou-lement de Stefan et l'effet de la perte de chaleur due aux rayonnements à la surface de la particule. Une bonne adéquation a été atteinte entre le sous-modèle et le modèle basé sur la CFD. En outre, le modèle basé sur la CFD a été comparé aux données expérimentales publiées dans la littérature (Makino et al. (2003) Combust. Flame 132, 743-753). Une bonne concordance a été atteinte entre les données prédites numériquement et celles obtenues expérimentalement pour les conditions d'entrée correspondant au régime contrôlé par la cinétique. La divergence maximale (10 %) entre les expériences et les résultats numériques a été observée dans le régime contrôlé par la diffusion. Enfin, nous discutons de l'influence du nombre de Reynolds, de la fraction massique d'O 2 ambiant et de la température ambiante sur le comportement de la particule de charbon. Abstract -From Detailed Description of Chemical Reacting Carbon Particles to Subgrid Models for CFD -This work is devoted to the development and validation of a sub-model for the partial oxidation of a spherical char particle moving in an air

This work is devoted to the numerical study of the impact of the Reynolds number and the ambient gas temperature on the partial oxidation of a single moving coal particle. The model includes six gaseous chemical species, three semi‐global heterogeneous surface reactions, and three homogeneous gas reactions. The Navier–Stokes equations coupled with the energy and species conservation equations were used to solve the problem. The diameter of the particles considered was set up as 2 mm and 200normalμm. An analysis of the simulations related to the influence of particle Reynolds numbers on integral characteristics such as surface‐averaged carbon consumption rates revealed that the oxidation rate increases with increasing gas velocity, which is logical. However, the increase in the particle Reynolds number leads to the prolongation of the kinetically controlled regime from lower to higher temperatures, which is explained by the enhancement of the mass transfer between the particle and the surrounding gas. Using visualization of the temperature and species mass fraction distributions around the reacting particles predicted numerically, the three well‐known basic oxidation regimes, namely the diffusion‐controlled, transitional, and kinetically controlled regimes are described, taking into account the impact of the particle Reynolds number on the dynamics of oxidation. The influence of radiation in the gas phase on oxidation rates was studied numerically using P1 radiation model. Additionally the behaviour of heterogeneous Damköhler numbers, Thiele modulus and effectiveness factors depending on the ambient temperature and particle Reynolds number was analyzed and discussed.