Non-isothermal reactive transport in complicated porous media is diverse in nature and industrial applications. There are challenges in the modelling of multiple physicochemical processes in multiscale pore structures with various length scales ranging from nanometres to micrometres. This study focuses on coke combustion during in situ crude oil combustion techniques. A micro-continuum model was developed to perform an image-based simulation of coke combustion through a multiscale porous medium. The simulation coupled weakly compressible gas flow, species transport, conjugate heat transfer, heterogeneous coke oxidation kinetics and structural evolution. The unresolved nanoporous coke region was treated as a continuum, for which the random pore model, permeability model and species diffusivity model were integrated as sub-grid models to account for the sub-resolution reactive surface area, Darcy flow and Knudsen diffusion, respectively. A Pe–Da diagram was provided to present five characteristic combustion regimes covering the ignition temperature and air flux in realistic field operations and laboratory measurements. The present model proved to achieve more accurate predictions of the feasible ignition temperature than previous models. Compared with the air flux of $\phi \sim O\textrm{(1) s}{\textrm{m}^\textrm{3}}(\textrm{air})\;{({\textrm{m}^\textrm{2}}\ \textrm{h})^{ - 1}}$ in the field, the increasing air flux in the laboratory transformed the combustion regime from diffusion-limited to convection-limited, which led to an overpredicted burning temperature. Reactive fingering combustion was analysed to understand the potential risks in some experimental measurements. The findings provide a better understanding of coke combustion and can help engineers design sustainable combustion methods. The developed image-based model allows other types of multiscale and nonlinear reactive transport to be simulated.

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Co-coordinated nitrogen-doped carbons have been reported as highly active catalysts to oxygen reduction reaction (ORR) in fuel cell. Two CoN 4 -graphene catalysts with a hybrid structure of single Co atom embedded into pyridinic-N and pyrrolic-N doped graphenes, respectively, were studied. The detailed thermodynamic and kinetic behavior of the ORR on these two models was performed by DFT calculation. The results showed that both the two CoN 4 -G models possessed ORR activity. However, CoN 4 -G(A) catalyst showed higher catalytic activity but the CoN 4 -G(B) showed higher 4-electrons selectivity. On CoN 4 -G(A), both 2-electrons and 4-electrons pathways were feasible. Along the 4-electrons pathway, the OH reduction step was the thermodynamic and kinetic rate-determining step with the limiting potential of 0.43 V and a barrier of 0.42 eV. The formation barrier of H 2 O 2(ads) was 0.61 eV which was easy to overcome. Then the 2-electrons pathway was also possible. On CoN 4 -G(B), only 4-electrons ORR pathway was favorable. The most favorable reaction channel was arranged as: O 2 ! OOH ! 2OH ! OH + H 2 O ! 2H 2 O. The limiting potential of 4-electrons pathway was 0.35 V. The second step was the kinetic rate-determining step with the barrier of 0.86 eV.

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This paper deals with natural convection heat and moisture transfer with thermal radiation in a cavity partially filled with hygroscopic porous medium. The governing equations for the momentum and heat transfer in both free fluid and hygroscopic porous medium and moisture content transfer in hygroscopic porous medium were solved by the finite element method. The radiative heat transfer is calculated by making use of the radiosity of the surfaces that assumed to be grey. Comparisons with experimental and numerical results in the literature have been carried out. Effects of thermal radiation, Rayleigh number on natural convection and heat transfer in both free fluid and porous medium and moisture content transfer in porous medium were analyzed. It was found that surface thermal radiation can significantly change the temperature and moisture content fields in the regions of free flow and porous medium. The mean temperature at the interface decreases, and the temperature and moisture content gradients are created on the upper two corners of the porous medium region and the moisture content in the porous medium decreases in the porous medium as Ra increases. Downloaded by [University of Otago] at 13:16 28 July 2015 2

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