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In this paper, we report the extension of an earlier developed Direct Numerical Simulation (DNS) model to study coupled heat and mass transfer problems in particulate flows. The DNS model builds on an efficient ghost-cell based Immersed Boundary Method (IBM) which implicitly incorporates the boundary conditions into the discretized momentum, thermal and species conservation equations of the fluid phase. On the particles an exothermic surface reaction takes place. The heat and mass transport is coupled through the particle temperature, which offers a dynamic boundary condition for the fluid phase thermal energy equation. The present simulations are performed for four fluid-solid systems. Following the case of the unsteady mass and heat diffusion in a large pool of quiescent fluid, we consider a stationary sphere under forced convection. In both cases variable reaction rates are imposed at the particle surface, and the particle temperatures obtained from DNS show a good agreement with analytical/empirical solutions. After that, we apply our DNS model to the three-bead reactor and finally, a dense particle array consisting of hundreds of particles distributed in a random fashion is studied. The concentration and temperature profiles are compared with a ID heterogeneous reactor model and the heterogeneity inside the array is discussed. .

In this paper, an efficient ghost-cell based immersed boundary method is introduced to perform direct numerical simulation (DNS) of particulate flows. The fluid-solid coupling is achieved by implicit incorporation of the boundary conditions into the discretized momentum, thermal and species conservation equations of the fluid phase. Taking the advantage of a second order quadratic interpolation scheme, different boundary conditions could be realized consistently in our ghost-cell based immersed boundary method. The heat and mass transport in a fluid-particle system is coupled through the solid temperature, which offers a dynamic boundary condition for the fluid thermal equation. The present simulations are performed for three different fluidsolid systems. The first one is the unsteady mass and heat diffusion in a large pool of quiescent fluid. The solution of the solid temperature development obtained from DNS is compared with the “exact” solution obtained from a standard second-order finite difference technique. Following that, we consider a stationary sphere under forced convection. The steady state temperature of the particle can be calculated from the fluidsolid mass and heat transfer rates, which are obtained from the well-known empirical Ranz-Marshall and Frössling correlations. The last simulation case is an in-line array of three spheres, the so-called three-bead reactor. The computed adiabatic temperature rise obtained from DNS shows good agreement with the value calculated from the overall species conversion ratio of the reactor.