Filtered models for reacting gas–particle flows

Using the kinetic-theory-based two-fluid models as a starting point, we develop filtered two-fluid models for a gas–particle flow in the presence of an isothermal, first-order, solid-catalyzed reaction of a gaseous species. As a consequence of the filtering procedure, terms describing the filtered reaction rate and filtered reactant dispersion need to be constituted in order to close the filtered species balance equation. In this work, a constitutive relation for filtered reaction rate is developed by performing fine-grid, two-fluid model simulations of an isothermal, solid-catalyzed, first-order reaction in a periodic domain. It is observed that the cluster-scale effectiveness factor, defined as the ratio between the reaction rate observed in a fine-grid simulation to that observed in a coarse-grid simulation, can be substantially smaller than unity, and it manifests an inverted bell shape dependence on filtered particle volume fraction in all simulation cases. Moreover, the magnitude of the deviation in the cluster-scale effectiveness factor from unity is a strong function of the meso-scale Thiele modulus and dimensionless filter size. Thus coarse-grid simulations of a reacting gas–particle flow will over-estimate the reaction rate if the cluster-scale effectiveness factor is not accounted for.

► We demonstrate the need for development of coarse-grained two-fluid models to enable accurate coarse-grid simulation of reacting gas–particle flows.
► A coarse-grained model for effective reaction rates is presented for the case of an isothermal, first-order, solid-catalyzed gas phase reaction.
► It is shown that coarse-grid two-fluid model simulations of reacting gas–particle flow will over-predict reactant conversion if coarse-grained models for the effective reaction rate are not accounted for.