| Reacting flows are characterized by strong coupling between transport and chemistry, which is further enhanced in heterogeneous and multiphase reactors due to the interactions between the phases. Despite their numerous applications, the design and scale up of multiphase chemical reactors is not yet well understood. This work considers three different kinds of reacting systems (including homogeneous CSTR and multiphase reactors) and presents simplified engineering models for their design and analysis.; The first problem considered is that of a fluid-solid monolith reactor. Here, we present a mathematical framework for solving the coupled convection-diffusion equations in the fluid phase and diffusion-reaction equations in the solid phase. We show that by defining shape normalized length scales for fluid and washcoat and normalized reaction rate, the effect of channel geometric shape can be eliminated. We also determine the influence of washcoat properties on the fluid-solid mass transfer coefficient.; The second problem considered is that of the homogeneous continuous flow stirred tank reactor. We use the Liapunov-Schmidt method of spatial averaging on the three dimensional convection-diffusion-reaction equations and derive a low-dimensional two mode model involving two mixing times for the isothermal case. The first mixing time captures the effect of micro as well as macromixing in the tank, while the second one accounts for the feed distribution. We use the new model to explain experimental results in the literature, including the opposing selectivity trends observed for series-parallel reactions under different operating conditions.; The third problem considered is that of gas-liquid, fluid-solid and gas-liquid-solid multiphase reactors. Liapunov-Schmidt method is used to spatially average the coupled convection-diffusion-reaction equations and obtain multi-mode (multi-scale) low dimensional models. When only two phases are involved, we show that the traditional transfer coefficient concept is valid but the driving force gets modified. For the case of gas-liquid-solid reactor, we show that the concept of binary mass or heat transfer between gas and liquid or liquid and solid phases is not valid and the new averaged model contains transfer term that is not a linear combination of the same for individual phases. |
