Heat transport regimes in structured reactors: CFD analysis and influence of reactor diameter and length

• Detailed CFD study to reveal heat removal mechanisms in a structured reactor • Change of predominant heat transport mechanism depending on the reactor diameter • Reactor diameter doubles, absolute temperature triples • Thermal radiation lowers temperature increase by up to 60% • Three regimes introduced based on the predominant heat transport mechanism Temperature control in catalytic reactors is critical to ensure high yields and a stable process for highly exothermic reactions. To better understand the processes within structured reactors, it has already been shown that heat source based Computational Fluid Dynamics (CFD) is a simple and valid way to mimic the heat intake of catalytic surface reactions and to capture general heat transport properties. In case of structured reactors, the heat transport is highly dominated by thermal conduction. Building on these achievements, this work systematically investigates the influence of the reactor diameter and length on heat transfer and temperature distribution in a Periodic Open Cell Structure (POCS) reactor. It is found that the typically high percentage of thermal conductivity is reduced by up to 50% if the reactor diameter changes from 20 mm to 50 mm. Furthermore, heat transport regimes are introduced along the reactor axis separating reactor parts with different predominant heat transfer mechanisms. This provides a fundamental comprehension of heat transfer in structured reactors and highlights the necessity to consider a sufficient reactor length. Lastly, the influence of thermal radiation is isolated. In addition to lowering the temperature increase significantly (from 1,300 K to 500 K in a specific case), it can also enhance the heat conduction through the solid by increasing the solid's temperature close to the reactor wall. Although the heat source simulations are a simplification, they are ideal to understand the reactor systems from a heat transport perspective.