Temperature Distribution Assessment in Gas-Solid Reactive and Nonreactive Systems Heated by Microwaves

Researchstudies have shown that selective heating of differentphases in gas-solid systems exposed to microwave (MW) irradiationleads to a temperature gradient between gas and MW absorber solids.This can suppress undesired secondary gas-phase reactions and yieldapparent kinetic improvements and energy savings. However, the effectsof reaction exothermicity/endothermicity, gas velocity, temperatureprobe location at the microscale, and MW penetration depth in fixedbeds on the temperature difference between solid and gas phases exposedto MWs and temperature distribution in the fixed beds are poorly understood.Highlighting these effects was targeted in this study and accomplishedwith the help of multiphysics simulations by COMSOL Multiphysics (5.6).The corresponding COMSOL model was initially verified and validatedby data collected from literature studies and those obtained experimentallyby the authors in this study. Simulation results from the verifiedand validated model indicated that the temperature gradient betweenthe gas and the MW absorber solid increases by increasing the gasvelocity or switching from an endothermic reaction to no reactionand/or an exothermic reaction. In addition, the collected resultsshow nonuniform temperature distribution in a fixed-bed reactor madeof MW absorber particles irradiated by MWs due to the limited penetrationdepth of MWs and hotspot formation. This operational deficiency makesthe large-scale design of this type of reactor very challenging forMW heating-assisted reactions.