Computational Fluid Dynamics Simulation of Gas-Solid Flow during Steam Reforming of Glycerol in a Fluidized Bed Reactor

A computational fluid dynamics simulation of gas-solid flow in a fluidized bed reactor was performed to investigate the steam reforming of glycerol using a three-step reaction scheme, motivated by the worldwide increase of crude glycerol produced by the transesterification of vegetable oil into biodiesel. The Eulerian-Eulerian two-fluid approach was adopted to simulate hydrodynamics of fluidization, and chemical reactions were modeled by the laminar finite-rate model. The gas-solid system exhibited a more heterogeneous structure. Clusters were observed to fall and stack together along the wall, and the process of wall slug formation was very evident. This suggests the bed should be agitated to maintain satisfactory fluidizing conditions. The results showed that the glycerol conversion increased with increasing reaction time, and most of the gas products-H2, CO2, CH4, and CO-were formed during the initial 2 s. The prediction of the gas-solid phase flows and mixing, glycerol conversion, and products distribution will provide helpful data to design and operate a bench-scale catalytic fluidized bed reactor

The effect of ink dilution and evaporation on the microstructures of catalyst layers in polymer electrolyte membrane fuel cells

The microstructures of catalyst layers (CLs) in proton exchange membrane fuel cells determine cell performance and durability. Delicate ink preparation processes and coating/drying processes affect the resulting microstructures including active sites, pore networks, ionomer networks and Pt/C networks. This paper reports our recent experimental observations of the effect of ink dilution and evaporation condition on the microstructures. The microstructures of dried ink droplets are presented and compared among different dilution ratios and different evaporation conditions in terms of the spatial distributions of Pt/C particles, ionomers, and pores. The method through which the microstructures are visualized is also introduced in this paper. It is observed that ink dilution ratio and evaporation condition can significantly alter resulting microstructure patterns through affecting viscosity and particle flow patterns during the evaporation. More concentrated solution makes catalyst inks less spread out on a substrate surface, leading to larger droplet height and larger contact angle. Ambient relative humidity has a significant impact on catalyst deposition patterns. Under low relative humidity condition, catalyst particles are concentrated both near the central and the periphery of the droplet; while under high relative humidity, the central part is uniform, and the particles move towards the edge of the deposition, forming a stripe-like structure. This indicates that ink dilution and evaporation is key to the CL microstructure formation and must be properly controlled in order to obtain the quality and consistency of the CLs in fabrication