(409f) Computational Fluid Dynamic Modeling of a Microplasma Fuel Reformer

Batteries are present in everyday life as the primary means to provide portable power to most of our electrical devices. Due to the low energy densities of batteries, portable fuel cell technologies have been heavily considered as a potential replacement. Fuel cells have the beneficial advantages of higher overall efficiencies, no moving parts, and low temperature operation, but exhibit the limitation of not having a readily available stream of hydrogen. Microplasma reactors have been successfully designed, fabricated, and experimented as a novel fuel reformer. However experimental measurements from the devices presented low energy efficiencies making the dynamics of the fluid transport in the novel devices an important aspect of further investigation. To learn more about the reactive microplasma environment a computational fluid dynamic (CFD) model of the microplasma reactor was created. Additionally this model will ultimately be used to inform the ideal system conditions and improve microreactor designs in future generations of the experimental devices.

The low efficiencies are likely due to the large bulk volume allowing for a large portion of the feed to pass around the microplasma. The volume of the microreactor holder is 375 µL, where the reactive microchannel is at most 0.5 µL. The CFD model was designed in COMSOL Multiphysics version 5.2. The object of study is the channel and the bulk volume above the reactor. In the model only the channel volume is reactive. The model captures both momentum and mass transport. As reactants are fed into the holder in a gas phase they pass over and through the microchannel, the material in the microchannel is reacted and then products diffuse into the bulk volume, while more reactant diffuses into the channel. Based on the inconsistency of the microplasma size throughout experiments, three model variations were developed for each experiment that accounts for the 100% of the channel being reactive as well as 5% and 50%. Each model simulates experimented results to determine accuracy of the model. Due to reactor variation the model are also parameterizable with respect to width, depth, oxide thickness, inlet flow rate, reaction rate and electric current.

To date all models have been tested with a carbon dioxide decomposition reaction; forming oxygen and carbon monoxide. The carbon dioxide reaction study was performed to analyze the microreactors, where carbon dioxide was chosen due to its ease in developing a plasma and simplicity in products. Currently the CFD model has presented reaction rates from 125 to 18,153 mol/m³-s (2.5E-8 to 9E-8 mol/s). This work aim is to not only determine unique reaction characteristics of the microplasma environment, but also to determine key parameters to study optimization of device performance. We plan to present the results of the model, and the ideal parameters to obtain the highest energy efficiency of the microplasma fuel reformer.