Liquids with solids have material processing complexities that arise when pumped, coated, and dried compared to pure fluids, uniquely increasing process downtime and processing challenges. I utilized experiments and applied knowledge in liquid-solid flow properties and particulate film drying to solve challenges in underground drilling and fuel cell production to de-risk processing and manufacturing developments.
My doctoral studies introduced me to solids handling and the complexities of concentrated dispersion rheology in underground drilling. Comminution and fluidization of soil material is the basis of underground drilling, a continuous process to break down, disperse, then pump soil particles to construct a borehole. In collaboration with machinists and engineers, we constructed a flow loop to pump in circulation, dispersed soil slurries and measured its viscosity under variable conditions and predicted drilling fluid pressures for drilling operation. We learned that soil slurry viscosity is complex because of its sensitivity to solids content, mineralogy, and flow rate. This experience helped develop a fundamental understanding in suspension and dispersion rheology for fluids laden with particulates and potential processing challenges that can occur.
In my postdoctoral position, I pivoted slurry processing into energy conversion. Low-temperature, hydrogen fuel cells generate on-demand electricity from converting hydrogen into water. The electrodes of fuel cells are where the reactions take place and have the most potential for process-structure-performance benefits. Electrodes are complex polymer-stabilized, catalyst particle dispersions sensitive to processing history. When coated into thin films, defects can develop; catalyst particles can aggregate on the coating head and create streaks without catalyst material. Using a failure-mode analysis, I scrutinized recirculation flows in the coating head, catalyst particle surface chemistry, and coating head gaps as potential origins of streak defects. Recirculating flows were ruled out with rheological characterizations to not cause streaks. Coating trials showed that catalyst particles with lower surface activity prevented streaks. Operating at larger coating head gaps was also another means to eliminate streaks. Subsequently, we identified that electrode film drying rate could affect their microstructure and resulting fuel cell performance. Drying rate was found to alter the material distribution in the electrode coatings and could be leveraged to improve mass transport within the fuel cell, thereby improving performance. This experience taught me about coating flows and film drying dynamics, expanding my solids handling skillset with theoretical and experimental knowledge of coating and drying operations.
Wet solids handling will have unique material processing challenges specific to each system. Understanding the connection between fundamental material properties and process design will be vital to reduce operational costs and de-risk manufacturing developments. I am motivated and prepared to tackle obstacles in this translational space, and I look forward to future opportunities at this intersection.
This work was authored by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding provided by the Hydrogen and Fuel Cell Technologies Office. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.