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The morphology of free-flowed and gravity consolidated crystal powder beds of the alpha and beta polymorphic forms of L-glutamic acid, together with a detailed analysis of particle density and microstructure within alpha form tablets using state -of-the-art X-ray computed tomography (XCT), is presented. The Carr's index is measured to be 19.7 and 35.2 for the bulk powders of the prismatic alpha form and needle-like beta form, respectively, revealing the alpha forms increased powder flowability versus the beta form. XCT reveals the alpha form consolidates under gravity more efficiently than beta, where the final measured bed density of the alpha form is 0.724 g/cm 3 compared to 0.248 g/cm 3 for the beta form, which is found to be caused by the inability of the beta particles to pack efficiently along their needle axis. Tabletting studies reveal that the alpha form consolidates into compacts of intermediate tensile strength, whereas the beta form cannot be compacted under these conditions. XCT analysis of tablets formed from α-form crystals reveals two discrete density regimes, one low-density region of fine powder which accounts for 53.8% of the compact, and highdensity regions of largely intact single crystals which account for 44.2% of the compact. Further analysis of the tablet microstructure reveals that the crystal particles are generally orientated with their basal {0 0 1} plane, normal to the compaction force and that small microcracks which appear within the particles generally occur perpendicular to the surface and are orientated through possible {1 1 0} and {1 0 1} fracture planes. XCT also reveals evidence for incipient transformation between the meta-stable alpha to stable beta phase at concentrations below that detected using laboratory X-ray diffraction. The results show that XCT can accurately measure the extent of tapping induced densification and reveals the powder bed mesostructure characteristics and tablet microstructure for the two polymorphic forms of alpha and beta L-glutamic acid.

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Fuel flexibility is a significant advantage of solid oxide fuel cells (SOFCs) and can be attributed to their high operating temperature. Here we consider a direct internal reforming solid oxide fuel cell setup in which a separate fuel reformer is not required. We construct a multidimensional, detailed model of a planar solid oxide fuel cell, where mass transport in the fuel channel is modeled using the Stefan‐Maxwell model, whereas the mass transport within the porous electrodes is simulated using the Dusty‐Gas model. The resulting highly nonlinear model is built into COMSOL Multiphysics, a commercial computational fluid dynamics software, and is validated against experimental data from the literature. A number of parametric studies is performed to obtain insights on the direct internal reforming solid oxide fuel cell system behavior and efficiency, to aid the design procedure. It is shown that internal reforming results in temperature drop close to the inlet and that the direct internal reforming solid oxide fuel cell performance can be enhanced by increasing the operating temperature. It is also observed that decreases in the inlet temperature result in smoother temperature profiles and in the formation of reduced thermal gradients. Furthermore, the direct internal reforming solid oxide fuel cell performance was found to be affected by the thickness of the electrochemically‐active anode catalyst layer, although not always substantially, due to the counter‐balancing behavior of the activation and ohmic overpotentials.

Keywords:NEMCA backspillover multi-scale modelling CFD-kMC coupling Electrochemically Promoted CO oxidation on Pt/YSZ A B S T R A C T The objective of this work is the formulation of a multi-scale framework for electrochemically promoted systems. We have constructed a 3-Dimensional, isothermal, solid oxide single pellet, multi-scale framework, which describes the chemical and electrochemical phenomena taking place in a solid oxide single pellet under closed-circuit conditions, while the electrochemically promoted oxidation of CO over Pt/YSZ is used as an illustrative system. The proposed framework combines a 3-D macroscopic model which employs the finite element method (FEM) for the simulation of the charge transport and the electrochemical phenomena taking place in the pellet, and an in-house developed efficient implementation of a 2-D lattice kinetic Monte Carlo method (kMC) for the simulation of the reaction-diffusion micro-processes taking place on the catalytic surface. Comparison between the multiscale framework and a macroscopic model [1] is carried out for several sets of operating conditions. Differences between the steady-state outputs of the two models are presented and discussed. A subsequent parametric study using the multi-scale framework is performed to investigate the effect of the gaseous species partial pressures and of the temperature on the CO 2 production rate.