Insights on the interaction of serpentine channels and gas diffusion layer in an operating polymer electrolyte fuel cell: Numerical modeling across scales
“…Overall, this analysis demonstrates that such wide fields of view are necessary to capture these defects as smaller domains do not provide an accurate representation 75 . This study’s domain measures equivalently 3600 3 with gas channels imposed, which is orders of magnitude higher than the typical imaged and synthetic domains for flow modelling studies (100 3 63 , 64 , at the exception of a single-phase study on a 650 3 domain 56 ). Fig.…”
Section: Resultsmentioning
confidence: 95%
“…These reveal that water predominantly accumulates near weave holes and under the lands (see animated video with flow-flood-purge cycle in Supplementary Video 1) . This simulation domain and routine overcomes the size limitations of previous large-scale studies by two orders of magnitude 56 , and successfully models multi-phase flow dynamics. Fig.…”
Section: Resultsmentioning
confidence: 95%
“…Furthermore, electrochemical models may be incorporated into flow modelling at various length scales using direct and agglomeration approaches with co-simulation 53 – 55 . These approaches allow more efficient, lower spatial-fidelity modelling to be conducted, which can mimic PEMFC operando multi-physics dynamics 2 , 17 , 18 , 56 .…”
Section: Introductionmentioning
confidence: 99%
“…As a result, direct multi-phase flow simulations of PEMFCs are usually performed on domains in the order of 200 3 using workstation-class resources 39 , 57 , 58 , 63 – 66 , and focus exclusively on the GDL or MPL. LBM studies on larger PEMFCs derived from micro-CT imaging 56 , 67 treat water as a solid phase and gas as single-phase flow. More advanced multi-component studies suffer from small fields of view (1.5 mm 2 ) or poor voxel resolution (5 μm) issues 68 , 69 (see Supplementary Table 1b ).…”
Proton exchange membrane fuel cells, consuming hydrogen and oxygen to generate clean electricity and water, suffer acute liquid water challenges. Accurate liquid water modelling is inherently challenging due to the multi-phase, multi-component, reactive dynamics within multi-scale, multi-layered porous media. In addition, currently inadequate imaging and modelling capabilities are limiting simulations to small areas (<1 mm2) or simplified architectures. Herein, an advancement in water modelling is achieved using X-ray micro-computed tomography, deep learned super-resolution, multi-label segmentation, and direct multi-phase simulation. The resulting image is the most resolved domain (16 mm2 with 700 nm voxel resolution) and the largest direct multi-phase flow simulation of a fuel cell. This generalisable approach unveils multi-scale water clustering and transport mechanisms over large dry and flooded areas in the gas diffusion layer and flow fields, paving the way for next generation proton exchange membrane fuel cells with optimised structures and wettabilities.
“…Overall, this analysis demonstrates that such wide fields of view are necessary to capture these defects as smaller domains do not provide an accurate representation 75 . This study’s domain measures equivalently 3600 3 with gas channels imposed, which is orders of magnitude higher than the typical imaged and synthetic domains for flow modelling studies (100 3 63 , 64 , at the exception of a single-phase study on a 650 3 domain 56 ). Fig.…”
Section: Resultsmentioning
confidence: 95%
“…These reveal that water predominantly accumulates near weave holes and under the lands (see animated video with flow-flood-purge cycle in Supplementary Video 1) . This simulation domain and routine overcomes the size limitations of previous large-scale studies by two orders of magnitude 56 , and successfully models multi-phase flow dynamics. Fig.…”
Section: Resultsmentioning
confidence: 95%
“…Furthermore, electrochemical models may be incorporated into flow modelling at various length scales using direct and agglomeration approaches with co-simulation 53 – 55 . These approaches allow more efficient, lower spatial-fidelity modelling to be conducted, which can mimic PEMFC operando multi-physics dynamics 2 , 17 , 18 , 56 .…”
Section: Introductionmentioning
confidence: 99%
“…As a result, direct multi-phase flow simulations of PEMFCs are usually performed on domains in the order of 200 3 using workstation-class resources 39 , 57 , 58 , 63 – 66 , and focus exclusively on the GDL or MPL. LBM studies on larger PEMFCs derived from micro-CT imaging 56 , 67 treat water as a solid phase and gas as single-phase flow. More advanced multi-component studies suffer from small fields of view (1.5 mm 2 ) or poor voxel resolution (5 μm) issues 68 , 69 (see Supplementary Table 1b ).…”
Proton exchange membrane fuel cells, consuming hydrogen and oxygen to generate clean electricity and water, suffer acute liquid water challenges. Accurate liquid water modelling is inherently challenging due to the multi-phase, multi-component, reactive dynamics within multi-scale, multi-layered porous media. In addition, currently inadequate imaging and modelling capabilities are limiting simulations to small areas (<1 mm2) or simplified architectures. Herein, an advancement in water modelling is achieved using X-ray micro-computed tomography, deep learned super-resolution, multi-label segmentation, and direct multi-phase simulation. The resulting image is the most resolved domain (16 mm2 with 700 nm voxel resolution) and the largest direct multi-phase flow simulation of a fuel cell. This generalisable approach unveils multi-scale water clustering and transport mechanisms over large dry and flooded areas in the gas diffusion layer and flow fields, paving the way for next generation proton exchange membrane fuel cells with optimised structures and wettabilities.
“…This approach is widely utilized in complex geometries such as porous media, where it is not always possible to refine the grid everywhere in the domain and the Knudsen number can be very small (Kn 0.01). It results in a specific value for the relaxation time, for which the spurious numerical slip vanishes [5,[9][10][11][12]. Chai et al [13] used a modified relaxation time based on the flow Knudsen number to incorporate the effect of velocity slip at the solid boundary.…”
A lattice Boltzmann (LB) interfacial gas-solid 3D model is developed for isothermal multicomponent flows with strongly non-equimolar catalytic reactions, further accounting for the presence of velocity slips and concentration jumps. The model includes diffusion coefficients of all reactive species in the calculation of the catalytic reaction rates as well as an updated velocity at the reactive boundary node. Lattice Boltzmann simulations are performed in a catalytic channel-flow geometry under a wide range of Knudsen (Kn) and surface Damköhler (Das) numbers. Comparisons with simulations from a computational fluid dynamics (CFD) Navier-Stokes solver show good agreement in the continuum regime (Kn < 0.01) in terms of flow velocity and reactive species distributions, while comparisons with literature Direct Simulation Monte Carlo (DSMC) results attest the model's applicability in capturing the correct slip velocity at Kn as high as 0.1, even with significantly reduced number of grid points (N = 10) in the cross-flow direction. Theoretical and numerical results demonstrate that the term Das × Kn × A2 (where A2 is a function of the mass accommodation coefficient) determines the significance of the concentration jump on the catalytic reaction rate. The developed model is applicable for many catalytic microflow systems with complex geometries (such as reactors with porous networks) and large velocity/concentration slips (such as catalytic microthrusters for space applications).
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