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Mechanical failures in the operating stacks of solid oxide fuel cells (SOFCs) are frequently related to thermal stresses generated by a temperature gradient and its variation. In this study, a computational fluid dynamics (CFD) model is developed and further applied in full-size SOFC stacks, which are fully coupled and implemented for analysis of heat flow electrochemical phenomena, aiming to predict thermal stress distribution. The primary object of the present investigation is to explore features and characteristics of the thermal stress influenced by electrochemical reactions and various transport processes within the stacks. It is revealed that the volume ratio of the higher thermal stress region differs nearly 30% for different stack flow configurations; the highest probability of potential failure appears in the cell cathodes; the more cells applied in the stack, the greater the difference in the predicted temperature/thermal stress between the cells; the counter-flow stack performs the best in terms of output power, but the predicted thermal stress is also higher; the cross-flow stack exhibits the lowest thermal stress and a lower output power; and although the temperature and thermal stress distributions are similar, the differences between the unit cells are bigger in the longer stacks than those predicted for shorter stacks. The findings from this study may provide a useful guide for assessing the thermal behavior and impact on SOFC performance.

A fully coupled electro-thermo-mechanical CFD model is developed and applied to illuminate the crucial factors influencing the overall performance of a solid oxide electrolysis cell (SOEC), particularly the configuration and geometry parameters of its inter-connector (IC), comprising ribs and channels. Expanding on a selected width ratio of 4:3, the gradient ribs/channels are further investigated to assess electrochemical and thermo-mechanical performance. It is elucidated that, while maintaining constant maximum temperature and thermal stress levels, employing a non-regular geometry IC with gradient channels may yield a 30% enhancement in hydrogen production. These nuanced explorations illuminate the complex interplay between IC configuration, thermal stresses, and electrolysis efficiency within SOECs.

A three-dimensional computational fluid dynamics (CFD) method coupled with multi-physics phenomena is developed and applied for a 10-cell full-scale SOEC stack in this study. Effects of gas flow patterns, operating temperature, and manifold configurations are simulated and analyzed for stack performance and thermal stress. It is demonstrated the hydrogen production and thermal stress obtained in cross-flow mode stack are about 8% and 36 MPa higher compared to that in other flow cases. Furthermore, it is found the temperature gradient is the predominant factor affecting the thermal stress distribution and failure probability. Lastly, a stack arrangement with 2-inlet and 1-outlet is proposed and analyzed to enhance gas distribution uniformity within the cell channels. The findings of this study hold significance as a reference for investigating the impact on the SOEC stack performance and thermal stress distribution.

In this work, a 3D multi-physics coupled model was developed to analyze the temperature and thermal stress distribution in a planar solid oxide fuel cell (SOFC) stack, and then the effects of different flow channels (co-flow, counter-flow and cross-flow) and electrolyte thickness were investigated. The simulation results indicate that the generated power is higher while the thermal stress is lower in the co-flow mode than those in the cross-flow mode. In the cross-flow mode, a gas inlet and outlet arrangement is proposed to increase current density by about 10%. The generated power of the stack increases with a thin electrolyte layer, but the temperature and its gradient of the stack also increase with increase of heat generation. The thermal stress for two typical sealing materials is also studied. The predicted results can be used for design and optimization of the stack structure to achieve lower stress and longer life.

An improved stochastic reconstruction method for a gas diffusion layer (GDL) of proton exchange membrane fuel cell is developed to promote the accuracy in evaluating effective gas diffusivity. Carbon fibers are generated using stochastic algorithm within a representative element volume. Structural characteristics, porosity distribution and fiber orientation distribution are set as constraints in reconstructing the microstructure. Morphological opening of image processing with structuring element is employed to add binder and polytetrafluoroethylene (PTFE), with disk and sphere binder configurations. Pore-scale simulations are subsequently carried out to compute the anisotropic, effective gas diffusivities of these reconstructed GDLs. Simulation results show that the reconstructed GDL with binder and PTFE produces significant decrease of the effective gas diffusivity. The diskshape binder appears to match the real GDL geometry visually, and the predicted effective gas diffusivity is also in good agreement with the reported experimental data in the literature. This demonstrates the importance of binder and PTFE in GDL reconstruction. Moreover, the correlations of the effective diffusivities in the through-plane and in-plane directions as functions of porosity and volume fraction of binder and PTFE are determined for the reconstructed GDLs. [ABSTRACT FROM AUTHOR]

In this study, X-ray computed tomography (XCT) and pore-scale simulation were employed to investigate the mechanical deformation of a porous electrode material for a vanadium redox flow battery during compression and to quantify its impact on the effective transport properties of the electrode. Pore-scale simulations using the finite element method (FEM), pore-scale modeling (PSM), and lattice Boltzmann method (LBM) were adopted to obtain the deformed geometry and to compute the effective diffusivity, conductivity, and permeability. The structure of a carbon felt was first scanned and reconstructed by XCT; using the results, a 3D model was generated and meshed for solid mechanics simulations. In the FEM simulation, the displacement of the microstructure at different compression ratios (CRs) was investigated considering the contact, friction, extrusion, and bending interactions between the carbon fibers. The relationship between the CR and transport properties was quantified using in-house PSM and LBM codes. The results reveal that the carbon felt is highly anisotropic. When compressed, the displacement of the carbon fibers changes significantly in the through-plane and in-plane directions. The effective diffusivities and permeability of the felt decrease with increasing CR, and its electrical conductivity increases with increasing CR. The present study demonstrates a workflow that combines experimental characterization and solid mechanics simulation to produce deformed solid mechanics models, which can be subsequently employed for mesoscopic simulations in order to obtain effective transport properties. This approach will enable computational investigations into general porous electrode materials, and more importantly, it can be employed to design new materials that can be engineered for optimal performance. [ABSTRACT FROM AUTHOR]

This paper reports on the development of a novel approach to investigate the stress and strain distributions at the fiber's scale of PEMFC gas diffusion layers (GDLs). The present method includes stochastic reconstruction and finite element solution procedure. The microstructure of a GDL was randomly generated and meshed, upon which solid mechanics simulations were performed. Stress and strain distributions in three dimensions were obtained by considering dynamic contact, frictional motion and extruding deformation of the fibers. A sensitivity analysis on the present model showed that frictional coefficient between fibers has more influence on the model results than the mechanical properties of the fiber. Our simulation results show that under compression, the fiber's displacement in the through-plane direction is significantly more than the in-plane direction. Fibers intruding into the gas channel were also observed. For the case with 20% compression ratio, the computed stress is mostly below 100 kPa with a maximum in excess of 1,000 kPa. Simulation results, which include stress and displacement distributions under compression, are in qualitative agreement with actual observations in the literature. The present methodology can be extended to most porous electrodes that involve material deformation to allow accurate evaluation of their transport properties and performance. [ABSTRACT FROM AUTHOR]