Flow Channel Geometry Research Articles

Advanced Bipolar Plates for the Next Generation PEM Water Electrolyzers: Flow-Field Design, Fabrication, and Optimization

Flow-fields, responsible for distributing reactants, like water for electrolysis, evenly across the active area of the cell as well as removing by-products, are key to achieving high efficiency and longevity in proton exchange membrane water electrolyzers (PEMWEs). Current problems include the complex interplay between fluid dynamics and electrochemical reactions leading to uneven distribution of reactants, which can cause hot spots and accelerated degradation of the cell components. Furthermore, the geometry of flow channels can result in increased pressure drop and higher energy consumption for the pumping of reactant fluids, directly impacting the overall efficiency and scalability of the technology.For PEMWEs, hydration of reaction sites in the membrane is a crucial factor that significantly influences their efficiency and performance. This study explores the rapid production and testing of multiple novel flow field geometries, each designed to increase cell performance due to multiple different factors. Each flow-field is designed, fabricated, and tested with a state-of-the- art MEA at operating conditions typical for an industrial electrolyzer. The performance of each flow-field design is compared against all other designs explored. Critical information about the impact of the pressure drop and the flow-field contact area upon the electrode is collected. Using this data, the performance of various flow-field designs is derived and discussed in this work.

Advances in Fuel Cell Performance Using Simulation Analysis in Toshiba Energy Systems & Solutions Corporation

The influence of channel and rib width of bi-polar plates on gas diffusion performance was investigated by simulation and experimental measurement. Simulation results showed that a ch./rib ratio of about 2 is a compromise between diffusivity and resistance, and that higher performance can be expected. The advanced cell with bi-polar plates with this flow channel geometry was fabricated and its performance was evaluated. IV characteristics of advanced cell exceeded simulation results, indicating that the effect of improved GDL/MPL tortuosity on diffusion performance was greater than expected.

Advances in Fuel Cell Performance Using Simulation Analysis in Toshiba Energy Systems & Solutions Corporation

The influence of channel and rib width of bi-polar plates on gas diffusion performance was investigated by simulation and experimental measurement. Simulation results showed that a ch./rib ratio of about 2 is a compromise between diffusivity and resistance, and that higher performance can be expected. The advanced cell with bi-polar plates with this flow channel geometry was fabricated and its performance was evaluated. IV characteristics of advanced cell exceeded simulation results, indicating that the effect of improved GDL/MPL tortuosity on diffusion performance was greater than expected.

Multi-Dimensional Modelling of Bioinspired Flow Channels Based on Plant Leaves for PEM Electrolyser

The Polymer Electrolyte Membrane Water Electrolyser (PEMWE) has gained significant interest among various electrolysis methods due to its ability to produce highly purified, compressed hydrogen. The spatial configuration of bipolar plates and their flow channel patterns play a critical role in the efficiency and longevity of the PEM water electrolyser. Optimally designed flow channels ensure uniform pressure and velocity distribution across the stack, enabling high-pressure operation and facilitating high current densities. This study uses flow channel geometry inspired by authentic vine leaf patterns found in biomass, based on various plant leaves, including Soybean, Victoria Amazonica, Water Lily, Nelumbo Nucifera, Kiwi, and Acalypha Hispida leaves, as a novel channel pattern to design a PEM bipolar plate with a circular cross-section area of 13.85 cm2. The proposed bipolar design is further analysed with COMSOL Multiphysics to integrate the conservation of mass and momentum, molecular diffusion (Maxwell–Stefan), charge transfer equations, and other fabrication factors into a cohesive single-domain model. The simulation results showed that the novel designs have the most uniform velocity profile, lower pressure drop, superior pressure distribution, and heightened mixture homogeneity compared to the traditional serpentine models.

Performance enhancement in polymer electrolyte membrane fuel cell with flow traps and field gradients: A Numerical Study

Efficient reactant distribution and water removal are critical during polymer electrolyte fuel cell (PEFC) operation. The bipolar plate and its corresponding flow field design are vital among the PEFC components for enhancing reactant transport and water removal. The issues arising in the PEFC during the high current operation, such as reactant starvation and water removal, can be alleviated by improving the flow channel geometry. In this study, we analyze the variation in overall PEFC performance and corresponding reactant transport phenomenon for two independent design cases. The converging gradient design without channel traps at 0.4 V operating voltage exhibited a current density increment of 6.85% against the conventional design. Moreover, at 0.4 V, including channel traps enhanced the current density, as we observed a current density increment of 7.1% for the converging design with channel traps against the conventional design without channel traps. Likewise, at 0.4 V, the diverging design with channel traps exhibited a current density increment of 5.85% against the diverging design with no channel traps. Further, enhanced reactant distribution is observed in the catalyst layer upon introducing channel traps in the flow field design.

Significance of new geometry of flow channels in proton exchange membrane fuel cell with comparing experimental and numerical methods

The flow field geometry mainly affects the electrochemical reaction, the mass transfer, and gas diffusion layers. All these parameters affect the performance of a PEM fuel cell. In this study, a three-dimensional model is used for all parts of the fuel cell such as the flow channels, gas-diffusion electrodes, catalyst layers, and the membrane. These equations are numerically solved using a finite volume-based computational fluid dynamics technique to investigate the effect of using new geometries such as tubular, rectangular, elliptical, and triangular compared to planner-type fuel cells. Also, a test bench was designed and constructed for checking the cell and a series of experiments were done. The results show that there is good agreement between the numerical and experimental results. In summary, the tubular geometry has the best performance compared to others which can increase the execution of the fuel cell maximum by 43 %.

CFD Analysis of Pressure Drop Reduction in PEMFC Flow Channels with Distinct Cross-Section Shapes

Proton exchange membrane fuel cells (PEMFCs) have great potential to produce renewable, sustainable and clean energy and reduce air pollutants to mitigate climate change. PEMFCs consist of distinct parts including anode and cathode bipolar plates having flow channels, gas diffusion layers, catalyst layers, and membrane. The flow channel geometry influences the flow and pressure drop characteristics of the channel and cell performance. In this work, a three-dimensional (3D) CFD model is built employing SOLIDWORKS and ANSYS Workbench. The innovative configurations are generated by changing the half of 0.2 x 0.2 mm square channel to 0.3 x 0.1 mm, 0.3 x 0.15 mm, 0.3 x 0.2 mm and 0.3 x 0.25 mm rectangular section at the top. The results showed that increasing rectangular section height significantly reduced pressure drop at the anode and cathode with a slight decrease in the current density at 0.4 and 0.6 V. The new configuration with 0.2 x 0.1 mm half square section at the bottom and 0.3 x 0.25 mm rectangular section at the top decreases the current density, anode and cathode pressure drop of 11%, 69% and 58%, respectively in comparison to 0.2 x 0.2 flow channel at 0.4 V. Taking into account pressure loss along the flow channels, this configuration is a good option to improve the cell performance.

Investigation of the Effect of Graphite Bipolar Plate Flow Channel Inhomogeneities and Faults on HT-PEM Fuel Cell Stack Performance

Bipolar plates are a key component of fuel cell stacks. Bipolar plates have multiple functions. They connect the single cells of the stack electrically and must be therefore electrically conductive. They separate oxidant and fuel gases and distribute them on each side over the membrane-electrode-assembly (MEA). Bipolar plates separate coolant liquid too. Fuel cell stack is cooled by coolant liquid which is flowing through the cooling flow channels in the middle of bipolar plates.Especially the bipolar plates for HT-PEM must endure a low pH environment, continuous electrical potential, and higher temperatures up to 200°C. The focus here is on investigations of anode and cathode side flow channels of graphite bipolar plates. Inhomogeneities and faults of flow channels are examined and their effects on fuel cell stack performance are analyzed. The analyses are based on optical scan data of flow channel geometry and measurement data of a HT-PEM fuel cell full stack consisting of 120 cells operated on a testbed under different variations. Inlet pressure and stoichiometry of both anode and cathode were varied, anode was fed with pure hydrogen and with different reformate gas compositions consisting of hydrogen, nitrogen, carbon dioxide and carbon monoxide. For each variation point, polarization curves between 0 A/cm2 – 0,55 A/cm2 in step of 0,05 A/cm2 were recorded.With an on testbed installed cell voltage monitoring (CVM) system voltages of every cell were measured and logged. Enormous amount of optical scan data consisting of width and depth information of flow channels was merged to certain statistical data for anode and cathode bipolar plates. Correlations between statistical data and cell voltages are still being investigated. It is planned to repeat the measurements with another 120 cells HT-PEM fuel cell full stack and compare the results.

Influence of wall-slip on material removal in abrasive flow machining

Abrasive flow machining (AFM) process, as a widely known technique for finishing internal surfaces of complex parts, can significantly improve the performance and reliability of components in numerous industries. Prediction of material removal rate (MRR) is a vital task in AFM process because it significantly affects the efficiency and cost-effectiveness of the process. In-depth studies about the influence of input parameters on material removal in AFM process, however, are limited. In this paper, the mechanism of material removal was investigated, and a MRR modelling was then established in which viscoelastic extrusion modelling with wall slip conditions was employed in AFM process. A novel fixture with gradient shear flow channel was designed. MRR obtained by simulations and experiment showed a reasonable agreement. Finally, parameters, including abrasive media pressure, velocity and shape geometry of flow channel, were identified as key factors affecting MRR in AFM process. Established computational fluid dynamics (CFD) analysis and MRR modelling can be a powerful tool to determine MRR in future AFM process.

Optimal Sizing of Vanadium Flow Battery Stack

A number of effects impact on the performance a Vanadium Flow Battery (VFB) multicell stack, such as shunt currents, and hydraulic losses. The formers are caused by the different cell electric potentials which drive the vanadium charged species to move along the hydraulic flow paths inside the cells and stack, resulting in electric currents (dubbed “shunt”) and the related Joule losses [1]. The latter are due to the friction losses in the porous electrodes, in the stack hydraulic paths and in the external hydraulic piping. In addition, losses are also due to the hydraulic ancillary devices, to the cell electrochemical overpotentials and to self-discharge effects resulting from vanadium species crossover through the membranes [2]. Shunt-currents and hydraulic losses can be kept low with a proper hydraulic circuit design, even if they call for opposite choices. In fact, the trade-off between shunt current losses and pumping losses is the crucial issue in designing VRFB hydraulic circuits [3]. The evaluation of shunt current is quite difficult from experimental point of view [4]. Indeed, they can be computed numerically by solving an equivalent electrical circuit in which each cell was represented as an ideal voltage source E0,n in series with an internal resistance Ri,n , which represents the cell overpotential voltage drop, both parameters being SOC dependent. The electrolyte flow segments of the stack, i.e. manifolds, flow channels and felts, can be modelled as resistors [1]. In this work the authors provide a shunt current evaluation by calculating the electrical resistance of the n-th segment with length lk,n and cross section Ak,n as Rk,n, ± = lk,n /σk ± ,n Ak,n , where k stands for manifold (m) and cell flow channels and felts (c). In particular this work is focuses on the evaluation of Rc by means FEM analysis by varying the cell geometry. The final goal is a multiphysic optimization of a multicell VFB stack by reducing shunt currents losses and pressure loss, i.e. by optimizing the cell area and cell number. This work presents the preliminary results of such optimization analysis for VFBs stacks, performed at the Electrochemical Energy Storage and Conversion Laboratory (EESCoLab) at the University of Padua (Italy). In Fig. 1 is presented a preliminary evaluation of the electrical resistance of a flow channel geometry Rc of a large-scale cell, that is the starting point for the evaluation of the optimal size of the VFB stack for a desired power.

Numerical analysis of the effects of interconnector design and operating parameters on solid oxide fuel cell performance

Fuel cells can provide higher electrical conversion efficiency than traditional coal-fired power plants and electric generators based on internal combustion engines. In addition, high-efficiency solid oxide fuel cells (SOFC) have two specific advantages compared with other fuel cells as a result of their high-temperature operation. First, SOFCs are compatible with various fuels, ranging from hydrogen to CO and hydrocarbons. Second, SOFCs generate significant amounts of exhaust heat that can be used in combined heat and power systems. Furthermore, SOFCs have quiet and vibration-free operation, eliminating the noise typically associated with power generation systems. These fuel cells also produce no or very low levels of SO2 and NO emissions. In this study, we numerically investigated the performance of a planar SOFC with different interconnector designs at various operating temperatures. Multiple parameters were considered, such as interconnection geometries, anode and cathode materials, operating temperatures, and flow rates. As a result, the horizontal sinusoidal flow channel geometry, operating temperature of 600 °C, hydrogen gas flow rate of 86.5 SCCM/min, and oxygen gas flow rate of 28.75 SCCM/min, NiO anode material, and LSCF cathode material provided the greatest performance in terms of energy and current density.

Long‐term monitoring on a new channelized stream section: changes in mesohabitat, composition, and size structure of fish assemblages

The construction of riverine structures (weirs, bridges, or channelization) on riverbeds causes alterations in the flow regime and channel geometry. Once a new stretch is created, species must colonize it. The ecological succession processes that are entailed are decisive for adequate recovery after alterations, and understanding these processes would enable elaborate efficient restoration actions. We analyzed environmental variables and the colonization and succession patterns of fish assemblages in a new channelized stretch of a river from its construction to the present (from 1996 to 2020) in the northern Iberian Peninsula. During the studied period, habitat diversity increased, and mesohabitat became more complex. Depths, depth diversity, and the number of pools in the new channel increased with time. Water temperature decreased because of the new shade provided by riparian forests. The size‐related variables of the fish community (size diversity, mean, and maximum length) increased in the new section, achieving similar values to those in the control section. The slopes of the fish size spectra showed a slow evolution over 25 years from a fish assemblage dominated by small fish to a more size‐diversity fish community. Our results suggest that habitat complexity shape fish assemblage and structure. Moreover, size‐related variables can be effective ecological indicators of fish colonization and succession processes. Finally, small‐scale restoration measures in the riverbed and riparian forest are expected to increase the effectiveness of future restoration projects in rivers.

Flow channel structure optimization and analysis of proton exchange membrane fuel cell based on the finite data mapping and multi-field synergy principle

Design and optimization of the flow channel structure is an effective approach to improve the performance of the proton exchange membrane fuel cell (PEMFC). Based on the three-dimensional mathematical model of a single cell, this paper applied the artificial neural network method to obtain the exact relationship between the flow channel geometry size and the output performance of PEMFC with finite data by combining response surface analysis and central composite design. Under the Based on this model, the optimal double-inverted trapezoidal tapering channel structure and related dimensional parameters are obtained by NSGA-II algorithm. The comparisons show that the optimized PEMFC improves the peak power by 8.5% and extends the operating range of current density by 15.5%. Multi-field synergy principle analysis revealed a 5.95% increase in overall heat transfer capability, enhanced mass transfer capability on the cathode side, and a 28.57% increase in the average mass fraction of oxygen at the diffusion layer and runner crossover. In addition, the total drainage capacity was increased by 5.35%. In conclusion, the proposed finite data mapping optimization method and multi-field synergistic theoretical analysis can effectively guide and evaluate the design and optimization of the PEMFC.

Drift-flux model for upward dispersed two-phase flows in vertical medium-to-large round tubes

The void fraction prediction is critical in nuclear safety analyses. Available one-dimensional computational codes heavily depend on the two-fluid model. The interfacial drag force in the momentum equation of the two-fluid model is currently formulated using the drift-flux model. Thus, the drift-flux model is critical for advanced two-phase flow analysis computational codes. The drift-flux model is characterized by two essential parameters: the distribution parameter and the drift velocity. The distribution parameter expresses the covariance of the area-averaged product of a void fraction and mixture volumetric flux. Flow channel geometry is a significant factor affecting the distribution parameter. The drift velocity expresses the relative velocity between gas and liquid phases. A bubble shape regime affects the drift velocity. The bubble shape regime is susceptible to flow regime dependence on the bubble Reynolds number. Bubbles in a spherical or distorted particle regime (group-1 bubbles) dominate in bubbly flow at a low void fraction, whereas bubbles in a slug or cap bubble regime (group-2 bubbles) play a critical role in beyond-bubbly flow. Whether slug bubbles or cap bubbles appear depends on the channel size. Thus, flow channel size significantly affects the drift velocity. The drift velocity dynamically changes along the two-phase flow, transforming from bubbly to beyond-bubbly flows.The present study first formulates the evolution process of the drift velocity using the two-bubble-group approach. A two-group-based formulation is simplified to model the drift velocity behavior at the bubbly-to-beyond-bubbly flow transition. A scheme is proposed to explicitly calculate the distribution parameter and drift velocity using operating parameters. A drift-flux correlation with the new drift velocity model is evaluated by 750 data collected from 8 different sources. Tested fluid systems are nitrogen-water, air-water, and steam-water systems. Flow channel diameter ranges from 0.0508 to 0.305 m. Test section height (L)-to-channel diameter (D) ratio L/D ranges from 9.41 to 130. Superficial gas velocity is changed from 0.0100 to 11.2 m/s, whereas superficial liquid velocity is changed from 0 (pool condition) to 2.6 m/s. Operating pressure covers from 0.1 to 4.6 MPa. A systematic evaluation demonstrates the validity of the newly developed drift velocity model for a wide range of test conditions. This model is simple enough to be implemented into existing one-dimensional computational codes without any substantial code architecture change.

Development of Fused Deposition Modeling of Multiple Materials (FD3M) Through Dynamic Coaxial Extrusion.

Multimaterial additive manufacturing is expanding the design space realizable with 3D printing, yet is largely constrained to sequential deposition of each individual material. The ability to coextrude two materials and change the ratio of materials while printing would enable custom-tailored polymer composites. Here, the evolution of a dynamic material coextrusion process for additive manufacturing capable of printing any ratio between and including two neat input materials is described across 3 hot-end generations and 14 implemented design iterations. The designs evolved with increased understanding of manufacturing constraints associated with the additive manufacturing of metal components with internal flow bore diameters on the order of 2 mm and typical bore length around 50 mm. The second generation overcame this issue by partitioning the design into two pieces to locate the flow channel geometry at the interface between the components so that the details could be easily printed on the components' external surfaces. The third concept generation then focused on minimizing flow channel volume to reduce the average length when transitioning between materials by 92%. The third-generation design was also used to investigate the improvements in dimensional stability during annealing of acrylonitrile butadiene styrene (ABS) made possible by coextruding ABS with a polycarbonate (PC) core. The standard deviation of part shrinkage after annealing was 7.08% for the neat ABS but reduced to 0.24% for the coextruded ABS/PC components.

Investigation of reinforcement learning for shape optimization of 2D profile extrusion die geometries

Profile extrusion is a continuous production process for manufacturing plastic profiles from molten polymer. Especially interesting is the design of the die, through which the melt is pressed to attain the desired shape. However, due to an inhomogeneous velocity distribution at the die exit or residual stresses inside the extrudate, the final shape of the manufactured part often deviates from the desired one. To avoid these deviations, the shape of the die can be computationally optimized, which has already been investigated in the literature using classical optimization approaches [7,32,47].A new approach in the field of shape optimization is the utilization of RL as a learning-based optimization algorithm. RL is based on trial-and-error interactions of an agent with an environment. For each action, the agent is rewarded and informed about the subsequent state of the environment. While not necessarily superior to classical, e.g., gradient-based or evolutionary, optimization algorithms for one single problem, RL techniques are expected to perform especially well when similar optimization tasks are repeated since the agent learns a more general strategy for generating optimal shapes instead of concentrating on just one single problem.In this work, we investigate this approach by applying it to two 2D test cases. The flow-channel geometry can be modified by the RL agent using so-called FFD [34], a method where the computational mesh is embedded into a transformation spline, which is then manipulated based on the control-point positions. In particular, we investigate the impact of utilizing different agents on the training progress and the potential of wall time saving by utilizing multiple environments during training.

Quantitative Criteria for the Degree of Pathological Remodeling of the Aortic Duct

Analysis of the properties of the aorta was carried out by numerous researchers using several parameters. However, the general laws of change in the dynamic geometry of the aortic flow channel in connection with the hydrodynamics of the swirling blood flow have not been studied properly. Therefore, at present, attempts to correct various diseases are carried out based on the location of the aneurysm, and not in accordance with the general patterns of changes in the dynamic geometry of the entire aortic channel. For a proper understanding of the aortic flow channel remodeling mechanisms, it is necessary to determine the quantitative parameters that formalize the geometry of this channel. The geometric shape of the aorta primarily depends on the hydrodynamics of the flow inside the aortic flow channel, which is the only source of force impact on its walls. The main result of the present study was that we obtained the new quantitative parameters that characterize the normal aorta and the degree of its shape deviations caused by pathological changes of the aortic duct. These parameters were calculated based on the software processing of the three-dimensional aortic reconstruction in normal conditions and in the case of differently localized aortic aneurysm.

Heat Transfer and Pressure Drops in a Helical Flow Channel Liquid/Solid Fluidized Bed

Industrial liquid/solid fluidized bed heat exchangers are commonly used with particle recycling systems to allow an increased superficial velocity and higher heat transfer rates. Here, experimental results are reported on a novel helical flow channel geometry for liquid/solid fluidized beds which allow higher heat transfer rates and reduced complexity by operating below the particle transport fluid velocity. This eliminates the complexity of particle recycle systems whilst still delivering a compact heat exchanger. The qualitative character of the fluidization was studied for a range of particle types and sizes under several inclinations of the helices and various hydraulic diameters. The best fluidization combinations were further studied to obtain heat transfer coefficients and pressure drops. Improvements over the heat exchange from a plain concentric tube in an annulus were obtained to the following degree: vertical fluidized bed, 27%; helical baffles, 34 to 54%; and fluidized bed with helical baffles, 69 to 89%.

Quantification of reagent mixing in liquid flow cells for Liquid Phase-TEM

Liquid-Phase Transmission Electron Microscopy (LP-TEM) offers the opportunity to study nanoscale dynamics of phenomena related to materials and life science in a native liquid environment and in real time. Until now, the opportunity to control/induce such dynamics by changing the chemical environment in the liquid flow cell (LFC) has rarely been exploited due to an incomplete understanding of hydrodynamic properties of LP-TEM flow systems. This manuscript introduces a method for hydrodynamic characterization of LP-TEM flow systems based on monitoring transmitted intensity while flowing a strongly electron scattering contrast agent solution. Key characteristic temporal indicators of solution replacement for various channel geometries were experimentally measured. A numerical physical model of solute transport based on realistic flow channel geometries was successfully implemented and validated against experiments. The model confirmed the impact of flow channel geometry on the importance of convective and diffusive solute transport, deduced by experiment, and could further extend understanding of hydrodynamics in LP-TEM flow systems. We emphasize that our approach can be applied to hydrodynamic characterization of any customized LP-TEM flow system. We foresee the implemented predictive model driving the future design of application-specific LP-TEM flow systems and, when combined with existing chemical reaction models, to a flourishing of the planning and interpretation of experimental observations.

Operation and Multi-Objective Design Optimization of a Plate Heat Exchanger with Zigzag Flow Channel Geometry

The performance of a plate heat exchanger (PHE) using water as the working fluid with zigzag flow channels was optimized in the present study. The optimal operating conditions of the PHE are explored experimentally by the Taguchi method, with effectiveness as the objective function. The results are further verified by the analysis of variance (ANOVA). In addition, the zigzag flow channel geometry is optimized by the non-dominated sorting genetic algorithm-II (NSGA-II), in which the effectiveness and pressure drop of the PHE are considered the two objective functions in the multi-objective optimization process. The experimental results show that the ratio of flow rates is the most important factor affecting the effectiveness of the PHE. The optimal operating conditions are the temperatures of 95 °C and 10 °C at the inlets of hot and cold water flows, respectively, with a cold/hot flow rate ratio of 0.25. The resultant effectiveness is 0.945. Three geometric parameters of the zigzag flow channel are considered, including the entrance length, the bending angle, and the fillet radius. The sensitivity analysis of the parameters reveals that a conflict exists between the two objective functions, and multi-objective optimization is necessary for the zigzag flow channel geometry. The numerical simulations successfully obtain the Pareto optimal front for the two objective functions, which benefits the determination of the geometric design for the zigzag flow channel.