Uniform Distribution Of Reactants Research Articles

Modeling and simulation of novel bio-emulated flow field with improved branch channels on PEMFC performance

The channel geometry of the bipolar plate in the proton exchange membrane fuel cell (PEMFC) significantly influences its performance. In this study, a bio-emulated flow field (BEFF) pattern in the bipolar plate was used based on the external carotid artery design with its branches. A comprehensive investigation was conducted using a three-dimensional (3-D) multiphase computational fluid dynamics (CFD) model on bio-emulated flow fields with branch channels of zero (BE-0), six (BE-6), and ten (BE-10). The results obtained were compared with traditional parallel flow fields (TPFF) and traditional serpentine flow fields (TSFF). The BE-10 results showed reduced pressure drop, uniform distribution of reactants, and higher power output compared with other configurations. The peak power density of BE-10 surpassed that of TPFF by approximately 45.07% and exceeded BE-0 by 10.39%. The novel BEFF structure with an increase in branch channels showed that the reactants, temperature, and static pressure distribution are more uniform with better water management.

Enhanced water management in PEMFC cathode using streamlined baffles

This research investigates the impact of baffle configurations on water management within Polymer Electrolyte Membrane Fuel Cells (PEMFCs) using novel flow fields in configurations featuring staggered and parallel streamlined baffles. Utilizing the Volume of Fluid method, the two-phase flow is modeled within computational domains that encompass the flow field above the porous Catalyst and Gas Diffusion Layers. A key feature is the use of Dynamic Contact Angle model, accounting for surface tension and wall adhesion over time, which provides detailed insights into liquid water movement and pressure changes. Streamlined baffles significantly enhance water removal and reactant transport by creating circulations and increasing flow velocities. The parallel-baffle configuration demonstrated the highest water removal capability, reducing water content in flow channels by 20.08 % compared to straight channels and offering a more uniform distribution of reactants. Both baffled configurations improve performance by promoting reactant infiltration and water expulsion, but they also increase pressure drops. The parallel configuration experiences the highest pressure drop, about 4.5 times greater than the conventional straight channel, illustrating a trade-off between better water management and energy efficiency. This study provides important insights into how baffled flow field designs in PEMFCs influence flooding behavior and potentially overall performance.

Development of integrated packaged single fuel cell short stack based on titanium metal plates for mobile power generation

Bipolar plates (BPPs) and membrane electrode assemblies (MEAs) are the key components for proton exchange membrane fuel cells (PEMFCs), they are alternately arranged to construct a compact stack with high power generation. This stacking method may introduce several issues, such as the difficulties in maintenance, imprecise assembly and sealing. This paper presents a novel integrated packaged single fuel cell that employs titanium metal bipolar plates to construct a short stack with superior sealing performance and working reliability. To predict the performance of integrated packaged single cell, numerical model was developed to analyze the mass transfer of O2, H2 and H2O within the cell, revealing a uniform distribution of reactants and current. A short stack was manufactured with 10 layers of single cells, it retains excellent sealing properties and consistent output across a range of pressure conditions, with a leakage rate deviation lower than 0.03 mL/(min·cell) and membrane current density variation less than 5%. Finally, the electrochemical performance of the integrated packaged short stack was tested, its maximum power is 886.67 mW/cm2. It can achieve a rated output power of 169.14 W and an energy density of 1684.97 mW/cm3. Thus, our developed short stack has high energy utilization efficiency for power generation, and is anticipated to provide a durable power source for drones, robots and new energy vehicles.

The Effect of Obstacle Number, Shape and Blockage Degree in Flow Field of PEMFC on its Performance

<p>Proton exchange membrane fuel cell (PEMFC) has received extensive attention as it is the most common hydrogen energy utilization device. This research not only investigated the effect of obstacle number and shape on PEMFC performance, but also studied the effect of the blockage degree in the channel of PEMFC on its performance. It was found that compared with traditional scheme, longitudinally distributed obstacles scheme can significantly promote reactants transfer to catalyst layer, and the blockage degree in the channel effect PEMFC performance most. The scheme with 10 rectangular obstacles in single channel and 60% channel blockage had the best output performance and the most uniform distribution of reactants and products. Obstacle height distribution can significantly affect PEMFC performance, the blockage degree in the whole basin was large, particularly as the channel was blocked to higher degree in region 2 and region 3, higher net power density and better mass transfer effect can be obtained. Among them, the fuel cell with the blockage degree of 40%, 60% and 60% in region 1, region 2 and region 3 have the best PEMFC output performance and mass transfer, the net power density was 29.8% higher than that of traditional scheme.</p>

Numerical study of Tesla valve flow field on proton exchange membrane fuel cell performance

Effective flow channels in proton exchange membrane fuel cells (PEMFCs) can provide sufficient reactant and a more uniform reactant distribution, which allows the fuel cells to operate with high performances. The Tesla valve structure is thought to be a feasible structure for channel design due to its one-directional flow characteristics, yielding different performances with different flow directions. Numerical studies were conducted in this work to investigate the impacts of the channel structure, flow direction, and excess air coefficient on the fuel cell performance. Three types of flow channels (straight, symmetric Tesla valve, and asymmetric Tesla valve) and two flow directions (forward and reverse) were studied. The results showed that the maximum power density of the reversed asymmetric Tesla valve increased by 10.08 % compared to that of the conventional straight channel. Detailed research revealed that the Tesla valve resulted in a more intense flow than the conventional straight channel. The symmetric Tesla valve resulted in a greater pressure drop than the asymmetric valve. The Tesla valves with reverse flow could significantly limit the formation of an oxygen dead zone. Hence, enhanced Z-direction mass transfer and the lowest standard deviations of the oxygen and water distributions were observed. The effects of the excess air coefficient on the net power density were also studied. Increasing the excess air mass to the cathode facilitated the enhancement of the electrode voltage but required more parasitic power due to the growth in the pressure drop along the flow channel.

Porous Carbon Fiber Flow Fields for Heavy-Duty Polymer Electrolyte Fuel Cell (PEFC) Applications

The US Department of Energy (DOE) interim (2030) targets for polymer electrolyte fuel cells (PEFCs) in heavy duty vehicle applications accentuate reduced system cost (US $80/kW), increased peak efficiency (68%), and longer system lifetime (25,000 hrs) [1]. The bipolar plate in a PEFC has to serve several functions such as uniform reactant distribution with minimum pressure loss, efficient product water removal, and maintain high electronic and thermal conductivity. Multiple studies [e.g., 2-4] describe novel materials and engineered designs potentially meet these performance and durability requirements; however, cost is the limiting factor in most cases. For example, the cost of a state-of-the art stainless steel (SS 316L) plate, already approaching minimum feasible plate thickness, is estimated to be (US $3.5/kWnet), which is 17% higher than current DOE target [1]. Thus, low-cost substrate alternatives are required to reduce the cost and facilitate commercialization in heavy-duty applications. One such alternative is a novel PEFC architecture [5] utilizing a laminated structure consisting of flat thin metal foils that separate flow fields with channels formed into the porous gas diffusion layer (GDL). This architecture enables the use of much thinner metal plates compared to stamped ones, reducing the overall system mass and cost. The current study explores the performance of a wide aspect ratio (200 mm x 30 mm) PEFC test fixture with porous carbon fiber flow field compared to conventional solid flow field over a wide range of operating conditions. The wide aspect ratio and channel/rib dimensions for both the porous and the conventional solid flow field are chosen to provide a reasonable pressure loss relevant to heavy-duty PEFC stack application. This new architecture is expected to enable comparable system performance while reducing plate weight and cost.

Along-flow-path gradient flow field enabling uniform distributions of reactants for redox flow batteries

Designing flow fields that can lead to uniform distributions of reactants at a minimum pump work is critical to enhancing the performance of redox flow batteries. This paper reports on an improved design of conventional serpentine flow fields, in which the channel depth is linearly reduced from the inlet to the outlet, speeding up the flow speed along the flow path and enhancing the under-rid convection downstream toward the outlet. Three-dimensional numerical simulations reveal that the optimized gradient at 25% (the channel-depth ratio between the outlet and inlet) can lead to the highest pump-based voltage efficiency. Experimental validations demonstrate that the application of the optimized flow field to a vanadium redox flow battery leads to significant improvements in both energy efficiency and electrolyte utilization, which is 5.0% and 27.7%, respectively, higher than that with the conventional serpentine flow field at a relatively high current density and low flow rate (400 mA cm−2, 12 mL min−1 cm−2). The effectiveness of the flow field design in boosting the uniform reactant distribution provides a feasible approach for scaling up high-performance redox flow batteries.

Evaluating the effect of refined flow channels in a developed biomimetic flow field on PEMFC performance

In this study, an improved biomimetic flow field was proposed, and the effects of the number of refined flow channels on the pressure drop, species distribution and performance of the PEMFC were analyzed by numerical simulation. Subsequently, these developed biomimetic flow fields (BIFFs) were compared to the conventional parallel flow field (CPFF) and conventional serpentine flow field (CSFF). The results show that compared with CPFF, the BIFF with ten refined channels (BI-10) offered the benefits of a low-pressure drop, uniform reactant distribution, and higher output power. In addition, BI-10 showed superior heat dissipation compared with CSFF. As the number of refined flow channels increased, the oxygen distribution of the BI-10 became more uniform, and the fuel cell performance also improved. The peak power density of BI-10 was approximately 29.05% higher than that of CPFF and 17.80% higher than that of the original biomimetic flow field (BI-6). In addition, the net power density of BI-10 was similar to that of CSFF; however, BI-10 had a more suitable temperature distribution. Therefore, by increasing the number of refined flow channels, the distribution of reactants was more uniform, the pressure drop was smaller, and the hydrothermal management ability was better.

Bubble-derived contour regeneration of flow channel by in situ tracking for direct methanol fuel cells

A bubble-derived concept for contour regeneration of flow channel is developed to address the issues of carbon dioxide (CO2) management and reactant homogeneity in a direct methanol fuel cell (DMFC). The bubble contour is extracted from the visualization experiment based on the conventional sinusoidal flow channel (SFCH), which is used as a model to design and fabricate the bubble-derived flow channel (BDFCH). The simulation results indicate that this renewed channel shows a lower momentum loss and uniform reactant distribution. Because of the optimized amplitude (A) and period (W) of BDFCH, the regenerated flow channel displays superior cell performances under various testing conditions. The cell based on the renewed design produces a peak power density of 37.07 mW cm−2 at a flow rate of 1 mL min−1 and a methanol concentration of 6 M. The maximum performance improvement of the BDFCH is 30.8% higher than the SFCH with the combination of A = 0.15 and W = 5. The BDFCH based on the SFCH (A = 0.1 and W = 5) shows a higher cell performance than the SFCH at 6 M, demonstrating the scalability of BDFCHs. This new concept for precision design and construction of flow channels provides an efficient solution for practical flow field optimization of fuel cells.

A novel surrogate model for channel geometry optimization of PEM fuel cell based on Bagging-SVM Ensemble Regression

Channel structure plays an important role on the performance of proton exchange membrane fuel cell (PEMFC). In this study, the channel geometry of a PEMFC is optimized through genetic algorithm to obtain better performance. For the first time, a machine learning method called Bagging Ensemble Regression is employed as the surrogate model to calculate the fitness value of the algorithm, which accelerates the optimization process. First, a three-dimensional PEMFC simulation model is developed as the optimization prototype through CFD technology. Second, the Bagging ensemble model is trained through training data obtained from the CFD model. Then the Bagging ensemble model is integrated into the genetic algorithm to conduct the optimization process. Finally, the optimal model obtained is compared with the optimization prototype in terms of polarization curves, pressure drop, and reactant distribution, and the advantages of using Bagging ensemble model are discussed. Results show that the optimal model has a smaller pressure drop and a more uniform reactant distribution than the basic model at the expense of just a little power density. The presented surrogate model shows high prediction accuracy with only a small amount of training data, which is superior to the commonly used surrogate models.

Study of a Flow Field Design Suitable for Scaled-Up Fuel Cell Stacks

Fuel cells are used for automotive and stationary backup applications due to their lower operating temperature and high power density. The performance and robustness of Proton Exchange Membrane Fuel Cells are susceptible to the reactant distributions in the flow fields, operating pressure and humidity. It is crucial to maintain the critical parameters within the operating range to achieve improved performance. Moreover, water flooding on the cathode side is one of the significant issues associated with the scaled-up cells at higher power densities, leading to a drop in performance in PEMFC. This paper describes a novel flow field configuration used on the cathode side. In the present work, simulation and experimental validation are carried out on the scaled-up design consisting of oval and round shape patterns with uniform distribution at the inlet and outlet of the cathode side. A serpentine flow channel on the anode side and dual serpentine flow channel configuration as coolant flow channels are considered. This design achieves higher performance, low parasitic power requirement and uniform reactant distribution. The simulation results are validated against experiments and show good agreement with experiment results. A current density of 1.05 A/cm 2 at 0.58 V is obtained with the scaled-up design.

Study of novel flow channels influence on the performance of direct methanol fuel cell

The existing flow channels like parallel and gird channels have been modified for better fuel distribution in order to boost the performance of direct methanol fuel cell. The main objective of the work is to achieve minimized pressure drop in the flow channel, uniform distribution of methanol, reduced water accumulation, and better oxygen supply. A 3D mathematical model with serpentine channel is simulated for the cell temperature of 80 °C, 0.5 M methanol concentration. The study resulted in 40 mW/cm2 of power density and 190 mA/cm2 of current density at the operating voltage of 0.25 V. Further, the numerical study is carried out for modified flow channels to discuss their merits and demerits on anode and cathode side. The anode serpentine channel is unmatched by the modified zigzag and pin channels by ensuring the better methanol distribution under the ribs and increased the fuel consumption. But the cathode serpentine channel is lacking in water management. The modified channels at anode offered reduced pressure drop, still uniform reactant distribution is found impossible. The modified channels at cathode outperform the serpentine channel by reducing the effect of water accumulation, and uniform oxygen supply. So the serpentine channel is retained for methanol supply, and modified channel is chosen for cathode reactant supply. In comparison to cell with only serpentine channel, the serpentine anode channel combined with cathode zigzag and pin channel enhanced power density by 17.8% and 10.2% respectively. The results revealed that the zigzag and pin channel are very effective in mitigating water accumulation and ensuring better oxygen supply at the cathode.

High-temperature synthesis in TI+AL powder mixture exposed to gamma irradiation. The features of intermetallic phases formation

The purpose of the work presented is to study the processes of phase formation in mechanically activated Ti + Al powder mixture which was exposed to low doses of gamma radiation. A two-stage treatment of the initial powder mixture of the specified composition was conducted. At the first stage, the mixture was mechanically activated in order to achieve a high quality of contact between the reactants. At the second stage, the mixture was subjected to gamma irradiation in order to form a wide transition zone in the contact area. The irradiated mixture was heated by the external heating source. To study the processes of phase formation, the technique of time-resolved X-Ray diffraction was used. The comparative analysis of intermetallic phases formation sequences for irradiated and non-irradiated mixtures was carried out. It was found that the heterogeneous reactions pathways are significantly different for these cases. The detailed analysis of parallel and consecutives reactions was carried out at various stages of high-temperature synthesis taking into account the structure of the Ti–Al equilibrium diagram. It was found that the most probable mechanism of heterogeneous reaction in unirradiated mixture is the predominant dissolution of titanium with the formation of intermetallic phases TiAl, TiAl3. In the irradiated mixture, on the contrary, the flow of aluminum atoms dominates, which leads to the formation of the only synthesis product of the TiAl composition. In the case of forced cooling of the mixture after thermal explosion (TE), a uniform distribution of reactants is observed in the whole volume of the sample of the irradiated mixture which is similar in composition to the TiAl compound.

Learning from nature for healthcare, energy, and environment

Learning from nature for healthcare, energy, and environment

Effects of the membrane thickness and ionomer volume fraction on the performance of PEMFC with U-shaped serpentine channel

A three-dimensional, multi-component, single-phase model is applied for analyzing the electrochemical performance of the proton exchange membrane fuel cell (PEMFC) with U-shaped channel using COMSOL Multiphysics software. To validate the numerical model, the results are compared with the experimental data available in the literature. This work numerically investigates the effects of convection and diffusion under the rib, membrane thickness, ionomer content, and current density distribution at an interface between the gas diffusion layer and the catalyst layer. These effects were not studied for a U-shaped single serpentine channel despite having several benefits such as uniform reactant distribution through convection and diffusion under the rib and the resulting uniform current generation. A total of three membranes with 2, 3.5, and 5 mil thicknesses are analyzed, and an improvement of 17% in PEMFC performance with 2 mil thickness is observed owing to a decrease in internal resistance compared to 3.5 and 5 mil. Furthermore, an ionomer volume fraction in the catalyst layer is varied from 0.3 to 0.6, and the performance enhancement of 7% is reported at 0.5 volume fraction.

Scaling factors for channel width variations in tree-like flow field patterns for polymer electrolyte membrane fuel cells - An experimental study

To have a uniform distribution of reactants is an advantage to a fuel cell. We report results for such a distributor with tree-like flow field plates (FFP). Numerical simulations have shown that the width scaling parameters of tree-like patterns in FFPs used in polymer electrolyte membrane fuel cells (PEMFC) reduces the viscous dissipation in the channels. In this study, experimental investigations were conducted on a 2-layer FF plate possessing a tree-like FF pattern which was CNC milled on high-quality graphite. Three FF designs of different width scaling parameters were employed. I–V curves, power curves and impedance spectra were generated at 70%, 60% and 50% relative humidity (25 cm2 active area), and compared to those obtained from a conventional 1-channel serpentine FF. It was found that the FF design, with a width scaling factor of 0.917 in the inlet and 0.925 in the outlet pattern, exhibited the best peak power out of the three designs (only 11% - 0.08 W/cm2 lower than reference serpentine FF). Results showed that a reduction of the viscous dissipation in the flow pattern was not directly linked to a PEMFC performance increase. It was found that water accumulation, together with a slight increase in single PEMFC resistance, were the main reasons for the reduced power density. As further improvements, a reduction of the number of branching generation levels and width scaling factor were recommended.

Nature-Inspired Flow-Fields and Water Management for PEM Fuel Cells

Flow-field design is crucial to polymer electrolyte membrane fuel cell (PEMFC) performance, since non-uniform transport of species to and from the membrane electrode assembly (MEA) results in significant power losses. The long channels of conventional serpentine flow-fields cause large pressure drops between inlets and outlets, thus large parasitic energy losses and low fuel cell performance.Here, a nature-inspired approach is used to design flow-fields guided by the structure of the human lung.[1-4] Its fractal geometry provides scalable, uniform distribution of air from a single outlet (trachea) to multiple outlets (alveoli). Furthermore, the human lung transitions between two flow regimes: 14-16 upper generations of branches dominated by convection, and 7-9 lower generations of space-filling acini dominated by diffusion. The upper generations of branches reduce the gas flow to a rate compatible with the rate in the diffusional regime (Pé ~ 1); in addition, the channel dimensions between branching points are proportioned in a way that results in constant entropy production in both regimes and, thus, in minimal global entropy production over the entire structure of the human lung.By employing a three-dimensional (3D) fractal structure as flow-field inlet channel, we aim to yield similar benefits from replicating these characteristics of the human lung. The fractal pattern consists of repeating “H” shapes, where daughter “H’s” are located at the four tips of the parent “H”. The fractal geometry obeys Murray’s law, much like the human lung, hereby leading to minimal mechanical energy losses. Furthermore, the three-dimensional branching structure provides uniform local conditions on the surface of the catalyst layer, as only the outlets of the fractal inlet channel are exposed to the MEA.Numerical simulations were conducted to determine the number of generations required to achieve uniform reactant distribution and minimal entropy production. The results reveal that the ideal number of generations for minimum entropy production lies between N = 5 and 7, for 10 cm2 surface area.[3, 5] Guided by these simulation results, three flow-fields, with N = 3, 4 and 5, were 3D printed via direct metal laser sintering (DMLS), and experimentally validated against conventional serpentine flow-field based PEMFCs. The fractal flow-field based PEMFCs with N = 4 and 5 generations showed ~20% and ~30% increase in performance and maximum power density over serpentine flow-field based PEMFCs above 0.8 A cm-2 at 50% RH. At fully humidified conditions, though, the performance of a fractal flow-field based PEMFC with N = 5 significantly deteriorates due to flooding issues.[3]Another defining characteristic of the fractal approach is scalability, which is an important feature in nature. Fractal flow-fields can bridge multiple length scales by adding further generations, while preserving the building units and microscopic function of the system. Larger, 3D printed fractal flow-fields (25 cm2 surface area) with N = 4 are compared to conventional serpentine flow-fields. Performance results show that fractal and serpentine flow-field based PEMFCs have similar polarization curves, which is attributed to the significantly higher pressure drop (~ 25 kPa) of large serpentine flow-fields compared to fractal flow-fields. However, such excessive pressure drop renders the use of large serpentine flow-field prohibitive, thus favoring the fractal flow-field.[3]A shortcoming of these fractal flow-fields for PEMFCs operated at high humidity is, though, their susceptibility to flooding in the gas channels, due to low gas velocity. This problem has led to the development of a nature-inspired water management mechanism that draws inspiration from the ability of the Thorny Devil (Australian lizard) to passively transport liquid water across its skin using capillary pressure.[6] We have recently integrated this strategy with the fractal N = 4 flow-fields and verified the viability of the strategy using neutron imaging. Implementation of this water management strategy is expected to circumvent remaining problems of high-generation fractal flow-fields.

A comparison on the dynamical performance of a proton exchange membrane fuel cell (PEMFC) with traditional serpentine and an open pore cellular foam material flow channel

Minimising the pressure drop in flow channels, ensuring high efficiency and utilisation of open pore cellular foam (OPCF) material in place of a traditional serpentine channel are investigated in this work. The paper establishes novel mathematical model that takes into account the effect of pressure drop in the flow channel and compares the dynamics of a porous flow channel with those of the traditional serpentine flow channel. The performance of a Polymer Electrolyte Membrane fuel cell with porous foam flow channel is analysed under static and transient conditions. The fuel cell mass transport equations are used in the model that also takes into account the effect of varying the current on the stack temperature. The membrane water content and IV-curves are analysed and simulation results are presented based on the mathematical models of the proposed system using the MATLAB®/Simulink® environments. The effect of varying pore diameter, porosity, and the flow velocity on pressure drop are also investigated using sensitivity analysis. Due to the lower pressure drop provided by the uniform distribution of reactants in OPCF channel, an improvement of approximately 55% is observed in current density when compared with that of the serpentine channel under the same operating conditions. The investigation further concluded that a higher pore diameter can have a lower drop in pressure provided the flow velocity of the reactant does not exceed 6 m/s.

Towards uniform distributions of reactants via the aligned electrode design for vanadium redox flow batteries

Enhancing the hydraulic permeability of electrodes along both the through-plane and in-plane directions is essential in flow-field structured vanadium redox flow batteries, as it can promote uniform distributions of reactants, lower the concentration overpotential, and therefore improve battery performances. In this work, uniaxially-aligned carbon fiber electrodes with the fiber diameter ranging from 7 to 12 µm (average ~10 µm) are fabricated by electrospinning method. Attributed to the enhanced permeability of the aligned structure, the battery assembled with the prepared electrodes exhibits an energy efficiency of 84.4% at a current density of 100 mA cm−2, which is 13.2% higher than that with conventional electrospun fiber electrodes. The permeability in the in-plane direction is further tailored by adjusting the orientation of aligned fibers against the flow channels. Results show that when the orientation of aligned fibers is perpendicular to the direction of flow channels, the battery delivers the largest discharge capacity and the highest limiting current density (~900 mA cm−2). Such an enhancement in the battery performance can be ascribed to the more uniform in-plane distribution of reactants and current by maximizing the permeability along the direction vertical to the flow channels, as evidenced by a three-dimensional model.

A lung-inspired printed circuit board polymer electrolyte fuel cell

Fractal cathode flow-fields, inspired by the flow mechanism of air inside lungs, can provide homogeneous, scalable and uniform distribution of reactants to polymer electrolyte fuel cell (PEFC) electrodes. However, the complex 3D flow-fields demonstrated previously face manufacturing challenges, such as requiring selective laser sintering, an additive manufacturing method that is expensive to scale up. Here, a lung-inspired cathode flow-field is introduced and fabricated using low-cost, lightweight printed circuit boards (PCB). The uniformity and alignment between individual PCB layers producing the fractal hierarchy of flow channels have been characterised using X-ray computed tomography (X-ray CT). The performance of the fractal flow-field exceeds that of conventional single-serpentine flow-fields and is particularly beneficial when operating on air with a low relative humidity. The lung-inspired design is shown to lead to a more stable operation than the single-serpentine design, as a result of uniform distribution of reactants.