Current Density Distribution Research Articles

Effects of an easy-to-implement water management strategy on performance and degradation of polymer electrolyte fuel cells

Intermittent switching between wet and dry reactant gases during operation in a polymer electrolyte fuel cell (PEFC) can improve performance stability, alleviating the effects of flooding by controlling the water content within the system. However, lifetime durability may be affected due to membrane electrode assembly (MEA) boundary delamination and membrane damage. Two relative humidity (RH) control strategies were investigated, using electrochemical performance and MEA degradation as critical indicators. It was found that intermittent switching between wet and dry gases does not accelerate fuel cell degradation if the duration of the dry gas period is set reasonably (dry gases stops before the voltage reaches the apex of the hump). Additionally, current and temperature distribution mapping was utilised to capture the dynamic response between these transitional stages. The switching of dry gases first makes the current density distribution homogeneous, and the maximum current density is reduced subsequently. Then, the current density near the inlet keeps decreasing. Intermittent switching between wet and dry reactant gases is easy to implement and overcomes limitations in mass transfer at medium and high current densities.

Gas-liquid mass transfer characteristics of a novel three-dimensional flow field bipolar plate for laser additive manufacturing of proton exchange membrane fuel cell

Compared with the conventional two-dimensional flow field, the novel three-dimensional flow field can rely on the slope to force the reaction gas into the catalytic layer (CL), which effectively improves the performance of the proton exchange membrane fuel cell (PEMFC). Three novel three-dimensional flow field bipolar plates (3D-Ⅰ, 3D-Ⅱ, 3D-Ⅲ) composed of hollow slope units were designed and prepared by selective laser melting (SLM) technology in this study. The characteristics of gas-liquid mass transfer in different flow fields are compared by experiments and numerical simulations, and the effects of through-holes on the slope on the performance of PEMFC are discussed in depth. The results showed that the maximum power density generated by 3D-III was 451.4 mW/cm2, which is 21.2% and 3% higher than that of 3D-Ⅰ and 3D-Ⅱ, respectively. 3D-III was better than 3D-II in terms of oxygen concentration distribution, water distribution and uniformity of current density distribution. This is due to the through-holes on the main slope of 3D - Ⅲ can not only facilitate the discharge of product water and reduce the water delivered to CL but also makes full use of the hollow part of the slope unit, expanding the space in which the gas can flow.

Optimization of electromagnetic flow measurement system based on a new mesh electrode

Electromagnetic flowmeter(EMF) is a common volumetric flow measurement instrument widely used in industrial flow measurement. With the development of EMF in the direction of high precision and intelligence, it is increasingly urgent to further improve the accuracy of EMF measurement. The key to reducing measurement error and eliminating the impact of interference noise is optimizing the electromagnetic flow sensor structure. Aiming at the existing EMF electrode optimization deficiencies, a new mesh structure electrode is firstly proposed in this paper. Then, a theoretical study on the distribution of virtual current density based on this mesh structure electrode is carried out, different structure electrodes are verified and analyzed through COMSOL finite element simulation, and the optimal structure design parameters of the new mesh electrode are obtained. Finally, an experimental platform is built, and a comparative experiment is conducted on the electromagnetic flow measurement system composed of the new mesh structure electrodes. The experimental results show that the maximum relative error of the optimized electromagnetic flow measurement system (OEMFS) is reduced by 0.47% compared with the ordinary EMF in the non-axisymmetric flow test. In the low-flow velocity test, the maximum relative error of the OEMFS is reduced by 7.46% compared with the ordinary EMF. In the strong interference test, the steady-state fluctuation of the amplitude of the OEMFS is reduced by 5.01% compared with the ordinary EMF. The OEMFS has better anti-interference, and the relative error of the system is less affected by the change in flow rate.

Modeling and Comparative Performance Analysis of Perovskite Solar Cells with Planar or Nanorod SnO2 Electron-Transport Layers

Application of various electron-transport layers (ETLs) with desired morphology and dimensions is a key factor to be considered for the structural designs of perovskite solar cells (PSCs) in order to obtain enhanced optical and electrical properties. The metal-oxide ETLs composed of one-dimensional nanorod arrays are one of the most frequently used nanostructures for electron transporting in PSCs. In this work, computer-simulation methods are employed to investigate the optoelectrical properties of PSCs with planar and nanorod-based ${\mathrm{Sn}\mathrm{O}}_{2}$ ETLs. A two-dimensional optical model is used to determine the optical responses of devices and the standard drift-diffusion model is utilized to simulate their behavior and performance. The aspect ratio and the density of ${\mathrm{Sn}\mathrm{O}}_{2}$ nanorods are varied to examine their effect on the optical and the electrical properties of resulting devices and the findings are contrasted with those of planar devices. It is found that under optimum conditions, PSCs with thin planar ${\mathrm{Sn}\mathrm{O}}_{2}$ ETLs, which are referred to as reference planar devices, outperform PSCs with nanorod-based ${\mathrm{Sn}\mathrm{O}}_{2}$ ETLs even if the light-harvesting properties of the latter are improved with the implementation of structured ETLs. The underlying reasons for this phenomenon are analyzed and rationalized through a detailed analysis and comparison of electric field, current density, and carrier recombination distributions in PSCs. The findings of this work can be used as a theoretical guide for designing and fabrication of high-performance planar and structured PSCs using ${\mathrm{Sn}\mathrm{O}}_{2}$ ETLs.

A non-intrusive approach for physics-constrained learning with application to fuel cell modeling

A data-driven model augmentation framework, referred to as weakly-coupled Integrated Inference and Machine Learning (IIML), is presented to improve the predictive accuracy of physical models. In contrast to parameter calibration, this work seeks corrections to the structure of the model by (a) inferring augmentation fields that are consistent with the underlying model, and (b) transforming these fields into corrective model forms. The proposed approach couples the inference and learning steps in a weak sense via an alternating optimization approach. This coupling ensures that the augmentation fields remain learnable and maintain consistent functional relationships with local modeled quantities across the training dataset. An iterative solution procedure is presented in this paper, removing the need to embed the augmentation function during the inference process. This framework is used to infer an augmentation introduced within a polymer electrolyte membrane fuel cell (PEMFC) model using a small amount of training data (from only 14 training cases). These training cases belong to a dataset consisting of high-fidelity simulation data obtained from a high-fidelity model of a first generation Toyota Mirai. All cases in this dataset are characterized by different inflow and outflow conditions on the same geometry. When tested on 1224 different configurations, the inferred augmentation significantly improves the predictive accuracy for a wide range of physical conditions. Predictions and available data for the current density distribution are also compared to demonstrate the predictive capability of the model for quantities of interest which were not involved in the inference process. The results demonstrate that the weakly-coupled IIML framework offers sophisticated and robust model augmentation capabilities without requiring extensive changes to the numerical solver.

Numerical investigation of enhanced mass transfer flow field on performance improvement of high‐temperature proton exchange membrane fuel cell

AbstractThe enhanced mass transfer flow fields have been proven to be an effective measure to improve the cell performance of low‐temperature proton exchange membrane fuel cells, yet little research has been done for high‐temperature proton exchange membrane fuel cells (HT‐PEMFC). In this work, three types of cathode‐enhanced mass transfer flow fields (tapered, staggered‐blocked, and blocked) are designed. The effects of various flow fields on the reactant delivery, current density distribution uniformity, and net power output of HT‐PEMFC are quantitatively investigated and compared. It is found that the three enhanced mass transfer flow fields can effectively increase the performance of HT‐PEMFC by transforming the traditional diffusion into a combination of diffusion and forced convection. In the sight of the superior performance and lower flow resistance, the tapered flow field is thought to be the optimal candidate for HT‐PEMFC among the four flow fields, with a 12.21% net power increment and 5.32% current density distribution uniformity improvement at 1.4 A/cm2 compared to the conventional flow field. These results support further performance enhancements and applications of HT‐PEMFC.

Experimental study of the mechanism of prepulse current on Z-pinch plasma using Faraday rotation diagnosis.

The prepulse current is an effective way to optimize the load structure and improve the implosion quality of the Z-pinch plasma. Investigating the strong coupling between the preconditioned plasma and pulsed magnetic field is essential for the design and improvement of prepulse current. In this study, the mechanism of the prepulse current on the Z-pinch plasma was revealed by determining the two-dimensional magnetic field distribution of preconditioned and nonpreconditioned single-wire Z-pinch plasma with a high-sensitivity Faraday rotation diagnosis. When the wire was nonpreconditioned, the current path was consistent with the plasma boundary. When the wire was preconditioned, the distributions of current and mass density presented good imploding axial uniformity, and the imploding speed of the current shell was higher than that of the mass shell. In addition, the mechanism of the prepulse current suppressing the magneto-Rayleigh-Taylor instability was revealed, which formed a sharp density profile of the imploding plasma and slowed the shock wave driven by the magnetic pressure. This discovery is essential and instructive for the design of preconditioned wire-array Z-pinch experiments.

The pinhole effect on proton exchange membrane fuel cell (PEMFC) current density distribution and temperature distribution

The proton exchange membrane (PEM) is a critical portion of a proton exchange membrane fuel cell (PEMFC). However, it is strongly influenced by pinhole defects owing to degradation during its operation or manufacture. Such defects may accelerate chemical polymer decomposition, eventually causing fuel cell failure and other safety issues. Thus, it is necessary to detect and characterize pinhole degradation while determining the effect of pinhole on electrochemical behavior and fuel cell performance. Herein, pinholes of different sizes (10 and 100 µm) were fabricated on a 50-cm2 catalyst-coated membrane (CCM) and characterized using commercial current scan shunt (CSS) S++ Simulation Services (Hephas Energy) to investigate the effects of pinhole size on current density and temperature distributions of the PEMFC. Our analyses show that hydrogen crossover from the anode to the cathode through a pinhole can cause hydrogen diffusion and a hydrogen oxidation reaction (HOR) on the cathode electrode surface under certain conditions. Consequently, local reverse currents and hot spots are detected around the pinhole position under open-circuit voltage (OCV) and the corresponding current and temperature distribution trends are uniform. Conversely, the reverse current immediately disappeared from the current distribution map because water exists under operation conditions, resulting in membrane swelling and pinhole sealing. Thus, hydrogen crossover decreased and local reverse currents reappeared as a result of anode overpressure during fuel cell operation. The local reverse current becomes weaker when using the same-sized pinhole under the same anode overpressure because the overall current density increases. Furthermore, owing to the presence of water, the capillary force for the 100-µm pinhole was higher than that for the 10-µm pinhole, indicating that more anode overpressure is required to generate a local reverse current. Thus, the position and size of the pinhole can be effectively detected using in situ characterization.

Fabrication Tradeoff Based Optimal Synthesis of Winding Configurations for Planar Transformer in CLLC DC–DC Converter

Adhering to the objective of modelling and selecting the most optimal winding configuration for a high frequency planar transformer (HFPT) for auxiliary charging systems for more electric aircrafts (MEA) this paper elucidates numerous fabrication and design-based constraints and correlations to enable parametric modelling of various magnetic components. Instead of providing generalized solutions, this paper thoroughly characterizes all possible winding configurations for HFPT employed in a bidirectional CLLC DC/DC converter. A detailed analytical study is presented for each component and verified using several instances of 3D Finite Element Analysis (FEA) based model to synthesize the effective field and current density distribution in the windings. Several design-based trade-offs are graphically explained with various criteria pertaining to optimal winding selection to study the interdependence of the resultant parameters on hardware specifications, such as the PCB thickness and its fabrication layout, air gaps and conductor thickness. The paper presents a comprehensive comparison between the analytical, simulation and experimental analysis that portrays a strong agreement between these models with an average mismatch of up to 6.2%. An experimental prototype of CLLC converter rated for 1kW nominal power, operating at 500kHz resonant frequency is developed with the optimal HFPT characteristics that yields a peak efficiency of 98.49% with magnetics stage efficiency of 99.31%.

Experimental and numerical modeling of DC corona discharge in Wire-Cylinder-Plane configuration

The aim of this paper is to present a numerical and experimental study of the positive corona discharge in the Wire-Cylinder-Plane geometry intended for electrostatic charging of insulating materials. A detailed experimental procedure is described to determine the corona discharge characteristics where different electrode layouts have been tested to improve the performance of the charge process. In addition, the corona governing equations are successfully implemented and solved in the studied geometry using Comsol Multiphysics Software. The study focused on the effect of the presence of the non-ionizing cylinder on the coronating wire. It has been found that increasing the diameter of the cylinder or bringing it closer to the wire reinforces the shielding effect between the two electrodes, which results in the reduction of the corona current and current density at the level of the measurement plane. The measured I–V characteristics and current density distributions were found to be in good agreement with the corresponding numerical predictions.

Analysis of the Influence of Harmonics on Energy Efficiency of Typical Equipment in Distribution Network

With the continuous development of power systems, the number of non-linear loads is increasing. When harmonics flow through wires, transformers, filters, and other devices, additional harmonic losses will be generated, which will cause power loss and safety problems such as equipment overheating. However, there are few studies on loss in complex power quality environments. Considering the influence of skin effect when harmonics flow through the conductor, this paper studies the distribution of current density, explores the influence of conductor material, radius, and frequency of the current flowing through the metal on the current distribution, and proposes a calculation method of conductor harmonic resistance considering the influence of skin effect. Furthermore, the electrical energy consumption of typical devices in the distribution network is considered. Based on the theoretical calculation model, a simulation platform was established to carry out the equipment loss measurement experiment under each harmonic current, and the mutual verification between the theoretical calculation model and the experimental measurement was realized.

Research on the shielding effect of the electrode frames in the electrostatic precipitator

ABSTRACT The electrostatic precipitator (ESP) plays an important role in the dust removal from the flue gas. Currently, the shielding effect of electrode frames seriously affects the electric field distribution and dust removal efficiency of ESPs. In order to explore the shielding effect and propose an improved measurement, an experimental setup with RS barbed electrodes and a 480 C type dust collector electrode plate was built to evaluate the corona discharge characteristics. The current density distribution on the surface of the collecting plate was tested on an ESP experimental setup. The effect of electrode frames on the current density distribution was also systematically investigated. The test results show that the current density distribution on the position that directly opposites the needle of RS corona discharge is much higher, on the contrary, the current density on the position that directly opposites the frames is almost zero. It indicates that the frames have a shielding effect on the corona discharge. Therefore, the dust collection efficiency is low in actual ESPs due to the dust escape route caused by the shielding effect. To solve the problem, a new ESP with a split-level frame arrangement was proposed. Implications: The conventional electrostatic precipitators are often affected by the electrostatic shielding effect, which leads to uneven charging. The particulate removal efficiency decreases and escape channels are very easy to form. In this study, effective measures were proposed to solve the electrostatic shielding of dust collector frames by studying their electrostatic shielding mechanism. The study provides theoretical support for the improvement of electrostatic precipitators, while improving the dust removal efficiency.

Microwave polarization conversion and reflection loss mechanism of complementary-modeled Rossler-based chaotic metamaterial

The complementary-modeled Rossler chaotic metamaterial (CRCM) with FR-4 dielectric layer is proposed to design metamaterial absorber with multi-resonance peaks. Under “master-slave” boundary condition in high-frequency structure simulator (HFSS) software, the electric field between adjacent boundaries presents phase difference which can simulate an infinite array. The research results show that the CRCM demonstrates multi-resonant peaks from 4 GHz to 10 GHz, and the area of metal patterned-layer can obviously regulate the resonant peaks. The CRCM presents a linear polarization conversion peak around 5.80 GHz, its polarization conversion ratio (PCR) is near 100%. The PCR is also larger than 80% from 5.56 GHz to 5.95 GHz. Through the surface current density distribution and the comparison between the CRCM and complementary-modeled double ring metamaterial (CDRM), the main factors generating polarization conversion are the asymmetry of metal pattern layer and magnetic resonance caused by reverse current. The CRCM also has two strong absorption peaks located at 6.31 and 9.37 GHz, respectively. Dielectric loss and ohmic loss are the main microwave loss mechanisms proved by volume and surface power loss density distribution. The resonant frequencies derived from [Formula: see text] resonant circuit are well consistent with the simulation data and measurement results.

Influence of PEO Electrolyzer Geometry on Current Density Distribution and Resultant Coating Properties on Zr-1Nb Alloy.

This paper is devoted to the study of the current density distribution effect on plasma electrolytic oxidation process and resultant coatings on a Zr-1Nb alloy. The influence of the distance between the plates simultaneously placed into an electrolyzer was evaluated to assess the throwing power of the PEO process. The current density on the facing surfaces of the plates decreases when the distance between them shrinks. This current density has a notable impact on the resultant PEO coating in terms of the surface morphology parameters and electrochemically evaluated corrosion resistance. The influence of this effect is low on the stages of anodizing and spark discharges (60-120 s of the PEO), and significantly increases on the stage of microarc discharges (120-360 s of the PEO). The coating obtained with a smaller distance between the plates, while having the same coating thickness as the others, exhibits higher wear resistance. New correlations between the current density, diffusion coefficient, time constant of nucleation and the coating thickness in the middle of the facing samples were established; in addition, a correlation of the coating morphology in this area with the roughness parameters RPc, RSm was shown. This study contributes to the development of optimized PEO processes for the simultaneously coated several devices of complex shape, e.g., orthopedic implants.

Suppression Measures of Partial Discharge at Rod–Plate Connection in Composite Tower

Rods and plates at the connections in composite insulating material towers are commonly fixed to each other by metal bolts, which may cause electrical field distortion at the connections. So, the rod–plate connections are prone to partial discharge under polluted and wet conditions, and the resulting electric field and temperature changes can affect the mechanical and electrical performance of the whole tower. In this paper, an artificial pollution test synchronous observation platform with an infrared and visible light imager, leakage current, and voltage measurement was built to observe the dry band formation and partial discharge at the simplified rod–plate connections in the composite towers. Then, the electric field simulation of the rod–plate connection specimen showed the current density distribution. When combining the test and the simulation, it was concluded that the cause of the partial discharge was the distortion of the current density and, thus, measures to suppress the partial discharge at the rod–plate connections were proposed. Finally, it was verified that the measures can improve the current density distortion phenomenon, delay dry band formation, and effectively suppress the partial discharge at the rod–plate connections under the same test conditions.

A research on epilepsy source localization from scalp electroencephalograph based on patient-specific head model and multi-dipole model

Accurate source localization of the epileptogenic zone (EZ) is the primary condition of surgical removal of EZ. The traditional localization results based on three-dimensional ball model or standard head model may cause errors. This study intended to localize the EZ by using the patient-specific head model and multi-dipole algorithms using spikes during sleep. Then the current density distribution on the cortex was computed and used to construct the phase transfer entropy functional connectivity network between different brain areas to obtain the localization of EZ. The experiment result showed that our improved methods could reach the accuracy of 89.27% and the number of implanted electrodes could be reduced by (19.34 ± 7.15)%. This work can not only improve the accuracy of EZ localization, but also reduce the additional injury and potential risk caused by preoperative examination and surgical operation, and provide a more intuitive and effective reference for neurosurgeons to make surgical plans.

Performance Analysis and Design of Direct Ammonia Fuel Tubular Solid Oxide Fuel Cell for Shipborne Unmanned Aerial Vehicles

Ammonia is being considered as a promising alternative to hydrogen fuel in solid oxide fuel cells (SOFCs) due to its stability and ease of storage and transportation. This study investigates the feasibility of using ammonia fuel in a tubular SOFC for shipborne unmanned aerial vehicles (UAVs). The paper develops a 3D model of a tubular-anode-supported SOFC single cell and conducts numerical simulations to analyze the impact of different operating conditions on SOFC performance. The study optimizes the SOFC’s performance by adjusting its working parameters and overall structure, revealing that increasing temperature and porosity enhance performance, but excessively high values can cause deterioration and instability in the cell. The study also finds that the cathode-supported (CS)-SOFC outperforms the anode-supported (AS)-SOFC, mainly due to its thicker cathode layer, providing better sealing and oxygen supply, resulting in a more uniform current density distribution. The paper provides valuable insights into the potential use of ammonia fuel for shipborne UAVs and offers a foundation for future research and development in the field of SOFCs. The results indicate that increasing the temperature and porosity of the SOFC can enhance battery performance, but excessive values can cause deterioration and instability in the cell. The study also highlights the impact of different operating conditions on SOFC performance, with a significant performance improvement observed in the range of 0.6–0.8 V. Additionally, the CS-SOFC outperforms the AS-SOFC due to its thicker cathode layer, but both have significant potential for development.

ОБЧИСЛЕННЯ ПОПРАВОК ДИФЕРЕНЦІЙНИХ ДВОХЕЛЕКТРОДНИХ КОНДУКТОМЕТРИЧНИХ КОМІРОК ІЗ РОЗРАХУНКОВОЮ КОНСТАНТОЮ

The object of study is a differential two-electrode conductivity cell with a calculated constant, designed for the practical realization of the unit of length – a meter in national measurement standards of electrolytic conductivity of liquids. The differential cell consists of two tubes of the same diameter but different lengths. The article presents an idealized model for calculating cell constants and determining electrolytic conductivity. The presence of holes for filling the cell, caus-ing a distortion of the uniformity of the current density distribution in the middle of the cell, and a significant dielectric permeability of aqueous solutions lead to significant errors when measuring the resistance of liquid columns. The arti-cle presents mathematical expressions for calculating two types of corrections. First, the correction caused by the dis-tortion of the field uniformity due to the presence of the inlet and outlet holes of the cell. Secondly, the correction caused by the presence of bias currents in aqueous solutions of electrolytes. The appearance of a differential cell based on two tubes with a diameter of 9 mm and a length of 50 and 100 mm, respectively, which is being tested as a part of the national measurement standard of Ukraine, is given. References 7, figures 5, tables 2.

Simulation research on corrosion and thinning characteristics of water wall tubes based on electric field array

During service, the water wall tube will inevitably corrode due to various corrosive gases such as SO2, HCl, H2S, etc. To prevent the occurrence of tube burst accidents caused by thinning and income-pressure resistance of the water wall tube, it is necessary to monitor the wall thickness of the water wall tube row in real-time. This paper proposes an array-based method for monitoring the thickness of the water wall tube row, and the different corrosion characteristics models of the water wall tube row are established by using the finite element analysis software Maxwell. Based on the model, the influence of tube wall thickness and material on measurement accuracy is analyzed by current density distribution and electric field intensity. The error of calculation formula is analyzed by simulating different corrosion conditions of tube wall thinning. The calculation formula of the wall thickness after the corrosion of the water wall tube row and the correction formula of the wall thickness of a single water wall tube with the correction coefficient α of 3 are determined. And put forward to define the ”generalized average thickness” of the water wall corrosion of multiple tubes, and determine the correct formula for calculating the thickness of the water wall tube row with a correction coefficient β of 0.85 to 0.95.

Artificial intelligence based structural optimization of solid oxide fuel cell with three-dimensional reticulated trapezoidal flow field

Three-dimensional Reticulated trapezoidal flow field (RTFF) is promising in improving the performance and durability of the solid oxide fuel cell (SOFC). However, the structural complexity makes it challenging for the geometry configuration of the splitter and mixer. To this end, an intelligent optimization framework is proposed by coupling artificial neural network (ANN) and non-dominated sorting genetic algorithm-II (NSGA-II), in order to maximize the net power density and oxygen uniformity simultaneously. The ANN prediction model is trained to obtain the computationally efficient surrogate model of the computational fluid dynamics (CFD) numerical simulation. NSGA-II is used for the multi-objective optimization of the RTFF structural parameters. The results illustrate that the prediction model is of high prediction precision and generalization capability. In comparison to SOFC with conventional parallel flow fields (CPFF), the degree of the performance improvement of SOFC with optimized RTFF depends on the working condition, i.e., fuel and air flow rates and operating temperatures. The SOFC with the optimal RTFF achieves a higher molar concentration of oxygen and a more uniform distribution of oxygen and current density than the CPFF SOFC. The proposed optimization framework provides an efficient design method for the development of the next-generation SOFC flow field.