Ohmic Losses Research Articles

Performance enhancement of hydrogen PEM fuel cell using graphene coated graphite electrodes

The experimental tests were carried out on a hydrogen proton exchange membrane fuel cell (PEMFC) to analyze its performance with graphene (25 % by weight) coated on the surface of the graphite electrodes. The results are compared with the neat graphite electrodes. A single cell with 25 cm2 active area, 63.63 % porosity for graphite, 40 % platinum mixed with carbon by weight, Nafion 117 membrane, graphite monopolar plate, and current collector with copper was developed. The crystalline structure of the graphene is confirmed using Raman Spectroscopy which indicates the graphene coated electrodes has higher electrical conductance. The improved connected network of graphene with catalyst and electrodes leads to better charge transfer. The cell voltage increased significantly from 0.85 with graphite electrodes to 1.0 V with graphene-coated electrodes due to mainly a decrease in ohmic losses. Peak power density with graphene-coated electrodes (79.2 mW/cm2) is significantly improved compared with base graphite (53 mW/cm2) due to higher intrinsic mobility and lesser cracks. The contact angle with the graphene-coated is 143.7° indicating the hydrophobic nature of the electrode. The ohmic losses were reduced by 20.93 %. The results indicate the efficiency and power density of a hydrogen PEM fuel cell could significantly be improved using partially coated graphene electrodes.

Rational design of Zeocin binding protein variants for antibiotic resistance studies

Antibiotic resistance marker was used in this investigation because they are selected;e markers and effective in different hosts. This study used Zeocin binding protein (ZBP) due to its known 3D structure and applicability in prokaryotic and eukaryotic hosts. A library of 22 mutations was developed through a rational design strategy. Subsequently, a selection strategy was used to identify destabilizing mutations in the ZBP. ZBP variants were expressed in E.coli using a leaky expression approach, and minimum inhibitory concentration (MIC) was calculated by cultivating different variants at various Zeocin concentrations. Zeocin resistance was drastically decreased in some ZBP variants. Positive controls (wild-type ZBP) exhibited high resistance, while negative controls (pET vector without ZBP) showed susceptibility. Two variants (ZBP P9E and ZBP R26F) displayed drastic resistance loss. The variants reported in this study may identify molecular chaperones and folding modulators affecting proteostasis. These variants can potentially discover chemical chaperones that improve the stability and solubility of destabilized ZBP variants.

Comparative Study of Simulation of Temperature Rise in Ring Main Unit.

The Ring Main Unit (RMU) is a critical device in power distribution systems used for connecting and distributing electricity. However, due to its compact internal structure and high current load, heat dissipation issues are particularly prominent. To address this problem, this study innovatively proposes a simplified RMU model, employing finite element simulation methods to accurately solve for the ohmic losses of conductors under actual operating conditions and obtain ohmic loss data for various components. This is the first in-depth investigation of the RMU's temperature rise problem using such a comprehensive approach. Subsequently, the temperature field was solved using two different temperature field analysis modules, with a detailed comparison and analysis of the simulation results to identify similarities, differences, and trends in temperature distribution. The results indicate that the temperature field solution model, which considers convective heat transfer, is more accurate and aligns with actual operating conditions. This research provides an innovative approach and practical solutions for the design and optimization of RMUs. Future research can further explore multiphysics coupling analysis methods to address structural design and mandatory validation issues for high and ultra-high voltage RMUs and other electrical equipment, thereby providing important insights for engineering design.

Interdiffusion mechanism of hybrid interfacial layers for enhanced electrical resistivity and ultralow loss in Fe-based nanocrystalline soft magnetic composites

Soft magnetic composites (SMCs) composed of ferromagnetic particles and insulating binder are highly desired in energy-saving and high-efficiency devices for their high electrical resistivity and softer saturation characteristics. However, traditional insulation coatings are facing thermal instability, inhomogeneous distribution, and magnetic dilution, presenting a major challenge for the trade-off relationship between power loss and permeability. Here, the phosphate-coated FeSiBCuNb/SiO2 SMC is successfully fabricated by a unique interdiffusion effect in hybrid interfacial layers, which shows a combination of ultralow power loss of 135.8 kW/m3 (50 kHz/100 mT), high effective permeability of 80.6, and good temperature stability. The interdiffusion behavior between Si/O and Fe/P/O elements promotes the formation of ultrathin, uniform, and multilayer interface structure, which alleviates the magnetic dilution. Penetrating oxidation at the edge interface and elements interdiffusion effect contribute to a higher electrical resistivity induced by hot isostatic pressing with rapid quenching, leading to a low eddy current loss. Synergistic effect of isostatic pressures and rapid quenching facilitates the formation of high-density Cu clusters corresponding to ultrafine microstructure, which is beneficial for low coercivity and low hysteresis loss. This study involves the interdiffusion mechanism of hybrid interfacial layers and nanocrystalline behavior, providing a new strategy for the next-generation of high-performance SMCs.

Hypoglycemic Effect of Polysaccharides from Physalis alkekengi L. in Type 2 Diabetes Mellitus Mice.

Type 2 diabetes mellitus (T2DM) is a common metabolic disease that adversely impacts patient health. In this study, a T2DM model was established in ICR mice through the administration of a high-sugar and high-fat diet combined with the intraperitoneal injection of streptozotocin to explore the hypoglycemic effect of polysaccharides from Physalis alkekengi L. After six weeks of treatment, the mice in the high-dosage group (800 mg/kg bw) displayed significant improvements in terms of fasting blood glucose concentration, glucose tolerance, serum insulin level, insulin resistance, and weight loss (p < 0.05). The polysaccharides also significantly regulated blood lipid levels by reducing the serum contents of total triglycerides, total cholesterol, and low-density lipoproteins and increasing the serum content of high-density lipoproteins (p < 0.05). Furthermore, they significantly enhanced the hepatic and pancreatic antioxidant capacities, as determined by measuring the catalase and superoxide dismutase activities and the total antioxidant capacity (p < 0.05). The results of immunohistochemistry showed that the P. alkekengi polysaccharides can increase the expression of GPR43 in mice colon epithelial cells, thereby promoting the secretion of glucagon-like peptide-1. In summary, P. alkekengi polysaccharides can help to regulate blood glucose levels in T2DM mice and alleviate the decline in the antioxidant capacities of the liver and pancreas, thus protecting these organs from damage.

Asymmetrical Four-Phase 8/6 Switched Reluctance Motor for a Wide Constant Power Region

In this paper, the methodology for designing an asymmetrical four-phase 8/6 switched reluctance motor (SRM) that achieves approximately constant output power over a wide speed range is described. In an asymmetrical 8/6 SRM, orthogonal phase pairs are different in terms of the pole width and number of turns. The main comparison criterion between the asymmetrical and symmetrical 8/6 SRM is the power-speed characteristic, obtained for a given rated RMS phase current of the symmetrical drive. The obtained results demonstrate that the asymmetrical 8/6 SRM allows the shape of the power-speed characteristic to be modified, thereby extending the constant power region well beyond that of the symmetrical configuration with the same rated power level. To make a fair comparison between the asymmetrical and symmetrical 8/6 SRM drives, the converter volt-ampere rating, machine volume, slot fill factor, and ohmic losses per phase are kept constant in all analyzed cases. For determination of the optimal control parameters and maximal drive performance for both designs, the appropriate SRM mathematical model and differential evolution algorithm are used. The applied model includes all substantial non-linearities and mutual coupling between phases. The simulation results are verified using a Finite Element Method (FEM)-based model in the Ansys Electronics 2020 R2 software package.

Understanding the Effects of Anode Catalyst Conductivity and Loading on Catalyst Layer Utilization and Performance for Anion Exchange Membrane Water Electrolysis.

Anion exchange membrane water electrolysis (AEMWE) is a promising technology to produce hydrogen from low-cost, renewable power sources. Recently, the efficiency and durability of AEMWE have improved significantly due to advances in the anion exchange polymers and catalysts. To achieve performances and lifetimes competitive with proton exchange membrane or liquid alkaline electrolyzers, however, improvements in the integration of materials into the membrane electrode assembly (MEA) are needed. In particular, the integration of the oxygen evolution reaction (OER) catalyst, ionomer, and transport layer in the anode catalyst layer has significant impacts on catalyst utilization and voltage losses due to the transport of gases, hydroxide ions, and electrons within the anode. This study investigates the effects of the properties of the OER catalyst and the catalyst layer morphology on performance. Using cross-sectional electron microscopy and in-plane conductivity measurements for four PGM-free catalysts, we determine the catalyst layer thickness, uniformity, and electronic conductivity and further use a transmission line model to relate these properties to the catalyst layer resistance and utilization. We find that increased loading is beneficial for catalysts with high electronic conductivity and uniform catalyst layers, resulting in up to 55% increase in current density at 2 V due to decreased kinetic and catalyst layer resistance losses, while for catalysts with lower conductivity and/or less uniform catalyst layers, there is minimal impact. This work provides important insights into the role of catalyst layer properties beyond intrinsic catalyst activity in AEMWE performance.

A scale-bridging model for proton exchange membrane fuel cells: Understanding interactions among multi-physics transports, electrochemical reactions and heterogeneous aging

The lifetime issues caused by catalyst degradation is one of the most critical challenges for the commercial application of proton exchange membrane fuel cells. However, the understanding concerning the interactions among transport, reaction, and catalyst degradation is inadequate for further durability enhancement. Herein, a scale-bridging model that couples a cell-scaled model to reveal the reactive transport process and a catalyst-scaled model to unveil Pt degradation is proposed to capture the degradation characteristics. It is found that the heterogeneous aging is observed in both the through-plane and channel-rib directions due to the enhanced mass loss near the membrane and the water accumulation under the rib, resulting in the mitigation of the core reaction region away from the membrane, thereby causing an increase in ohmic loss after cycles. More importantly, the local oxygen transport resistance increases with degradation, leading to a remarkable cell performance loss under high current density. Additionally, the influences of cell voltage load and inlet humidity on Pt degradation are also investigated. And the proposed gradient catalyst layer shows a significant mitigating effect on Pt degradation. This work reveals the degradation-performance interactions, which is conducive to design the high-performance fuel cell to prolong lifetime.

AB5-based metal hydride embedded in polyethylene and polymethylmethacrylate for hydrogen storage

Loose powder in metal hydride reactors poses challenges, such as poor thermal conductivity and tube deformation. To address these issues, the metal powder can be encapsulated in a polymer-based matrix to form pellets. This encapsulation helps make the pellets oxygen-impermeable, capable of accommodating the volumetric expansion of metal hydrides, and increases system processability. This study investigates the use of polymer-based pellets containing AB5-based compounds for ambient hydrogen storage. Polymers were selected using ANSYS Granta software, and polyethylene and polymethylmethacrylate were chosen. The AB5 alloy activation in the pellet occurs efficiently after 3 min at 20 °C and 30 bar of hydrogen, facilitated by ball milling-induced reactive surfaces and increased grain boundaries. The optimized pellet, comprising 90 wt% AB5 powder in a PE matrix, exhibits stable hydrogen storage properties, with good mechanical resistance and minimal powder loss (below 3%) over 20 hydrogen sorption cycles in an in-house fabricated single-tube metal hydride reactor.

Optically transparent highly conductive contact based on ITO and copper metallization for solar cells

This paper presents the results of obtaining and studying the electrical and optical characteristics of an optically transparent highly conductive Ni/Cu/Ti/ITO contact in order to reduce electrical resistance losses on the front side of the silicon solar cell. The topology of the contact metallization is a square 50 × 50 mm2 with an interdigitated electrode structure. A Ni/Cu/Ti contact metallization formed on ITO layer reduces the surface resistance by more than 60 times. It has been shown that the use of a Ni/Cu/Ti contact with a finger thickness of at least 1.5 μm and a width of 17 μm was formed is a good alternative to traditional contacts for silicon solar cells based on silver paste.

Modification of GaAs(001)-β2(2x4) surface by Pd-decoration: A DFT study

Photoelectric modification mechanisms of Pd-decoration on GaAs(001)-β2(2 × 4) surface were examined through first-principles calculations based on density functional theory (DFT). Among all purposed Pd-decorated GaAs(001)-β2(2 × 4) models, seven demonstrated have good stability. Due to the adsorption of Pd atoms, band gap and work function of GaAs(001)-β2(2 × 4) surface decreased and further enhanced the photoemission capability of the structure. The evidence showed that the reduced transmission resistance and transmission loss of Pd-decorated GaAs(001)-β2(2 × 4) structure were due to the formation of the localized internal polarization field resulted from charge transfer between Pd and GaAs. When electron come across the Pd/GaAs interface, the internal electric field could accelerate electron passing though in just one dimension, which could reduce the interface recombination and enhance interface electron transmission capability. Additionally, Pd-decoration led to a red-shift in the absorption edge and enhanced light adsorption capability in the range of 0.7 to 1.7 eV. The optoelectronic modification effect could be utilized to address the interface transmission losses in multi-junction solar cells, and further optimize the solar cell performance.

Novel clamping modulation for three‐phase buck‐boost ac choppers

AbstractThree‐phase ac choppers feature output voltage amplitude controllability and enable more compact system realizations compared to autotransformers. For the practical realization advantageously standard power transistor with unipolar voltage blocking capability such as MOSFETs can be employed as a naturally resulting offset voltage between the grid and the input‐stage starpoint ensures purely positive power transistor voltages. This offset voltage is, however, not strictly defined and may drift to higher voltage values, resulting in high power transistor voltage stresses and finally a potential overvoltage breakdown. Traditionally, the offset voltage drift is prevented by introducing discharge resistors across the input‐stage capacitors which, however, results in substantial ohmic losses. This paper analyzes the offset voltage formation in ac choppers and proposes a novel clamping modulation scheme which ensures a strictly defined and minimum time‐varying offset voltage without need for discharge resistors. Theoretical analyses and circuit simulations are finally experimentally verified with a 400 V (rms, line‐to‐line) 50 Hz grid connected three‐phase buck‐boost ac chopper with 3 kW rated power.

Research of hydrodynamic processes in the flow part of a low-flow thermopressor

This research explores the hydrodynamic processes within the flow section of a low-flow thermopressor as a jet-type heat exchanger that utilizes the instantaneous evaporation of highly dispersed liquid in accelerated superheated gas flow resulting in reducing gas temperature with minimum resistance losses in contrast to conventional surface heat exchanger. The efficiency of thermopressor, as a contact heat exchanger, is highly dependent on the design of the flow section and the water injection nozzle. Geometric characteristics perform a crucial role in shaping gas-dynamic processes along the length of the thermopressor's flow section, influenced by resistance losses and local resistance in the tapering and expanding channel segments. Therefore, the optimum thermopressor design has to ensure minimize pressure losses. Using Computational Fluid Dynamics (CFD), the prototype thermopressor models were simulated and the results were compared with experimental data. The empirical equations for local resistance coefficients of thermopressor diffuser and confuser were received to evaluate the impact of various design parameters. The obtained local resistance coefficients for the confuser ranged from 0.02 to 0.08 and for the diffuser – from 0.08 to 0.32. The practical recommendations on geometric and operating parameters and characteristics for enhancing the efficiency of hydrodynamic processes in thermopressor flow part were given.

Development of carbon composite coatings for fire retardancy and electromagnetic interference shielding

This study has effectively showcased the feasibility of employing a carbon composite coatings, comprised of various carbon nanomaterials including carbon nanodots, carbon nanotubes, and graphene nanosheets integrated within a matrix of sodium metasilicate + gypsum, for applications in both flame retardancy and electromagnetic interference (EMI) shielding. The resulting carbon composite coatings, when applied to wooden substrates, demonstrate remarkable fireproof performance, as validated through fire injections at temperatures as high as 1050 °C. This underscores the pivotal role plays by the design of carbon composites in suppressing flame propagation and charring, leading to reduced carbonization areas. Thermogravimetric analysis further reveals that the carbon composite coating generates substantial char residue at 800 °C, signifying enhanced thermal insulating properties derived from the robust composite carbon architecture. Furthermore, the carbon composite coatings show a significant decrease in electromagnetic fields (electric field around 50 % and magnetic field around 44 %), indicating their efficient EMI shielding properties. This improved EMI shielding performance may be due to the deliberate insertion of CNs into the composite materials, which fine-tunes resistance and dielectric loss while allowing effective electromagnetic absorption by the carbon composites. The breakthroughs made in flame retardancy and EMI shielding highlight carbon composites as superior strengthens to flame-retardant and EMI-absorbing building coatings.

Numerical simulation and experimental study of aluminum heat exchanger based on Comsol Multiphysics

Controlling the temperature of the air flow during printing can greatly improve the data measurement of air flow and the printing effect of selective laser melting equipment. In this study, an aluminum-welded heat exchanger was designed and manufactured combined with an engineering application example. The thermal performances of heat exchanger were carried out by experiment and numerical simulation in Comsol Multiphysics. Results show that the model has high accuracy (the relative error is less than 12% in most cases and the absolute error is less than 16 Pa below the flow rate of 350 m3/h), and the overall pipeline resistance loss is small. The temperature difference between outlet and inlet is always lower than 6.5 °C during actual working conditions, which meets the requirements for use. The research can provide good theoretical guidance for the design and application of aluminum heat exchangers.

Multi-Objective Optimization towards Heat Dissipation Performance of the New Tesla Valve Channels with Partitions in a Liquid-Cooled Plate

The utilization of liquid-cooled plates has been increasingly prevalent within the thermal management of batteries for new energy vehicles. Using Tesla valves as internal flow channels of liquid-cooled plates can improve heat dissipation characteristics. However, conventional Tesla valve flow channels frequently experience challenges such as inconsistencies in heat dissipations and unacceptably high levels of pressure loss. In light of this, this paper proposes a new type of Tesla valve with partitions, which is used as internal channel for liquid-cooled plate. Its purpose is to solve the shortcomings of existing flow channels. Under the working conditions of Reynolds number equal to 1000, the neural network prediction-NSGA-II multi-objective optimization method is used to optimize the channel structural parameters. The objective is to identify the optimal structural configuration that exhibits the greatest Nusselt number while simultaneously exhibiting the lowest Fanning friction factor. The variables to consider are the half of partition thickness H, partition length L, and the fillet radius R. The study result revealed that the optimal parameter combination consisted of H = 0.25 mm, R = 1.253 mm, L = 0.768 mm, which demonstrated the best performance. The Fanning friction factor of the optimized flow channel is substantially reduced compared to the reference channel, reducing by approximately 16.4%. However, the Nusselt number is not noticeably increased, increasing by only 0.9%. This indicates that the optimized structure can notably reduce the fluid’s friction resistance and pressure loss and slightly enhance the heat dissipation characteristics.

Thermosetting benzoxazoles with endo-alkynyl groups: Excellent thermal stability and low dielectric loss

In this study, six thermosetting benzoxazole monomers with endo-alkynyl groups are prepared, and the effect of the endo-alkynyl groups and substituent group on the curing behavior and solubility of monomers, and on the thermal properties and dielectric properties of polybenzoxazoles are investigated. Our findings reveal that incorporating endo-alkynyl groups enhances the cross-linked network in the benzoxazole monomers, thereby improving their thermal stability, hydrophobicity, and dielectric constant. However, this modification also results in decreased solubility and curing properties of the monomers. In addition, the position of the fluorine atoms can affect the curing behavior of monomer and the dielectric properties of polybenzoxazoles. When a fluorine atom is positioned ortho to the cyano group, it impedes the curing of the cyanide group, which increases the curing reaction temperature. Moreover, while it is generally believed that the addition of fluorine typically lowers the dielectric constant of a material, the placement of fluorine atoms ortho to the cyano group can lead to overlapping electronic effects. This overlap may increase the polarity of the curing network, which increases the dielectric constant and dielectric loss of the polybenzoxazoles. Among the six thermosetting benzoxazole monomers studied, poly (2 F-JQ) containing m-diethynyl groups exhibit a 5 % thermal decomposition temperature (Td5) of 610 °C, and a low dielectric loss of 0.0045 at 1 MHz. Compared with other polybenzoxazoles, poly (2 F-JQ) possesses a moderate dielectric constant, excellent thermal stability, and extremely low dielectric loss. In summary, this study provides a new approach for preparing resins that feature high-temperature resistance and low dielectric loss.

Modeling and simulation of a high power InGaP/GaAs heterojunction alphavoltaic battery irradiated by americium-241

The design of semiconductor-based heterojunction structures can be turned useful to raise the efficiency of nuclear micro-batteries. In this study, we have investigated a micro-power alphavoltaic battery by using a lab-made software. The nuclear battery consists of an In0.49Ga0.51P/GaAs heterostructure irradiated by americium-241 (Am241) alpha particles with an average kinetic energy of 5.485 MeV. The alphavoltaic battery exhibits an overall active area of 1 cm2. Based on a comprehensive analytical model, the device current density-voltage J(V) and output electric power P(V) characteristics are simulated extracting the energy conversion efficiency. The model takes into account the reflection of the incident alpha particles, the ohmic losses, the effect of the boundary between the two layers, and the depletion region borders. Different values of the radioisotope apparent activity density, the emitter and base dopant concentrations, and the surface recombination velocities in both the front and back layers are considered during the simulations to optimize the battery performance. The present study reports that by irradiating by a 2.4 mCi/cm2 Am241 source, the obtained energy conversion efficiency of the battery can reach 10.31% with a maximum output power density of 16.07 µW/cm2. Therefore, In0.49Ga0.51P/GaAs heterostructure coupled with Am241 seems a promising design for long-term energy supply in harsh environments.

Excellent thermal conductivity and electrical insulation in polyimide/graphene oxide/carbon nanotubes composites

AbstractPolymer composites with heat resistance, good thermal conductivity, and insulation properties can meet the special needs of electronics and electrical appliances. In this work, graphene oxide (GO) and carbon nanotubes (CNTs) are coated by polydopamine (PDA). 4,4′‐diaminodiphenyl ether (ODA), pyromellitic dianhydride (PMDA), and 4,4′‐oxydiphthalic anhydride (ODPA) in‐situ polymerize to prepare poly(amide acid) (PAA) containing thermally conductive yet insulating fillers (PDA@GO, PDA@CNTs). As the concentration of fillers in PI composites increases, the thermal conductivity rises, but the insulation property decreases. Keeping the filler content constant and varying the ratio of PDA@GO and PDA@CNTs, the thermal conductivity increases and then decreases. When PDA@GO and PDA@CNTs have a mass ratio of 10:1, the significant synergistic effect affects the thermal conductivity. The PI/PG10C1–25 sample has a thermal conductivity of 1.46 W/(m·K), which is 6.9 times greater than the pure PI. Additionally, the volume resistivity, dielectric permittivity, and dielectric loss (100 kHz) of PI/PG10C1–25 are 2.8 × 1013 Ω cm, 5.4 and 0.28, respectively. The heat resistance of PI composites is almost the same as that of pure PI. Given these outstanding attributes, the developed PI composites offer vast applications in many fields.Highlights Synergistic PDA@GO and PDA@CNTs (10:1) optimize thermal conductivity. PI/PG10C1–25 achieves 6.9 times higher thermal conductivity than pure PI. Volume resistivity of PI/PG10C1–25 reaches 2.8 × 1013 Ω·cm. Dielectric permittivity of PI/PG10C1–25 reaches 5.4 at 100 kHz. Developed PI composites maintain excellent heat resistance.

Numerical and experimental studies on dissimilar joining of Hastelloy C-276 and SS-316L using microwave hybrid heating at 2.45 GHz

Dissimilar joints of SS-316L and C-276 (Hastelloy) were developed using C-276 powder with microwave exposure 600 s in microwave applicator (2.45 GHz, 900 W). A multi-physics model was validated with experimental studies and simulation were carried out to analyse the microwave-joint interaction characteristics. The simulation results showed that a concentrated electric field (5.86 × 104 V/m) and higher resistive losses (3.07 × 107 W/m3) at the joint region facilitated rapid heat generation locally. Microstructural characterization of the joint revealed the formation of cellular grains such as Fe-Ni intermetallic phases with Mo, Cr and W-carbides along the grain boundaries. Joints exhibited average microhardness of 290 HV, and tensile strength of 425 ± 10 MPa and 14% elongation with failure due to both ductile and brittle fracture modes.