Field Distribution Research Articles

Numerical Study on Combustion Characteristics of a 600 MW Boiler Under Low-Load Conditions

Under the background of achieving carbon dioxide peaking and carbon neutrality, the rapid development of renewable energy power generation poses new challenges to the flexible adjustment capabilities of traditional power plants. To explore the furnace combustion stability and optimal operation modes during deep peak shaving, a simulation of the combustion process under low-load conditions for a 600 MW wall-fired boiler is performed utilizing computational fluid dynamics (CFD) analysis. The impact of burner combination modes on the combustion process within the furnace is explored at 25% and 35% boiler maximum continuous ratings (BMCRs). This study investigates two configurations of burner combinations. One mode operates burners in layers A, B, and C, which include the lower layers of burners on the front and rear walls of the boiler, as well as the middle-layer burners on the rear wall, referred to as OM1. The other mode operates burners in layers A and C, which include the lower layers of burners on the front and rear walls of the boiler, referred to as OM2. The results indicate that OM2 exhibits superior capabilities in orchestrating the distribution of the airflow velocity field and temperature field under the premise of ensuring no more than a 1% decrease in the pulverized coal burnout rate. When OM1 is employed, the airflow ejected from the middle-level burners hinders the upward movement of pulverized coal sprayed from the lower-level burners, causing a larger proportion of pulverized coal to enter the ash hopper for combustion. Consequently, the ash hopper attains a peak mole fraction of CO2 at 0.163. OM2 delays the blending of pulverized coal with air by enhancing the injection quantity of pulverized coal per burner. As a result, the generation of CO in the ash hopper reaches a notable mole fraction of up to 0.108. The decreased furnace temperature promotes the formation of fuel-based NOx during low-load operation. Taking the 25% BMCR as an example, the NOx emissions measured at the furnace outlet are 743 and 1083 ppm for OM1 and OM2, respectively. This study focuses on the impact of combustion combinations on the combustion stability when the boiler is operating at low loads. The findings could enrich previous research on combustion stability and contribute to the optimization of combustion schemes for power plant boilers operating at low loads.

Theoretical Study of Quaternary nBp InGaAsSb SWIR Detectors for Room Temperature Condition

This paper presents a theoretical analysis of an nBp infrared barrier detector’s performance intended to operate at a room temperature (300 K) based on AIIIBV materials—In1-xGaxAsySb1−y quaternary compound—lattice-matched to the GaSb substrate with a p-n heterojunction ternary Al1−xGaxSb barrier. Numerical simulations were performed using a commercial Crosslight Software—package APSYS. The band structure of the nBp detector and the electric field distribution for the p-n heterojunction with and without a potential barrier were determined. The influence of the barrier-doping level on the detector parameters was analyzed. It was shown that Shockley-Read-Hall (SRH) recombination plays a decisive role in carrier transport for lifetimes shorter than 100 ns. The influence of the absorber/barrier thickness on the detector’s dark current density and photocurrent was investigated. It was shown that valence band offset does not influence the device’s performance. The quantum efficiency reaches its maximum value for an absorber’s thickness of ~3 μm. The performed simulations confirmed the possibility of the detector’s fabrication exhibiting high performance at room temperature based on quaternary compounds of AIIIBV materials for the short wavelength infrared range.

Comprehensive Analysis of Optical Resonances and Sensing Performance in Metasurfaces of Silicon Nanogap Unit

Metasurfaces composed of silicon nanogap units have a variety of optical resonances, including bound states in the continuum (BIC). We show comprehensive numerical results on metasurfaces of Si-nanogap units, analyze the optical resonances, and clarify optically prominent resonances as well as symmetry-forbidding resonances that are the BIC, based on the numerical analyses of optical spectra and resonant electromagnetic field distributions. Introducing asymmetry in the unit cell, the BIC become optically allowed, being identified as magnetic dipole, electric quadrupole, and magnetic quadrupole resonances. Moreover, the optical resonances are examined in terms of refractive index sensing performance. A pair of the resonances associated with electric field localization at the nanogap was found to be sensitive to the refractive index in contact with the metasurfaces. Consequently, the gap mode resonances are shown to be suitable for a wide range of refractive index sensing over 1.0–2.0.

A simulation on field distribution and particle capture characteristics in a multi-wire PHGMS system

ABSTRACT In the development history of high gradient magnetic separation (HGMS), the introduction of pulsating flow was extremely important, it successfully solved the problem of matrix clogging and allowed continuous and stable operation in the industry. However, the current pulsating HGMS (PHGMS) theory remains inadequately understood. In this paper, a 2D simulation model was established in COMSOL Multiphysics to reveal the magnetic field characteristics, flow field distribution, and particle capture dynamics in a PHGMS system. Quantitative comparisons were carried out between single-wire and multi-wire systems in the presence and absence of pulsation flow. The simulation results indicated that due to the coupled effect of neighboring magnetic wires in matrix, the magnetic field strength around an individual magnetic wire would slightly drop while the flow field velocity would increase. The introduction of pulsating flow could increase the peak value of fluid velocity and give particles a chance to move up and down. The analysis of particles travels length and capture probability indicated that the recovery for fine particles might be improved by increasing the strength of pulsating flow. This study provided a novel strategy for the highly efficient recovery of fine, weakly magnetic materials.

Mathematical model of velocity and distribution law in gas lift reverse circulation well washing flow field for drilling shaft sinking

To reveal the velocity distribution law of a gas lift reverse circulation well washing flow field in drilling shaft sinking, a velocity mathematical model of well washing flow field is established. The theoretical analytical solutions and velocity distribution laws in the drill pipe and bottom hole were provided and validated through numerical simulations and similar model tests. Furthermore, this study explores the impacts of mud circulation, wind pressure, rock debris, and mud properties on the flow field distribution, presenting the sensitivity order of the factors. This study indicated the following findings. (1) The velocity theoretical model of well washing flow field was validated through numerical simulation and similar model tests, and the relative error ranged from 4.2 to 18.5%, demonstrating the high consistency. (2) The rock debris and mud experienced slight and consistent deceleration within the drill pipe. Upon reaching the gas input end, the axial upward return of the multiphase flow resulted in a “jumping” sharp increase. (3) The mud circulation, wind pressure, and void fraction positively correlated with the multiphase fluid velocity in the drill pipe, but negatively correlated with the mud density and slag content. The axial upward velocity of the rock debris decreased with increasing particle size and density. (4) The sensitivity of each factor to the discharge speed of rock debris was summarized as follows: air content > mud circulation > wind pressure > mud density > rock debris density > rock debris particle size > slag content. These findings could offer a theoretical basis for selecting well washing parameters and enhancing drilling and washing efficiency.

High Permittivity Electroluminescence Coating for Improving Flashover Strength and Visualizing Surface Defects

Abstract In gas-insulated switchgear (GIS), the metallic particles on spacers initiate discharges and significantly reduce flashover strength. It is crucial to sensitively detect the surface defects and improve the flashover strength. In this work, a high permittivity electroluminescence coating, with ZnS:Cu as fillers and cyanoethyl cellulose (CEC) as polymer matrix was developed to improve flashover strength and visualize surface defects. The dielectric constant, flashover strength, and electroluminescence properties of ZnS:Cu/CEC coatings with different concentration of ZnS:Cu fillers were tested and the underlying mechanism was investigated. Due to the strong-polarity cyanide group in CEC and the effect of ZnS:Cu fillers on polymer chains, a high-permittivity coating was obtained, which can effectively mitigate the electric field distortion on spacers, and improve the flashover performance. For the basin insulator, maximum increments of flashover strength were realized by doping 12.5 wt% ZnS:Cu fillers, with 11.36%, 31.22%, and 5.83% improvements in air, 0.3 MPa air, and SF6 gas respectively. Moreover, the electroluminescence coating can effectively indicate the location of defects and the distribution of electric field on the surface of insulators. This paper provides a new insight into the electroluminescent materials used in non-destructive self-testing of surface defects and enhancement of flashover strength.

Effect of forced lateral vibration on flow and heat transfer performance within an annular fuel element

The investigation into the thermo-hydraulic characteristics of fuel elements under forced vibration conditions is of paramount importance in the design and application of offshore nuclear power platforms. This study employs a mathematical model of fluid-solid coupling and applies the theory of multi-field synergy to numerically analyze the flow and heat transfer features in an annular fuel element with internal and external double-sided cooling under forced lateral vibration conditions. The synergistic relationship of each flow field parameter is scrutinized for vibration conditions with frequencies ranging from 0 to 10 Hz and amplitudes from 0.005 to 0.2 m. The results demonstrate that increased amplitude and frequency contribute to enhancing the homogeneity of the temperature and velocity field distributions. Notably, the field synergy angles α, β, ψ, and γ attain minimal values at the gaps (X = 8 mm, X = 25 mm). Furthermore, the variation of vibration frequency and amplitude decreases the mean synergistic angle ψ by 5.14 % and 7.9 % and increases the mean field synergistic angle θ by 23.18 % and 31.21 %, respectively. It indicates that the vibration parameters have the least effect on the synergistic angle ψ and the greatest effect on the synergistic angle θ.

Experimental investigation of the electromagnetic acceleration mechanisms in an Applied-field Magnetoplasmadynamic Thruster

Abstract The high specific impulse and efficiency of the applied-field magnetoplasmadynamic thruster make it one of the most promising electric thrusters in deep space exploration. However, the crucial electromagnetic acceleration mechanisms are still not clearly investigated, which limits performance improvement. The electromagnetic acceleration mechanism is closely related to the current path and magnetic field distribution in the plume. Experiments are conducted using a water-cooled Hall probe in the steady-state applied-field magnetoplasmadynamic thruster plume. The radial, azimuthal and axial magnetic fields are measured, then the current density and Lorentz force density are calculated. The results show that the outflow current accounts for 63% to 82% of the thruster discharge current depending on the strength of the applied magnetic field. Moreover, the outflow current can extend the range of electromagnetic force action, which in turn increases the effect of electromagnetic acceleration. The radial Lorentz force is numerically dominant, and the combined effect of the radial Lorentz force and axial Lorentz force is to compress the plasma toward the axis. In electromagnetic acceleration, Self-field contributions are less than 5%, while E × B acceleration constitutes -12.2-21.2%, and Diamagnetic acceleration dominates at approximately 76.7-90.5%. Finally, a method for evaluating the rotational velocity was presented based on the MHD equations. The centrifugal force was then calculated by combining this with the plasma density. At the thruster outlet, the centrifugal force is significant and cannot be ignored in comparison to the radial Lorentz force.

PCA-Kriging-Based Oscillating Jet Actuator Optimization and Wing Separation Flow Control

In order to improve the separation control effect of an oscillating jet, the external flow field of the actuators and the wing wake are obtained via hot-wire measurements to optimize the actuator and achieve wing separation flow control. The optimization objectives are to improve the sweeping uniformity and range of the jet. In the present study, the PCA method is used for the modal decomposition of the velocity distribution. The modal-based actuator evaluation parameters are proposed, and the kriging surrogate models of the modal coefficients (principal components) on the actuator parameters are established. The multi-objective genetic algorithm was utilized to complete the optimization of the actuator, and the effect of flow separation control on the wing was verified. The results show that three patterns exist in the time-averaged velocity distribution of the external flow field: unimodal, broad and bimodal, from unimodal to bimodal, the degree of the jet sweeping uniformity gradually decreases, and the sweeping range gradually increases. The pattern of the velocity distribution modals affects the degree of jet sweeping uniformity, while the distance of the modal peaks affects the jet sweeping range. The two evaluation parameters are negatively correlated: insufficient sweeping range or poor sweeping uniformity of the jet are not conducive to wing separation flow control, and the two must be coordinated to achieve the optimal control effect.

Influence of heat pipe layout parameters on the cooling effect of spontaneous combustion coal gangue dumps

Existing research has found that the number, insertion depth and angle, filling rate, and working fluid of heat pipe (HP) can affect the distribution of temperature field inside coal gangue dumps. However, there is relatively little research on the optimal arrangement of heat pipes (HPs) in coal gangue dumps. In response to the above issues, based on the theoretical model of HP heat transfer, the influence of HPs layout on the temperature field of coal gangue dumps is analyzed through a combination of numerical simulation and experiments, and the optimal layout of HPs is obtained. The results show that the presence of HPs can change the heat conduction path in a coal gangue dump and help the coal gangue dumps to dissipate heat in time. As the insertion spacing of the HPs decreases and the insertion depth of the HPs increases, the area of the spontaneous combustion danger zone (SCDZ) decreases, the maximum temperature value (Tmax) decreases, and the better the cooling effect. The influence of the insertion spacing of HPs on the spontaneous combustion volume of coal gangue dumps is greater than the influence of the insertion depth of HPs. When the insertion spacing of HPs is 3 m and the insertion depth of HPs is 7 m, the spontaneous combustion volume and the highest temperature point respectively decrease by 11755m3 and 302.57 ℃, and the cooling effect of coal gangue dumps is the best. Consequently, this study provides a reference for the design and optimization of coal gangue fire fighting engineering with HP application in the future.

Analysis of the air gap magnetic field in cylindrical magnetic couplings based on mathematical and finite element approach

The air gap magnetic field of a magnetic coupling plays a crucial role in the examination of its static torque and eddy current losses. Precise characterization of the air gap magnetic field is essential for ensuring the accuracy of performance assessments of the magnetic coupling. This study focuses on the cylindrical magnetic coupling as the subject of investigation, employing mathematical analysis and finite element methods to evaluate and quantify the magnetic field properties. The study establishes a mathematical model of the magnetic field of a magnetic coupling based on electromagnetic field principles and the superposition theorem. An analytical formula for the magnetic flux density distribution of the air-gap magnetic field is derived. Subsequently, a three-dimensional magnetic field finite element model is created using the finite element method to numerically calculate the air gap magnetic field and validate the analytical formula. The research also explores the periodic distribution characteristics of the magnetic field in the air gap, analyzing axial differences in magnetic flux density value and direction distribution influenced by end effects.

Model for restoring obstructed beam transmission in atmospheric turbulence based on BP neural network

Atmospheric turbulence and obstacles can distort rays during transmission, resulting in significant wavefront distortion and loss of optical field information. This paper employs the phase screen method to simulate the transmission characteristics of a Gaussian plane wave in turbulent conditions, establishing an obstacle grid at the receiver to represent beam obstruction. A dataset of unobstructed transmissions is used to train a Backpropagation Neural Network, constructing neurons and connection weights. By scanning optical field data systematically, the model compensates for the obstructed portions of the optical field distribution. The results are compared to unobstructed transmissions, focusing on image similarity, and demonstrate the entire process from compensation to distortion correction. Simulation results indicate that the Backpropagation Neural Network effectively compensates for optical field information loss, showcasing strong performance within a certain time scale.

Optimal design configuration of grading ring for polymeric insulator under different environmental conditions

Polymeric insulators play a crucial role in power transmission lines. To ensure safe and reliable operation at High Voltage (HV), they are often equipped with single or double grading rings to uniformly distribute the electric field and voltage along the creepage distance. This study investigates the impact of optimal grading ring configurations on electric field distribution using the Finite Element Method (FEM). In addition, an adaptable method for achieving optimal grading ring design is proposed. Numerical results demonstrate that employing the Nelder-Mead (NM) optimization algorithm helps determine the ideal configuration for grading ring material, dimensions, and location to achieve uniform electric field distribution compared to insulators without grading rings or with original designs. This method has also been adapted for different environmental conditions, including pollution, water droplets, and icing conditions.

Direct Three-Dimensional Observation of the Plasmonic Near-Fields of a Nanoparticle with Circular Dichroism.

Characterizing the spatial distribution of the electromagnetic fields of a plasmonic nanoparticle is crucial for exploiting its strong light-matter interaction for optoelectronic and catalytic applications. However, observing the near-fields in three dimensions with a high spatial resolution is still challenging. To realize efficient three-dimensional (3D) nanoscale mapping of the plasmonic fields of nanoparticles with complex shapes, this work established autoencoder-embedded electron energy loss spectroscopy (EELS) tomography. A 432-symmetric chiral gold nanoparticle, a nanoparticle with a high optical dissymmetry factor, was analyzed to relate its geometrical features to its exotic optical properties. Our deep-learning-based feature extraction method discriminated plasmons with different energies in the EEL spectra of the nanoparticle in which signals from multiple plasmons were intermixed; this component was key for acceptable 3D visualization of each plasmonic field separately using EELS tomography. With this methodology, the electric field of the plasmon that induces far-field circular dichroism was observed in 3D. The field linked to this chiroptical property was strong along the swirling edges of the particle, as predicted by a numerical calculation. This study provides insight into the correlation between structural and optical chiralities through direct 3D observation of the plasmonic fields. Furthermore, the strategy of implementing an autoencoder for EELS tomography can be generalized to achieve competent 3D analysis of other features, including the optical properties of the dielectrics and chemical states.

Numerical simulation for spray spatial distribution of swirl nozzle and its target dustfall area prediction.

The droplet breakup and distribution of the internal flow field and external spray field of a nozzle were obtained under different pressures. The thickness of the liquid film increased with pressure as a quadratic function. The maximum value of 0.281mm at 2MPa decreased to 0.172mm at 10MPa, equivalent to 38.8% decrease. The MATLAB was used to obtain the particle size distribution characteristics of the droplets under different pressures. At 2MPa, droplet breakup dominated the axial interval [0-700mm]. With the increase of pressure, D50 distribution as a whole continues to decrease, 2-6MPa change, the particle size reduction is larger, every increase of 2MPa reduced by about 15%. 6-10MPa change, the particle size reduction is smaller, every increase of 2MPa reduced by about 8%. A model to predict the optimal dust reduction areas under varying pressures was developed. The prediction results indicate that at pressures of 5MPa and 9MPa, the target dust removal areas were [344mm, 710mm] and [424mm, 942mm] along the axial direction, respectively.

Device physics of perovskite light-emitting diodes

Perovskite light-emitting diodes (LEDs) have emerged as a potential solution-processible technology that can offer efficient light emission with high color purity. Here, we explore the device physics of perovskite LEDs using simple analytical and drift-diffusion modeling, aiming to understand how the distribution of electric field, carrier densities, and recombination in these devices differs from those assumed in other technologies such as organic LEDs. High barriers to electron and hole extraction are responsible for the efficient recombination and lead to sharp build-up of electrons and holes close to the electron- and hole-blocking barriers, respectively. Despite the strongly varying carrier distributions, bimolecular recombination is surprisingly uniform throughout the device thickness, consistent with the assumption typically made in optical models. The current density is largely determined by injection from the metal electrodes, with a balance of electron and hole injection maintained by redistribution of electric field within the device by build-up of space charge.

Temperature Distribution of Frozen Wall Formed by Irregular Hole Arrangement During In Situ Repair of Underground Shield Machine

In order to study the development law of the irregular hole freezing temperature field, combined with the shield solution project of the Nanjing Water Supply Corridor, the distribution characteristics and influencing factors of the irregular freezing temperature field of the river bottom shield machine are studied by numerical simulation. The following conclusions are obtained: (1) The extension length of the outer ring pipe is correlated approximately positively with the thickness and average temperature of the freezing wall at the bottom of the cup. The thickness increases by 0.25 m, and the average temperature decreases by 1.25 °C for every 1 m increase in the extension length. (2) The intersection time decreases logarithmically with the increase in the extension length of the outer ring tube. (3) As the ratio of the axial angle between the two adjacent tubes in the weak area of the outer ring tube becomes larger, the temperature of the weak point in the center of the two tubes increases approximately linearly. The midpoint temperature of the two tubes increases by 3.3 °C for every 1 increase in the angle coefficient. (4) With the increase in the opening angle of the inner ring hole, the thickness and average temperature change, respectively, at 150 d are not more than 0.15 m and 0.6 °C. The results show that under the irregular freezing form, the angle and length of the outer ring pipe have a great influence on the temperature field, and the angle of the inner ring pipe has little influence on the final distribution of the temperature field. The average temperature and the temperature distribution of the weak points show a trend of decreasing first and then increasing along the shield advancing direction, reaching a minimum near the cutterhead.

Optical tweezer-assisted cell pairing and fusion for somatic cell nuclear transfer within an open microchannel.

Somatic cell nuclear transfer (SCNT), referred to as somatic cell cloning, is a pivotal biotechnological technique utilized across various applications. Although robotic SCNT is currently available, the subsequent oocyte electrical activation/reconstructed embryo electrofusion is still manually completed by skilled operators, presenting challenges in efficient manipulation due to the uncontrollable positioning of the reconstructed embryo. This study introduces a robotic SCNT-electrofusion system to enable high-precision batch SCNT cloning. The proposed system integrates optical tweezers and microfluidic technologies. An optical tweezer is employed to facilitate somatic cells in precisely reaching the fusion site, and a specific polydimethylsiloxane (PDMS) chip is designed to assist in positioning and pairing oocytes and somatic cells. Enhancement in the electric field distribution between two parallel electrodes by PDMS pillars significantly reduces the required external voltage for electrofusion/electrical activation. We employed porcine oocytes and porcine fetal fibroblasts for SCNT experiments. The experimental results show that 90.56% of oocytes successfully paired with somatic cells to form reconstructed embryos, 76.43% of the reconstructed embryos successfully fused, and 70.55% of these embryos underwent cleavage. It demonstrates that the present system achieves the robotic implementation of oocyte electrical activation/reconstructed embryo electrofusion. By leveraging the advantages of batch operations using microfluidics, it proposes an innovative robotic cloning procedure that scales embryo cloning.

Effects of openings on postbuckling behavior of large‐size composite C‐beam under bending‐shear coupling load

AbstractProper design and accurate mechanical assessment of composite C‐beam after opening are of great importance in structure engineering. This paper aims to experimentally and analytically investigate the postbuckling response of large‐size C‐beam with web opening under bending‐shear coupling load. New specimen with four different open shapes were designed and tested. Strain gauges and displacement measurements were applied to monitor its buckling behavior, strain field distribution and critical failure load. Four specimens with various openings were loaded until catastrophic failure occurred. Additionally, an analytical model was introduced to predict the residual strength of circular opening. The results indicate that while the presence of an opening significantly decreases the load carrying capacity, it has minimal effect on the bending stiffness. Compared with intact specimen, the initial delamination, buckling and ultimate strength of the circular opening decreases less than those of the rectangular opening. By altering the position of the rectangular opening, improvements can be made in terms of initial delamination resistance and buckling load; however, ultimate strength remains largely unaffected. Reinforcing the edge of an opening further reduces resistance to initial delamination but other two indicators are improved. Overall, from buckling to failure stages, post‐buckling bearing capacity after opening decreases by 40%. Moreover, the shear failure mode is observed during catastrophic failures. And the analysis method employed is relatively conservative.Highlights Ten large size composite C beams are conducted under coupling loads. Deformation, strain distribution and failure mode are presented. Influence of openings on postbuckling behavior of beam is analyzed. An analysis method is employed to predict the residual strength of beam. It could provide valuable insights for assisting in designing beam openings.

Probing plexciton emission from 2D materials on gold nanotrenches

Probing strongly coupled quasiparticle excitations at their intrinsic length scales offers unique insights into their properties and facilitates the design of devices with novel functionalities. In this work, we investigate the formation and emission characteristics of plexcitons, arising from the interaction between surface plasmons in narrow gold nanotrenches and excitons in monolayer WSe2. We study this strong plasmon–exciton coupling in both the far-field and the near-field. Specifically, we observe a Rabi splitting in the far-field reflection spectra of about 80 meV under ambient conditions, consistent with our theoretical modeling. Using a custom-designed near-field probe, we find that plexciton emission originates predominantly from the lower-frequency branch, which we can directly probe and map its local field distribution. We precisely determine the plexcitonʼs spatial extension, similar to the trench width, with nanometric precision by collecting spectra at controlled probe locations. Our work opens exciting prospects for nanoscale mapping and engineering of plexcitons in complex nanostructures with potential applications in nanophotonic devices, optoelectronics, and quantum electrodynamics in nanoscale cavities.