In general,thermal processes can be classified into two categories: heat-work conversion processes and heat transfer processes. Correspondingly,the optimization of thermal processes has to have two different criteria:...In general,thermal processes can be classified into two categories: heat-work conversion processes and heat transfer processes. Correspondingly,the optimization of thermal processes has to have two different criteria:the well known entropy generation minimization method and the recently proposed entransy dissipation maximization method. This study analyzes the thermal issues in a heat exchanger group,and optimizes the unit arrangements under different constraints based on a suitable optimization crite-rion. The result indicates that the principle of minimum entropy generation rate is valid for optimizing heat exchangers in a ther-modynamic cycle with given boundary temperatures. In contrast,the entransy dissipation maximization is more suitable in heat exchanger optimizations involving only heat transfer processes. Furthermore,the entropy generation rate induced by dumping used streams into ambient surroundings has to be taken into account,except for that originating from the hot and cold-ends of heat exchangers,when using the entropy generation minimization to optimize heat exchangers undergoing a thermodynamic cycle.展开更多
As the world's biggest carbon dioxide(CO_(2))emitter and the largest developing country,China faces daunting challenges to peak its emissions before 2030 and achieve carbon neutrality within 40 years.This study fu...As the world's biggest carbon dioxide(CO_(2))emitter and the largest developing country,China faces daunting challenges to peak its emissions before 2030 and achieve carbon neutrality within 40 years.This study fully considered the carbon-neutrality goal and the temperature rise constraints required by the Paris Agreement,by developing six long-term development scenarios,and conducting a quantitative evaluation on the carbon emissions pathways,energy transformation,technology,policy and investment demand for each scenario.This study combined both bottom-up and top-down methodologies,including simulations and analyses of energy consumption of end-use and power sectors(bottom-up),as well as scenario analysis,investment demand and technology evaluation at the macro level(top-down).This study demonstrates that achieving carbon neutrality before 2060 translates to significant efforts and overwhelming challenges for China.To comply with the target,a high rate of an average annual reduction of CO_(2) emissions by 9.3%from 2030 to 2050 is a necessity,which requires a huge investment demand.For example,in the 1.5℃ scenario,an investment in energy infrastructure alone equivalent to 2.6%of that year's GDP will be necessary.The technological pathway towards carbon neutrality will rely highly on both conventional emission reduction technologies and breakthrough technologies.China needs to balance a long-term development strategy of lower greenhouse gas emissions that meets both the Paris Agreement and the long-term goals for domestic economic and social development,with a phased implementation for both its five-year and long-term plans.展开更多
As typical prosumers,commercial buildings equipped with electric vehicle(EV)charging piles and solar photovoltaic panels require an effective energy management method.However,the conventional optimization-model-based ...As typical prosumers,commercial buildings equipped with electric vehicle(EV)charging piles and solar photovoltaic panels require an effective energy management method.However,the conventional optimization-model-based building energy management system faces significant challenges regarding prediction and calculation in online execution.To address this issue,a long short-term memory(LSTM)recurrent neural network(RNN)based machine learning algorithm is proposed in this paper to schedule the charging and discharging of numerous EVs in commercial-building prosumers.Under the proposed system control structure,the LSTM algorithm can be separated into offline and online stages.At the offline stage,the LSTM is used to map states(inputs)to decisions(outputs)based on the network training.At the online stage,once the current state is input,the LSTM can quickly generate a solution without any additional prediction.A preliminary data processing rule and an additional output filtering procedure are designed to improve the decision performance of LSTM network.The simulation results demonstrate that the LSTM algorithm can generate near-optimal solutions in milliseconds and significantly reduce the prediction and calculation pressures compared with the conventional optimization algorithm.展开更多
The fast-response feature from a superconducting magnetic energy storage(SMES)device is favored for suppressing instantaneous voltage and power fluctuations,but the SMES coil is much more expensive than a conventional...The fast-response feature from a superconducting magnetic energy storage(SMES)device is favored for suppressing instantaneous voltage and power fluctuations,but the SMES coil is much more expensive than a conventional battery energy storage device.In order to improve the energy utilization rate and reduce the energy storage cost under multiple-line power distribution conditions,this paper investigates a new interline DC dynamic voltage restorer(IDC-DVR)scheme with one SMES coil shared among multiple compensating circuits.In this new concept,an improved current-voltage(I/V)chopper assembly,which has a series of input/output power ports,is introduced to connect the single SMES coil with multiple power lines,and thereby satisfy the independent energy exchange requirements of any line to be compensated.Specifically,if two or more power lines have simultaneous compensating demands,the SMES coil can be selectively controlled to compensate the preferable line according to the priority order of the line.The feasibility of the proposed scheme is technically verified to maintain the transient voltage stability in multiple-line voltage swell and sag cases caused by either output voltage fluctuations from external power sources or power demand fluctuations from local sensitive loads.The simulation results provide a technical basis to develop a cost-effective SMES-based IDC-DVR for use in various DC distribution networks.展开更多
This paper offers an extensive overview of the utilization of sequential approximate optimization approaches in the context of numerically simulated large-scale continuum structures.These structures,commonly encounter...This paper offers an extensive overview of the utilization of sequential approximate optimization approaches in the context of numerically simulated large-scale continuum structures.These structures,commonly encountered in engineering applications,often involve complex objective and constraint functions that cannot be readily expressed as explicit functions of the design variables.As a result,sequential approximation techniques have emerged as the preferred strategy for addressing a wide array of topology optimization challenges.Over the past several decades,topology optimization methods have been advanced remarkably and successfully applied to solve engineering problems incorporating diverse physical backgrounds.In comparison to the large-scale equation solution,sensitivity analysis,graphics post-processing,etc.,the progress of the sequential approximation functions and their corresponding optimizersmake sluggish progress.Researchers,particularly novices,pay special attention to their difficulties with a particular problem.Thus,this paper provides an overview of sequential approximation functions,related literature on topology optimization methods,and their applications.Starting from optimality criteria and sequential linear programming,the other sequential approximate optimizations are introduced by employing Taylor expansion and intervening variables.In addition,recent advancements have led to the emergence of approaches such as Augmented Lagrange,sequential approximate integer,and non-gradient approximation are also introduced.By highlighting real-world applications and case studies,the paper not only demonstrates the practical relevance of these methods but also underscores the need for continued exploration in this area.Furthermore,to provide a comprehensive overview,this paper offers several novel developments that aim to illuminate potential directions for future research.展开更多
Perovskite solar cells(PSCs)emerging as a promising photovoltaic technology with high efficiency and low manufacturing cost have attracted the attention from all over the world.Both the efficiency and stability of PSC...Perovskite solar cells(PSCs)emerging as a promising photovoltaic technology with high efficiency and low manufacturing cost have attracted the attention from all over the world.Both the efficiency and stability of PSCs have increased steadily in recent years,and the research on reducing lead leakage and developing eco-friendly lead-free perovskites pushes forward the commercialization of PSCs step by step.This review summarizes the main progress of PSCs in 2020 and 2021 from the aspects of efficiency,stability,perovskite-based tandem devices,and lead-free PSCs.Moreover,a brief discussion on the development of PSC modules and its challenges toward practical application is provided.展开更多
Use of nonlinearconductive SiC/silicone rubber(SR)field grading material(FGM)can improve the local field concentration of composite insulators.Adding large volume fraction and large-size SiC particles(SiCp)into SR can...Use of nonlinearconductive SiC/silicone rubber(SR)field grading material(FGM)can improve the local field concentration of composite insulators.Adding large volume fraction and large-size SiC particles(SiCp)into SR can obtain a good field grading effect,but it is accompanied by the deterioration of mechanical properties.Compounding SiC with different shapes can solve this contradiction.By incorporating one-dimensional SiC whiskers(SiCw)to synergize with granular SiCp,SiC/SR FGM with better field-dependent conductivity,mechanical properties and thermal conductivity than large-size SiCp and large volume fraction filling case can be obtained by using smaller size SiCp and lower filling contents.The simulations of 500 kv line insulators show that the modified SiC/SR FGM can reduce the maximum field strength along the insulator surface and at sheath-core rod interfaces by 55%and 71.4%,respectively.The combined application of FGM and grading ring can achieve a complementary effect.Using FGM to partially replace the role of the grading rings,the field strength indicators can still meet the operational requirements after the tube radius and shielding depth of the grading rings at both ends are reduced by 36.2%and 40%separately,which is a benefit to alleviating the problems of high weight and large volume faced by traditional field grading methods.展开更多
Heating,ventilation,and air conditioning(HVAC)systems account for one-third of the total energy consumption in office buildings.The use of airflow measurements to control the operation of HVAC systems can reduce energ...Heating,ventilation,and air conditioning(HVAC)systems account for one-third of the total energy consumption in office buildings.The use of airflow measurements to control the operation of HVAC systems can reduce energy consumption;thus,a sensor capable of monitoring airflow in a duct system is critical.Triboelectric nanogenerators(TENGs)can be utilized as self-powered sensors in airflow-driven TENGs(ATENGs)as self-powered sensors.By employing ferroelectric materials and surface modifications,the surface charges of TENGs can be increased.In this study,fibrous-mat TENGs were prepared using ferroelectric materials consisting of poly(vinylidene fluoride-co-trifluoroethylene)(PVDF-TrFE)and polyamide 11(nylon-11).And these materials were subsequently investigated.Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)was added to PVDF-TrFE to enhance the ferroelectric crystalline phase.X-ray diffraction analysis revealed that this incorporation affects theβphase.In addition,the surface of nylon-11 was modified using the electrospray technique for post-treatment,thereby improving the interfacial adhesion between the fibers.These materials were then utilized in fibrous-mat ATENGs(FM-ATENGs)to demonstrate their practical application.The FM-ATENGs can be effectively used in an Arduino airflowcheck sensor,showcasing their potential for application in HVAC systems,to enhance airflow control and energy efficiency.展开更多
With the growth of intermittent renewable energy generation in power grids,there is an increasing demand for controllable resources to be deployed to guarantee power quality and frequency stability.The flexibility of ...With the growth of intermittent renewable energy generation in power grids,there is an increasing demand for controllable resources to be deployed to guarantee power quality and frequency stability.The flexibility of demand response(DR)resources has become a valuable solution to this problem.However,existing research indicates that problems on flexibility prediction of DR resources have not been investigated.This study applied the temporal convolution network(TCN)-combined transformer,a deep learning technique to predict the aggregated flexibility of two types of DR resources,that is,electric vehicles(EVs)and domestic hot water system(DHWS).The prediction uses historical power consumption data of these DR resources and DR signals(DSs)to facilitate prediction.The prediction can generate the size and maintenance time of the aggregated flexibility.The accuracy of the flexibility prediction results was verified through simulations of case studies.The simulation results show that under different maintenance times,the size of the flexibility changed.The proposed DR resource flexibility prediction method demonstrates its application in unlocking the demand-side flexibility to provide a reserve to grids.展开更多
Defective electrocatalysts,especially for intrinsic defective carbon,have aroused a wide concern owing to high spin and charge densities.However,the designated nitrogen species favorable for creating defects by the re...Defective electrocatalysts,especially for intrinsic defective carbon,have aroused a wide concern owing to high spin and charge densities.However,the designated nitrogen species favorable for creating defects by the removal of nitrogen,and the influence of defects for the coordination structure of active site and oxygen reduction reaction(ORR)activity have not been elucidated.Herein,we designed and synthesized a pair of electrocatalysts,denoted as Fe-N/C and Fe-ND/C for coordination sites of atomic iron-nitrogen and iron-nitrogen/defect configuration embedded in hollow carbon spheres,respectively,through direct pyrolysis of their corresponding hollow carbon spheres adsorbed with Fe(acac)3.The nitrogen defects were fabricated via the evaporation of pyrrolic-N on nitrogen doped hollow carbon spheres.Results of comparative experiments between Fe-N/C and Fe-ND/C reveal that Fe-ND/C shows superior ORR activity with an onset potential of 30 mV higher than that of Fe-N/C.Fe-ND sites are more favorable for the enhancement of ORR activity.Density functional theory(DFT)calculation demonstrates that Fe-ND/C with proposed coordination structure of FeN_(4-x)(0<x<4)anchored by OH as axial ligand during ORR,weakens the strong binding of OH^(*)intermediate and promotes the desorption of OH^(*)as rate-determining step for ORR in alkaline electrolyte.Thus,Fe-ND/C electrocatalysts present much better ORR activity compared with that of Fe-N/C with proposed coordination structure of FeN_(4).展开更多
Electroluminescent composites have considerable potential for applications in photoelectric display,electric field measurement and other fields due to their advantages of simple preparation and uniform luminescence.Ho...Electroluminescent composites have considerable potential for applications in photoelectric display,electric field measurement and other fields due to their advantages of simple preparation and uniform luminescence.However,high voltage required by the operation of electroluminescent composites hinders their applications in the electric domain,and research on the relationship between electroluminescence principle of composites and filler intrinsic attributes is insufficient.In this paper,the effects of electric field strength,filler mass fraction and voltage frequency on the electroluminescence intensity of ZnS:Cu/epoxy composites are studied,which are majorly used as the luminescent layer of electroluminescent devices.To enhance the electroluminescence intensity of composites,high-temperature sintered BaTiO_(3)and zinc oxide whiskers(ZnOw)particles are introduced in the base matrix.The finite element method is applied to verify that the matrix of high dielectric constant is in favour of improving the electroluminescence intensity of composites.The band structure of the ZnS:Cu particle is calculated based on the density functional theory+U method to analyse the intrinsic relationship between electroluminescence and particle electronic structure.This paper provides a basis for the research of high electroluminescence intensity devices and will be conducive to better understanding on the relationship between electroluminescence principle and filler intrinsic attributes.展开更多
Lithium-rich oxide is one of the most promising cathodes that meet high energy density requirement for batteries of the future, but its phase transformation from layer to spinel structure caused by the lattice instabi...Lithium-rich oxide is one of the most promising cathodes that meet high energy density requirement for batteries of the future, but its phase transformation from layer to spinel structure caused by the lattice instability presents severe challenge to cycling stability and the actually accessible capacity. The currently available approaches to suppress this undesired irreversible process often resort to limit the high voltages that lithium-rich oxide is exposed to. However, cycling stability thus improved is at the expense of the eventual energy output. In this work, we identified a new mechanism that is directly responsible for the lithium-rich oxide phase transformation and established a clear correlation between the successive consumption of Li+on anode due to incessant interphase repairing and the over-delithiation of lithium-rich oxide cathode. This new mechanism enables a simple but effective solution to the cathode degradation, in which an electrolyte additive is used to build a dense and protective interphase on anode with the intention to minimize Li depletion at cathode. The application of this new interphase effectively suppresses both electrolyte decomposition at anode and the phase transformation of lithium-rich oxide cathode, leading to high capacity and cycling stability.展开更多
For unshrouded blade tip,the high-temperature gas flows through the tip clearance by force of the lateral pressure difference.Thereby,the blade tip endures increasing thermal load.Furthermore,the conventional blade ti...For unshrouded blade tip,the high-temperature gas flows through the tip clearance by force of the lateral pressure difference.Thereby,the blade tip endures increasing thermal load.Furthermore,the conventional blade tip treatment cannot continuously provide protection for the deteriorating service environment.In the present study,aerothermal characteristics of the squealer blade tip with staggered ribs,partial squealer rim and different partial squealer rim thickness were investigated to explore the influences of ribbed-cavity tip on the tip heat transfer,leakage flow and turbine stage efficiency.The numerical results indicate that the ribbed-cavity tips are beneficial for the reduction of the blade tip thermal load and leakage flow.Among the present six blade tip designs,the minimal area-averaged heat transfer coefficient is obtained by the case with the staggered ribs and a deeper squealer rim,which is reduced by 31.41%relative to the squealer tip.Plus,the blade tip modification closer to leading edge or tip mid-chord region performs better than trailing edge in reducing the tip leakage flow.展开更多
Persistent severe smog and dust weather exists in many regions of China.Particles accu-mulate on the surface of high‐voltage transmission lines,which affects the surface morphology of the transmission line and induce...Persistent severe smog and dust weather exists in many regions of China.Particles accu-mulate on the surface of high‐voltage transmission lines,which affects the surface morphology of the transmission line and induces corona discharge.This work mainly studies the influence of electric field and photocatalysis on the corona characteristics of transmission lines.In this work,plasma spraying is used to prepare a dense,smooth and excellent photocatalytic TiO_(2)coating on the surface of transmission wires.An electron microscope and a white light interference profilometer is used to study the surface condition of the samples.The variation in the surface condition of the samples is observed under different fouling,light time and electric field intensity.The corona characteristics of power transmission lines under different surface conditions are studied.The results show that light and applied electric field promote the photocatalytic effect of TiO_(2),which helps to decompose the contamination on the surface of power transmission wires and thus reduce the corona discharge of transmission lines.The increase in corona inception voltage reduces the corona current pulse repetition rate and the ion current density during corona discharge.展开更多
A depth behavioral understanding for each layer in perovskite solar cells （PSCs） and their inter[acial interactions as a whole has been emerged for further enhancement in power conversion efficiency （PCE）. Herein,...A depth behavioral understanding for each layer in perovskite solar cells （PSCs） and their inter[acial interactions as a whole has been emerged for further enhancement in power conversion efficiency （PCE）. Herein, NiO@Carbon was not only simulated as a hole transport layer but also as a counter electrode at the same time in the planar heterojunction based PSCs with the program wxAMPS （analysis of microelectronic and photonic structures）-lD. Simulation results revealed a high dependence of PCE on the effect of band offset between hole transport material （HTM） and perovskite layers. Meanwhile, the valence band offset （AEv） of NiO-HTM was optimized to be -0.1 to -0.3 eV lower than that of the perovskite layer. Additionally, a barrier cliff was identified to significantly influence the hole extraction at the HTM/absorber interface. Conversely, the AEv between the active material and NiO@Carbon-HTM was derived to be -0.15 to 0.15 eV with an enhanced efficiency from 15% to 16%.展开更多
Although perovskite solar cells with power conversion efficiencies(PCEs) more than 22% have been realized with expensive organic charge-transporting materials, their stability and high cost remain to be addressed. In ...Although perovskite solar cells with power conversion efficiencies(PCEs) more than 22% have been realized with expensive organic charge-transporting materials, their stability and high cost remain to be addressed. In this work, the perovskite configuration of MAPbX(MA = CH_3 NH_3,X = I_3, Br_3, or I_2Br) integrated with stable and low-cost Cu:Ni Oxhole-transporting material, ZnO electron-transporting material, and Al counter electrode was modeled as a planar PSC and studied theoretically. A solar cell simulation program(wx AMPS), which served as an update of the popular solar cell simulation tool(AMPS: Analysis of Microelectronic and Photonic Structures), was used. The study yielded a detailed understanding of the role of each component in the solar celland its effect on the photovoltaic parameters as a whole. The bandgap of active materials and operating temperature of the modeled solar cell were shown to influence the solar cell performance in a significant way. Further, the simulation results reveal a strong dependence of photovoltaic parameters on the thickness and defect density of the light-absorbing layers. Under moderate simulation conditions, the MAPb Br_3 and MAPbI _2 Br cells recorded the highest PCEs of 20.58 and 19.08%, respectively, while MAPbI_3 cell gave a value of 16.14%.展开更多
DC circuit breakers are major enabling components for multi-terminal HVDC systems.Their key design targets are operating speed and efficiency.This paper proposes a novel moving coil actuator using a compensation coil ...DC circuit breakers are major enabling components for multi-terminal HVDC systems.Their key design targets are operating speed and efficiency.This paper proposes a novel moving coil actuator using a compensation coil topology to operate mechanical circuit breakers.This topology aims to significantly improve the magnetic field saturation and reduce the system inductance,so that the operating speed is increased.Four possible connection methods for the compensation coils are proposed and analyzed using finite element modeling,ensuing simulation results are compared and discussed.The operating speed of the moving coil actuator with compensation coils is significantly improved compared with the original moving coil actuator.The moving coil actuator with compensation coils can open a distance of 5 mm within 2.8 ms and the peak efficiency is 47%.展开更多
Drum level sloshing is the latest discovery in the application of heat recovery steam generator (HRSG) in combined cycle, and shows certain negative influence on drum level controlling. In order to improve drum level ...Drum level sloshing is the latest discovery in the application of heat recovery steam generator (HRSG) in combined cycle, and shows certain negative influence on drum level controlling. In order to improve drum level controlling, influence factors on the drum level sloshing were investigated. Firstly, drum sub-modules were developed using the method of modularization modeling, and then the model of drum level sloshing was set up as well. Experiments were carried out on the experimental rig, and the model was validated using the obtained experimental results. Dynamic simulation was made based on the model to get a 3-D graph of drum level sloshing, which shows a vivid procedure of drum level sloshing. The effect of feed-water flow rate, main-steam flow rate and heating quantity on the drum level sloshing was analyzed. The simulation results indicate that the signals with frequency higher than 0.05 Hz are that of drum level sloshing, the signals with frequency of 0.0-0.05 Hz are that of drum level trendy and "false water level", and variation of the feed-water flow rates, main-steam flow rates and heating quantities can change the frequency of drum level sloshing, i.e., the frequency of sloshing increases with the increase of feed-water flow rate, or the decrease of the main-steam flow rate and the heating quantity. This research work is fundamental to improve signal-to-noise ratio of drum level signal and precise controlling of drum level.展开更多
As the effect of climate plays a significant role in corona discharge under combined voltages,the variation of corona inception voltage with different air pressure and humidities is studied.An experimental platform,ba...As the effect of climate plays a significant role in corona discharge under combined voltages,the variation of corona inception voltage with different air pressure and humidities is studied.An experimental platform,based on a rod-to-plane electrode,is constructed with adjustable air pressure from 0.06 MPa to 0.10 MPa and with a relative humidity(RH)from 20%to 90%.The variation of ultraviolet(UV)photon count and corona inception voltage is obtained at various climate conditions under different applied voltages:the single AC,single DC,and combined AC-DC.It turns out that all the corona inception voltages decline with the drop of air pressure and the rise of humidity under different applied voltages.The influence between different voltages primarily relies on space charge,as more AC components make it easier to accumulate positive ions.The existence of AC makes ions move forward and backward while the existence of DC dominates the polarity of corona and general drift directions.At last the fitting formula of hybrid corona inception voltage combining air pressure and relative humidity is given.展开更多
In this study,a packed bed reactor was developed to investigate the gasification process of coal particles.The effects of coal particle size and heater temperature of reactor were examined to identify the thermochemic...In this study,a packed bed reactor was developed to investigate the gasification process of coal particles.The effects of coal particle size and heater temperature of reactor were examined to identify the thermochemical processes through the packed bed.Three different coal samples with varying size,named as A,B,and C,are used,and the experimental results show that the packed bed with smaller coal size has higher temperature,reaching 624°C,582°C,and 569°C for coal A,B,and C,respectively.In the case of CO formation,the smaller particle size has greater products in the unit of mole fraction over the area of generation.However,the variation in the porosity of the packed bed due to different coal particle sizes affects the reactions through the oxygen access.Consequently,the CO formation is least from the coal packed bed formed by the smallest particle size A.A second test with the temperature variations shows that the higher heater temperature promotes the chemical reactions,resulting in the increased gas products.The findings indicate the important role of coal seam porosity in underground coal gasification application,as well as temperature to promote the syngas productions.展开更多
基金supported by the National Natural Science Foundation of China (51006060)China Postdoctoral Science Foundation (2009-02080)
文摘In general,thermal processes can be classified into two categories: heat-work conversion processes and heat transfer processes. Correspondingly,the optimization of thermal processes has to have two different criteria:the well known entropy generation minimization method and the recently proposed entransy dissipation maximization method. This study analyzes the thermal issues in a heat exchanger group,and optimizes the unit arrangements under different constraints based on a suitable optimization crite-rion. The result indicates that the principle of minimum entropy generation rate is valid for optimizing heat exchangers in a ther-modynamic cycle with given boundary temperatures. In contrast,the entransy dissipation maximization is more suitable in heat exchanger optimizations involving only heat transfer processes. Furthermore,the entropy generation rate induced by dumping used streams into ambient surroundings has to be taken into account,except for that originating from the hot and cold-ends of heat exchangers,when using the entropy generation minimization to optimize heat exchangers undergoing a thermodynamic cycle.
文摘As the world's biggest carbon dioxide(CO_(2))emitter and the largest developing country,China faces daunting challenges to peak its emissions before 2030 and achieve carbon neutrality within 40 years.This study fully considered the carbon-neutrality goal and the temperature rise constraints required by the Paris Agreement,by developing six long-term development scenarios,and conducting a quantitative evaluation on the carbon emissions pathways,energy transformation,technology,policy and investment demand for each scenario.This study combined both bottom-up and top-down methodologies,including simulations and analyses of energy consumption of end-use and power sectors(bottom-up),as well as scenario analysis,investment demand and technology evaluation at the macro level(top-down).This study demonstrates that achieving carbon neutrality before 2060 translates to significant efforts and overwhelming challenges for China.To comply with the target,a high rate of an average annual reduction of CO_(2) emissions by 9.3%from 2030 to 2050 is a necessity,which requires a huge investment demand.For example,in the 1.5℃ scenario,an investment in energy infrastructure alone equivalent to 2.6%of that year's GDP will be necessary.The technological pathway towards carbon neutrality will rely highly on both conventional emission reduction technologies and breakthrough technologies.China needs to balance a long-term development strategy of lower greenhouse gas emissions that meets both the Paris Agreement and the long-term goals for domestic economic and social development,with a phased implementation for both its five-year and long-term plans.
基金This work was supported by the National Natural Science Foundation of China(No.51877078)the State Key Laboratory of Smart Grid Protection and Operation Control Open Project(No.SGNR0000KJJS1907535)the Beijing Nova Program(No.Z201100006820106)。
文摘As typical prosumers,commercial buildings equipped with electric vehicle(EV)charging piles and solar photovoltaic panels require an effective energy management method.However,the conventional optimization-model-based building energy management system faces significant challenges regarding prediction and calculation in online execution.To address this issue,a long short-term memory(LSTM)recurrent neural network(RNN)based machine learning algorithm is proposed in this paper to schedule the charging and discharging of numerous EVs in commercial-building prosumers.Under the proposed system control structure,the LSTM algorithm can be separated into offline and online stages.At the offline stage,the LSTM is used to map states(inputs)to decisions(outputs)based on the network training.At the online stage,once the current state is input,the LSTM can quickly generate a solution without any additional prediction.A preliminary data processing rule and an additional output filtering procedure are designed to improve the decision performance of LSTM network.The simulation results demonstrate that the LSTM algorithm can generate near-optimal solutions in milliseconds and significantly reduce the prediction and calculation pressures compared with the conventional optimization algorithm.
基金This work was supported in part by the National Natural Science Foundation of China under Grant No.51807128State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources under Grant No.LAPS20017.
文摘The fast-response feature from a superconducting magnetic energy storage(SMES)device is favored for suppressing instantaneous voltage and power fluctuations,but the SMES coil is much more expensive than a conventional battery energy storage device.In order to improve the energy utilization rate and reduce the energy storage cost under multiple-line power distribution conditions,this paper investigates a new interline DC dynamic voltage restorer(IDC-DVR)scheme with one SMES coil shared among multiple compensating circuits.In this new concept,an improved current-voltage(I/V)chopper assembly,which has a series of input/output power ports,is introduced to connect the single SMES coil with multiple power lines,and thereby satisfy the independent energy exchange requirements of any line to be compensated.Specifically,if two or more power lines have simultaneous compensating demands,the SMES coil can be selectively controlled to compensate the preferable line according to the priority order of the line.The feasibility of the proposed scheme is technically verified to maintain the transient voltage stability in multiple-line voltage swell and sag cases caused by either output voltage fluctuations from external power sources or power demand fluctuations from local sensitive loads.The simulation results provide a technical basis to develop a cost-effective SMES-based IDC-DVR for use in various DC distribution networks.
基金financially supported by the National Key R&D Program (2022YFB4201302)Guang Dong Basic and Applied Basic Research Foundation (2022A1515240057)the Huaneng Technology Funds (HNKJ20-H88).
文摘This paper offers an extensive overview of the utilization of sequential approximate optimization approaches in the context of numerically simulated large-scale continuum structures.These structures,commonly encountered in engineering applications,often involve complex objective and constraint functions that cannot be readily expressed as explicit functions of the design variables.As a result,sequential approximation techniques have emerged as the preferred strategy for addressing a wide array of topology optimization challenges.Over the past several decades,topology optimization methods have been advanced remarkably and successfully applied to solve engineering problems incorporating diverse physical backgrounds.In comparison to the large-scale equation solution,sensitivity analysis,graphics post-processing,etc.,the progress of the sequential approximation functions and their corresponding optimizersmake sluggish progress.Researchers,particularly novices,pay special attention to their difficulties with a particular problem.Thus,this paper provides an overview of sequential approximation functions,related literature on topology optimization methods,and their applications.Starting from optimality criteria and sequential linear programming,the other sequential approximate optimizations are introduced by employing Taylor expansion and intervening variables.In addition,recent advancements have led to the emergence of approaches such as Augmented Lagrange,sequential approximate integer,and non-gradient approximation are also introduced.By highlighting real-world applications and case studies,the paper not only demonstrates the practical relevance of these methods but also underscores the need for continued exploration in this area.Furthermore,to provide a comprehensive overview,this paper offers several novel developments that aim to illuminate potential directions for future research.
基金supported by the National Natural Science Foundation of China(Grant Nos.11834011 and 12074245)the support from the Energy Materials and Surface Sciences Unit of the Okinawa Institute of Science and Technology Graduate University。
文摘Perovskite solar cells(PSCs)emerging as a promising photovoltaic technology with high efficiency and low manufacturing cost have attracted the attention from all over the world.Both the efficiency and stability of PSCs have increased steadily in recent years,and the research on reducing lead leakage and developing eco-friendly lead-free perovskites pushes forward the commercialization of PSCs step by step.This review summarizes the main progress of PSCs in 2020 and 2021 from the aspects of efficiency,stability,perovskite-based tandem devices,and lead-free PSCs.Moreover,a brief discussion on the development of PSC modules and its challenges toward practical application is provided.
基金supported by Science and Technology Project of State Grid Corporation of China(7000-202158440A-0-0-00)。
文摘Use of nonlinearconductive SiC/silicone rubber(SR)field grading material(FGM)can improve the local field concentration of composite insulators.Adding large volume fraction and large-size SiC particles(SiCp)into SR can obtain a good field grading effect,but it is accompanied by the deterioration of mechanical properties.Compounding SiC with different shapes can solve this contradiction.By incorporating one-dimensional SiC whiskers(SiCw)to synergize with granular SiCp,SiC/SR FGM with better field-dependent conductivity,mechanical properties and thermal conductivity than large-size SiCp and large volume fraction filling case can be obtained by using smaller size SiCp and lower filling contents.The simulations of 500 kv line insulators show that the modified SiC/SR FGM can reduce the maximum field strength along the insulator surface and at sheath-core rod interfaces by 55%and 71.4%,respectively.The combined application of FGM and grading ring can achieve a complementary effect.Using FGM to partially replace the role of the grading rings,the field strength indicators can still meet the operational requirements after the tube radius and shielding depth of the grading rings at both ends are reduced by 36.2%and 40%separately,which is a benefit to alleviating the problems of high weight and large volume faced by traditional field grading methods.
基金supported by the Korea Institute of Energy Technology Evaluation and Planning(KETEP)grant funded by the Korean government(MOTIE)(grant number:20202020800030).
文摘Heating,ventilation,and air conditioning(HVAC)systems account for one-third of the total energy consumption in office buildings.The use of airflow measurements to control the operation of HVAC systems can reduce energy consumption;thus,a sensor capable of monitoring airflow in a duct system is critical.Triboelectric nanogenerators(TENGs)can be utilized as self-powered sensors in airflow-driven TENGs(ATENGs)as self-powered sensors.By employing ferroelectric materials and surface modifications,the surface charges of TENGs can be increased.In this study,fibrous-mat TENGs were prepared using ferroelectric materials consisting of poly(vinylidene fluoride-co-trifluoroethylene)(PVDF-TrFE)and polyamide 11(nylon-11).And these materials were subsequently investigated.Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)was added to PVDF-TrFE to enhance the ferroelectric crystalline phase.X-ray diffraction analysis revealed that this incorporation affects theβphase.In addition,the surface of nylon-11 was modified using the electrospray technique for post-treatment,thereby improving the interfacial adhesion between the fibers.These materials were then utilized in fibrous-mat ATENGs(FM-ATENGs)to demonstrate their practical application.The FM-ATENGs can be effectively used in an Arduino airflowcheck sensor,showcasing their potential for application in HVAC systems,to enhance airflow control and energy efficiency.
基金This work was supported by the National Natural Science Foundation of China(51877078 and 52061635102)the Beijing Nova Program(Z201100006820106).
文摘With the growth of intermittent renewable energy generation in power grids,there is an increasing demand for controllable resources to be deployed to guarantee power quality and frequency stability.The flexibility of demand response(DR)resources has become a valuable solution to this problem.However,existing research indicates that problems on flexibility prediction of DR resources have not been investigated.This study applied the temporal convolution network(TCN)-combined transformer,a deep learning technique to predict the aggregated flexibility of two types of DR resources,that is,electric vehicles(EVs)and domestic hot water system(DHWS).The prediction uses historical power consumption data of these DR resources and DR signals(DSs)to facilitate prediction.The prediction can generate the size and maintenance time of the aggregated flexibility.The accuracy of the flexibility prediction results was verified through simulations of case studies.The simulation results show that under different maintenance times,the size of the flexibility changed.The proposed DR resource flexibility prediction method demonstrates its application in unlocking the demand-side flexibility to provide a reserve to grids.
基金the National Natural Science Foundation of China(Nos.21905271,21701168)Liaoning Natural Science Foundation(Nos.20180510029,20180510043,20180510050)+2 种基金the Dalian National Laboratory for Clean Energy(DNL)CAS,DNL Cooperation Fund,CAS(No.DNL180402)Australian Research Council(No.DP180100568).For XAFS measurement,we gratefully acknowledge 1W1B beamline of Beijing Synchrotron Radiation Facility(BSRF)Beijing,China for providing the beam time.
文摘Defective electrocatalysts,especially for intrinsic defective carbon,have aroused a wide concern owing to high spin and charge densities.However,the designated nitrogen species favorable for creating defects by the removal of nitrogen,and the influence of defects for the coordination structure of active site and oxygen reduction reaction(ORR)activity have not been elucidated.Herein,we designed and synthesized a pair of electrocatalysts,denoted as Fe-N/C and Fe-ND/C for coordination sites of atomic iron-nitrogen and iron-nitrogen/defect configuration embedded in hollow carbon spheres,respectively,through direct pyrolysis of their corresponding hollow carbon spheres adsorbed with Fe(acac)3.The nitrogen defects were fabricated via the evaporation of pyrrolic-N on nitrogen doped hollow carbon spheres.Results of comparative experiments between Fe-N/C and Fe-ND/C reveal that Fe-ND/C shows superior ORR activity with an onset potential of 30 mV higher than that of Fe-N/C.Fe-ND sites are more favorable for the enhancement of ORR activity.Density functional theory(DFT)calculation demonstrates that Fe-ND/C with proposed coordination structure of FeN_(4-x)(0<x<4)anchored by OH as axial ligand during ORR,weakens the strong binding of OH^(*)intermediate and promotes the desorption of OH^(*)as rate-determining step for ORR in alkaline electrolyte.Thus,Fe-ND/C electrocatalysts present much better ORR activity compared with that of Fe-N/C with proposed coordination structure of FeN_(4).
基金National Natural Science Foundation of China,Grant/Award Number:51877082Science and Technology Project of State Grid Corporation of China,Grant/Award Number:7000-202158440A-0-0-00。
文摘Electroluminescent composites have considerable potential for applications in photoelectric display,electric field measurement and other fields due to their advantages of simple preparation and uniform luminescence.However,high voltage required by the operation of electroluminescent composites hinders their applications in the electric domain,and research on the relationship between electroluminescence principle of composites and filler intrinsic attributes is insufficient.In this paper,the effects of electric field strength,filler mass fraction and voltage frequency on the electroluminescence intensity of ZnS:Cu/epoxy composites are studied,which are majorly used as the luminescent layer of electroluminescent devices.To enhance the electroluminescence intensity of composites,high-temperature sintered BaTiO_(3)and zinc oxide whiskers(ZnOw)particles are introduced in the base matrix.The finite element method is applied to verify that the matrix of high dielectric constant is in favour of improving the electroluminescence intensity of composites.The band structure of the ZnS:Cu particle is calculated based on the density functional theory+U method to analyse the intrinsic relationship between electroluminescence and particle electronic structure.This paper provides a basis for the research of high electroluminescence intensity devices and will be conducive to better understanding on the relationship between electroluminescence principle and filler intrinsic attributes.
基金supported by the National Natural Science Foundation of China(Grant No.21872058)the Key Project of Science and Technology in Guangdong Province(2017A010106006)
文摘Lithium-rich oxide is one of the most promising cathodes that meet high energy density requirement for batteries of the future, but its phase transformation from layer to spinel structure caused by the lattice instability presents severe challenge to cycling stability and the actually accessible capacity. The currently available approaches to suppress this undesired irreversible process often resort to limit the high voltages that lithium-rich oxide is exposed to. However, cycling stability thus improved is at the expense of the eventual energy output. In this work, we identified a new mechanism that is directly responsible for the lithium-rich oxide phase transformation and established a clear correlation between the successive consumption of Li+on anode due to incessant interphase repairing and the over-delithiation of lithium-rich oxide cathode. This new mechanism enables a simple but effective solution to the cathode degradation, in which an electrolyte additive is used to build a dense and protective interphase on anode with the intention to minimize Li depletion at cathode. The application of this new interphase effectively suppresses both electrolyte decomposition at anode and the phase transformation of lithium-rich oxide cathode, leading to high capacity and cycling stability.
基金the support of National Natural Science Foundation of China(No.52006178,51936008)National Key R&D Program of China(No.Y2019-Ⅷ-0007-0168)+1 种基金the Fundamental Research Funds for the Central Universitiesthe Innovation Capacity Support Plan in Shaanxi Province of China(Grant No.2023-CX-TD-19)。
文摘For unshrouded blade tip,the high-temperature gas flows through the tip clearance by force of the lateral pressure difference.Thereby,the blade tip endures increasing thermal load.Furthermore,the conventional blade tip treatment cannot continuously provide protection for the deteriorating service environment.In the present study,aerothermal characteristics of the squealer blade tip with staggered ribs,partial squealer rim and different partial squealer rim thickness were investigated to explore the influences of ribbed-cavity tip on the tip heat transfer,leakage flow and turbine stage efficiency.The numerical results indicate that the ribbed-cavity tips are beneficial for the reduction of the blade tip thermal load and leakage flow.Among the present six blade tip designs,the minimal area-averaged heat transfer coefficient is obtained by the case with the staggered ribs and a deeper squealer rim,which is reduced by 31.41%relative to the squealer tip.Plus,the blade tip modification closer to leading edge or tip mid-chord region performs better than trailing edge in reducing the tip leakage flow.
基金supported by the National Natural Science Foundation of China(51877082,51377096)the Fok Ying‐Tong Education Foundation,China Grant No.151,058the Fundamental Research Funds for the Central Uni-versities 2019MS011.
文摘Persistent severe smog and dust weather exists in many regions of China.Particles accu-mulate on the surface of high‐voltage transmission lines,which affects the surface morphology of the transmission line and induces corona discharge.This work mainly studies the influence of electric field and photocatalysis on the corona characteristics of transmission lines.In this work,plasma spraying is used to prepare a dense,smooth and excellent photocatalytic TiO_(2)coating on the surface of transmission wires.An electron microscope and a white light interference profilometer is used to study the surface condition of the samples.The variation in the surface condition of the samples is observed under different fouling,light time and electric field intensity.The corona characteristics of power transmission lines under different surface conditions are studied.The results show that light and applied electric field promote the photocatalytic effect of TiO_(2),which helps to decompose the contamination on the surface of power transmission wires and thus reduce the corona discharge of transmission lines.The increase in corona inception voltage reduces the corona current pulse repetition rate and the ion current density during corona discharge.
基金Project supported by the National High-tech Research and Development Program of China(Grant No.2015AA034601)the National Natural Science Foundation of China(Grant Nos.51772096,91333122,51372082,51402106,and 11504107)+2 种基金the Ph.D.Programs Foundation of Ministry of Education of China(Grant No.20130036110012)the Par-Eu Scholars Program,Beijing Municipal Science and Technology Project,China(Grant No.Z161100002616039)the Fundamental Research Funds for the Central Universities of China(Grant Nos.2016JQ01,2015ZZD03,2015ZD07,and 2017ZZD02)
文摘A depth behavioral understanding for each layer in perovskite solar cells （PSCs） and their inter[acial interactions as a whole has been emerged for further enhancement in power conversion efficiency （PCE）. Herein, NiO@Carbon was not only simulated as a hole transport layer but also as a counter electrode at the same time in the planar heterojunction based PSCs with the program wxAMPS （analysis of microelectronic and photonic structures）-lD. Simulation results revealed a high dependence of PCE on the effect of band offset between hole transport material （HTM） and perovskite layers. Meanwhile, the valence band offset （AEv） of NiO-HTM was optimized to be -0.1 to -0.3 eV lower than that of the perovskite layer. Additionally, a barrier cliff was identified to significantly influence the hole extraction at the HTM/absorber interface. Conversely, the AEv between the active material and NiO@Carbon-HTM was derived to be -0.15 to 0.15 eV with an enhanced efficiency from 15% to 16%.
基金supported partially by National Natural Science Foundation of China (Grant Nos. 51772096, 51372082, 51402106, and 11504107)Beijing Natural Science Foundation (17L20075)+4 种基金Joint Funds of the Equipment Pre-Research and Ministry of Education (6141A020225)National High-tech R&D Program of China (863 Program, No. 2015AA034601)Par-Eu Scholars ProgramBeijing Municipal Science and Technology Project (Z161100002616039)the Fundamental Research Funds for the Central Universities (2016JQ01, 2017ZZD02)
文摘Although perovskite solar cells with power conversion efficiencies(PCEs) more than 22% have been realized with expensive organic charge-transporting materials, their stability and high cost remain to be addressed. In this work, the perovskite configuration of MAPbX(MA = CH_3 NH_3,X = I_3, Br_3, or I_2Br) integrated with stable and low-cost Cu:Ni Oxhole-transporting material, ZnO electron-transporting material, and Al counter electrode was modeled as a planar PSC and studied theoretically. A solar cell simulation program(wx AMPS), which served as an update of the popular solar cell simulation tool(AMPS: Analysis of Microelectronic and Photonic Structures), was used. The study yielded a detailed understanding of the role of each component in the solar celland its effect on the photovoltaic parameters as a whole. The bandgap of active materials and operating temperature of the modeled solar cell were shown to influence the solar cell performance in a significant way. Further, the simulation results reveal a strong dependence of photovoltaic parameters on the thickness and defect density of the light-absorbing layers. Under moderate simulation conditions, the MAPb Br_3 and MAPbI _2 Br cells recorded the highest PCEs of 20.58 and 19.08%, respectively, while MAPbI_3 cell gave a value of 16.14%.
文摘DC circuit breakers are major enabling components for multi-terminal HVDC systems.Their key design targets are operating speed and efficiency.This paper proposes a novel moving coil actuator using a compensation coil topology to operate mechanical circuit breakers.This topology aims to significantly improve the magnetic field saturation and reduce the system inductance,so that the operating speed is increased.Four possible connection methods for the compensation coils are proposed and analyzed using finite element modeling,ensuing simulation results are compared and discussed.The operating speed of the moving coil actuator with compensation coils is significantly improved compared with the original moving coil actuator.The moving coil actuator with compensation coils can open a distance of 5 mm within 2.8 ms and the peak efficiency is 47%.
基金Project(51276023) supported by the National Natural Science Foundation of ChinaProject(09k069) supported by the Open Project Funded by Universities Innovation Platform, Hunan Province, ChinaProject(2011GK311) supported by the Office of Science and Technology of Hunan Province, China
文摘Drum level sloshing is the latest discovery in the application of heat recovery steam generator (HRSG) in combined cycle, and shows certain negative influence on drum level controlling. In order to improve drum level controlling, influence factors on the drum level sloshing were investigated. Firstly, drum sub-modules were developed using the method of modularization modeling, and then the model of drum level sloshing was set up as well. Experiments were carried out on the experimental rig, and the model was validated using the obtained experimental results. Dynamic simulation was made based on the model to get a 3-D graph of drum level sloshing, which shows a vivid procedure of drum level sloshing. The effect of feed-water flow rate, main-steam flow rate and heating quantity on the drum level sloshing was analyzed. The simulation results indicate that the signals with frequency higher than 0.05 Hz are that of drum level sloshing, the signals with frequency of 0.0-0.05 Hz are that of drum level trendy and "false water level", and variation of the feed-water flow rates, main-steam flow rates and heating quantities can change the frequency of drum level sloshing, i.e., the frequency of sloshing increases with the increase of feed-water flow rate, or the decrease of the main-steam flow rate and the heating quantity. This research work is fundamental to improve signal-to-noise ratio of drum level signal and precise controlling of drum level.
基金supported by the National Natural Science Foundation of China(51877082)Fok Ying-Tong Education Foundation(151058)the Fundamental Research Funds for the Central Universities(2019MS011).
文摘As the effect of climate plays a significant role in corona discharge under combined voltages,the variation of corona inception voltage with different air pressure and humidities is studied.An experimental platform,based on a rod-to-plane electrode,is constructed with adjustable air pressure from 0.06 MPa to 0.10 MPa and with a relative humidity(RH)from 20%to 90%.The variation of ultraviolet(UV)photon count and corona inception voltage is obtained at various climate conditions under different applied voltages:the single AC,single DC,and combined AC-DC.It turns out that all the corona inception voltages decline with the drop of air pressure and the rise of humidity under different applied voltages.The influence between different voltages primarily relies on space charge,as more AC components make it easier to accumulate positive ions.The existence of AC makes ions move forward and backward while the existence of DC dominates the polarity of corona and general drift directions.At last the fitting formula of hybrid corona inception voltage combining air pressure and relative humidity is given.
基金The first author gratefully acknowledges the Ministry of Research,Technology,and Higher Education(KEMENRISTEKDIKTI)of Republic Indonesia for the scholarship funding through the Research and Innovation in Science and Technology Project(RISET-Pro)program and also the University of Glasgow for supporting this research.
文摘In this study,a packed bed reactor was developed to investigate the gasification process of coal particles.The effects of coal particle size and heater temperature of reactor were examined to identify the thermochemical processes through the packed bed.Three different coal samples with varying size,named as A,B,and C,are used,and the experimental results show that the packed bed with smaller coal size has higher temperature,reaching 624°C,582°C,and 569°C for coal A,B,and C,respectively.In the case of CO formation,the smaller particle size has greater products in the unit of mole fraction over the area of generation.However,the variation in the porosity of the packed bed due to different coal particle sizes affects the reactions through the oxygen access.Consequently,the CO formation is least from the coal packed bed formed by the smallest particle size A.A second test with the temperature variations shows that the higher heater temperature promotes the chemical reactions,resulting in the increased gas products.The findings indicate the important role of coal seam porosity in underground coal gasification application,as well as temperature to promote the syngas productions.
