Flash Joule heating(FJH),as a high-efficiency and low-energy consumption technology for advanced materials synthesis,has shown significant potential in the synthesis of graphene and other functional carbon materials.B...Flash Joule heating(FJH),as a high-efficiency and low-energy consumption technology for advanced materials synthesis,has shown significant potential in the synthesis of graphene and other functional carbon materials.Based on the Joule effect,the solid carbon sources can be rapidly heated to ultra-high temperatures(>3000 K)through instantaneous high-energy current pulses during FJH,thus driving the rapid rearrangement and graphitization of carbon atoms.This technology demonstrates numerous advantages,such as solvent-and catalyst-free features,high energy conversion efficiency,and a short process cycle.In this review,we have systematically summarized the technology principle and equipment design for FJH,as well as its raw materials selection and pretreatment strategies.The research progress in the FJH synthesis of flash graphene,carbon nanotubes,graphene fibers,and anode hard carbon,as well as its by-products,is also presented.FJH can precisely optimize the microstructures of carbon materials(e.g.,interlayer spacing of turbostratic graphene,defect concentration,and heteroatom doping)by regulating its operation parameters like flash voltage and flash time,thereby enhancing their performances in various applications,such as composite reinforcement,metal-ion battery electrodes,supercapacitors,and electrocatalysts.However,this technology is still challenged by low process yield,macroscopic material uniformity,and green power supply system construction.More research efforts are also required to promote the transition of FJH from laboratory to industrial-scale applications,thus providing innovative solutions for advanced carbon materials manufacturing and waste management toward carbon neutrality.展开更多
Lithium-ion batteries(LIBs)are critical for the rapid growth of electric vehicles(EVs),but their inherent lifespan leads to numerous retirements and resource challenges.The efficacy of conventional recycling technique...Lithium-ion batteries(LIBs)are critical for the rapid growth of electric vehicles(EVs),but their inherent lifespan leads to numerous retirements and resource challenges.The efficacy of conventional recycling techniques is increasingly compromised by their high energy consumption and secondary pollution,rendering them less responsive to greener and more sustainable requirement of rapid development.Thus,the direct recycling process emerged and was considered as a more expedient and convenient method of recycling compared to the conventional recycling modes that are currently in study.However,due to the reliance on the indispensable sintering process,direct recycling still faces considerable challenges,motivating researchers to explore faster,greener,and more cost-effective strategies for LIBs recycling,Inspiringly,Joule heating recycling(JHR),an emerging technique,offers rapid,efficient impurity removal and material regeneration with minimal environmental impact,addressing limitations of existing methods.This method reduces the time for direct recycling of spent LIBs by a factor of at least three orders of magnitude and exhibits significant potential for future industrial production.Unfortunately,due to the lack of systematic organization and reporting,this next generation approach to direct recycling of spent LIBs has not yet gained much interest.To facilitate a more profound comprehension of rising flash recycling strategy,in this study,JHR is distinguished into two distinctive implementation pathways(including flash Joule heating and carbon thermal shock),designed to accommodate varying pretreatment stages and diverse spent LIBs materials.Subsequently,the advantages of the recently developed JHR of spent LIBs in terms of material performance,environmental friendliness,and economic viability are discussed in detail.Ultimately,with the goal of achieving more attractive society effects,the future direction of JHR of spent LIBs and its potential for practical application are proposed and envisaged.展开更多
Friction rolling additive manufacturing(FRAM)is a solid-state additive manufacturing technology that plasticizes the feed and deposits a material using frictional heat generated by the tool head.The thermal efficiency...Friction rolling additive manufacturing(FRAM)is a solid-state additive manufacturing technology that plasticizes the feed and deposits a material using frictional heat generated by the tool head.The thermal efficiency of FRAM,which depends only on friction to generate heat,is low,and the thermal-accumulation effect of the deposition process must be addressed.An FRAM heat-balance-control method that combines plasma-arc preheating and instant water cooling(PC-FRAM)is devised in this study,and a temperature field featuring rapidly increasing and decreasing temperature is constructed around the tool head.Additionally,2195-T87 Al-Li alloy is used as the feed material,and the effects of heating and cooling rates on the microstructure and mechanical properties are investigated.The results show that water cooling significantly improves heat accumulation during the deposition process.The cooling rate increases by 11.7 times,and the high-temperature residence time decreases by more than 50%.The grain size of the PC-FRAM sample is the smallest,i.e.,3.77±1.03μm,its dislocation density is the highest,and the number density of precipitates is the highest,the size of precipitates is the smallest,which shows the best precipitation-strengthening effect.The hardness test results are consistent with the precipitation distribution.The ultimate tensile strength,yield strength and elongation of the PC-FRAM samples are the highest(351±15.6 MPa,251.3±15.8 MPa and 16.25%±1.25%,respectively)among the samples investigated.The preheating and water-cooling-assisted deposition simultaneously increases the tensile strength and elongation of the deposited samples.The combination of preheating and instant cooling improves the deposition efficiency of FRAM and weakens the thermal-softening effect.展开更多
Grain-oriented silicon steels were prepared at different heating rates during high temperature annealing,in which the evolution of magnetic properties,grain orientations and precipitates were studied.To illustrate the...Grain-oriented silicon steels were prepared at different heating rates during high temperature annealing,in which the evolution of magnetic properties,grain orientations and precipitates were studied.To illustrate the Zener factor,the diameter and number density of precipitates of interrupted testing samples were statistically calculated.The effect of precipitate ripening on the Goss texture and magnetic property was investigated.Data indicated that the trend of Zener factor was similar under different heating rates,first increasing and then decreasing,and that the precipitate maturing was greatly inhibited as the heating rate increased.Secondary recrystallization was developed at the temperature of 1010℃when a heating rate of 5℃/h was used,resulting in Goss,Brass and{110}<227>oriented grains growing abnormally and a magnetic induction intensity of 1.90T.Furthermore,increasing the heating rate to 20℃/h would inhibit the development of undesirable oriented grains and obtain a sharp Goss texture.However,when the heating rate was extremely fast,such as 40℃/h,poor secondary recrystallization was developed with many island grains,corresponding to a decrease in magnetic induction intensity to 1.87 T.At a suitable heating rate of 20℃/h,the sharpest Goss texture and the highest magnetic induction of 1.94 T with an onset secondary recrystallization temperature of 1020℃were found among the experimental variables in this study.The heating rate affected the initial temperature of secondary recrystallization by controlling the maturation of precipitates,leading to the deviation and dispersion of Goss texture,thereby reducing the magnetic properties.展开更多
Geothermal energy,a form of renewable energy,has been extensively utilized for building heating.However,there is a lack of detailed comparative studies on the use of shallow and medium-deep geothermal energy in buildi...Geothermal energy,a form of renewable energy,has been extensively utilized for building heating.However,there is a lack of detailed comparative studies on the use of shallow and medium-deep geothermal energy in building energy systems,which are essential for decision-making.Therefore,this paper presents a comparative study of the performance and economic analysis of shallow and medium-deep borehole heat exchanger heating systems.Based on the geological parameters of Xi’an,China and commonly used borehole heat exchanger structures,numerical simulationmethods are employed to analyze performance and economic efficiency.The results indicate that increasing the spacing between shallow borehole heat exchangers can effectively reduce thermal interference between the pipes and improve heat extraction performance.As the flow rate increases,the outlet water temperature ranges from 279.3 to 279.7 K,with heat extraction power varying between 595 and 609 W.For medium-deep borehole heat exchangers,performance predictions show that a higher flow rate results in greater heat extraction power.However,when the flow rate exceeds 30 m^(3)/h,further increases in flow rate have only a minor effect on enhancing heat extraction power.Additionally,the economic analysis reveals that the payback period for shallow geothermal heating systems ranges from 10 to 11 years,while for medium-deep geothermal heating systems,it varies more widely from 3 to 25 years.Therefore,the payback period for medium-deep geothermal heating systems is more significantly influenced by operational and installation parameters,and optimizing these parameters can considerably shorten the payback period.The results of this study are expected to provide valuable insights into the efficient and cost-effective utilization of geothermal energy for building heating.展开更多
This study investigates the feasibility and efficiency of geothermal energy for heating applications in Azerbaijan,with a specific focus on the Khachmaz region.Despite the country’s growing interest in sustainable en...This study investigates the feasibility and efficiency of geothermal energy for heating applications in Azerbaijan,with a specific focus on the Khachmaz region.Despite the country’s growing interest in sustainable energy,limited research has addressed the potential of ground-source heat pump(GSHP)systems under local climatic and soil conditions.To address this gap,the study employs GeoT*SOL simulation to evaluate systemperformance,incorporating site-specific parameters such as soil thermal conductivity,heating demand profiles,and regional weather data.The results show that the GSHP system achieves a maximum seasonal performance factor(SPF)of 5.62 and an average SPF of 4.86,indicating high operational efficiency.Additionally,the system provides an estimated annual CO_(2) emissions reduction of 1956 kg per household,highlighting its environmental benefits.Comparative analysis with conventional heating systems demonstrates considerable energy savings and emissions mitigation.The study identifies technical(e.g.,initial installation complexity)and economic(e.g.,high upfront costs)challenges to widespread implementation.Based on these insights,practical recommendations are proposed:policymakers are encouraged to support financial incentives and policy frameworks;urban planners should consider GSHP integration in regional heating plans;and engineers may adopt the simulation-based approach presented here for feasibility studies.This research contributes to the strategic advancement of renewable heating technologies in Azerbaijan.展开更多
The development of efficient and clean heating technologies is crucial for reducing carbon emissions in regions with severe cold regions.This research designs a novel two-stage phase change heat storage coupled solar-...The development of efficient and clean heating technologies is crucial for reducing carbon emissions in regions with severe cold regions.This research designs a novel two-stage phase change heat storage coupled solar-air source heat pump heating system structure that is specifically designed for such regions.The two-stage heat storage device in this heating system expands the storage temperature range of solar heat.The utilization of the two-stage heat storage device not onlymakes up for the instability of the solar heating system,but can also directlymeet the building heating temperature,and can reduce the influence of low-temperature outdoor environments in severe cold regions on the heating performance of the air source heat pump by using solar energy.Therefore,the two-stage phase change heat storage coupled to the solar energy-air source heat pump heating system effectively improves the utilization rate of solar energy.A numerical model of the system components and their integration was developed using TRNSYS software in this study,and various performance aspects of the system were simulated and analyzed.The simulation results demonstrated that the two-stage heat storage device can effectively store solar energy,enabling its hierarchical utilization.The low-temperature solar energy stored by the two-stage phase change heat storage device enhances the coefficient of performance of the air source heat pump by 11.1%in severe cold conditions.Using the Hooke-Jeeves optimization method,the annual cost and carbon emissions are taken as optimization objectives,with the optimized solar heat supply accounting for 52.5%.This study offers valuable insights into operational strategies and site selection for engineering applications,providing a solid theoretical foundation for the widespread implementation of this system in severe cold regions.展开更多
When air gas heat exchanger works with high temperature combustion gas, the temperature of inner wall will be very high, which affects the safety of the exchanger. Considering that heat transfer with impinging jet is...When air gas heat exchanger works with high temperature combustion gas, the temperature of inner wall will be very high, which affects the safety of the exchanger. Considering that heat transfer with impinging jet is one of the high efficient heat transfer forms , it can greatly decrease the temperature of inner wall to use it on air side of the heat exchanger. This paper presents the results of experimental investigations on heat transfer at the surface flown by an array of round impinging jets with the spent air exhaust on one side. The effects of the factors such as velocity of jet, spacing from jet to test plate and hole to hole spacing etc. on the coefficient of heat transfer are considered and analysed. An empirical equation correlated from more than 90 sets of experimental data was obtained and it has been used in design for a heat exchanger of an experimental furnace.展开更多
This paper aims to investigate the tamed Euler method for the random periodic solution of semilinear SDEs with one-sided Lipschitz coefficient.We introduce a novel approach to analyze mean-square error bounds of the n...This paper aims to investigate the tamed Euler method for the random periodic solution of semilinear SDEs with one-sided Lipschitz coefficient.We introduce a novel approach to analyze mean-square error bounds of the novel schemes,without relying on a priori high-order moment bound of the numerical approximation.The expected order-one mean square convergence is attained for the proposed scheme.Moreover,a numerical example is presented to verify our theoretical analysis.展开更多
The aim of this paper was to characterize through experiment the moisture and temperature kinetic behavior of Eucalyptus gomphocephala wood samples using microwave heating(MWH)in two scenarios:intermittently and conti...The aim of this paper was to characterize through experiment the moisture and temperature kinetic behavior of Eucalyptus gomphocephala wood samples using microwave heating(MWH)in two scenarios:intermittently and continuously.The mechanical properties and surface appearance of the heated samples were also investigated.Continuous and intermittent microwave drying kinetic experiments were conducted at a frequency of 2.45 GHz using a microwave laboratory oven at 300,500,and 1000 watts.Drying rate curves indicated three distinct phases of MWH.Increasing the microwave power with a shorter drying time led to rapid increases in internal temperature and water evaporation rates of the heated samples.Mechanical results indicated that samples heated under continuous MW(Microwave)power at 300 watts had a modulus of rupture(MOR)and modulus of elasticity(MOE)in three static bending tests higher than 29%and 36%,respectively,than samples heated at 1000 watts.Intermittent microwave heating(IMWH)of samples at 300 and 1000 watts produced the highest MOR and MOE values of 31%and 51%,respectively,unlike those heated under continuous microwave heating(CMWH).External qualitative observation showed that samples heated at high microwave power had severe surface checks.These defects were missing when using IMWH.An analysis of variance(ANOVA)showed that mechanical properties were linked to both microwave power level and the heating scenario,except for MOR in axial compression under CMWH.展开更多
The demand for flexible electric heating devices has increased due to technology advancement and improved living standards.These devices have various applications including personal thermal management,hyperthermia,def...The demand for flexible electric heating devices has increased due to technology advancement and improved living standards.These devices have various applications including personal thermal management,hyperthermia,defrosting,agricultural heating film,and oil-water separation.Joule heat,generated by electric currents,is commonly used in electrical appliances.To incorporate Joule heating into flexible electronics,new materials with excellent mechanical properties are necessary.Traditional polymers,used as reinforcements,limit the continuity of conductive networks in composites.Therefore,there is a need to develop flexible Joule thermal composite materials with enhanced mechanical strength and conductivity.Cellulose,a widely available renewable resource,is attracting attention for its excellent mechanical properties.It can be used as a dispersant and reinforcing agent for conductive fillers in cellulose-based composites,creating highly conductive networks.Various forms of cellulose,such as wood,nanocellulose,pulp fiber,bacterial cellulose,cellulose paper,textile clothing,and aramid fiber,have been utilized to achieve high-performance Joule thermal composites.Researchers have achieved excellent mechanical properties and developed efficient electric heating devices by designing cellulose-based composites with different structures.The scalable production methods enable large-scale application of cellulose-based devices,each with unique advantages in 1D,2D,and 3D structures.This review summarizes recent advancements in cellulose-based Joule thermal composites,providing insights into different structural devices,and discussing prospects and challenges in the field.展开更多
Extraterrestrial dust exhibits a wide range of textural,chemical and oxygen isotopic compositions due to the heterogeneity of their precursors and modification during atmospheric entry.Experimental heating provides an...Extraterrestrial dust exhibits a wide range of textural,chemical and oxygen isotopic compositions due to the heterogeneity of their precursors and modification during atmospheric entry.Experimental heating provides an opportunity to investigate the relationship between thermal processing and micrometeorite composition for a known precursor material.We conducted experiments to simulate the atmospheric entry of micrometeorites(MMs)using controlled,short-duration(10-50 s)flash heating(400-1600℃)of CI chondrite chips(<1500µm)in atmospheric air(1 bar,21%O2)combined with microanalysis(textures,chemical and isotopic compositions)of the experimental products.The heated chips closely resemble natural samples,with materials similar to unmelted MMs,partially melted(scoriaceous)MMs and fully melted cosmic spherules produced.We reproduced several key features such as dehydration cracks,magnetite rims,volatile gas release,vesicle formation and coalescence,melting and quench cooling.Our parameter space allows for discriminating peak temperature and heating duration effects.Peak temperature is the first-order control on MM mineralogy,while heating duration controls vesicle coalescence and homogenization.When compared against previous heating experiments,our data demonstrates that CI chondrite dust is more thermally resistant,relative to CM chondrite dust,by approximately+200℃.The 207 measurement of O-isotopes allows,for the first time,petrographic effects(such as volatile degassing and melting)to be correlated against bulk O-isotope evolution.Our results demonstrate findings applicable to CI chondrites and potentially to all fine-grained hydrated carbonaceous chondrite dust grains:(1)O-isotope variations arising during sub-solidus heating are dominated by the release of water from phyllosilicates,forcing the residual MM composition towards its anhydrous precursor composition.(2)Oxygen isotope compositions undergo the most significant changes at supra-solidus temperatures.As previously demonstrated and now empirically confirmed,most of these changes are driven by a mass-dependent fractionation effect caused by evaporation,which shifts residual rock compositions toward heavier values.Mixing with atmospheric air alters compositions toward the terrestrial fractionation line.Notably,these two processes do not begin simultaneously.Our data indicate that at 1200℃,isotopic evolution is dominated by evaporative mass loss.However,at higher temperatures(1400-1600℃),both pronounced evaporation and mixing with atmospheric oxygen become active,resulting in a more complex isotopic signature.(3)The total change in Δ17O during heating up to 1600℃is<3‰and in most scenarios<2‰.展开更多
This study conducted the experimental investigation of aerodynamic heating of Micro-scale Rotational Shearing Flow with Axial Limited-Length(MRSFALL).The temperature riseof the stator is captured by the high response ...This study conducted the experimental investigation of aerodynamic heating of Micro-scale Rotational Shearing Flow with Axial Limited-Length(MRSFALL).The temperature riseof the stator is captured by the high response thermocouples.The eccentricity ratio and clearanceheight are guaranteed by means of instantaneous trajectory and torsion monitoring of the rotator.The result shows that the maximum temperature rise takes place upstream of the minimum clear-ance height along circumferential direction.The distribution of temperature rise presents asymmet-ric curve along axial direction,and peak value occurs near the dimensionless axial position of-0.18.The effect of aerodynamic heating becomes notable as the rotational speed is larger than3×10^(4)r/min.The effect of end leakage and the viscous dissipation have great impact on temper-ature rise of MRSFALL.More specially,the peak value of temperature rise at dimensionless clear-ance height of 0.0080 is larger than the case at dimensionless clearance height of 0.0044.Furthermore,when the eccentricity ratio is too large,the viscous dissipation is induced,and theadditional temperature rise is achieved.The heat flux identification of shear flow has been realizedby Sequential Function Specification Method(SFSM)and its estimation of thermal load has been given.The heat flux induced by the aerodynamic heating in this study varies from 950 W/m^(2)to1330 W/m^(2).展开更多
In the realm of all-electric aircraft research,the integration of cathode-open proton exchange membrane fuel cells(PEMFC)with lithiumbatteries as a hybrid power source for small to medium-sized unmanned aerial vehicle...In the realm of all-electric aircraft research,the integration of cathode-open proton exchange membrane fuel cells(PEMFC)with lithiumbatteries as a hybrid power source for small to medium-sized unmanned aerial vehicles(UAVs)has garnered significant attention.The PEMFC,serving as the primary energy supply,markedly extends the UAV’s operational endurance.However,due to payload limitations and spatial constraints in the airframe layout of UAVs,the stack requires customized adaptation.Moreover,the implementation of auxiliary systems to facilitate cold starts of the PEMFC under low-temperature conditions is not feasible.Relying solely on thermal insulation measures also proves inadequate to address the challenges posed by complex low-temperature startup scenarios.To overcomethis,our study leverages the UAV’s lithium battery to heat the cathode inlet airflow,aiding the cathode-open PEMFC cold start process.To validate the feasibility of the proposed air-assisted heating strategy during the conceptual design phase,this study develops a transient,non-isothermal 3Dcathode-open PEMF Cunitmodel incorporating cathode air-assisted heating and gas-ice phase change.The model’s accuracy was verified against experimental cold-start data from a stack composed of identical single cells.This computational framework enables quantitative analysis of temperature fields and ice fraction distributions across domains under varying air-assisted heating powers during cold starts.Building upon this model,the study further investigates the improvement in cold start performance by heating the cathode intake air with varying power levels.The results demonstrate that the fuel cell achieves self-startup at temperatures as low as−13℃ under a constant current density of 100mA/cm^(2) without air-assisted heating.At an ambient temperature of−20℃,a successful start-up can be achieved with a heating power of 0.45 W/cm^(2).The temperature variation overtime during the cold start process can be represented by a sum of two exponential functions.The air-assisted heating scheme proposed in this study has significantly improved the cold start performance of fuel cells in low-temperature environments.Additionally,it provides critical reference data and validation support for component selection and feasibility assessment of hybrid power systems.展开更多
With the continuous advancement of electronic devices,flexible thin films with both thermal manage-ment functions and excellent electromagnetic interference(EMI)shielding properties have received much attention.Hence,...With the continuous advancement of electronic devices,flexible thin films with both thermal manage-ment functions and excellent electromagnetic interference(EMI)shielding properties have received much attention.Hence,inspired by Janus,a CNF/MXene/ZnFe2O4@PANI composite film with an asymmetric gradient alternating structure was successfully prepared by adjusting the filler content of the conduc-tive and magnetic layers using a vacuum-assisted filtration method.Benefiting from the magnetic reso-nance and hysteresis loss of ZnFe2O4@PANI,conductive loss and dipole polarization of MXene,as well as the exclusive"absorption-reflection-reabsorption"shielding feature in the alternating multilayered films,CM&CZFP-4 G film has superior EMI shielding performance,with an EMI SE of up to 45.75 dB and shield-ing effectiveness of 99.99%.Surprisingly,the composite film maintains reliable EMI shielding properties even after prolonged erosion in harsh environments such as high/low temperatures,high humidity,acids and alkalis.Furthermore,the CM&CZFP-4 G responded quickly within about 50 s and reached a maximum steady-state temperature of 235.8℃ at an applied voltage of 9.0 V,indicating the obtained film acquired outstanding and controllable Joule heating performance.This result was attributed to the homogeneous dispersion of MXene to build up a conductive network and endow the CNF/MXene with high conduc-tivity.Meanwhile,the fire resistance of CM&CZFP-4 G was significantly improved compared to pure CNF,which guaranteed fire safety during its application.Additionally,contributed by long fiber entanglement of CNF,extensive hydrogen-bonding interactions and multilayer structural design,the CM&CZFP-4 G film exhibits excellent mechanical characteristics,with the tensile strength and fracture strain of 27.74 MPa and 6.21%,separately.This work offers a creative avenue to prepare multifunctional composite films with electromagnetic shielding and Joule heating for various application environments.展开更多
This paper establishes an amplitude modulation heating model, simulating the far-field radiation of ELF/VLF signals generated by modulation heating, as well as the specific location and longitudinal extent of the radi...This paper establishes an amplitude modulation heating model, simulating the far-field radiation of ELF/VLF signals generated by modulation heating, as well as the specific location and longitudinal extent of the radiation source. We consider various modulation waveforms and find that square-wave modulation has the highest excitation efficiency for ELF/VLF signals, and that square-wave modulation with a smaller duty cycle(<50%) exhibits higher excitation efficiency for ELF/VLF signals, while the sin^(2)t waveform modulation yields the lowest proportion of harmonic energy in the generated signals. The amplitude of the second harmonic generated by the sin^(2)t waveform is less than one-tenth that of the fundamental frequency, and the energy of higher-frequency harmonics can be negligibly small compared with those of the fundamental wave. It is a challenging task to achieve a balance between enhancing the excitation efficiency of ELF/VLF signals and also suppressing harmonics generated by the modulated heating process. This is because the harmonics are correspondingly enhanced as the excitation efficiency of the signals is increased. However, we find that under conditions of varying effective radiant power and modulation frequency, as long as the modulation waveform is unchanged, the energy ratio between the fundamental frequency signal generated by modulated heating and each harmonic is relatively fixed, with changes only in signal intensity and the location of the radiation source zone. This implies that one can first select modulation waveforms that make the signal less prone to distortion, then increase the effective radiated power to enhance the signal strength, without concern for harmonic interference of the fundamental signal.展开更多
The stress-strain behavior of confined concrete under heating and residual conditions has been preliminarily addressed in previous research;however,its behavior at subsequent cooling temperatures after being heated to...The stress-strain behavior of confined concrete under heating and residual conditions has been preliminarily addressed in previous research;however,its behavior at subsequent cooling temperatures after being heated to peak temperature has yet to be thoroughly investigated.It is crucial for determining confined concrete structures’post-fire performance and burnout resistance.The paper presents the fundamental behavior of the confined concrete constitutive parameters and stress-strain curve at subsequent cooling temperatures after being heated to peak temperature.The study includes the stress-stress relationship of a 200 mm diameter cylinder with two distinct confinement spacings of 60 mm and 120 mm.The constitutive parameters for confined concrete were initially determined for a peak heating temperature of 750℃ and then modified to establish the stress-strain relationship for successive cooling temperatures of 500℃,250℃,and ambient temperature.The study results show that confinement has a considerable impact on compressive strength,stiffness,and ductility at ambient and fire conditions.After being heated to peak temperature,the confined concrete compressive strength recovers during successive cooling temperatures,with the recovery dependent on confinement spacing.The established stress-strain relationship can assist in better comprehending structural performance and capacity degradation for different tie spacings,and is useful for the analysis and design of confined RC(reinforced concrete)elements during and after a fire.展开更多
ENN He Long-2(EHL-2)is the next-generation large mega-Ampere(MA)spherical torus(ST)proposed and funded by the ENN company.The design parameters are:Ti0>30 keV,n_(e0)~1×10^(20)m^(-3),Ip~3 MA,Bt~3 T.One of the b...ENN He Long-2(EHL-2)is the next-generation large mega-Ampere(MA)spherical torus(ST)proposed and funded by the ENN company.The design parameters are:Ti0>30 keV,n_(e0)~1×10^(20)m^(-3),Ip~3 MA,Bt~3 T.One of the biggest challenges of EHL-2 is how to achieve several MA current flat-tops with limited voltage-seconds(Vs)of the center solenoid(CS)coils.In order to minimize the consumption of Vs,a fully non-inductive start-up by electron cyclotron resonance heating(ECRH)will be applied in EHL-2.The ramp-up phase will be accomplished with the synergetic mode between the CS and non-inductive methods.The strategy of non-inductive start-up and ramp-up with synergetic mode has been verified on EXL-50U’s experiments.Based on this strategy,numerical simulations indicate the feasibility of EHL-2 achieving 3 MA plasma current.A high-performance steady-state scenario with Ip~1.5 MA is also designed.In this scenario,the bootstrap current fraction fBS>70%,the safety factor q at the magnetic axis q0>2,the minimum safety factor qmin>1,the poloidal betaβp>3 and normalized betaβN>2.3.Each design iteration integrates the validation of physical models with the constraints of engineering implementation,gradually optimizing the performance of the heating and current drive(H&CD)systems.Numerical simulation results for general auxiliary H&CD systems such as neutral beam injection(NBI),electron cyclotron(EC)wave,ion cyclotron wave(ICW),and lower hybrid wave(LHW)are presented.These simulation results ensure that the 31 MW H&CD systems comprehensively cover all scenarios while maintaining engineering feasibility.展开更多
In this study,an analytical investigation is carried out to assess the impact of magnetic field-dependent(MFD)viscosity on the momentum and heat transfers inside the boundary layer of a Jeffrey fluid flowing over a ho...In this study,an analytical investigation is carried out to assess the impact of magnetic field-dependent(MFD)viscosity on the momentum and heat transfers inside the boundary layer of a Jeffrey fluid flowing over a horizontally elongating sheet,while taking into account the effects of ohmic dissipation.By applying similarity transformations,the original nonlinear governing equations with partial derivatives are transformed into ordinary differential equations.Analytical expressions for the momentum and energy equations are derived,incorporating the influence of MFD viscosity on the Jeffrey fluid.Then the impact of different parameters is assessed,including magnetic viscosity,magnetic interaction,retardation time,Deborah number,and Eckert number,on the velocity and temperature profiles in the boundary layer.The findings reveal that an increase in magnetic viscosity leads to a decrease in the local Nusselt number,thereby impairing heat transfer.Moreover,a higher retardation time enhances the local Nusselt number by thinning the momentum and thermal boundary layers,while a higher Deborah number decreases the local Nusselt number due to the reduction in fluid viscosity.展开更多
Intermittent heating is an energy-saving heating mode,which can save energy in terms of time,and thus is worth promoting,particularly in residential heating scenarios.Conventional radiant heating terminals,that is flo...Intermittent heating is an energy-saving heating mode,which can save energy in terms of time,and thus is worth promoting,particularly in residential heating scenarios.Conventional radiant heating terminals,that is floor heating,and convective heating terminals,that is fan coils,cannot achieve both intermittent and thermal comfort during intermittent heating.Therefore,this study proposes a switchable convective-radiant heating regulation method for floor heating and fan coils to achieve a comfortable indoor environment with high thermal response speed.Furthermore,a novel combined radiant-convective heating terminal was proposed for a reliable and effective solution.Results showed that the proposed switchable method could increase both intermittence and thermal comfort.In addition,the heating terminal showed better heating performance than the combination of two conventional terminals at the key points of heating capacity,flexibility,and thermal response.It could initially heat up a typical residential space within 20-40 min and then stabilize the room temperature in a comfortable range of 18-22℃,showing great potential for intermittent heating in room-scale heating conditions.This study provides a reference technique for intermittent heating with reduced system complexity and precise environmental control.展开更多
基金supported by the National Natural Science Foundation of China(52276196)the Foundation of State Key Laboratory of Coal Combustion(FSKLCCA2508)the High-level Talent Foundation of Anhui Agricultural University(rc412307).
文摘Flash Joule heating(FJH),as a high-efficiency and low-energy consumption technology for advanced materials synthesis,has shown significant potential in the synthesis of graphene and other functional carbon materials.Based on the Joule effect,the solid carbon sources can be rapidly heated to ultra-high temperatures(>3000 K)through instantaneous high-energy current pulses during FJH,thus driving the rapid rearrangement and graphitization of carbon atoms.This technology demonstrates numerous advantages,such as solvent-and catalyst-free features,high energy conversion efficiency,and a short process cycle.In this review,we have systematically summarized the technology principle and equipment design for FJH,as well as its raw materials selection and pretreatment strategies.The research progress in the FJH synthesis of flash graphene,carbon nanotubes,graphene fibers,and anode hard carbon,as well as its by-products,is also presented.FJH can precisely optimize the microstructures of carbon materials(e.g.,interlayer spacing of turbostratic graphene,defect concentration,and heteroatom doping)by regulating its operation parameters like flash voltage and flash time,thereby enhancing their performances in various applications,such as composite reinforcement,metal-ion battery electrodes,supercapacitors,and electrocatalysts.However,this technology is still challenged by low process yield,macroscopic material uniformity,and green power supply system construction.More research efforts are also required to promote the transition of FJH from laboratory to industrial-scale applications,thus providing innovative solutions for advanced carbon materials manufacturing and waste management toward carbon neutrality.
基金financially supported by the National Key Research and Development Program of China(No.2023YFC3904800)the National Outstanding Young Scientists Fund(No.5a2125002)+7 种基金the National Science Foundation of China(No.22476073)the Key Project of Jiangxi Provincial Research and Development Program(Nos.20223BBG74006 and 20243BBI91001)the China Postdoctoral Science Foundation(No.2024M751282)the “Thousand Talents Program”of Jiangxi Province(S_(2)021GDQN2161)the Key Project of Ganzhou City Research and Development Program(No.2023PGX17350)the Science&Technology Talent Lifting Project of Hunan Province(No.2022TJ-N16)the Natural Science Foundation of Hunan Province China(No.2024JJ4022,2023JJ30277)the Open-End Fund for National-Local Joint Engineering Research Center of Heavy Metals Pollutants Control and Resource Utilization(ES_(2)02480184)。
文摘Lithium-ion batteries(LIBs)are critical for the rapid growth of electric vehicles(EVs),but their inherent lifespan leads to numerous retirements and resource challenges.The efficacy of conventional recycling techniques is increasingly compromised by their high energy consumption and secondary pollution,rendering them less responsive to greener and more sustainable requirement of rapid development.Thus,the direct recycling process emerged and was considered as a more expedient and convenient method of recycling compared to the conventional recycling modes that are currently in study.However,due to the reliance on the indispensable sintering process,direct recycling still faces considerable challenges,motivating researchers to explore faster,greener,and more cost-effective strategies for LIBs recycling,Inspiringly,Joule heating recycling(JHR),an emerging technique,offers rapid,efficient impurity removal and material regeneration with minimal environmental impact,addressing limitations of existing methods.This method reduces the time for direct recycling of spent LIBs by a factor of at least three orders of magnitude and exhibits significant potential for future industrial production.Unfortunately,due to the lack of systematic organization and reporting,this next generation approach to direct recycling of spent LIBs has not yet gained much interest.To facilitate a more profound comprehension of rising flash recycling strategy,in this study,JHR is distinguished into two distinctive implementation pathways(including flash Joule heating and carbon thermal shock),designed to accommodate varying pretreatment stages and diverse spent LIBs materials.Subsequently,the advantages of the recently developed JHR of spent LIBs in terms of material performance,environmental friendliness,and economic viability are discussed in detail.Ultimately,with the goal of achieving more attractive society effects,the future direction of JHR of spent LIBs and its potential for practical application are proposed and envisaged.
基金supported by the National Natural Science Foundation of China(Nos.52275299,52105313)R&D Program of Beijing Municipal Education Commission(No.KM202210005036)+1 种基金Natural Science Foundation of Chongqing,China(No.CSTB2023NSCQ-MSX0701)National Defense Basic Research Projects of China(No.JCKY2022405C002).
文摘Friction rolling additive manufacturing(FRAM)is a solid-state additive manufacturing technology that plasticizes the feed and deposits a material using frictional heat generated by the tool head.The thermal efficiency of FRAM,which depends only on friction to generate heat,is low,and the thermal-accumulation effect of the deposition process must be addressed.An FRAM heat-balance-control method that combines plasma-arc preheating and instant water cooling(PC-FRAM)is devised in this study,and a temperature field featuring rapidly increasing and decreasing temperature is constructed around the tool head.Additionally,2195-T87 Al-Li alloy is used as the feed material,and the effects of heating and cooling rates on the microstructure and mechanical properties are investigated.The results show that water cooling significantly improves heat accumulation during the deposition process.The cooling rate increases by 11.7 times,and the high-temperature residence time decreases by more than 50%.The grain size of the PC-FRAM sample is the smallest,i.e.,3.77±1.03μm,its dislocation density is the highest,and the number density of precipitates is the highest,the size of precipitates is the smallest,which shows the best precipitation-strengthening effect.The hardness test results are consistent with the precipitation distribution.The ultimate tensile strength,yield strength and elongation of the PC-FRAM samples are the highest(351±15.6 MPa,251.3±15.8 MPa and 16.25%±1.25%,respectively)among the samples investigated.The preheating and water-cooling-assisted deposition simultaneously increases the tensile strength and elongation of the deposited samples.The combination of preheating and instant cooling improves the deposition efficiency of FRAM and weakens the thermal-softening effect.
文摘Grain-oriented silicon steels were prepared at different heating rates during high temperature annealing,in which the evolution of magnetic properties,grain orientations and precipitates were studied.To illustrate the Zener factor,the diameter and number density of precipitates of interrupted testing samples were statistically calculated.The effect of precipitate ripening on the Goss texture and magnetic property was investigated.Data indicated that the trend of Zener factor was similar under different heating rates,first increasing and then decreasing,and that the precipitate maturing was greatly inhibited as the heating rate increased.Secondary recrystallization was developed at the temperature of 1010℃when a heating rate of 5℃/h was used,resulting in Goss,Brass and{110}<227>oriented grains growing abnormally and a magnetic induction intensity of 1.90T.Furthermore,increasing the heating rate to 20℃/h would inhibit the development of undesirable oriented grains and obtain a sharp Goss texture.However,when the heating rate was extremely fast,such as 40℃/h,poor secondary recrystallization was developed with many island grains,corresponding to a decrease in magnetic induction intensity to 1.87 T.At a suitable heating rate of 20℃/h,the sharpest Goss texture and the highest magnetic induction of 1.94 T with an onset secondary recrystallization temperature of 1020℃were found among the experimental variables in this study.The heating rate affected the initial temperature of secondary recrystallization by controlling the maturation of precipitates,leading to the deviation and dispersion of Goss texture,thereby reducing the magnetic properties.
基金support by the Shanghai Engineering Research Center for Shallow Geothermal Energy(DRZX-202306)Shaanxi Coal Geology Group Co.,Ltd.(SMDZ-ZD2024-23)+4 种基金Key Laboratory of Coal Resources Exploration and Comprehensive Utilization,Ministry of Natural Resources,China(ZP2020-1)Shaanxi Investment Group Co.,Ltd.(SIGC2023-KY-05)Key Research and Development Projects of Shaanxi Province(2023-GHZD-54)Shaanxi Qinchuangyuan Scientist+Engineer Team Construction Project(2022KXJ-049)China Postdoctoral Science Foundation(2023M742802,2024T170721).
文摘Geothermal energy,a form of renewable energy,has been extensively utilized for building heating.However,there is a lack of detailed comparative studies on the use of shallow and medium-deep geothermal energy in building energy systems,which are essential for decision-making.Therefore,this paper presents a comparative study of the performance and economic analysis of shallow and medium-deep borehole heat exchanger heating systems.Based on the geological parameters of Xi’an,China and commonly used borehole heat exchanger structures,numerical simulationmethods are employed to analyze performance and economic efficiency.The results indicate that increasing the spacing between shallow borehole heat exchangers can effectively reduce thermal interference between the pipes and improve heat extraction performance.As the flow rate increases,the outlet water temperature ranges from 279.3 to 279.7 K,with heat extraction power varying between 595 and 609 W.For medium-deep borehole heat exchangers,performance predictions show that a higher flow rate results in greater heat extraction power.However,when the flow rate exceeds 30 m^(3)/h,further increases in flow rate have only a minor effect on enhancing heat extraction power.Additionally,the economic analysis reveals that the payback period for shallow geothermal heating systems ranges from 10 to 11 years,while for medium-deep geothermal heating systems,it varies more widely from 3 to 25 years.Therefore,the payback period for medium-deep geothermal heating systems is more significantly influenced by operational and installation parameters,and optimizing these parameters can considerably shorten the payback period.The results of this study are expected to provide valuable insights into the efficient and cost-effective utilization of geothermal energy for building heating.
文摘This study investigates the feasibility and efficiency of geothermal energy for heating applications in Azerbaijan,with a specific focus on the Khachmaz region.Despite the country’s growing interest in sustainable energy,limited research has addressed the potential of ground-source heat pump(GSHP)systems under local climatic and soil conditions.To address this gap,the study employs GeoT*SOL simulation to evaluate systemperformance,incorporating site-specific parameters such as soil thermal conductivity,heating demand profiles,and regional weather data.The results show that the GSHP system achieves a maximum seasonal performance factor(SPF)of 5.62 and an average SPF of 4.86,indicating high operational efficiency.Additionally,the system provides an estimated annual CO_(2) emissions reduction of 1956 kg per household,highlighting its environmental benefits.Comparative analysis with conventional heating systems demonstrates considerable energy savings and emissions mitigation.The study identifies technical(e.g.,initial installation complexity)and economic(e.g.,high upfront costs)challenges to widespread implementation.Based on these insights,practical recommendations are proposed:policymakers are encouraged to support financial incentives and policy frameworks;urban planners should consider GSHP integration in regional heating plans;and engineers may adopt the simulation-based approach presented here for feasibility studies.This research contributes to the strategic advancement of renewable heating technologies in Azerbaijan.
基金This work was supported by the project of the Research on Energy Consumption of Office Space in Colleges and Universities under the“Dual Carbon Target”(No.CJ202301006).
文摘The development of efficient and clean heating technologies is crucial for reducing carbon emissions in regions with severe cold regions.This research designs a novel two-stage phase change heat storage coupled solar-air source heat pump heating system structure that is specifically designed for such regions.The two-stage heat storage device in this heating system expands the storage temperature range of solar heat.The utilization of the two-stage heat storage device not onlymakes up for the instability of the solar heating system,but can also directlymeet the building heating temperature,and can reduce the influence of low-temperature outdoor environments in severe cold regions on the heating performance of the air source heat pump by using solar energy.Therefore,the two-stage phase change heat storage coupled to the solar energy-air source heat pump heating system effectively improves the utilization rate of solar energy.A numerical model of the system components and their integration was developed using TRNSYS software in this study,and various performance aspects of the system were simulated and analyzed.The simulation results demonstrated that the two-stage heat storage device can effectively store solar energy,enabling its hierarchical utilization.The low-temperature solar energy stored by the two-stage phase change heat storage device enhances the coefficient of performance of the air source heat pump by 11.1%in severe cold conditions.Using the Hooke-Jeeves optimization method,the annual cost and carbon emissions are taken as optimization objectives,with the optimized solar heat supply accounting for 52.5%.This study offers valuable insights into operational strategies and site selection for engineering applications,providing a solid theoretical foundation for the widespread implementation of this system in severe cold regions.
文摘When air gas heat exchanger works with high temperature combustion gas, the temperature of inner wall will be very high, which affects the safety of the exchanger. Considering that heat transfer with impinging jet is one of the high efficient heat transfer forms , it can greatly decrease the temperature of inner wall to use it on air side of the heat exchanger. This paper presents the results of experimental investigations on heat transfer at the surface flown by an array of round impinging jets with the spent air exhaust on one side. The effects of the factors such as velocity of jet, spacing from jet to test plate and hole to hole spacing etc. on the coefficient of heat transfer are considered and analysed. An empirical equation correlated from more than 90 sets of experimental data was obtained and it has been used in design for a heat exchanger of an experimental furnace.
基金supported by the National Natural Science Foundation of China(Nos.12471394,12371417)Natural Science Foundation of Changsha(No.kq2502101)。
文摘This paper aims to investigate the tamed Euler method for the random periodic solution of semilinear SDEs with one-sided Lipschitz coefficient.We introduce a novel approach to analyze mean-square error bounds of the novel schemes,without relying on a priori high-order moment bound of the numerical approximation.The expected order-one mean square convergence is attained for the proposed scheme.Moreover,a numerical example is presented to verify our theoretical analysis.
文摘The aim of this paper was to characterize through experiment the moisture and temperature kinetic behavior of Eucalyptus gomphocephala wood samples using microwave heating(MWH)in two scenarios:intermittently and continuously.The mechanical properties and surface appearance of the heated samples were also investigated.Continuous and intermittent microwave drying kinetic experiments were conducted at a frequency of 2.45 GHz using a microwave laboratory oven at 300,500,and 1000 watts.Drying rate curves indicated three distinct phases of MWH.Increasing the microwave power with a shorter drying time led to rapid increases in internal temperature and water evaporation rates of the heated samples.Mechanical results indicated that samples heated under continuous MW(Microwave)power at 300 watts had a modulus of rupture(MOR)and modulus of elasticity(MOE)in three static bending tests higher than 29%and 36%,respectively,than samples heated at 1000 watts.Intermittent microwave heating(IMWH)of samples at 300 and 1000 watts produced the highest MOR and MOE values of 31%and 51%,respectively,unlike those heated under continuous microwave heating(CMWH).External qualitative observation showed that samples heated at high microwave power had severe surface checks.These defects were missing when using IMWH.An analysis of variance(ANOVA)showed that mechanical properties were linked to both microwave power level and the heating scenario,except for MOR in axial compression under CMWH.
基金supported by the fund of the National Natural Science Foundation of China(Nos.22378249,22078184,and 22171170)the China Postdoctoral Science Foundation(No.2019M653853XB)the Natural Science Advance Research Foundation of Shaanxi University of Science and Technology(No.2018QNBJ-03).
文摘The demand for flexible electric heating devices has increased due to technology advancement and improved living standards.These devices have various applications including personal thermal management,hyperthermia,defrosting,agricultural heating film,and oil-water separation.Joule heat,generated by electric currents,is commonly used in electrical appliances.To incorporate Joule heating into flexible electronics,new materials with excellent mechanical properties are necessary.Traditional polymers,used as reinforcements,limit the continuity of conductive networks in composites.Therefore,there is a need to develop flexible Joule thermal composite materials with enhanced mechanical strength and conductivity.Cellulose,a widely available renewable resource,is attracting attention for its excellent mechanical properties.It can be used as a dispersant and reinforcing agent for conductive fillers in cellulose-based composites,creating highly conductive networks.Various forms of cellulose,such as wood,nanocellulose,pulp fiber,bacterial cellulose,cellulose paper,textile clothing,and aramid fiber,have been utilized to achieve high-performance Joule thermal composites.Researchers have achieved excellent mechanical properties and developed efficient electric heating devices by designing cellulose-based composites with different structures.The scalable production methods enable large-scale application of cellulose-based devices,each with unique advantages in 1D,2D,and 3D structures.This review summarizes recent advancements in cellulose-based Joule thermal composites,providing insights into different structural devices,and discussing prospects and challenges in the field.
基金ISRO-RESPOND GAP3332 and PMN-MOES GAP2175 Project support this work.
文摘Extraterrestrial dust exhibits a wide range of textural,chemical and oxygen isotopic compositions due to the heterogeneity of their precursors and modification during atmospheric entry.Experimental heating provides an opportunity to investigate the relationship between thermal processing and micrometeorite composition for a known precursor material.We conducted experiments to simulate the atmospheric entry of micrometeorites(MMs)using controlled,short-duration(10-50 s)flash heating(400-1600℃)of CI chondrite chips(<1500µm)in atmospheric air(1 bar,21%O2)combined with microanalysis(textures,chemical and isotopic compositions)of the experimental products.The heated chips closely resemble natural samples,with materials similar to unmelted MMs,partially melted(scoriaceous)MMs and fully melted cosmic spherules produced.We reproduced several key features such as dehydration cracks,magnetite rims,volatile gas release,vesicle formation and coalescence,melting and quench cooling.Our parameter space allows for discriminating peak temperature and heating duration effects.Peak temperature is the first-order control on MM mineralogy,while heating duration controls vesicle coalescence and homogenization.When compared against previous heating experiments,our data demonstrates that CI chondrite dust is more thermally resistant,relative to CM chondrite dust,by approximately+200℃.The 207 measurement of O-isotopes allows,for the first time,petrographic effects(such as volatile degassing and melting)to be correlated against bulk O-isotope evolution.Our results demonstrate findings applicable to CI chondrites and potentially to all fine-grained hydrated carbonaceous chondrite dust grains:(1)O-isotope variations arising during sub-solidus heating are dominated by the release of water from phyllosilicates,forcing the residual MM composition towards its anhydrous precursor composition.(2)Oxygen isotope compositions undergo the most significant changes at supra-solidus temperatures.As previously demonstrated and now empirically confirmed,most of these changes are driven by a mass-dependent fractionation effect caused by evaporation,which shifts residual rock compositions toward heavier values.Mixing with atmospheric air alters compositions toward the terrestrial fractionation line.Notably,these two processes do not begin simultaneously.Our data indicate that at 1200℃,isotopic evolution is dominated by evaporative mass loss.However,at higher temperatures(1400-1600℃),both pronounced evaporation and mixing with atmospheric oxygen become active,resulting in a more complex isotopic signature.(3)The total change in Δ17O during heating up to 1600℃is<3‰and in most scenarios<2‰.
基金supports from the National Natural Science Foundation of China(No.52206091)the Aeronautical Science Foundation of China(No.201928052008)the Natural Science Foundation of Jiangsu Province,China(No.BK20210303)。
文摘This study conducted the experimental investigation of aerodynamic heating of Micro-scale Rotational Shearing Flow with Axial Limited-Length(MRSFALL).The temperature riseof the stator is captured by the high response thermocouples.The eccentricity ratio and clearanceheight are guaranteed by means of instantaneous trajectory and torsion monitoring of the rotator.The result shows that the maximum temperature rise takes place upstream of the minimum clear-ance height along circumferential direction.The distribution of temperature rise presents asymmet-ric curve along axial direction,and peak value occurs near the dimensionless axial position of-0.18.The effect of aerodynamic heating becomes notable as the rotational speed is larger than3×10^(4)r/min.The effect of end leakage and the viscous dissipation have great impact on temper-ature rise of MRSFALL.More specially,the peak value of temperature rise at dimensionless clear-ance height of 0.0080 is larger than the case at dimensionless clearance height of 0.0044.Furthermore,when the eccentricity ratio is too large,the viscous dissipation is induced,and theadditional temperature rise is achieved.The heat flux identification of shear flow has been realizedby Sequential Function Specification Method(SFSM)and its estimation of thermal load has been given.The heat flux induced by the aerodynamic heating in this study varies from 950 W/m^(2)to1330 W/m^(2).
基金funded by Zhejiang Province Spearhead and Leading Goose Research and Development Key Program,grant number 2023C01239.
文摘In the realm of all-electric aircraft research,the integration of cathode-open proton exchange membrane fuel cells(PEMFC)with lithiumbatteries as a hybrid power source for small to medium-sized unmanned aerial vehicles(UAVs)has garnered significant attention.The PEMFC,serving as the primary energy supply,markedly extends the UAV’s operational endurance.However,due to payload limitations and spatial constraints in the airframe layout of UAVs,the stack requires customized adaptation.Moreover,the implementation of auxiliary systems to facilitate cold starts of the PEMFC under low-temperature conditions is not feasible.Relying solely on thermal insulation measures also proves inadequate to address the challenges posed by complex low-temperature startup scenarios.To overcomethis,our study leverages the UAV’s lithium battery to heat the cathode inlet airflow,aiding the cathode-open PEMFC cold start process.To validate the feasibility of the proposed air-assisted heating strategy during the conceptual design phase,this study develops a transient,non-isothermal 3Dcathode-open PEMF Cunitmodel incorporating cathode air-assisted heating and gas-ice phase change.The model’s accuracy was verified against experimental cold-start data from a stack composed of identical single cells.This computational framework enables quantitative analysis of temperature fields and ice fraction distributions across domains under varying air-assisted heating powers during cold starts.Building upon this model,the study further investigates the improvement in cold start performance by heating the cathode intake air with varying power levels.The results demonstrate that the fuel cell achieves self-startup at temperatures as low as−13℃ under a constant current density of 100mA/cm^(2) without air-assisted heating.At an ambient temperature of−20℃,a successful start-up can be achieved with a heating power of 0.45 W/cm^(2).The temperature variation overtime during the cold start process can be represented by a sum of two exponential functions.The air-assisted heating scheme proposed in this study has significantly improved the cold start performance of fuel cells in low-temperature environments.Additionally,it provides critical reference data and validation support for component selection and feasibility assessment of hybrid power systems.
基金supported by the National Natural Science Foundation of China(Nos.22005277,52474256 and 52074247)the Natural Science Foundation of Hubei Province(No.2024AFB662)+1 种基金the Young Top-notch Talent Cultivation Program of Hubei Province,Opening Foundation of State Key Laboratory of Organic-Inorganic Composites,Beijing University of Chemical Technology(No.oic-202401012)the Fundamental Research Funds for National Universities,China University of Geosciences(No.2024XLA93).
文摘With the continuous advancement of electronic devices,flexible thin films with both thermal manage-ment functions and excellent electromagnetic interference(EMI)shielding properties have received much attention.Hence,inspired by Janus,a CNF/MXene/ZnFe2O4@PANI composite film with an asymmetric gradient alternating structure was successfully prepared by adjusting the filler content of the conduc-tive and magnetic layers using a vacuum-assisted filtration method.Benefiting from the magnetic reso-nance and hysteresis loss of ZnFe2O4@PANI,conductive loss and dipole polarization of MXene,as well as the exclusive"absorption-reflection-reabsorption"shielding feature in the alternating multilayered films,CM&CZFP-4 G film has superior EMI shielding performance,with an EMI SE of up to 45.75 dB and shield-ing effectiveness of 99.99%.Surprisingly,the composite film maintains reliable EMI shielding properties even after prolonged erosion in harsh environments such as high/low temperatures,high humidity,acids and alkalis.Furthermore,the CM&CZFP-4 G responded quickly within about 50 s and reached a maximum steady-state temperature of 235.8℃ at an applied voltage of 9.0 V,indicating the obtained film acquired outstanding and controllable Joule heating performance.This result was attributed to the homogeneous dispersion of MXene to build up a conductive network and endow the CNF/MXene with high conduc-tivity.Meanwhile,the fire resistance of CM&CZFP-4 G was significantly improved compared to pure CNF,which guaranteed fire safety during its application.Additionally,contributed by long fiber entanglement of CNF,extensive hydrogen-bonding interactions and multilayer structural design,the CM&CZFP-4 G film exhibits excellent mechanical characteristics,with the tensile strength and fracture strain of 27.74 MPa and 6.21%,separately.This work offers a creative avenue to prepare multifunctional composite films with electromagnetic shielding and Joule heating for various application environments.
基金supported by the National Key R&D Program of China (No. 2022YFE0204100)the National Natural Science Foundation of China (12205067 and 12375199)the Fundamental Research Funds for the Central Universities (Grant No. HIT.OCEF. 2022036)。
文摘This paper establishes an amplitude modulation heating model, simulating the far-field radiation of ELF/VLF signals generated by modulation heating, as well as the specific location and longitudinal extent of the radiation source. We consider various modulation waveforms and find that square-wave modulation has the highest excitation efficiency for ELF/VLF signals, and that square-wave modulation with a smaller duty cycle(<50%) exhibits higher excitation efficiency for ELF/VLF signals, while the sin^(2)t waveform modulation yields the lowest proportion of harmonic energy in the generated signals. The amplitude of the second harmonic generated by the sin^(2)t waveform is less than one-tenth that of the fundamental frequency, and the energy of higher-frequency harmonics can be negligibly small compared with those of the fundamental wave. It is a challenging task to achieve a balance between enhancing the excitation efficiency of ELF/VLF signals and also suppressing harmonics generated by the modulated heating process. This is because the harmonics are correspondingly enhanced as the excitation efficiency of the signals is increased. However, we find that under conditions of varying effective radiant power and modulation frequency, as long as the modulation waveform is unchanged, the energy ratio between the fundamental frequency signal generated by modulated heating and each harmonic is relatively fixed, with changes only in signal intensity and the location of the radiation source zone. This implies that one can first select modulation waveforms that make the signal less prone to distortion, then increase the effective radiated power to enhance the signal strength, without concern for harmonic interference of the fundamental signal.
文摘The stress-strain behavior of confined concrete under heating and residual conditions has been preliminarily addressed in previous research;however,its behavior at subsequent cooling temperatures after being heated to peak temperature has yet to be thoroughly investigated.It is crucial for determining confined concrete structures’post-fire performance and burnout resistance.The paper presents the fundamental behavior of the confined concrete constitutive parameters and stress-strain curve at subsequent cooling temperatures after being heated to peak temperature.The study includes the stress-stress relationship of a 200 mm diameter cylinder with two distinct confinement spacings of 60 mm and 120 mm.The constitutive parameters for confined concrete were initially determined for a peak heating temperature of 750℃ and then modified to establish the stress-strain relationship for successive cooling temperatures of 500℃,250℃,and ambient temperature.The study results show that confinement has a considerable impact on compressive strength,stiffness,and ductility at ambient and fire conditions.After being heated to peak temperature,the confined concrete compressive strength recovers during successive cooling temperatures,with the recovery dependent on confinement spacing.The established stress-strain relationship can assist in better comprehending structural performance and capacity degradation for different tie spacings,and is useful for the analysis and design of confined RC(reinforced concrete)elements during and after a fire.
基金supported by ENN Group and ENN Energy Research Institute.The authors would like to express their gratitude for the contributions of the ENN fusion team and collaborators,such as Tiantian Sun,Haojie Ma,and Yong Guo,in supporting these endeavours.The authors also acknowledge the support of the National SuperComputer Center in Tianjin and Beijing PARATERA Tech Corp.,Ltd.,for providing HPC resources that have contributed to the research results reported in this paper.This work was partly supported by National Natural Science Fundation of China(Nos.12375215 and 12475210).
文摘ENN He Long-2(EHL-2)is the next-generation large mega-Ampere(MA)spherical torus(ST)proposed and funded by the ENN company.The design parameters are:Ti0>30 keV,n_(e0)~1×10^(20)m^(-3),Ip~3 MA,Bt~3 T.One of the biggest challenges of EHL-2 is how to achieve several MA current flat-tops with limited voltage-seconds(Vs)of the center solenoid(CS)coils.In order to minimize the consumption of Vs,a fully non-inductive start-up by electron cyclotron resonance heating(ECRH)will be applied in EHL-2.The ramp-up phase will be accomplished with the synergetic mode between the CS and non-inductive methods.The strategy of non-inductive start-up and ramp-up with synergetic mode has been verified on EXL-50U’s experiments.Based on this strategy,numerical simulations indicate the feasibility of EHL-2 achieving 3 MA plasma current.A high-performance steady-state scenario with Ip~1.5 MA is also designed.In this scenario,the bootstrap current fraction fBS>70%,the safety factor q at the magnetic axis q0>2,the minimum safety factor qmin>1,the poloidal betaβp>3 and normalized betaβN>2.3.Each design iteration integrates the validation of physical models with the constraints of engineering implementation,gradually optimizing the performance of the heating and current drive(H&CD)systems.Numerical simulation results for general auxiliary H&CD systems such as neutral beam injection(NBI),electron cyclotron(EC)wave,ion cyclotron wave(ICW),and lower hybrid wave(LHW)are presented.These simulation results ensure that the 31 MW H&CD systems comprehensively cover all scenarios while maintaining engineering feasibility.
基金supported by the United Arab Emirates University,Al Ain,United Arab Emirates,under Grant No.12R283.
文摘In this study,an analytical investigation is carried out to assess the impact of magnetic field-dependent(MFD)viscosity on the momentum and heat transfers inside the boundary layer of a Jeffrey fluid flowing over a horizontally elongating sheet,while taking into account the effects of ohmic dissipation.By applying similarity transformations,the original nonlinear governing equations with partial derivatives are transformed into ordinary differential equations.Analytical expressions for the momentum and energy equations are derived,incorporating the influence of MFD viscosity on the Jeffrey fluid.Then the impact of different parameters is assessed,including magnetic viscosity,magnetic interaction,retardation time,Deborah number,and Eckert number,on the velocity and temperature profiles in the boundary layer.The findings reveal that an increase in magnetic viscosity leads to a decrease in the local Nusselt number,thereby impairing heat transfer.Moreover,a higher retardation time enhances the local Nusselt number by thinning the momentum and thermal boundary layers,while a higher Deborah number decreases the local Nusselt number due to the reduction in fluid viscosity.
基金supported by the China National Key Research and Development Program"Integrated convection/radiation coupling terminals for local environment"(2022YFC3801502)the National Natural Science Foundation of China(52108082,52130803,and 52394223)+2 种基金the China Postdoctoral Science Foundation(2023M732479)the Natural Science Foundation of Sichuan Province of China(2024NSFSC0916)the New Cornerstone Science Foundation through the XPLORER PRIZE。
文摘Intermittent heating is an energy-saving heating mode,which can save energy in terms of time,and thus is worth promoting,particularly in residential heating scenarios.Conventional radiant heating terminals,that is floor heating,and convective heating terminals,that is fan coils,cannot achieve both intermittent and thermal comfort during intermittent heating.Therefore,this study proposes a switchable convective-radiant heating regulation method for floor heating and fan coils to achieve a comfortable indoor environment with high thermal response speed.Furthermore,a novel combined radiant-convective heating terminal was proposed for a reliable and effective solution.Results showed that the proposed switchable method could increase both intermittence and thermal comfort.In addition,the heating terminal showed better heating performance than the combination of two conventional terminals at the key points of heating capacity,flexibility,and thermal response.It could initially heat up a typical residential space within 20-40 min and then stabilize the room temperature in a comfortable range of 18-22℃,showing great potential for intermittent heating in room-scale heating conditions.This study provides a reference technique for intermittent heating with reduced system complexity and precise environmental control.
