The influence of temperature on mode coupling effect in piezoelectric vibrators remains unclear.In this work,we discuss the influence of temperature on two-dimensional(2D)mode coupling effect and electromechanical cou...The influence of temperature on mode coupling effect in piezoelectric vibrators remains unclear.In this work,we discuss the influence of temperature on two-dimensional(2D)mode coupling effect and electromechanical coupling coefficient of cylindrical[001]c-poled Mn-doped 0.24PIN-0.46PMN-0.30PT piezoelectric single-crystal vibrator with an arbitrary configuration ratio.The electromechanical coupling coefficient kt decreases with temperature increasing,whereas k33 is largely invariant in a temperature range of 25℃-55℃.With the increase of temperature,the shift in the‘mode dividing point’increases the scale of the poling direction of the piezoelectric vibrator.The temperature has little effect on coupling constantΓ.At a given temperature,the coupling constantΓof the cylindrical vibrator is slightly greater than that of the rectangular vibrator.When the temperature changes,the applicability index(M)values of the two piezoelectric vibrators are close to 1,indicating that the coupling theory can be applied to piezoelectric vibrators made of late-model piezoelectric single crystals.展开更多
Double pipe heat exchangers(DPHEs)are normally utilized in various manufacturing uses owing to their simple design and low maintenance requirements.For that,performance enhancement by improved heat transfer is ongoing...Double pipe heat exchangers(DPHEs)are normally utilized in various manufacturing uses owing to their simple design and low maintenance requirements.For that,performance enhancement by improved heat transfer is ongoing.Air injections are a good strategy for enhancing the thermal performance of the DPHE.In the present work,the influence of air bubble injection in a DPHE was experimentally investigated,and the system’s hydrothermal performance improvement parameters were evaluated.Two modes were designed,manufactured,and used to conduct the experiments.The first mode was conducted with no air injection,named a single phase mode,while in the second mode,air was injected into the annulus of DPHE throughout different perforated rings on the side of the annular.Three different ring types were used and coded as R-1,R-2,and R-3,with an added case of insertion of the three rings inside the annulus.The airflow rate was fixed at 1.5 LPM with a 25○C inlet temperature.Also,the hot water rate in the inner pipe was maintained continuously at 3 LPM with a controlled 70○C temperature at the inlet.Five different cold water flow rates,3,3.5,4,4.5,and 5 LPM,in the annulus,were considered with a controlled inlet temperature at 17○C.Additionally,the effectiveness of the heat exchanger,the number of transfer units(NTU),and the overall heat transfer were predicted and considered for performance evaluation and comparison.The outcomes proved that the injection of air and the bubbly flow creation in the heat exchanger’s hot side is an effective method to strengthen the DPHE performance.Moreover,the total heat transfer coefficient was enhanced by 41%in R-1,58.8%in R-2,and 40.1%in R-3 at 4 LPM of cold water.The optimal ring,which yielded the most improvement,was R-2,achieving a 65%improvement in NTU,with a maximum enhancement in effectiveness of 56%.展开更多
A method to investigate the effect of gas bubble on cell voltage oscillations was established. The whole aluminum electrolysis cell was treated as a resistance circuit, and the dynamic simulation of the cell equivalen...A method to investigate the effect of gas bubble on cell voltage oscillations was established. The whole aluminum electrolysis cell was treated as a resistance circuit, and the dynamic simulation of the cell equivalent circuit was modeled with Matlab/Simulink simulation software. The time-series signals of cell voltage and anode current were obtained under different bubble conditions, and analyzed by spectral and statistical analysis methods. The simulation results show that higher bubble release frequency has a significant effect on the cell voltage oscillations. When the bubble coverage of one anode block exceeds 80%, the cell voltage may exceed its normal fluctuation amplitude. The simulation also proves that the anode effect detected by computer in actual production is mainly the whole cell anode effect.展开更多
In the framework of the Skyrme–Hartree–Fock–Bogoliubov approach with the Sk T interaction, the pairing effects on the proton bubble structures of ^(46)Ar and ^(206)Hg are discussed. In calculations, three kinds of ...In the framework of the Skyrme–Hartree–Fock–Bogoliubov approach with the Sk T interaction, the pairing effects on the proton bubble structures of ^(46)Ar and ^(206)Hg are discussed. In calculations, three kinds of pairing forces (volume, surface and mixed pairing interactions) are used. For ^(46)Ar, it is shown that the bubble structure with the volume pairing is almost the same as that with the mixed pairing. The bubble with the surface pairing is less pronounced than those with the volume and mixed pairings. Analyzing the density distributions and occupation probabilities of the proton s states and the quasi-degeneracy between the proton 2s_(1/2) and 1d_(3/2) orbitals, we explain the difference between the bubble structure with the surface pairing and those with the volume and mixed pairings. For ^(206)Hg, it is seen that the proton density distribution with the surface pairing is different from those with the volume and mixed pairings in the whole region of the radial distance. In addition, it is found that the bubbles with the three pairing forces are different from each other and the least pronounced bubble is obtained with the surface pairing. Thus the selection of the pairing force is important for the study of the nuclear bubble structure.展开更多
Effects of Reynolds(Re)number and Schmidt(Sc)number on the flow structures and variable density mixing are numerically investigated through the canonical shock cylindrical bubble interaction.By determining the viscosi...Effects of Reynolds(Re)number and Schmidt(Sc)number on the flow structures and variable density mixing are numerically investigated through the canonical shock cylindrical bubble interaction.By determining the viscosity and diffusivity within a wide range,the controlling parameters,total vortex circulation,and compression rate,are conservative under a broad range of Re and Sc numbers(Re≈10^(3)-10^(5)and Sc≈0.1-5)in the same shock Mach(Ma)number condition(Ma=2.4).As for the Re number effect,the circulation of secondary baroclinic vorticity(SBV),induced by the main vortex centripetal acceleration,is observed to be higher in high Re number and vice versa.Based on the vorticity transport equation decomposition,a growth-inhibition vorticity dynamics balance mechanism is revealed:the vorticity viscous term grows synchronously with baroclinic production to inhibit SBV production in low Re number.By contrast,the viscous term terminates the baroclinic term with a time lag in high Re number,leading to the SBV production.Since the SBV reflects the local stretching enhancement based on the advection-diffusion equation,mixing is influenced by the Sc number in a different behavior if different Re numbers are considered.The time-averaged variable density mixing rate emerges a scaling law with Sc number asχ^(∗)=β·Sc^(−α),where the coefficientβ∼Re−0.2 and the scaling exponentα∼Re−0.385.The understanding of Re number and Sc number effect on variable density mixing provides an opportunity for mixing enhancement from the perspective of designing the viscosity and diffusivity of the fluid mixture.展开更多
Effect of the injected plasma on the effective radius of the magnetic bubble in plasma sail is discussed. Results from solving both the two-dimensional magneto-hydrodynamic（MHD） equations and the magnetic flux conse...Effect of the injected plasma on the effective radius of the magnetic bubble in plasma sail is discussed. Results from solving both the two-dimensional magneto-hydrodynamic（MHD） equations and the magnetic flux conservation equation indicate that the effective radius of the magnetic bubble formed by the pure dipole field is very small, and the rate of the falloff of the magnetic field can be effectively reduced by the inflation of the high-density plasma. The falloff rate of the magnetic field can be r^-1.4. The effective radius of the magnetic bubble can hence be 8.2 km. The effective radius of the magnetic bubble increases about thirty-six times, comparing to the case of the pure dipole field.展开更多
The shock-induced ignition and detonation wave propagation in reactive elliptic premixed bubbles are numerically studied.Close attention is paid to the bubble geometry effect on the ignition pattern and the ensuing bu...The shock-induced ignition and detonation wave propagation in reactive elliptic premixed bubbles are numerically studied.Close attention is paid to the bubble geometry effect on the ignition pattern and the ensuing bubble behavior.Five elliptic bubbles with different aspect ratios are examined.According to the numerical results,three typical ignition patterns are identified under the same incident shock strength and the underlying mechanisms are interpreted.The difference in ignition pattern shows that,comparing with the inert shock-bubble interaction,the geometry effect in reactive shock-bubble interaction(RSBI)has more implications.In addition to the aspect ratio,the ignition location and the distance from the ignition spot to the nearest/farthest bubble surface should also be considered as elements of the geometry effect in RSBI.展开更多
The cavitation dynamics and mechanical stress in viscoelastic tissues, as the primary mechanisms of some ultrasound therapies, are extremely complex due to the interactions of cavitation bubble with adjacent bubbles a...The cavitation dynamics and mechanical stress in viscoelastic tissues, as the primary mechanisms of some ultrasound therapies, are extremely complex due to the interactions of cavitation bubble with adjacent bubbles and surrounding tissues.Therefore, the cavitation dynamics and resultant mechanical stress of two-interacting bubbles in the viscoelastic tissues are numerically investigated, especially focusing on the effects of the adjacent bubble. The results demonstrate that the mechanical stress is highly dependent on the bubble dynamics. The compressive stress and tensile stress are generated at the stage of bubble expansion and collapse stage, respectively. Furthermore, within the initial parameters examined in this paper, the effects of the adjacent bubble will distinctly suppress the radial expansion of the small bubble and consequently lead its associated stresses to decrease. Owing to the superimposition of two stress fields, the mechanical stresses surrounding the small bubble in the direction of the neighboring bubble are smaller than those in other directions. For two interacting cavitation bubbles, the suppression effects of the nearby bubble on both the cavitation dynamics and the stresses surrounding the small bubble increase as the ultrasound amplitude and the initial radius of the large bubble increase, whereas they decrease with the inter-bubble distance increasing. Moreover, increasing the tissue viscoelasticity will reduce the suppression effects of the nearby bubble, except in instances where the compressive stress and tensile stress first increase and then decrease with the tissue elasticity and viscosity increasing respectively. This study can provide a further understanding of the mechanisms of cavitation-associated mechanical damage to the adjacent tissues or cells.展开更多
Dynamics of a single cavitation bubble in sodium dodecyl sulfate（SDS） aqueous solutions is investigated experimentally and theoretically. The bubble pulsation is measured by a phase-locked integrated imaging techniq...Dynamics of a single cavitation bubble in sodium dodecyl sulfate（SDS） aqueous solutions is investigated experimentally and theoretically. The bubble pulsation is measured by a phase-locked integrated imaging technique,and the ambient radius is obtained by fitting the numerical calculation based on the Rayleigh–Plesset bubble dynamics model to the experimental data. The results show that, under the same driving condition, the ambient radius of the cavitation bubble decreases correspondingly with the increase of SDS concentration within the critical micelle concentration, while the compression ratio of the radius increases, which indicates that the addition of SDS decreases the internal molecular number of the cavitation bubble and increases the power capability of the cavitation bubble. In addition, bubble oscillation increases the concentration of the surfactant molecules on the bubble wall, so that the effect of SDS on a single cavitation bubble is reduced when the SDS concentration is greater than 0.8 m M.展开更多
The He production rate(i.e.,He/dpa)in nuclear reactors strongly affects the degradation of material prop-erties.This is an important but not yet fully understood issue.Here,the effect of He/dpa on bubble char-acterist...The He production rate(i.e.,He/dpa)in nuclear reactors strongly affects the degradation of material prop-erties.This is an important but not yet fully understood issue.Here,the effect of He/dpa on bubble char-acteristics in Fe9Cr1.5W0.4Si ferrite-martensitic(F/M)steel was in situ studied during 400 keV Fe^(+)and 30 keV He^(+)dual-beam irradiation at 723 K with three ratios of 100,500,and 2500 appm He/dpa and subsequent stepwise annealing using transmission electron microscopy(TEM).He/dpa strongly affected the bubble characteristics.During irradiation,the higher the He/dpa,the smaller the size of irradiated bubbles,but the higher their density.However,He/dpa didn’t affect the final saturation size of irradiated bubbles for all three cases,which was-2.2 nm.During annealing,high He/dpa caused large,immobile,dense polyhedral bubbles with a wider bubble size distribution,while low He/dpa caused small,low-mobility,and relatively low-density spherical bubbles.It was found that the higher the He/dpa ratio,the greater the swelling during irradiation and annealing,and annealing further enhanced the swelling.Moreover,the tunnel structure was first found in body-centered cubic(BCC)F/M steel during in-situ irra-diation.The current work provides valuable and potential insights for further understanding the He/dpa effects in materials serving in different nuclear reactors.展开更多
This paper explores some behavioral factors that may explain the formation of speculative bubbles in financial markets. The study adopts an experimental approach focused on the agents’ behavior when facing a “true...This paper explores some behavioral factors that may explain the formation of speculative bubbles in financial markets. The study adopts an experimental approach focused on the agents’ behavior when facing a “true” bubble and is incentivized to herd and/or receive information about the market sentiment. For this purpose, a straightforward laboratory experiment that reproduces the dotcom market bubble and asks subjects to forecast asset prices in a true dynamic information scenario. The experiment was conducted in the laboratory of the Faculty of Economics at the University of Salamanca and involved 137 undergraduate students in the degree of economics. The results show that incentives to the herding behavior increase the forecasted volatility and thus contribute to the bubble inflation. Nevertheless, this effect may be offset by giving information to the agents about the expected market trend. Therefore, under herding effects, it is the absence of clear signals about market sentiments what inflates the bubble.展开更多
The internal pressure within fission gas bubbles(FGBs)in irradiated nuclear fuels drives mechanical interactions with the surrounding fuel skeleton.To investigate the micromechanical stress fields in irradiated nuclea...The internal pressure within fission gas bubbles(FGBs)in irradiated nuclear fuels drives mechanical interactions with the surrounding fuel skeleton.To investigate the micromechanical stress fields in irradiated nuclear fuels containing pressurized FGBs,a mechanical constitutive model for the equivalent solid of FGBs was developed and validated.This model was based on the modified Van der Waals equation,incorporating the effects of surface tension.Using this model,the micromechanical fields in irradiated U-10Mo fuels with randomly distributed FGBs were calculated during uniaxial tensile testing via the finite element(FE)method.The macroscopic elastic constants of the irradiated U-10Mo fuels were then derived using homogenization theory,and the influences of bubble pressure,bubble size,and porosity on these constants were examined.Results show that adjacent FGBs exhibit mechanical interactions,which leads to distinct stress concentrations in the surrounding fuel skeleton.The macroscopic elastic constants of irradiated U-10Mo fuels decrease with increasing the macroscopic porosity,which can be quantitatively described by the Mori-Tanaka model.In contrast,bubble pressure and size have negligible effects on these constants.展开更多
The vibration mill is a high-efficiency ultrafine grinding device;its dynamic char-acteristics,along with the motion of the grinding medium,directly influence both grinding efficiency and product quality.However,there...The vibration mill is a high-efficiency ultrafine grinding device;its dynamic char-acteristics,along with the motion of the grinding medium,directly influence both grinding efficiency and product quality.However,there is a challenge in efficiently simulating the complex behavior of the grinding media within vibratory mills to maximize energy efficiency and enhance grinding performance.To bridge this,the research employs an integrated kinematic-discrete element method-experimental approach specifically designed for eccentric vibration mills.Kinematic analysis reveals that the mill's motion follows a crank-slider mechanism.Engineering discrete element method(EDEM)simulations,experimentally validated through grinding tests,were used to analyze media collision dynamics(including frequency,contact forces,energy distribution,and trajectories)at filling rates of 60%,70%,80%,and 90%.The results indicate that an 80%media filling rate optimizes performance:the collision number is 36035,contact force reaches about 450 N,showing a wave form of a sine function.Through an actual test of the grinding effect under different media filling rates,the newly generated−0.018 mm size fraction content and grinding efficiency reach their highest levels at 0.441 t/m^(3)·h and 0.00557 t/kW·h,respectively.The particle size distribution of the ground material is uniform,validating simulation rationality.Conversely,60%and 70%filling rates yielded suboptimal grinding efficiency,while a 90%filling rate sharply reduces both efficiency and product uniformity due to concentric media motion and low contact forces.This work successfully maps the relationship between filling rate and crushing energy efficiency,provid-ing a validated framework for the operation of eccentric vibratory mills.展开更多
This study presents a numerical analysis of the effects of a rigid flat wall with oscillating motion on the pressure wave propagation during a single spherical cavitation bubble collapse at different initial bubble po...This study presents a numerical analysis of the effects of a rigid flat wall with oscillating motion on the pressure wave propagation during a single spherical cavitation bubble collapse at different initial bubble positions.Different nondimensional distances S=0.8,0.9,1.0,1.1,1.2 and 1.3 were considered to investigate the effects of initial in-phase and out-of-phase oscillations of the flat wall.Numerical simulations of cavitation bubble collapse near an oscillating wall were conducted using a compressible two-phase flow model.This model incorporated the Volume of Fluid(VOF)interface-sharpening technique on a general curvilinear moving grid.The numerical results were consistent with published experimental data.The simulation examined the impact of oscillating walls on bubble behavior and the resulting pressure peaks observed on the wall surface.The numerical results demonstrate the significant impact of wall oscillation conditions on bubble collapse and migration behavior,and consequently,the generation of pressure waves with significantly different propagation and pressure peaks induced by shock impact on the rigid wall.Different behaviors were observed in the trendlines of the pressure peaks and maximum jet velocity under in-phase and out-of-phase oscillating walls,with distinct values.At S≥1.0,a higher-pressure peak on the wall was observed in the case of the out-of-phase oscillating condition,whereas a higher-pressure peak was found in the case of the in-phase condition at S<1.0.The highest-pressure peak was found at S=0.8 in trend lines of in-phase and S=1.1 in trend lines of out-of-phase oscillation effects.展开更多
Terahertz (THz) radiation, an emerging frequency band of the electromagnetic spectrum, has been widely appliedacross various fields. However, its ability to resonate with the energy levels of biomolecules has raised s...Terahertz (THz) radiation, an emerging frequency band of the electromagnetic spectrum, has been widely appliedacross various fields. However, its ability to resonate with the energy levels of biomolecules has raised significant concernsregarding its biosafety. A growing body of research indicates that THz radiation can markedly influence the structure andfunction of proteins. Alzheimer’s disease (AD), a neurodegenerative disorder characterized by the abnormal aggregationof amyloid proteins, has been shown in prior studies to be modulated by THz radiation in terms of amyloid aggregation.Building on this, the present study utilized the CL4176 strain of Caenorhabditis elegans as an animal model for AD.Using a self-designed and constructed radiation system based on quantum cascade lasers, the study investigated changesin the pathological progression of AD under 3.1-THz electromagnetic radiation exposure. By evaluating lifespan, motility,feeding behavior, reactive oxygen species (ROS) levels, and aging markers in the Caenorhabditis elegans model, thestudy highlights the potential biological risks of 3.1-THz radiation for individuals with AD. These findings provide crucialexperimental evidence to support the promotion and standardization of THz technology applications.展开更多
A new piezoelectric energy harvester is proposed which employs the coupling effect between a piezoelectric beam and an elastic-supported sphere to capture wind energy from multiple directions.As wind flows across the ...A new piezoelectric energy harvester is proposed which employs the coupling effect between a piezoelectric beam and an elastic-supported sphere to capture wind energy from multiple directions.As wind flows across the sphere,it induces vortical vibrations that transfer to the piezoelectric beam,converting wind energy into electricity.A nonlinear coupled dynamic theoretical model based on the Euler-Lagrange equation is developed to study the interactions between the sphere and beam vibrations.The vortex-induced force acting on the sphere is determined,and the dynamic model of the coupled system is validated through experiments.The results show that in order to reach convergence,at least four modes are required in the Galerkin discretization.Moreover,the output performance of the energy harvester strongly depends on the frequency ratio between the sphere and the piezoelectric beam.We find that at a frequency ratio of approximately 1.34,the harvester achieves a maximum average power of 190μW at a wind speed of 3.90 m/s,with the lock-in region between 2.63 and 5.30 m/s.Subsequently,the impact of wind flow direction on the electrical performance of the energy harvester is investigated in a wind tunnel,by adjusting the angle between the harvester and incoming flows ranging from 0°to 360°.The findings indicate that the harvester maintains strong and consistent performance across variable wind flow directions and speeds.Particularly within the lock-in region,the output voltage fluctuations are below 5.5%,showcasing the robustness of the design.This result points to the potential utility of this novel harvester in complex environments.Our study also provides a theoretical basis for the development of small-scale offshore wind energy harvesting technologies.展开更多
The wheel-rail dynamic load(WRL)and its vibration energy transfer(VET)are foundational for studying ballastless track dynamics in high-speed railways.In this study,the higher-order modal parameters of track beds with ...The wheel-rail dynamic load(WRL)and its vibration energy transfer(VET)are foundational for studying ballastless track dynamics in high-speed railways.In this study,the higher-order modal parameters of track beds with different isolating layers were identified experimentally and a vehicle-track coupled dynamic model considering track bed broadband vibrations(TBBVs)was established.The WRL and its VET were investigated,and the contribution law as well as the influence mechanism of TBBVs on them was determined.The results showed the WRL and track bed vibration energy exhibited significant resonances,with more prominent high-frequency resonance peaks in the track bed vibration energy.TBBVs had a significant effect on low-frequency WRLs,and markedly influenced the VET across various frequency bands.Intense low-frequency and weak high-frequency intermodulation effects between the wheel-rail and track beds were observed.The effect of track bed vibrations can be disregarded when focusing on high-frequency WRLs above 200 Hz.Variations in the isolating layer stiffness have more significant effects on the track bed vibration energy than the WRL.Rational stiffness of the isolating layer should be selected to avoid mode-coupling resonance from track beds to the wheel-rail subsystem.展开更多
In the process of electrocatalytic water splitting, the management of gaseous products is an important task. Timely detachment of gaseous products from the electrode surface and the electrolyte is beneficial to the re...In the process of electrocatalytic water splitting, the management of gaseous products is an important task. Timely detachment of gaseous products from the electrode surface and the electrolyte is beneficial to the reduction of energy consumption of the electrolytic cell. In the existing industrial electrolytic cells, the circulating pump drives the electrolyte flowing to discharge the gaseous products. Up to now, several much more advanced strategies have been explored to deal with the negative effects of bubbles. In this review, we summarized various strategies for bubble detachment, including electrode design, external field imposing and system upgrading. We also elaborated the principle, functional features, practicability, advantages and limitations of each method. Finally, challenges and perspectives are also provided for the further development of advanced bubbles detachment strategies for efficient hydrogen evolution.展开更多
基金Project supported by the Basic Scientific Research Foundation of College and University in Heilongjiang Province,China(Grant No.2018QNL-16)the Guiding Science and Technology Project of Daqing City(GSTPDQ),China(Grant No.zd-2019-03)the National Natural Science Foundation of China(Grant Nos.11304061 and 51572056).
文摘The influence of temperature on mode coupling effect in piezoelectric vibrators remains unclear.In this work,we discuss the influence of temperature on two-dimensional(2D)mode coupling effect and electromechanical coupling coefficient of cylindrical[001]c-poled Mn-doped 0.24PIN-0.46PMN-0.30PT piezoelectric single-crystal vibrator with an arbitrary configuration ratio.The electromechanical coupling coefficient kt decreases with temperature increasing,whereas k33 is largely invariant in a temperature range of 25℃-55℃.With the increase of temperature,the shift in the‘mode dividing point’increases the scale of the poling direction of the piezoelectric vibrator.The temperature has little effect on coupling constantΓ.At a given temperature,the coupling constantΓof the cylindrical vibrator is slightly greater than that of the rectangular vibrator.When the temperature changes,the applicability index(M)values of the two piezoelectric vibrators are close to 1,indicating that the coupling theory can be applied to piezoelectric vibrators made of late-model piezoelectric single crystals.
文摘Double pipe heat exchangers(DPHEs)are normally utilized in various manufacturing uses owing to their simple design and low maintenance requirements.For that,performance enhancement by improved heat transfer is ongoing.Air injections are a good strategy for enhancing the thermal performance of the DPHE.In the present work,the influence of air bubble injection in a DPHE was experimentally investigated,and the system’s hydrothermal performance improvement parameters were evaluated.Two modes were designed,manufactured,and used to conduct the experiments.The first mode was conducted with no air injection,named a single phase mode,while in the second mode,air was injected into the annulus of DPHE throughout different perforated rings on the side of the annular.Three different ring types were used and coded as R-1,R-2,and R-3,with an added case of insertion of the three rings inside the annulus.The airflow rate was fixed at 1.5 LPM with a 25○C inlet temperature.Also,the hot water rate in the inner pipe was maintained continuously at 3 LPM with a controlled 70○C temperature at the inlet.Five different cold water flow rates,3,3.5,4,4.5,and 5 LPM,in the annulus,were considered with a controlled inlet temperature at 17○C.Additionally,the effectiveness of the heat exchanger,the number of transfer units(NTU),and the overall heat transfer were predicted and considered for performance evaluation and comparison.The outcomes proved that the injection of air and the bubbly flow creation in the heat exchanger’s hot side is an effective method to strengthen the DPHE performance.Moreover,the total heat transfer coefficient was enhanced by 41%in R-1,58.8%in R-2,and 40.1%in R-3 at 4 LPM of cold water.The optimal ring,which yielded the most improvement,was R-2,achieving a 65%improvement in NTU,with a maximum enhancement in effectiveness of 56%.
基金Project(2012BAE08B09)supported by the National Key Technology R&D Program of China
文摘A method to investigate the effect of gas bubble on cell voltage oscillations was established. The whole aluminum electrolysis cell was treated as a resistance circuit, and the dynamic simulation of the cell equivalent circuit was modeled with Matlab/Simulink simulation software. The time-series signals of cell voltage and anode current were obtained under different bubble conditions, and analyzed by spectral and statistical analysis methods. The simulation results show that higher bubble release frequency has a significant effect on the cell voltage oscillations. When the bubble coverage of one anode block exceeds 80%, the cell voltage may exceed its normal fluctuation amplitude. The simulation also proves that the anode effect detected by computer in actual production is mainly the whole cell anode effect.
基金Supported by the National Natural Science Foundation of China under Grant Nos U1832120 and 11675265the State Scholarship Fund of China Scholarship Council under Grant No 201708130035the Natural Science Foundation for Outstanding Young Scholars of Hebei Province of China under Grant No A2018210146
文摘In the framework of the Skyrme–Hartree–Fock–Bogoliubov approach with the Sk T interaction, the pairing effects on the proton bubble structures of ^(46)Ar and ^(206)Hg are discussed. In calculations, three kinds of pairing forces (volume, surface and mixed pairing interactions) are used. For ^(46)Ar, it is shown that the bubble structure with the volume pairing is almost the same as that with the mixed pairing. The bubble with the surface pairing is less pronounced than those with the volume and mixed pairings. Analyzing the density distributions and occupation probabilities of the proton s states and the quasi-degeneracy between the proton 2s_(1/2) and 1d_(3/2) orbitals, we explain the difference between the bubble structure with the surface pairing and those with the volume and mixed pairings. For ^(206)Hg, it is seen that the proton density distribution with the surface pairing is different from those with the volume and mixed pairings in the whole region of the radial distance. In addition, it is found that the bubbles with the three pairing forces are different from each other and the least pronounced bubble is obtained with the surface pairing. Thus the selection of the pairing force is important for the study of the nuclear bubble structure.
基金This work was supported by the National Natural Science Foundation of China(NSFC)(Grant No.91941301)the Key Research and Development Project of Sichuan Province(Grant No.2019ZYZF0002)。
文摘Effects of Reynolds(Re)number and Schmidt(Sc)number on the flow structures and variable density mixing are numerically investigated through the canonical shock cylindrical bubble interaction.By determining the viscosity and diffusivity within a wide range,the controlling parameters,total vortex circulation,and compression rate,are conservative under a broad range of Re and Sc numbers(Re≈10^(3)-10^(5)and Sc≈0.1-5)in the same shock Mach(Ma)number condition(Ma=2.4).As for the Re number effect,the circulation of secondary baroclinic vorticity(SBV),induced by the main vortex centripetal acceleration,is observed to be higher in high Re number and vice versa.Based on the vorticity transport equation decomposition,a growth-inhibition vorticity dynamics balance mechanism is revealed:the vorticity viscous term grows synchronously with baroclinic production to inhibit SBV production in low Re number.By contrast,the viscous term terminates the baroclinic term with a time lag in high Re number,leading to the SBV production.Since the SBV reflects the local stretching enhancement based on the advection-diffusion equation,mixing is influenced by the Sc number in a different behavior if different Re numbers are considered.The time-averaged variable density mixing rate emerges a scaling law with Sc number asχ^(∗)=β·Sc^(−α),where the coefficientβ∼Re−0.2 and the scaling exponentα∼Re−0.385.The understanding of Re number and Sc number effect on variable density mixing provides an opportunity for mixing enhancement from the perspective of designing the viscosity and diffusivity of the fluid mixture.
基金supported by National Natural Science Foundation of China (No. 10975136)
文摘Effect of the injected plasma on the effective radius of the magnetic bubble in plasma sail is discussed. Results from solving both the two-dimensional magneto-hydrodynamic（MHD） equations and the magnetic flux conservation equation indicate that the effective radius of the magnetic bubble formed by the pure dipole field is very small, and the rate of the falloff of the magnetic field can be effectively reduced by the inflation of the high-density plasma. The falloff rate of the magnetic field can be r^-1.4. The effective radius of the magnetic bubble can hence be 8.2 km. The effective radius of the magnetic bubble increases about thirty-six times, comparing to the case of the pure dipole field.
基金This work was supported by the National Natural Science Foundation of China(Grant 12002102).
文摘The shock-induced ignition and detonation wave propagation in reactive elliptic premixed bubbles are numerically studied.Close attention is paid to the bubble geometry effect on the ignition pattern and the ensuing bubble behavior.Five elliptic bubbles with different aspect ratios are examined.According to the numerical results,three typical ignition patterns are identified under the same incident shock strength and the underlying mechanisms are interpreted.The difference in ignition pattern shows that,comparing with the inert shock-bubble interaction,the geometry effect in reactive shock-bubble interaction(RSBI)has more implications.In addition to the aspect ratio,the ignition location and the distance from the ignition spot to the nearest/farthest bubble surface should also be considered as elements of the geometry effect in RSBI.
基金Project supported by the National Natural Science Foundation of China (Grant No.11904042)the Natural Science Foundation of Chongqing,China (Grant No.cstc2019jcyj-msxmX0534)the Science and Technology Research Program of Chongqing Municipal Education Commission,China (Grant No.KJQN202000617)。
文摘The cavitation dynamics and mechanical stress in viscoelastic tissues, as the primary mechanisms of some ultrasound therapies, are extremely complex due to the interactions of cavitation bubble with adjacent bubbles and surrounding tissues.Therefore, the cavitation dynamics and resultant mechanical stress of two-interacting bubbles in the viscoelastic tissues are numerically investigated, especially focusing on the effects of the adjacent bubble. The results demonstrate that the mechanical stress is highly dependent on the bubble dynamics. The compressive stress and tensile stress are generated at the stage of bubble expansion and collapse stage, respectively. Furthermore, within the initial parameters examined in this paper, the effects of the adjacent bubble will distinctly suppress the radial expansion of the small bubble and consequently lead its associated stresses to decrease. Owing to the superimposition of two stress fields, the mechanical stresses surrounding the small bubble in the direction of the neighboring bubble are smaller than those in other directions. For two interacting cavitation bubbles, the suppression effects of the nearby bubble on both the cavitation dynamics and the stresses surrounding the small bubble increase as the ultrasound amplitude and the initial radius of the large bubble increase, whereas they decrease with the inter-bubble distance increasing. Moreover, increasing the tissue viscoelasticity will reduce the suppression effects of the nearby bubble, except in instances where the compressive stress and tensile stress first increase and then decrease with the tissue elasticity and viscosity increasing respectively. This study can provide a further understanding of the mechanisms of cavitation-associated mechanical damage to the adjacent tissues or cells.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11334005 and 11574150
文摘Dynamics of a single cavitation bubble in sodium dodecyl sulfate（SDS） aqueous solutions is investigated experimentally and theoretically. The bubble pulsation is measured by a phase-locked integrated imaging technique,and the ambient radius is obtained by fitting the numerical calculation based on the Rayleigh–Plesset bubble dynamics model to the experimental data. The results show that, under the same driving condition, the ambient radius of the cavitation bubble decreases correspondingly with the increase of SDS concentration within the critical micelle concentration, while the compression ratio of the radius increases, which indicates that the addition of SDS decreases the internal molecular number of the cavitation bubble and increases the power capability of the cavitation bubble. In addition, bubble oscillation increases the concentration of the surfactant molecules on the bubble wall, so that the effect of SDS on a single cavitation bubble is reduced when the SDS concentration is greater than 0.8 m M.
基金supported by the National Natural Science Foun-dation of China(No.U1967211)the National Science Fund for Distinguished Young Scholars of China(No.12225506).
文摘The He production rate(i.e.,He/dpa)in nuclear reactors strongly affects the degradation of material prop-erties.This is an important but not yet fully understood issue.Here,the effect of He/dpa on bubble char-acteristics in Fe9Cr1.5W0.4Si ferrite-martensitic(F/M)steel was in situ studied during 400 keV Fe^(+)and 30 keV He^(+)dual-beam irradiation at 723 K with three ratios of 100,500,and 2500 appm He/dpa and subsequent stepwise annealing using transmission electron microscopy(TEM).He/dpa strongly affected the bubble characteristics.During irradiation,the higher the He/dpa,the smaller the size of irradiated bubbles,but the higher their density.However,He/dpa didn’t affect the final saturation size of irradiated bubbles for all three cases,which was-2.2 nm.During annealing,high He/dpa caused large,immobile,dense polyhedral bubbles with a wider bubble size distribution,while low He/dpa caused small,low-mobility,and relatively low-density spherical bubbles.It was found that the higher the He/dpa ratio,the greater the swelling during irradiation and annealing,and annealing further enhanced the swelling.Moreover,the tunnel structure was first found in body-centered cubic(BCC)F/M steel during in-situ irra-diation.The current work provides valuable and potential insights for further understanding the He/dpa effects in materials serving in different nuclear reactors.
文摘This paper explores some behavioral factors that may explain the formation of speculative bubbles in financial markets. The study adopts an experimental approach focused on the agents’ behavior when facing a “true” bubble and is incentivized to herd and/or receive information about the market sentiment. For this purpose, a straightforward laboratory experiment that reproduces the dotcom market bubble and asks subjects to forecast asset prices in a true dynamic information scenario. The experiment was conducted in the laboratory of the Faculty of Economics at the University of Salamanca and involved 137 undergraduate students in the degree of economics. The results show that incentives to the herding behavior increase the forecasted volatility and thus contribute to the bubble inflation. Nevertheless, this effect may be offset by giving information to the agents about the expected market trend. Therefore, under herding effects, it is the absence of clear signals about market sentiments what inflates the bubble.
基金National Natural Science Foundation of China(12135008,12132005)。
文摘The internal pressure within fission gas bubbles(FGBs)in irradiated nuclear fuels drives mechanical interactions with the surrounding fuel skeleton.To investigate the micromechanical stress fields in irradiated nuclear fuels containing pressurized FGBs,a mechanical constitutive model for the equivalent solid of FGBs was developed and validated.This model was based on the modified Van der Waals equation,incorporating the effects of surface tension.Using this model,the micromechanical fields in irradiated U-10Mo fuels with randomly distributed FGBs were calculated during uniaxial tensile testing via the finite element(FE)method.The macroscopic elastic constants of the irradiated U-10Mo fuels were then derived using homogenization theory,and the influences of bubble pressure,bubble size,and porosity on these constants were examined.Results show that adjacent FGBs exhibit mechanical interactions,which leads to distinct stress concentrations in the surrounding fuel skeleton.The macroscopic elastic constants of irradiated U-10Mo fuels decrease with increasing the macroscopic porosity,which can be quantitatively described by the Mori-Tanaka model.In contrast,bubble pressure and size have negligible effects on these constants.
基金funded by Hebei Province innovation ability improvement plan project(23564201D)Open Foundation of State Key Laboratory of Mineral Processing(BGRIMM-KJSKL-2021-21).
文摘The vibration mill is a high-efficiency ultrafine grinding device;its dynamic char-acteristics,along with the motion of the grinding medium,directly influence both grinding efficiency and product quality.However,there is a challenge in efficiently simulating the complex behavior of the grinding media within vibratory mills to maximize energy efficiency and enhance grinding performance.To bridge this,the research employs an integrated kinematic-discrete element method-experimental approach specifically designed for eccentric vibration mills.Kinematic analysis reveals that the mill's motion follows a crank-slider mechanism.Engineering discrete element method(EDEM)simulations,experimentally validated through grinding tests,were used to analyze media collision dynamics(including frequency,contact forces,energy distribution,and trajectories)at filling rates of 60%,70%,80%,and 90%.The results indicate that an 80%media filling rate optimizes performance:the collision number is 36035,contact force reaches about 450 N,showing a wave form of a sine function.Through an actual test of the grinding effect under different media filling rates,the newly generated−0.018 mm size fraction content and grinding efficiency reach their highest levels at 0.441 t/m^(3)·h and 0.00557 t/kW·h,respectively.The particle size distribution of the ground material is uniform,validating simulation rationality.Conversely,60%and 70%filling rates yielded suboptimal grinding efficiency,while a 90%filling rate sharply reduces both efficiency and product uniformity due to concentric media motion and low contact forces.This work successfully maps the relationship between filling rate and crushing energy efficiency,provid-ing a validated framework for the operation of eccentric vibratory mills.
基金sponsored by the Vietnam Academy of Science and Technology(VAST),granted to Prof.Duong Ngoc Hai under Project No.VAST01.02/22-23by the National Research Foundation(NRF)of the Republic of Korea,granted to Prof.Warn-Gyu Park under Project No.RS-2023-00248070.
文摘This study presents a numerical analysis of the effects of a rigid flat wall with oscillating motion on the pressure wave propagation during a single spherical cavitation bubble collapse at different initial bubble positions.Different nondimensional distances S=0.8,0.9,1.0,1.1,1.2 and 1.3 were considered to investigate the effects of initial in-phase and out-of-phase oscillations of the flat wall.Numerical simulations of cavitation bubble collapse near an oscillating wall were conducted using a compressible two-phase flow model.This model incorporated the Volume of Fluid(VOF)interface-sharpening technique on a general curvilinear moving grid.The numerical results were consistent with published experimental data.The simulation examined the impact of oscillating walls on bubble behavior and the resulting pressure peaks observed on the wall surface.The numerical results demonstrate the significant impact of wall oscillation conditions on bubble collapse and migration behavior,and consequently,the generation of pressure waves with significantly different propagation and pressure peaks induced by shock impact on the rigid wall.Different behaviors were observed in the trendlines of the pressure peaks and maximum jet velocity under in-phase and out-of-phase oscillating walls,with distinct values.At S≥1.0,a higher-pressure peak on the wall was observed in the case of the out-of-phase oscillating condition,whereas a higher-pressure peak was found in the case of the in-phase condition at S<1.0.The highest-pressure peak was found at S=0.8 in trend lines of in-phase and S=1.1 in trend lines of out-of-phase oscillation effects.
文摘Terahertz (THz) radiation, an emerging frequency band of the electromagnetic spectrum, has been widely appliedacross various fields. However, its ability to resonate with the energy levels of biomolecules has raised significant concernsregarding its biosafety. A growing body of research indicates that THz radiation can markedly influence the structure andfunction of proteins. Alzheimer’s disease (AD), a neurodegenerative disorder characterized by the abnormal aggregationof amyloid proteins, has been shown in prior studies to be modulated by THz radiation in terms of amyloid aggregation.Building on this, the present study utilized the CL4176 strain of Caenorhabditis elegans as an animal model for AD.Using a self-designed and constructed radiation system based on quantum cascade lasers, the study investigated changesin the pathological progression of AD under 3.1-THz electromagnetic radiation exposure. By evaluating lifespan, motility,feeding behavior, reactive oxygen species (ROS) levels, and aging markers in the Caenorhabditis elegans model, thestudy highlights the potential biological risks of 3.1-THz radiation for individuals with AD. These findings provide crucialexperimental evidence to support the promotion and standardization of THz technology applications.
基金supported by the National Key R&D Program of China(No.2021YFF0501001)the National Natural Science Foundation of China(Nos.52308315,51922046,and 52192661)+4 种基金the Research Funds of Huazhong University of Science and Technology(No.2023JCYJ014)the China Postdoctoral Science Foundation(No.2023M731206)the Research Funds of China Railway Siyuan Survey and Design Group Co.,Ltd.(Nos.KY2023014S,KY2023126S,2021K085,2020K006,and 2020K172)the Research Fund of China Construction Science and Industry(No.CSCEC-PT-004-2022-KT-3.3)the Autonomous Innovation Fund of Hubei Province(No.5003242027),China.
文摘A new piezoelectric energy harvester is proposed which employs the coupling effect between a piezoelectric beam and an elastic-supported sphere to capture wind energy from multiple directions.As wind flows across the sphere,it induces vortical vibrations that transfer to the piezoelectric beam,converting wind energy into electricity.A nonlinear coupled dynamic theoretical model based on the Euler-Lagrange equation is developed to study the interactions between the sphere and beam vibrations.The vortex-induced force acting on the sphere is determined,and the dynamic model of the coupled system is validated through experiments.The results show that in order to reach convergence,at least four modes are required in the Galerkin discretization.Moreover,the output performance of the energy harvester strongly depends on the frequency ratio between the sphere and the piezoelectric beam.We find that at a frequency ratio of approximately 1.34,the harvester achieves a maximum average power of 190μW at a wind speed of 3.90 m/s,with the lock-in region between 2.63 and 5.30 m/s.Subsequently,the impact of wind flow direction on the electrical performance of the energy harvester is investigated in a wind tunnel,by adjusting the angle between the harvester and incoming flows ranging from 0°to 360°.The findings indicate that the harvester maintains strong and consistent performance across variable wind flow directions and speeds.Particularly within the lock-in region,the output voltage fluctuations are below 5.5%,showcasing the robustness of the design.This result points to the potential utility of this novel harvester in complex environments.Our study also provides a theoretical basis for the development of small-scale offshore wind energy harvesting technologies.
基金supported by the National Natural Science Foundation of China(No.52308468)the China Postdoctoral Science Foundation(No.2022M723390)the Jiangsu Provincial Excellent Postdoctoral Program(No.2023ZB020),China.
文摘The wheel-rail dynamic load(WRL)and its vibration energy transfer(VET)are foundational for studying ballastless track dynamics in high-speed railways.In this study,the higher-order modal parameters of track beds with different isolating layers were identified experimentally and a vehicle-track coupled dynamic model considering track bed broadband vibrations(TBBVs)was established.The WRL and its VET were investigated,and the contribution law as well as the influence mechanism of TBBVs on them was determined.The results showed the WRL and track bed vibration energy exhibited significant resonances,with more prominent high-frequency resonance peaks in the track bed vibration energy.TBBVs had a significant effect on low-frequency WRLs,and markedly influenced the VET across various frequency bands.Intense low-frequency and weak high-frequency intermodulation effects between the wheel-rail and track beds were observed.The effect of track bed vibrations can be disregarded when focusing on high-frequency WRLs above 200 Hz.Variations in the isolating layer stiffness have more significant effects on the track bed vibration energy than the WRL.Rational stiffness of the isolating layer should be selected to avoid mode-coupling resonance from track beds to the wheel-rail subsystem.
基金the National Natural Science Foundation of China(No.51902101)the Youth Natural Science Foundation of Hunan Province(No.2021JJ40044)+2 种基金Natural Science Foundation of Jiangsu Province(No.BK20201381)Science Foundation of Nanjing University of Posts and Telecommunications(Nos.NY219144 and NY221046)the National College Student Innovation and Entrepreneurship Training Program(No.202210293171 K).
文摘In the process of electrocatalytic water splitting, the management of gaseous products is an important task. Timely detachment of gaseous products from the electrode surface and the electrolyte is beneficial to the reduction of energy consumption of the electrolytic cell. In the existing industrial electrolytic cells, the circulating pump drives the electrolyte flowing to discharge the gaseous products. Up to now, several much more advanced strategies have been explored to deal with the negative effects of bubbles. In this review, we summarized various strategies for bubble detachment, including electrode design, external field imposing and system upgrading. We also elaborated the principle, functional features, practicability, advantages and limitations of each method. Finally, challenges and perspectives are also provided for the further development of advanced bubbles detachment strategies for efficient hydrogen evolution.
