The activation of CO on iron-based materials is a key elementary reaction for many chemical processes.We investigate CO adsorption and dissociation on a series of Fe,Fe_(3)C,Fe_(5)C_(2),and Fe_(2)C catalysts through d...The activation of CO on iron-based materials is a key elementary reaction for many chemical processes.We investigate CO adsorption and dissociation on a series of Fe,Fe_(3)C,Fe_(5)C_(2),and Fe_(2)C catalysts through density functional theory calculations.We detect dramatically different performances for CO adsorption and activation on diverse surfaces and sites.The activation of CO is dependent on the local coordination of the molecule to the surface and on the bulk phase of the underlying catalyst.The bulk properties and the different local bonding environments lead to varying interactions between the adsorbed CO and the surface and thus yielding different activation levels of the C-O bond.We also examine the prediction of CO adsorption on different types of Fe-based catalysts by machine learning through linear regression models.We combine the features originating from surfaces and bulk phases to enhance the prediction of the activation energies and perform eight different linear regressions utilizing the feature engineering of polynomial representations.Among them,a ridge linear regression model with2nd-degree polynomial feature generation predicted the best CO activation energy with a mean absolute error of 0.269 eV.展开更多
It is regretful that the Acknowledgments part was lost in the final process of publication.The Acknowledgments part should be added as follow.The work described in this paper was supported by the grants from the Resea...It is regretful that the Acknowledgments part was lost in the final process of publication.The Acknowledgments part should be added as follow.The work described in this paper was supported by the grants from the Research Grants Council of the Hong Kong Special Administrative Region,China(Project No.16205721).展开更多
Featuring low cost, high abundance, low electrochemical potential, and large specific capacity, zinc(Zn)metal holds great potential as an anode material for next-generation rechargeable aqueous batteries.However, the ...Featuring low cost, high abundance, low electrochemical potential, and large specific capacity, zinc(Zn)metal holds great potential as an anode material for next-generation rechargeable aqueous batteries.However, the poor reversibility resulting from dendrite formation and side reactions poses a major obstacle for its practical application. Electrolyte, which is regarded as the “blood” of batteries, has a direct impact on reaction kinetics, mass transport, and side reactions and thus plays a key role in determining the electrochemical performance of Zn electrodes. Therefore, considerable efforts have been devoted to modulating the electrolytes to improve the performance of Zn electrodes. Although significant progress has been made, achieving stable and highly reversible Zn electrodes remains a critical challenge. This review aims to provide a systematic summary and discussion on electrolyte strategies for highperformance aqueous Zn batteries. The(electro)-chemical behavior and fundamental challenges of Zn electrodes in aqueous electrolytes are first discussed. Electrolyte modulation strategies developed to address these issues are then classified and elaborated according to the underlying mechanisms.Finally, remaining challenges and promising future research directions on aqueous electrolyte engineering are highlighted. This review offers insights into the design of highly efficient electrolytes for new generation of rechargeable Zn batteries.展开更多
Fischer-Tropsch synthesis(FTS),an important route for the conversion of syngas into high-value-added chemicals,often relies on Fe-and Co-based catalysts.Catalyst performance has been improved by promoters,supports,and...Fischer-Tropsch synthesis(FTS),an important route for the conversion of syngas into high-value-added chemicals,often relies on Fe-and Co-based catalysts.Catalyst performance has been improved by promoters,supports,and optimization of the activation process;however,in-depth studies on the evolution of the phase during catalyst activation,reaction,and deactivation are still lacking.In situ X-ray diffraction(XRD)effectively reveals the phase evolution of catalytic materials in real time.In this review,the use of in situ XRD to elucidate the influence of activation mode,promoters,and supports on the phase evolution and performance of Fe-and Co-based catalysts is examined.The challenges and opportunities in studying the phase evolution of FTS catalysts using in situ XRD techniques are summarized and discussed,and theoretical guidance for the design of FTS catalysts is provided in order to promote their development.展开更多
Boron arsenide(BAs)is a promising integrated circuit thermal management material with ultra-high thermal conductivity(κ)and exceptional semiconductor properties.In practical devices,mechanical stress and strain cause...Boron arsenide(BAs)is a promising integrated circuit thermal management material with ultra-high thermal conductivity(κ)and exceptional semiconductor properties.In practical devices,mechanical stress and strain caused by thermal expansion inevitably affect the thermodynamic properties of heat sink materials.Consequently,investigation of the effects of stress and strain on theκof BAs is essential.Accurate assessment and regulation of theκand phonon heat transport of BAs requires consideration of both three-phonon(3ph)and four-phonon(4ph)interactions.However,anharmonicity computation using density functional theory is computationally expensive,particularly for the fourth-order interatomic force constants.This work uses a machine learning-driven moment tensor potential method to evaluate higher-order anharmonicity and extends it to include fourth-order forces,accelerating the calculations significantly.Results show that theκof BAs calculated using the moment tensor potential method when considering both 3ph and 4ph processes agrees well with experimental data.In contrast,considering the 3ph interaction alone causesκto be overestimated.The machine learning approach reduces computational costs by approximately 94%while maintaining comparable accuracy to density functional theory.By solving the phonon Boltzmann transport equation,the thermal transport properties of BAs under biaxial tensile strains ranging up to 7%are evaluated.BAs shows an anomalousκenhancement when including both 3ph and 4ph interactions,with a maximum enhancement of 15%at a small strain of 1%,primarily because of the weakening of the 3ph scattering.Beyond 2%strain,both the 3ph and 4ph scattering rates increase significantly,causing shorter phonon lifetimes and a monotonic reduction inκ.Additionally,theκtemperature dependence under strain is explored,highlighting temperature’s role in modulating phonon scattering.This study provides machine learning-driven insights into the BAs thermal response under biaxial tensile strain and offers a new perspective for understanding similar anomalous strain-induced phenomena in other materials.展开更多
Gas pulsation is an efficient enhancing way for fluidized bed drying process.In this work,the influence of gas pulsation on mass and heat transfer performance in a fluidized bed with non-spherical wet particles is num...Gas pulsation is an efficient enhancing way for fluidized bed drying process.In this work,the influence of gas pulsation on mass and heat transfer performance in a fluidized bed with non-spherical wet particles is numerically investigated via the computational fluid dynamics−discrete element method(CFD-DEM)approach,where the liquid transfer between particles and the heat transfer by liquid bridge are considered.The aspect ratio effect of non-spherical particle on drying process is revealed.It is found that the increase of aspect ratio can weaken the overall drying quality.The influence of gas pulsation on the drying of non-spherical particle is analyzed.The results reveal that adjusting a suitable gas pulsation mode can efficiently regulate the drying process of non-spherical wet particles with greater aspect ratios.展开更多
The conversion of CO_(2) into high value added chemicals via the Fischer-Tropsch synthesis(FTS)reaction has attracted significant attention.The surface oxygenation environment is a significant factor influencing the p...The conversion of CO_(2) into high value added chemicals via the Fischer-Tropsch synthesis(FTS)reaction has attracted significant attention.The surface oxygenation environment is a significant factor influencing the performance of the catalyst.In this work,spin-polarized density-functional theory calculations have been used to investigate the adsorption and reactions of CO_(2) and H to generate CH4 and CH3OH on Fe_(5)C_(2)(100)surfaces with varying OH∗coverage.On the pure Fe_(5)C_(2)(100)surface,surface C^(∗) preferentially reacts with hydrogen to form CH4,exposing C^(∗) vacancy.CO_(2) favors adsorbing on the C^(∗) vacancy to further dissociating and activating.The co-adsorption of OH∗promotes the C^(∗) cycle process by facilitating the hydrogenation of C^(∗).The Fe_(5)C_(2) surface with an oxide interface is favorable for reducing FexOy,thereby maintaining the dynamic stability of the surface.Therefore,surface oxidation is inevitably involved in the entire C^(∗) cycle of the FTS reaction and regulates the relative content of iron oxides and iron carbides.Our work can contribute to the rational modulation of the surface C^(∗) cycle,thereby enhancing catalyst performance.展开更多
This paper is concerned with the forced convective heat transfer of dilute liquid suspensions of nanoparticles （nanofluids） flowing through a straight pipe under laminar conditions. Stable nanofluids are formulated ...This paper is concerned with the forced convective heat transfer of dilute liquid suspensions of nanoparticles （nanofluids） flowing through a straight pipe under laminar conditions. Stable nanofluids are formulated by using the high shear mixing and ultrasonication methods. They are then characterised for their size, surface charge,thermal and rheological properties and tested for their convective heat transfer behaviour. Mathematical modelling is performed to simulate the convective heat transfer of nanofluids using a single phase flow model and considering nanofluids as both Newtonian and non-Newtonian fluid. Both experiments and mathematical modelling show that nanofluids can substantially enhance the convective heat transfer. Analyses of the results suggest that the non-Newtonian character of nanofluids influences the overall enhancement, especially for nanofluids with an obvious non-Newtonian character.展开更多
In this paper,a 3D meta-atom-based structure is constructed for the multifunctional compatible design of visible,infrared,and microwave.To achieve high performance,a novel dispersion tailoring strategy is proposed.Thr...In this paper,a 3D meta-atom-based structure is constructed for the multifunctional compatible design of visible,infrared,and microwave.To achieve high performance,a novel dispersion tailoring strategy is proposed.Through the incorporation of multiple controllable losses within the 3D meta-atom,the dispersion characteristics are tailored to the desired target region.The effectiveness of the strategy is verified with an error rate of less than5%.A proof-of-concept prototype is designed and fabricated,exhibiting high visible transparency,low infrared emission of 0.28,and microwave ultra-broadband absorption with a fractional bandwidth of 150%under 2.7 to18.7 GHz.This work contributes a novel design strategy for the development of high-performance multispectral stealth materials with wide applications.展开更多
Compared to traditional optical domes, domes of sapphire coated with films can effectively reduce emissivity and increase transmittance. The purpose of this work is to investigate the thermal radiation effect on sapph...Compared to traditional optical domes, domes of sapphire coated with films can effectively reduce emissivity and increase transmittance. The purpose of this work is to investigate the thermal radiation effect on sapphire optical dome coated with yttrium oxide by a radio frequency mag- netron sputtering method. The emissivity of sapphire coated with Y203 films is studied by both numerical and experi- mental methods. The results indicate that the emissivity of sapphire substrate is reduced effectively with increasing the thickness of the Y203 film. In addition, a finite element model is developed to simulate the radiation intensity of the optical dome. The thermal responses indicate that the max- imum temperature is reduced apparently compared with the uncoated sapphire as Y203 film thicknesses increase. The average irradiance distribution at different film thicknesses with time shows that the self-thermal radiation disturbance of sapphire optical dome delays 0.93 s when the thickness of Y203 film is 200μm, which can guarantee the dome works properly and effectively even in a harsh environment.展开更多
The photothermal self-driving process of Janus microparticles has wide application prospects in the fields of biomedicine.Since silica and gold have good biocompatibility and high photothermal conversion efficiency,th...The photothermal self-driving process of Janus microparticles has wide application prospects in the fields of biomedicine.Since silica and gold have good biocompatibility and high photothermal conversion efficiency,the SiO_(2)@Au Janus microparticles are widely used as drug carriers.Based on the multiphysics coupling method,the photothermal self-driving process of SiO_(2)@Au Janus microparticles was investi-gated,wherein the substrate was SiO_(2)particles and one side of the particles was coated with gold film.Under a continuous wave laser with irradiation of 20 W/cm^(2),the distance covered by the Janus particles was increased by increasing the thickness of the gold film and reducing the size of the SiO_(2)particles;the self-driving characteristics of the Janus particles were controlled substantially by increasing the intensity of the incident laser.Based on the simulation results,the thermophoretic motion and Brownian motion of particles can be measured by comparing the absolute values of the thermophoretic force impulse,Brownian force impulse,and drag force impulse.The Brownian force acting on Janus microparticles under low laser power cannot be ignored.Furthermore,the minimum laser power required for Janus particles to overcome Brownian motion was calculated.The results can effectively guide the design of Janus particles in biomedicine and systematically analyze the mechanism of particle thermophoretic motion during drug delivery.展开更多
Size-controlled hollow Fe3O4 nanospheres were synthesized via a one-pot hydrothermal method as a function of reaction time and sodium citrate,polyacrylamide,and urea content.Multiple characterization techniques such a...Size-controlled hollow Fe3O4 nanospheres were synthesized via a one-pot hydrothermal method as a function of reaction time and sodium citrate,polyacrylamide,and urea content.Multiple characterization techniques such as scanning and transmission electron microscopy and Raman spectroscopy were employed to investigate the crystal structure and morphology of the obtained nanospheres.The Fe3O4 nanosphere formation mechanism was elucidated from analyzing the characterization data.High levels of sodium citrate and longer reaction times were observed to increase the diameter of the nanospheres until hollow structures formed.Furthermore,polyacrylamide and urea promoted the formation of hollow structures.The hollow-structured Fe3O4 nanospheres exhibited high magnetization saturation values in the range of 48.8-58.7 emu/g.The facile synthesis method described herein,to generate size-controlled Fe3O4 nanospheres with tailored properties,demonstrates potential across a wide range of fields from drug-delivery and stealth devices,to environmental and energy applications.展开更多
This paper presents a flexible radio-frequency microelectromechanical system(RF MEMS)switch integrated on cyclo-olefin polymer(COP)substrate using a modified surface MEMS processing technology,which could be used in t...This paper presents a flexible radio-frequency microelectromechanical system(RF MEMS)switch integrated on cyclo-olefin polymer(COP)substrate using a modified surface MEMS processing technology,which could be used in the 17-19 GHz frequency band of satellite communication.Through systematic simulation analysis,it is found that flexible RF MEMS switch can achieve certain bending radius by miniaturizing the electronic dimension,without degrading the RF performance.It is demonstrated that the RF characteristics of flexible RF MEMS switch with special anchor structural design,fabricated by modified surface MEMS processing,are not sensitive to bending deformation under the curvature of 0 mm^(-1),0.05 mm^(-1),0.10 mm^(-1).Furthermore,the range of bending curvature which will affect the RF characteristics is given through systematic simulation.The flexible RF MEMS switch with high process compatibility and stable RF performance is believed to be promising candidates for future microwave communications and other consumer electronics.展开更多
In this work, a discrete particle model （DPM） was applied to investigate the dynamic characteristics in a gas-solid bubbling fluidized bed of binary solid particles. The solid phase was simulated by the hard- sphere...In this work, a discrete particle model （DPM） was applied to investigate the dynamic characteristics in a gas-solid bubbling fluidized bed of binary solid particles. The solid phase was simulated by the hard- sphere discrete particle model. The large eddy simulation （LES） method was used to simulate the gas phase. To improve the accuracy of the simulation, an improved sub-grid scale （SGS） model in the LES method was also applied. The mutative Smagorinsky constant case was compared with the previously published experimental data. The simulation by the mutative Smagorinsky constant model exhibited better agreement with the experimental data than that by the common invariant Smagorinsky constant model. Various restitution coefficients and different compositions of binary solids were investigated to determine their influences on the rotation characteristics and granular temperatures of the particles. The particle translational and rotational characteristic distributions were related to certain simulation parameters.展开更多
A novel multispectral smart window has been proposed,which features dynamic modulation of light transmittance and effective shielding against electromagnetic microwave radiation.This design integrates liquid crystal d...A novel multispectral smart window has been proposed,which features dynamic modulation of light transmittance and effective shielding against electromagnetic microwave radiation.This design integrates liquid crystal dynamic scattering and dye doping techniques,enabling the dual regulation of transmittance and scattering within a singlelayer smart window.Additionally,the precise control of conductive film thickness ensures the attainment of robust microwave signal shielding.We present a theoretical model for ion movement in the presence of an alternating electric field,along with a novel approach to manipulate negative dielectric constant.The proposed model successfully enables a rapid transition between light transparent,absorbing and haze states,with an optimum drive frequency adjustable to approximately 300 Hz.Furthermore,the resistive design of the conductive layer effectively mitigates microwave radiation within the 2−18 GHz range.These findings offer an innovative perspective for future advancements in environmental construction.展开更多
The discrete hard sphere particle model （DPM） is applied in this work to study numerically the distribu- tions of particle and bubble granular temperatures in a bubbling fluidized bed. The dimensions of the bed and ...The discrete hard sphere particle model （DPM） is applied in this work to study numerically the distribu- tions of particle and bubble granular temperatures in a bubbling fluidized bed. The dimensions of the bed and other parameters are set to correspond to those of Miuller et al（2008）. Various drag models and oper- ational parameters are investigated to find their influence on particle and bubble granular temperatures. Various inlet superficial gas velocities are used in this work to obtain their effect on flow characteristics. It is found that the superficial gas velocity has the most important effect on granular temperatures including bubble granular temperature, particle translational granular temperature and particle rotational granular temperature. The drag force model affects more seriously the large scale variables such as the bubble gran- ular temperature. Restitution coefficient influences all granular temperatures to some degree. Simulation results are compared with experimental results by Muller et al. （2008） showing reasonable agreement.展开更多
基金financially supported from the National Natural Science Foundation of China (No.22002008)Ningxia Key Research and Development Project,China (Nos.2022BEE03002 and 2022BSB03056)funding support from Synfuels China,Co.,Ltd.and Beijing Advanced Innovation Center for Materials Genome Engineering。
文摘The activation of CO on iron-based materials is a key elementary reaction for many chemical processes.We investigate CO adsorption and dissociation on a series of Fe,Fe_(3)C,Fe_(5)C_(2),and Fe_(2)C catalysts through density functional theory calculations.We detect dramatically different performances for CO adsorption and activation on diverse surfaces and sites.The activation of CO is dependent on the local coordination of the molecule to the surface and on the bulk phase of the underlying catalyst.The bulk properties and the different local bonding environments lead to varying interactions between the adsorbed CO and the surface and thus yielding different activation levels of the C-O bond.We also examine the prediction of CO adsorption on different types of Fe-based catalysts by machine learning through linear regression models.We combine the features originating from surfaces and bulk phases to enhance the prediction of the activation energies and perform eight different linear regressions utilizing the feature engineering of polynomial representations.Among them,a ridge linear regression model with2nd-degree polynomial feature generation predicted the best CO activation energy with a mean absolute error of 0.269 eV.
文摘It is regretful that the Acknowledgments part was lost in the final process of publication.The Acknowledgments part should be added as follow.The work described in this paper was supported by the grants from the Research Grants Council of the Hong Kong Special Administrative Region,China(Project No.16205721).
文摘Featuring low cost, high abundance, low electrochemical potential, and large specific capacity, zinc(Zn)metal holds great potential as an anode material for next-generation rechargeable aqueous batteries.However, the poor reversibility resulting from dendrite formation and side reactions poses a major obstacle for its practical application. Electrolyte, which is regarded as the “blood” of batteries, has a direct impact on reaction kinetics, mass transport, and side reactions and thus plays a key role in determining the electrochemical performance of Zn electrodes. Therefore, considerable efforts have been devoted to modulating the electrolytes to improve the performance of Zn electrodes. Although significant progress has been made, achieving stable and highly reversible Zn electrodes remains a critical challenge. This review aims to provide a systematic summary and discussion on electrolyte strategies for highperformance aqueous Zn batteries. The(electro)-chemical behavior and fundamental challenges of Zn electrodes in aqueous electrolytes are first discussed. Electrolyte modulation strategies developed to address these issues are then classified and elaborated according to the underlying mechanisms.Finally, remaining challenges and promising future research directions on aqueous electrolyte engineering are highlighted. This review offers insights into the design of highly efficient electrolytes for new generation of rechargeable Zn batteries.
基金supported in part by the National Natural Science Foundation of China(22468042)the Natural Science Foundation of Ningxia(2022AAC03040).
文摘Fischer-Tropsch synthesis(FTS),an important route for the conversion of syngas into high-value-added chemicals,often relies on Fe-and Co-based catalysts.Catalyst performance has been improved by promoters,supports,and optimization of the activation process;however,in-depth studies on the evolution of the phase during catalyst activation,reaction,and deactivation are still lacking.In situ X-ray diffraction(XRD)effectively reveals the phase evolution of catalytic materials in real time.In this review,the use of in situ XRD to elucidate the influence of activation mode,promoters,and supports on the phase evolution and performance of Fe-and Co-based catalysts is examined.The challenges and opportunities in studying the phase evolution of FTS catalysts using in situ XRD techniques are summarized and discussed,and theoretical guidance for the design of FTS catalysts is provided in order to promote their development.
基金supported by the National Key R&D Program of China(Grant No.2020YFA0709700).
文摘Boron arsenide(BAs)is a promising integrated circuit thermal management material with ultra-high thermal conductivity(κ)and exceptional semiconductor properties.In practical devices,mechanical stress and strain caused by thermal expansion inevitably affect the thermodynamic properties of heat sink materials.Consequently,investigation of the effects of stress and strain on theκof BAs is essential.Accurate assessment and regulation of theκand phonon heat transport of BAs requires consideration of both three-phonon(3ph)and four-phonon(4ph)interactions.However,anharmonicity computation using density functional theory is computationally expensive,particularly for the fourth-order interatomic force constants.This work uses a machine learning-driven moment tensor potential method to evaluate higher-order anharmonicity and extends it to include fourth-order forces,accelerating the calculations significantly.Results show that theκof BAs calculated using the moment tensor potential method when considering both 3ph and 4ph processes agrees well with experimental data.In contrast,considering the 3ph interaction alone causesκto be overestimated.The machine learning approach reduces computational costs by approximately 94%while maintaining comparable accuracy to density functional theory.By solving the phonon Boltzmann transport equation,the thermal transport properties of BAs under biaxial tensile strains ranging up to 7%are evaluated.BAs shows an anomalousκenhancement when including both 3ph and 4ph interactions,with a maximum enhancement of 15%at a small strain of 1%,primarily because of the weakening of the 3ph scattering.Beyond 2%strain,both the 3ph and 4ph scattering rates increase significantly,causing shorter phonon lifetimes and a monotonic reduction inκ.Additionally,theκtemperature dependence under strain is explored,highlighting temperature’s role in modulating phonon scattering.This study provides machine learning-driven insights into the BAs thermal response under biaxial tensile strain and offers a new perspective for understanding similar anomalous strain-induced phenomena in other materials.
基金the National Natural Science Foundation of China(grant No.U20A20304)financial support from the Fundamental Research Funds for the Central Universities(grant No.FRFCU5710050721).
文摘Gas pulsation is an efficient enhancing way for fluidized bed drying process.In this work,the influence of gas pulsation on mass and heat transfer performance in a fluidized bed with non-spherical wet particles is numerically investigated via the computational fluid dynamics−discrete element method(CFD-DEM)approach,where the liquid transfer between particles and the heat transfer by liquid bridge are considered.The aspect ratio effect of non-spherical particle on drying process is revealed.It is found that the increase of aspect ratio can weaken the overall drying quality.The influence of gas pulsation on the drying of non-spherical particle is analyzed.The results reveal that adjusting a suitable gas pulsation mode can efficiently regulate the drying process of non-spherical wet particles with greater aspect ratios.
基金the National Natural Science Foundation of China(22002008,22202226,22468042)Ningxia Key Research and Development Project(2022BEE03002,2022 BSB03056)+1 种基金the Fourth Batch of Ningxia Youth Talents Supporting Program(TJGC2019022)West Light Foundation of the Chinese Academy of Sciences(XAB2019AW02).
文摘The conversion of CO_(2) into high value added chemicals via the Fischer-Tropsch synthesis(FTS)reaction has attracted significant attention.The surface oxygenation environment is a significant factor influencing the performance of the catalyst.In this work,spin-polarized density-functional theory calculations have been used to investigate the adsorption and reactions of CO_(2) and H to generate CH4 and CH3OH on Fe_(5)C_(2)(100)surfaces with varying OH∗coverage.On the pure Fe_(5)C_(2)(100)surface,surface C^(∗) preferentially reacts with hydrogen to form CH4,exposing C^(∗) vacancy.CO_(2) favors adsorbing on the C^(∗) vacancy to further dissociating and activating.The co-adsorption of OH∗promotes the C^(∗) cycle process by facilitating the hydrogenation of C^(∗).The Fe_(5)C_(2) surface with an oxide interface is favorable for reducing FexOy,thereby maintaining the dynamic stability of the surface.Therefore,surface oxidation is inevitably involved in the entire C^(∗) cycle of the FTS reaction and regulates the relative content of iron oxides and iron carbides.Our work can contribute to the rational modulation of the surface C^(∗) cycle,thereby enhancing catalyst performance.
基金supported by Chinese Heilongjiang Postdoctoral FoundationChinese Heilongjiang Postdoctoral Science Funding No.LBH-Q07036+1 种基金the Science Creative Foundation for Distinguished Young Scholars in Harbin (Grant No. 2008RFLG005)Project Supported by Natural Scientific Research Innovation Foundation in Harbin Institute of Technology No.HIT.NSRIF. 2008.43.
文摘This paper is concerned with the forced convective heat transfer of dilute liquid suspensions of nanoparticles （nanofluids） flowing through a straight pipe under laminar conditions. Stable nanofluids are formulated by using the high shear mixing and ultrasonication methods. They are then characterised for their size, surface charge,thermal and rheological properties and tested for their convective heat transfer behaviour. Mathematical modelling is performed to simulate the convective heat transfer of nanofluids using a single phase flow model and considering nanofluids as both Newtonian and non-Newtonian fluid. Both experiments and mathematical modelling show that nanofluids can substantially enhance the convective heat transfer. Analyses of the results suggest that the non-Newtonian character of nanofluids influences the overall enhancement, especially for nanofluids with an obvious non-Newtonian character.
基金Open Fund of Key Laboratory(JZX7Y201911SY008601)Key Project of National Natural Science Foundation of China(52032004)National Natural Science Foundation for Distinguished Young Scholars of China(51625201)。
文摘In this paper,a 3D meta-atom-based structure is constructed for the multifunctional compatible design of visible,infrared,and microwave.To achieve high performance,a novel dispersion tailoring strategy is proposed.Through the incorporation of multiple controllable losses within the 3D meta-atom,the dispersion characteristics are tailored to the desired target region.The effectiveness of the strategy is verified with an error rate of less than5%.A proof-of-concept prototype is designed and fabricated,exhibiting high visible transparency,low infrared emission of 0.28,and microwave ultra-broadband absorption with a fractional bandwidth of 150%under 2.7 to18.7 GHz.This work contributes a novel design strategy for the development of high-performance multispectral stealth materials with wide applications.
文摘Compared to traditional optical domes, domes of sapphire coated with films can effectively reduce emissivity and increase transmittance. The purpose of this work is to investigate the thermal radiation effect on sapphire optical dome coated with yttrium oxide by a radio frequency mag- netron sputtering method. The emissivity of sapphire coated with Y203 films is studied by both numerical and experi- mental methods. The results indicate that the emissivity of sapphire substrate is reduced effectively with increasing the thickness of the Y203 film. In addition, a finite element model is developed to simulate the radiation intensity of the optical dome. The thermal responses indicate that the max- imum temperature is reduced apparently compared with the uncoated sapphire as Y203 film thicknesses increase. The average irradiance distribution at different film thicknesses with time shows that the self-thermal radiation disturbance of sapphire optical dome delays 0.93 s when the thickness of Y203 film is 200μm, which can guarantee the dome works properly and effectively even in a harsh environment.
基金supported by the Heilongjiang Province Natural Science Foundation(Grant No.LH2019E053)Fundamental Research Funds for Central Universities(Grant No.FRFCU5710051421).
文摘The photothermal self-driving process of Janus microparticles has wide application prospects in the fields of biomedicine.Since silica and gold have good biocompatibility and high photothermal conversion efficiency,the SiO_(2)@Au Janus microparticles are widely used as drug carriers.Based on the multiphysics coupling method,the photothermal self-driving process of SiO_(2)@Au Janus microparticles was investi-gated,wherein the substrate was SiO_(2)particles and one side of the particles was coated with gold film.Under a continuous wave laser with irradiation of 20 W/cm^(2),the distance covered by the Janus particles was increased by increasing the thickness of the gold film and reducing the size of the SiO_(2)particles;the self-driving characteristics of the Janus particles were controlled substantially by increasing the intensity of the incident laser.Based on the simulation results,the thermophoretic motion and Brownian motion of particles can be measured by comparing the absolute values of the thermophoretic force impulse,Brownian force impulse,and drag force impulse.The Brownian force acting on Janus microparticles under low laser power cannot be ignored.Furthermore,the minimum laser power required for Janus particles to overcome Brownian motion was calculated.The results can effectively guide the design of Janus particles in biomedicine and systematically analyze the mechanism of particle thermophoretic motion during drug delivery.
基金This work was financially supported by the National Natural Science Foundation of China(Grant No.51676060)the Natural Science Funds of Heilongjiang Province for Distinguished Young Scholars(Grant No.JC2016009)the Science Creative Foundation for Distinguished Young Scholars in Harbin(Grant No.2014RFYXJ004).
文摘Size-controlled hollow Fe3O4 nanospheres were synthesized via a one-pot hydrothermal method as a function of reaction time and sodium citrate,polyacrylamide,and urea content.Multiple characterization techniques such as scanning and transmission electron microscopy and Raman spectroscopy were employed to investigate the crystal structure and morphology of the obtained nanospheres.The Fe3O4 nanosphere formation mechanism was elucidated from analyzing the characterization data.High levels of sodium citrate and longer reaction times were observed to increase the diameter of the nanospheres until hollow structures formed.Furthermore,polyacrylamide and urea promoted the formation of hollow structures.The hollow-structured Fe3O4 nanospheres exhibited high magnetization saturation values in the range of 48.8-58.7 emu/g.The facile synthesis method described herein,to generate size-controlled Fe3O4 nanospheres with tailored properties,demonstrates potential across a wide range of fields from drug-delivery and stealth devices,to environmental and energy applications.
基金supported by BOE Technology Group Co.,Ltd.Y.L.acknowledges support from the National Natural Science Foundation of China under grant numbers 61825102 and U21A20460.
文摘This paper presents a flexible radio-frequency microelectromechanical system(RF MEMS)switch integrated on cyclo-olefin polymer(COP)substrate using a modified surface MEMS processing technology,which could be used in the 17-19 GHz frequency band of satellite communication.Through systematic simulation analysis,it is found that flexible RF MEMS switch can achieve certain bending radius by miniaturizing the electronic dimension,without degrading the RF performance.It is demonstrated that the RF characteristics of flexible RF MEMS switch with special anchor structural design,fabricated by modified surface MEMS processing,are not sensitive to bending deformation under the curvature of 0 mm^(-1),0.05 mm^(-1),0.10 mm^(-1).Furthermore,the range of bending curvature which will affect the RF characteristics is given through systematic simulation.The flexible RF MEMS switch with high process compatibility and stable RF performance is believed to be promising candidates for future microwave communications and other consumer electronics.
基金financially supported by the National Natural Science Foundation of China(Grant No.51322601)the National Natural Science Foundation of China-China National Petroleum Corporation Joint Fund of Petrochemical Engineering(U1162122)the Fundamental Research Funds for the Central Universities (Grant No.HIT.BRETIV.201315)
文摘In this work, a discrete particle model （DPM） was applied to investigate the dynamic characteristics in a gas-solid bubbling fluidized bed of binary solid particles. The solid phase was simulated by the hard- sphere discrete particle model. The large eddy simulation （LES） method was used to simulate the gas phase. To improve the accuracy of the simulation, an improved sub-grid scale （SGS） model in the LES method was also applied. The mutative Smagorinsky constant case was compared with the previously published experimental data. The simulation by the mutative Smagorinsky constant model exhibited better agreement with the experimental data than that by the common invariant Smagorinsky constant model. Various restitution coefficients and different compositions of binary solids were investigated to determine their influences on the rotation characteristics and granular temperatures of the particles. The particle translational and rotational characteristic distributions were related to certain simulation parameters.
基金the financial supports from the National Key Research and Development Program of China(Grant No.2023YFB3811600)the National Science Fund for Distinguished Young Scholars(Grant No.51625201)+6 种基金State Key Program of National Natural Science of China(Grant No.52032004)National Youth Science Funds of China(Grant No.52102039)Key Research and Development Program of Heilongjiang Province(Grant No.GA21D001,2022ZX06C05)the Fundamental Research Funds for the Central Universities(Grant No.HIT.OCEF.2022011)the Major Program of Harbin Institute of Technology(Grant NO.2023FRFK01002)the Fundamental Research Funds for the Central Universities(2022FRFK060026)the National Youth Science Funds of China(Grant No.52302172).
文摘A novel multispectral smart window has been proposed,which features dynamic modulation of light transmittance and effective shielding against electromagnetic microwave radiation.This design integrates liquid crystal dynamic scattering and dye doping techniques,enabling the dual regulation of transmittance and scattering within a singlelayer smart window.Additionally,the precise control of conductive film thickness ensures the attainment of robust microwave signal shielding.We present a theoretical model for ion movement in the presence of an alternating electric field,along with a novel approach to manipulate negative dielectric constant.The proposed model successfully enables a rapid transition between light transparent,absorbing and haze states,with an optimum drive frequency adjustable to approximately 300 Hz.Furthermore,the resistive design of the conductive layer effectively mitigates microwave radiation within the 2−18 GHz range.These findings offer an innovative perspective for future advancements in environmental construction.
基金supported by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (Grant No. 51121004)the National Natural Science Foundation of China–China National Petroleum Corporation Joint Fund of Petrochemical Engineering (U1162122) the Program for New Century Excellent Talents in University (NCET-08-0159)
文摘The discrete hard sphere particle model （DPM） is applied in this work to study numerically the distribu- tions of particle and bubble granular temperatures in a bubbling fluidized bed. The dimensions of the bed and other parameters are set to correspond to those of Miuller et al（2008）. Various drag models and oper- ational parameters are investigated to find their influence on particle and bubble granular temperatures. Various inlet superficial gas velocities are used in this work to obtain their effect on flow characteristics. It is found that the superficial gas velocity has the most important effect on granular temperatures including bubble granular temperature, particle translational granular temperature and particle rotational granular temperature. The drag force model affects more seriously the large scale variables such as the bubble gran- ular temperature. Restitution coefficient influences all granular temperatures to some degree. Simulation results are compared with experimental results by Muller et al. （2008） showing reasonable agreement.
