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Effects of thermophoresis on Brownian coagulation of spherical particles over the entire particle size regime

Particuology 2022年第8期20卷 8-17页

作者： Kaiyuan Wang Pei Wang suyuan yu Institute of Applied Physics and Computational Mathematics Bejing 100094.China Center forCombustionEergy.Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Department of Energyand PowerEngineeringTsinghua UniversityBejing 100084.China Smoore International Holdings Ltd.Shenzhen 518102 China

In many energy and combustion applications.particles experience large temperature gradients,which can affect the coagulation process due to thermophoresis.This study presents a rigorous theory of thermophoretically modified Brownian coagulation in the entire particle size regime.The theoretical derivations are based on the kinetictheory forthe free-molecular regime and the harmonic mean method for the transition regime.The coagulation kernels in different size regimes can be expressed as the basic Brownian coagulation kernel times an enhancement factor,The enhancement factor represents the coagulationrate enhancement induced by thermophoresis and is a function of specific dimensionless numbers.Based on the enhancement factor,the thermophoretic enhancement effects on particle coagulation are further analyzed under a wide range of gas and particle conditions.The results show that thermophoretic enhancement effects are ignorable in the free-molecular regime,but need to be considered in the continuum regime and the transition regime.In addition,the enhancement effects increase significantly with increase of gas temperature and temperature gradient while decrease with increase of gas pressure.The present study can improve understanding ofthermophoretic effects on Brownian coagulation in the entire size regime and provide a useful tool to calculate the coagulation rates in presence of thermophoresis.

关键词： Thermophoresis Brownian coagulation Enhancement factor Knudsen number

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Experimental and mechanistic study of dispersed micrometer-sized particle resuspension in a square straight duct with rough walls

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Particuology 2023年第12期83卷 101-114页

作者： Qi Sun suyuan yu Wei Peng Institute of Nuclear and New Energy Technology Cooperation Innovation Center of Advanced Nuclear Energy TechnologyKey Laboratory of Advanced Reactor Engineering and Safety of Ministry of EducationTsinghua UniversityBeijing100084China Center for Combustion Energy Key Laboratory for Thermal Science and Power Engineering of the Ministry of EducationDepartment of Energy and Power EngineeringTsinghua UniversityBeijing100084China

The resuspension of graphite dust is an important phenomenon in the release of radioactivity and the safety of nuclear reactors during severe accidents.In this study,a visualization experimental platform is constructed to study effects of particle size,flow velocity,and wall roughness on the resuspension characteristics of graphite particles.A statistical model of particle resuspension applicable to monolayer dispersed particles is developed based on the moment equilibrium of the particles and the flow field characteristics,as calculated by the large-eddy simulation framework.The results show that particle resuspension can be divided into short-and long-term resuspension stages.Most particle resuspension occurs during the short-term stage.With increases in flow velocity and particle diameter,the aerodynamic or adhesion force acting on the particles increases,and corresponding particle resuspension fraction increases.The influence of rough walls on particle resuspension is related to both the force on the particles and the arm ratio between the wall morphology and the particle diameter.A comparison with the experimental results demonstrates that the particle resuspension model developed in this study accurately predicts the impact of flow velocity,particle size,and wall roughness on particle resuspension.

关键词： Particle resuspension Statistical model Moment equilibrium High temperature gas-cooled reactor(HTGR)

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Selectively nucleotide-derived RuP on N,P-codoped carbon with engineered mesopores for energy-efficient hydrogen production assisted by hydrazine oxidation

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SusMat 2024年第1期4卷 166-177页

作者： Xiya Guan yu Sun Simeng Zhao Haibo Li suyuan Zeng Qingxia Yao Rui Li Hongyan Chen Konggang Qu School of Chemistry and Chemical Engineering Shandong Provincial Key Laboratory/Collaborative Innovation Center of Chemical Energy Storage&Novel Cell TechnologyLiaocheng UniversityLiaochengChina

Integrating hydrogen evolution reaction(HER)with hydrazine oxidation reaction(HzOR)has an encouraging prospect for the energy-saving hydrogen production,demanding the high-performance bifunctional HER/HzOR electrocatalyst.Ruthenium phosphide/doped carbon composites have exhibited superior activity towardmultiple electrocatalytic reactions.To explore the decent water-soluble precursors containing bothNand P elements is highly attractive to facilely prepare metal phosphide/doped carbon composites.Herein,as one kind ecofriendly biomolecules,adenine nucleotide was first employed to selectively fabricate the highly pure RuP nanoparticles embedded into porous N,P-codoped carbons(RuP/PNPC)with a straightforward“mix-and-pyrolyze”approach.The newly prepared RuP/PNPC only requires 4.0 and−83.0 mV at 10 mA/cm^(2) separately in alkaline HER and HzOR,outperforming most of reported electrocatalysts,together with the outstanding neutral bifunctional performance.Furthermore,the two-electrode alkaline and neutral overall hydrazine splitting both exhibit significant power-efficiency superiority to the corresponding overall water splitting with the voltage difference of larger than 2 V,which can be also easily driven by the fuel cells and solar cells with considerableH2 generation.Our report innovates the N-and P-bearing adenine nucleotide to effortlessly synthesize the high-quality RuP/doped carbon composite catalysts,highly potential as a universal platform for metal phosphide-related functional materials.

关键词： bifunctional electrocatalyst hydrazine oxidation hydrogen energy hydrogen evolution RuP

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Evaluation of thermophoretic effects on graphite dust coagulation in high-temperature gas-cooled reactors

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Particuology 2020年第4期18卷 45-52页

作者： Kaiyuan Wang suyuan yu Wei Peng Center for Combustion Energy Key Laboratory for Thermal Science and Power Engineering of Ministry of EducationDepartment of Energy and Power EngineeringTsinghua UniversityBeijing 100084China Institute of Nuclear and New Energy Technology Advanced Nuclear Energy Technology Cooperation Innovation CenterKey Laboratory of Advanced Nuclear Engineering and Safety of Ministry of EducationTsinghua UniversityBeijing 100084China

In high-temperature gas-cooled reactors,graphite dust particles within the reactor core and the heat transfer equipment experience large temperature gradients.Under such conditions,thermophoresis may play an important role in determining aerosol evolution.This study presents a theoretical and numerical analysis of the thermophoretic effects on aerosol coagulation within these reactors.The coagulation rates for Brownian versus thermophoretic coagulation are calculated and compared for various temperature gradients.Our results show that thermophoretic coagulation dominates over Brownian coagulation for large temperature gradients.We defined an enhancement factor to evaluate the role of thermophoretic coagulation under various reactor conditions.The enhancement factor increased dramatically with increasing temperature gradient,decreasing pressure and increasing particle diameter,but was not very sensitive to temperature change.The time evolution of the particle size distribution related to combined Brownian and thermophoretic coagulation was simulated using a log-skew-normal method of moments.The simulation results indicate that aerosol evolution can be strongly accelerated by thermophoretic coagulation under large temperature gradients.

关键词： Graphite dust High-temperature gas-cooled reactor Thermophoretic coagulation Log-skew-normal method of moments Particle size distribution

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Deposition of non-spherical microparticles in the human upper respiratory tract

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Particuology 2018年第1期16卷 185-189页

作者： Lixing Jia Lianzhong Zhang suyuan yu School of Physics Nankai University Tianjin 300071 China Institute of Nuclear and New Energy Technology Tsinghua University Beijing 100084 China

We investigated the deposition pattern of microparticles with different particle diameters, shape factors, and initial flow conditions in a realistic human upper respiratory tract model. We identified a close relationship between the deposition fraction and the particle shape factor. The deposition fraction of the particles decreased sharply with increasing particle shape factor because of the decreasing drag force. We also found that the deposition varied at different positions in the upper respiratory tract. At low shape factors, the highest fraction of particles deposited at the mouth and pharynx. However, with increasing shape factor, the deposition fraction in the trachea and lungs increased. Moreover, for a given shape factor, larger particles deposited at the mouth and pharynx, which indicates that the deposition fraction of microparticles in the human upper respiratory tract is affected first and foremost by particle inertia as well as by the drag force.

关键词： Particle deposition Non-spherical microparticles Human upper airway Shape factor

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Modeling micro-particle deposition in human upper respiratory tract under steady inhalation

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Particuology 2011年第1期9卷 39-43页

作者： Jianhua Huang Lianzhong Zhang suyuan yu School of Physics Nankai University Tianjin 300071 China State Key Laboratory of Loess and Quaternary Geology Institute of Earth Environment Chinese Academy of Sciences Xi'an 710075 China Institute of Nuclear Energy and New Energy Technology Tsinghua University Beijing 100084 China

A representative human upper respiratory tract （URT） with idealized oral region and asymmetric tracheo- bronchial （TB） airway has been modeled, and laminar-to-turbulent airflow for typical inhalation modes as well as micro-particle transport and deposition has been simulated using CFX10.0 software from Ansys Inc. on a personal computer. The asymmetric TB airway could not be replaced by an extended straight tube as outlet of the oral region while investigating the tracheal airflow field and particle deposition. Compared to an idealized oral airway with an extended straight tube, several differences could be noted：（i） The laryngeal jet extends further down the trachea and inclines towards the anterior wall; （ii） the turbulence level in trachea is less and decays more quickly; （iii） three recirculation zones are visible with intense adverse current after the glottis; （iv） deposition of small particles in trachea is reduced due to lower turbulence. Refined unstructured mesh with densified boundary layer mesh could be a proper substitute for the structured mesh in the human URT model with asymmetric TB airway. Based on the refined unstructured mesh, the physiological structure of uvula in the soft palate is properly simulated in the present human URT model.

关键词： Human upper airway model Asymmetric tracheobronchial (TB) airway Particle deposition Computational fluid-particle dynamic simulations

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Graphite dust deposition in the HTR-10 steam generator

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Particuology 2013年第5期11卷 533-539页

作者： Wei Peng Yanan Zhen Xiaoyong Yang suyuan yu Institute of Nuclear and New Energy Technology of Tsinghua University The Key Laboratory of Advanced Reactor Engineering and SafetyMinistry of Education

Graphite dust has an important effect on the safe operation of a high-temperature gas-cooled reactor （HTR）. The present study analyzes temperature and flow field distributions in the HTR-10 steam genera- tor. The temperature and flow field distributions are then used to study thermophoretic deposition and turbulent deposition. The results show that as the dust diameter increases, the thermophoretic deposition decreases, while the turbulent deposition first decreases and then increases. The thermophoretic deposi- tion is higher at higher reactor powers, with turbulent deposition growing more rapidly at higher reactor power. For small particles, the thermophoretic deposition effect is greater than the turbulent deposition effect, while for large particles, the turbulent deposition effect is dominant.

关键词： Graphite dustHigh-temperature gas-cooled reactorSteam generatorDeposition

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Graphite dust resuspension in an HTR-10 steam generator

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Particuology 2014年第6期12卷 149-157页

作者： Wei Peng Tianqi Zhang Yanan Zhen suyuan yu Institute of Nuclear and New Energy Technology of Tsinghua University Key Laboratory of Advanced Reactor Engineering and Safety of Ministry of Education Center for Combustion Energy Key Laboratory for Thermal Science and Power Engineering of Ministry of EducationsDepartment of Thermal EngineeringTsinghua University

Graphite dust has an important effect on the safety of high-temperature gas-cooled reactors（HTR）.The flow field in the steam generator was studied by the computational fluid dynamics（CFD） method,with the results indicating that the friction velocity in the windward and the leeward of the heat transfer tubes is relatively low and is higher at the sides.Further analysis of the resuspension of graphite dust indicates that the resuspension fraction reaches nearly zero for particles with a diameter less than 1 μm,whereas it will increases as the helium velocity in the steam generator increases for particle size larger than 1 μm.Moreover,the resuspension fraction increases as the particle size increases.The results also indicate that resuspension of the particles with sizes larger than 1 μm exhibited obvious differences in different parts of the steam generator.

关键词： Graphite dust High-temperature gas-cooled reactor（HTR） Steam generator Resuspension

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New Fabrication and Mechanical Properties of Styrene-Butadiene Rubber/Carbon Nanotubes Nanocomposite

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Journal of Materials Science & Technology 2010年第12期26卷 1127-1132页

作者： Xiangwen Zhou yuefeng Zhu Ji Liang suyuan yu Key Laboratory for Advanced Materials Processing Technology Ministry of Education Department of Mechanical Engineering Tsinghua University Beijing 100084 China Institute of Nuclear and New Energy Technology Tsinghua University Beijing 100084 China

A novel technology to prepare styrene-butadiene rubber （SBR）/carbon nanotubes （CNTs） composites was developed by combining a spray drying method and a subsequent mechanical mixing process. The cross-linking degrees of the vulcanized composites increased gradually with the additive CNTs contents. By comparing with those of the pure SBR composites, the mechanical properties such as tensile strength, tear strength and hardness of the composites filled with CNTs at certain contents were dramatically improved almost by 600%, 250% and 70%, respectively. The fabrication of the CNTs filled with SBR composites by combination of the spray drying method and subsequent mechanical mixing process was effective for enhancing the reinforcement effects of CNTs in rubbers. The novel technology can also open a new route for the modification and reinforcement on the nanocomposites with large amount of CNTs.

关键词： Carbon nanotubes Styrene-butadiene rubber Spray drying Mechanical mixing Nanocomposite Mechanical property

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SOOT PARTICLES ANALYSIS IN LAMINAR PREMIXED PROPANE/OXYGEN(C_(3)H_(8)/O_(2))FLAMES USING PUBLISHED MEASUREMENT DATA

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China Particuology 2003年第4期1卷 168-171页

作者： Jinling Li suyuan yu Institute of Nuclear Energy Technology Tsinghua UniversityBeijing 100084P.R.China

A laminar premixed Propane/Air flame with a fuel equivalence ratio of 2.1 was employed for analysis of soot particles. Zeroth-order lognormal distributions (ZOLD) were used in the analysis of experimental distribution phe-nomena at different residence times during soot formation in the flame. Rayleigh抯 theory and Mie抯 scattering theory were combined with agglomerate analysis using scattering and extinction data to determine the following soot charac-teristics: agglomerate parameters, volumetric fractions, mass flow rates and surface growth rate. Soot density meas-urements were carried out to determine density variations at different stages of growth. The measured results show that for long residence times the soot clearly crystallizes with higher density (up to 1.8 g.cm-3). The increases of soot volu-metric fraction and mass flow rate indicate that the surface growth rate of soot particles exceeds the oxidation rates in the flame studied. The data obtained in this work would be used to study soot oxidation rate under flaming condition.

关键词： soot particles ZOLD agglomerate parameters surface growth rate density

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