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11th Asia-Pacific Conference on Combustion, ASPACC 2017

作者： Shilong, Guo Meng, Zhang Jinhua, Wang Zuohua, Huang State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

Thickened flame (TF) model is one of the effective methods to simulate combustion phenomenon. Theoretically, it could be extended to multi-step chemical reaction mechanism. However, the results in the present work shown that TF model coupled with multi-step mechanism will underestimate burnt gas temperature, whether in confined or unconfined space. Meanwhile, some post-flame species (CO, OH) concentration are overestimated, which means the decrease in burnt gas temperature is mainly caused by enhanced species diffusion. Dynamic thickened flame (DTF) model coupled with multi-step mechanism performs well for predicting species concentration and combustion state. So it is not recommended to use TF model coupled with a multi-step chemical reaction mechanism. However, the dynamically thickened flame thickness is obviously thinner than the theoretical expectations for the dynamic thickening factor, which is always used to determine thickening factor for a certain mesh size. The main heat release rate zone couldn’t be thickened as expected. A new DTF model used for multi-step reaction mechanism was proposed. The results show that it can both predict the flame structure accurately and get the flame thickness as expected. © 2018 Combustion Institute. All Rights Reserved.

关键词： Gas temperature

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Mixed convective heat transfer of supercritical carbon dioxide flowing in a vertically-upward tube with low mass flux 17

Mixed convective heat transfer of supercritical carbon dioxi...

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17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2017

作者： Zhang, Qian Li, Huixiong Liu, Jialun Zhang, Jun Lei, Xianliang State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi'an Shaanxi China

Experimental investigation was carried out to study heat transfer characteristics of supercritical CO2 at low mass flux conditions. A vertical tube with an inner diameter of 16 mm was tested at various heat fluxes and pressures. The flow was driven by mixed convection with strong buoyancy force owing to low mass flux and high heat flux. The experimental results shown that a "no wall temperature peak" heat transfer deterioration with an exactly large temperature difference between the tube and fluid occurred at high enthalpy region, which was especially different from the general deterioration phenomenon with a wall temperature peak occurred at normal mass flux in previous studies. Heat transfer in low mass flux was accompanied with a heat transfer enhancement phenomenon before the pseudo critical point and a deterioration after that. With increasing heat flux, the deterioration was strengthened, but the enhancement was little weakened and moved towards the low enthalpy region due to the combined effect of buoyancy and specific heat of fluid. The effect of pressure on heat transfer in various cases was different. Heat transfer was reduced with a rising pressure at low heat flux cases, but when heat flux became larger, heat transfer was enhanced with the increase of pressure. The parameters representing to buoyancy and thermal acceleration effects were also introduced respectively to explain the mechanism of heat transfer. Results shown the buoyancy effect and the distribution of large specific heat fluid were greatly responsible for the enhancement and the deterioration in heat transfer. While the effect of thermal acceleration on heat transfer in the present study could be neglected. © 2016 Association for Computing Machinery Inc. All Rights Reserved.

关键词： Buoyancy

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MPS analysis of molten corium jet and structure interaction during nuclear severe accident 17

MPS analysis of molten corium jet and structure interaction ...

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17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2017

作者： Li, Gen Zhang, Jun Yan, Junjie State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

The melt jet and structure interaction is an important phenomenon in the progression of nuclear severe accident. It could happen when molten corium relocates onto core plate and Reactor Pressure Vessel (RPV) lower head, and in the ex-vessel accident, the molten corium may directly impinge onto and Erode concrete. In the present study, a numerical code was developed based on Moving Particle Semi-implicit (MPS) method, to analyze the erosion scenario of RPV wall and dry concrete by melt jet. The numerical modeling was validated by comparing structure erosion configuration and time-dependent erosion depth with the experimental data. In the analysis of RPV wall erosion, it indicates that no crust layer presented at the interaction of stainless steel (SS) melt jet and RPV wall, while for Zr, ZrO2 and UO2 melt jets the crust layer presented. At a superheat temperature equal to 300 K, the erosion rate by SS melt was the fastest, even though the absolute temperature was the lowest compared with other cases. In the analysis of melt jet and concrete interaction, the core melt was divided as metallic material (SS-Zr) and oxide material (ZrO2-UO2). The results indicate that the crust and ablated concrete layer presented at the interface of UO2-ZrO2 melt and concrete, whereas no crust could be found in the interaction of SS-Zr melt with concrete. The erosion progression was faster in the erosion by metallic melt jet than by oxidic melt jet. The present analysis demonstrates that the erosion rate was affected not only by temperature, but also by crust layer, and the major threat to structure was metallic melt, especially at high temperature. © 2016 Association for Computing Machinery Inc. All Rights Reserved.

关键词： Erosion

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Experimental and kinetic study on ignition delay times of 2, 5-DMF/n-heptane blends 9

Experimental and kinetic study on ignition delay times of 2,...

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9th International Conference on Modeling and Diagnostics for Advanved Engine Systems, COMODIA 2017

作者： Hu, Erjiang Gao, Zhenhua Ku, Jinfeng Meng, Xin Huang, Zuohua State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

Ignition delay times of 2, 5-dimethylfuran(2, 5-DMF)/n-heptane/oxygen/argon mixtures were measured in this study. Experiments were performed at the stoichiometric mixtures in the temperature range of 1200-1800K. A blend model for 2, 5-DMF/n-heptane blends was developed by combining two selected models for each individual fuel component. According to the combined model, the ignition delay time increases with an increase in the 2, 5-DMF addition level, non-linearly. Kinetic analysis was conducted to investigate interaction effects between two fuels. At relatively low blending ratios of 2, 5-DMF, the two fuels have negligible impacts on the reaction path of each other. As the 2, 5-DMF addition increases to relatively higher levels, decomposition path of n-heptane is significantly changed due to the competition for small radical. Copyright © 2017 by the Japan Society of Mechanical Engineers.

关键词： Heptane

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Time-resolved investigation of droplet size and velocity inside diesel fuel sprays 11

Time-resolved investigation of droplet size and velocity ins...

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11th Asia-Pacific Conference on Combustion, ASPACC 2017

作者： Feng, Zehao Zhang, Mingzhi Yang, Jiapei Tang, Chenglong Huang, Zuohua State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

To better understand the microscopic spray characteristics, measurements of temporal changes in the size and velocity of droplets inside diesel fuel sprays were conducted at a fixed measurement position of 40mm downstream from the injector tip. Particle/droplet image analysis (PDIA) system was applied to obtain the microscopic droplet images in a long time scale (0-10 ms) which consists of continuous injection stage (0-2.1 ms) and the spray free development stage (2.1-10 ms). The results show that the droplet size distribution has a significant variation at the beginning, but basically independent of time after 1.6 ms. The Sauter mean diameter (SMD) increases significantly at the continuous injection stage, but slightly decreases at the free development stage. In addition, it is observed that most droplets’ velocity are 2-3 m/s while the maximum value is 25 m/s. An interesting similar bimodal shape of velocity distribution probability curves was found at different time after start of injection. What’s more, the scalar velocities gradually decrease as time goes on, but the direction of the velocities is messy due to the air entrainment. © 2018 Combustion Institute. All Rights Reserved.

关键词： Velocity

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Microstructure evolution and properties evaluation of a novel bondline based on Cu@Sn Preform during temperature treatment

Microstructure evolution and properties evaluation of a nove...

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第十九届国际电子封装技术会议(ICEPT 2018)

作者： Hongyan xu Ju Xu Puqi Ning Jianqiang Li Beijing Engineering Laboratory of Electrical Drive System & Power Electronic Device Packaging Techno State Key Laboratory of Multiphase Complex System Institute of Process EngineeringChinese Academy o

The microstructure and properties of Cu@Cu3Sn@Cu6Sn5three-dimensional network bonding interconnections based on Cu@Sn preform was *** through holes were observed at the bulk in as-reflowed,aged and temperature cycling *** evolution and phase transformation during thermal treatment test were studied,the shear strength of three-dimensional network bondlines for as-reflowed and thermal treating samples were compared and *** phase composition of as-reflowed interconnects was Cu/Cu6Sn5 and transformed to Cu/Cu3Sn/Cu6Sn5 after thermal *** failure modes of as-reflowed,aged and temperature cycling test were found in three-dimensional network structure *** average shear strength of the as-reflowed and the thermal treatment bonding interconnections are 49.5 Mpa and 24.9 Mpa,respectively,and crack initiated and propagated that perpendicular to substrate during the aging *** fracture surfaces of the temperature treatment bonding interconnections after shearing test were characterized in *** results show that the Cu3Sn phases in Cu@Cu3Sn@Cu6Sn5 three-dimensional network structure affected its strength and fracture *** Cu-rich substrate side at the fracture surfaces is always regular while the bulk phases are often accompanied by shear bands and dimples.

关键词： microstructure evolution as-reflowed aging test temperature cycling shearing strength

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Numerical analysis of the static performance of an annular aerostatic gas thrust bearing applied in the cryogenic turbo-expander of the EAST subsystem

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Plasma Science and Technology 2017年第2期19卷 115-122页

作者： Tianwei LAI Bao FU Shuangtao CHEN Qiyong ZHANG Yu HOU State Key Laboratory of Multiphase Flow in Power Engineering Xi＇an Jiaotong University Xi＇an 710049 People＇s Republic of China Institute of Plasma Physics Chinese Academy of Sciences Hefei 230031 People＇s Republic of China

The EAST superconducting tokamak, an advanced steady-state plasma physics experimental device, has been built at the Institute of Plasma Physics, Chinese Academy of Sciences. All the toroidal field magnets and poloidal field magnets, made of NbTi/Cu cable-in-conduit conductor, are cooled with forced flow supercritical helium at 3.8 K. The cryogenic system of EAST consists of a 2 kW/4 K helium refrigerator and a helium distribution system for the cooling of coils, structures, thermal shields, bus-lines, etc. The high-speed turbo-expander is an important refrigerating component of the EAST cryogenic system. In the turbo-expander, the axial supporting technology is critical for the smooth operation of the rotor bearing system. In this paper, hydrostatic thrust bearings are designed based on the axial load of the turbo-expander. Thereafter, a computational fluid dynamics-based numerical model of the aerostatic thrust bearing is set up to evaluate the bearing performance. Tilting effect on the pressure distribution and bearing load is analyzed for the thrust beating. Bearing load and stiffness are compared with different static supply pressures. The net force from the thrust bearings can be calculated for different combinations of bearing clearance and supply pressure.

关键词： EAST helium cryogenic system aerostatic thrust beating inclination bearing load

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Theoretical insights into the hydrophobicity of low index CeO2 surfaces

arXiv

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arXiv 2019年

作者： Fronzi, Marco N. Assadi, M. Hussein Hanaor, Dorian A.H. International Research Centre for Renewable Energy State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’anShaanxi710049 China 1-1 Namiki TsukubaIbaraki305-0044 Japan Chair of Advanced Ceramic Materials Institute for Materials Science and Technology Technische Universität Berlin Berlin10653 Germany

The hydrophobicity of CeO2 surfaces is examined here. Since wettability measurements are extremely sensitive to experimental conditions, we propose a general approach to obtain contact angles between water and ceria surfaces of specified orientations based on density functional calculations. In particular, we analysed the low index surfaces of this oxide to establish their interactions with water. According to our calculations, the CeO2 (111) surface was the most hydrophobic with a contact angle of Θ = 112.53° followed by (100) with Θ = 93.91°. The CeO2 (110) surface was, on the other hand, mildly hydrophilic with Θ = 64.09°. By combining our calculations with an atomistic thermodynamic approach, we found that the O terminated (100) surface was unstable unless fully covered by molecularly adsorbed water. We also identified a strong attractive interaction between the hydrogen atoms in water molecules and surface oxygen, which gives rise to the hydrophilic behaviour of (110) surfaces. Interestingly, the adsorption of water molecules on the lower-energy (111) surface stabilises oxygen vacancies, which are expected to enhance the catalytic activity of this plane. The findings here shed light on the origin of the intrinsic wettability of rare earth oxides in general and CeO2 surfaces in particular and also explain why CeO2 (100) surface properties are so critically dependant on applied synthesis methods. Copyright © 2019, The Authors. All rights reserved.

关键词： Density functional theory

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A High-Performance VS2-Modifed Separator for Lithium–Sulfur Batteries

A High-Performance VS2-Modifed Separator for Lithium–Sulfur...

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中国化学会第三届中国能源材料化学研讨会

作者： Jianan Wang Guorui Yang Shanshan Yi Ling Wang Silan Wang Wei Yan Shujiang Ding Department of Environmental Science and Engineering State Key Laboratory of Multiphase Flow in Power EngineeringXi'an Jiaotong University Department of Applied Chemistry School of ScienceState Key Laboratory for Electrical Insulation and Power EquipmentXi'an Jiaotong Univrsity School of Electronic and Information Engineering Xi'an Jiaotong University

Lithium–sulfur（Li-S） batteries are a promising candidate to couple renewable energy sources for green transportation and large-scale energy storage because of their relatively low cost and high theoretical specific capacity(1,675 mA h g).However,a major problem preventing the practical applications of Li-S batteries is the rapid capacity fading,predominantly due to the "shuttle effect" of polysulphides（LiPSs）.

关键词： A High-Performance VS2-Modifed Separator for Lithium Sulfur Batteries

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Theoretical analyses of the sub-grid quantities' effect on filtered eulerian drag force

arXiv

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arXiv 2018年

作者： Chen, Xiao Jiang, Ming Zhou, Qiang State Key Laboratory of Multiphase Flow in Power Engineering Xian Jiaotong University Xian710049 China School of Chemical Engineering and Technology Xian Jiaotong University Xian710049 China

An expression of the filtered Eulerian drag force is proposed based on the second order Taylor polynomial approximation of the microscopic Eulerian drag coefficient. Theoretical computations of the expression are performed at low Reynolds numbers based on an available microscopic drag model. It shows that four sub-grid quantities, i.e., the gas drift velocity, the solid drift velocity, the scalar variance of solid volume fraction and a third-order moment, defined as the covariance of squared solid volume fraction and the slip velocity, are significant for an accurate estimation of the filtered drag force at low Reynolds numbers. The gas drift velocity is nothing but the drift velocity defined by Parmentier et al. (AIChE Journal, 2012, 58 (4): 1084-1098), and in analogy to the gas drift velocity, we defines the solid drift velocity in the present work. The great relevance of the gas drift velocity and the scalar variance of solid volume fraction to the filtered drag force have been demonstrated through numerous correlative analyses of fully resolved simulations. Present theoretical analysis shows that the gas drift velocity term is primarily responsible for the drag reduction, whereas the solid drift velocity term is prone to attenuate this reduction, especially at moderate and high solid volume fractions. The scalar variance of solid volume fraction term is found to increase the filtered drag force in the full range of solid volume fractions. The third-order term has exactly the same coefficient with that of the variance term, and it mostly attains negative values with the trend to decrease the filtered drag force. Copyright © 2018, The Authors. All rights reserved.

关键词： Drag

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