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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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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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Time-domain study on the density wave oscillation of supercritical water in multiple parallel channel system 17

Time-domain study on the density wave oscillation of supercr...

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

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

A time-domain model suitable for the study on the density wave instability of supercritical water in multiple parallel channel system (the number of channels is more than 2) was established. The present model developed an iterative solution to solve the coupling among parallel channels. Then the program was verified by the experimental data obtained in open literature. After that, the model was used to study the effect of system pressure (23-28 MPa), inlet fluid temperature (240-350 °C), and adding perturbation in different channels on the density wave instability of supercritical water in multiple parallel channel system. It was found that when the same perturbation was added on some of channels at the initial time (the other working conditions were kept unchanged), the number of perturbation channels had almost no effect on the oscillation period and the system stability. The stability of the multiple channel system increased with the increasing in system pressure. It was also found that a critical value about the inlet fluid temperature, denoted by Tin-cr, existed, and when the inlet fluid temperature was lower than the critical value Tin-cr, the stability of the multiple channel system dropped with the increase of inlet fluid temperature, and that was improved when inlet fluid temperature was higher than Tin-cr. The critical value Tin-cr increased gradually with the increasing in the amount of parallel channels. Moreover, Tin-cr was lower than and near the pseudo-critical temperature of supercritical water, and almost had no changes with varying system pressure. © 2016 Association for Computing Machinery Inc. All Rights Reserved.

关键词： System stability

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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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Pore-scale simulation of gas-water two-phase flow in volcanic gas reservoir based on Volume of Fluid method

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Journal of Natural Gas Science and engineering 2022年 106卷

作者： Yongfei Yang Quan Xu Xinze Li Lianjin Zhang Xuemei Lan Junjie Wang Kai Zhang Hai Sun Lei Zhang Jun Yao Key Laboratory of Unconventional Oil & Gas Development (China University of Petroleum (East China)) Ministry of Education Qingdao 266580 PR China Research Center of Multiphase Flow in Porous Media School of Petroleum Engineering China University of Petroleum (East China) Qingdao 266580 PR China Sichuan Oil and Gas Mine of Southwest Oil and Gas Field Company of PetroChina Chengdu 629000 Sichuan China Exploration and Development Research Institute of PetroChina Southwest Oil & Gas Field Company Cheng du 610041 Sichuan China

Understanding the transport process of gas-water flow in volcanic gas reservoir is of key importance for natural gas production . However, there is still limited evidence on the precise influence of volcanic reservoir type, capillary number and wettability . We thus performed gas-water flow simulations (using Volume of Fluid method) at different capillary numbers under different wettability conditions directly on microcomputed tomography (μ-CT) images. The simulation results demonstrated that the eddy current in dead-end corners is the main mechanism for the formation of residual gas . The gas phase near the wall of fractured porous medium was mainly dominated by drag force, resulting in lower residual gas saturation. Moreover, it is generally believed that a low capillary number facilitates the displacement of residual gas in dead-end corners. However, we found that under high temperature (>100 °C) and high pressure (>100 MPa), less residual gas distributed in dead-end corners at higher capillary number. This showed that the conventional percolation law was unlikely to provide reliable predictions in fluid distribution under high temperature and high pressure . The wettability of rock affected the shape of displacement front. The water-gas flow dynamics under water-wet condition was piston like. However, fingering flow occurred under non-hydrophilic condition, and snap-off trapping was more likely to occur, resulting in higher residual gas saturation. This work provides fundamental data on the influence of pore structure, capillary number and wettability on gas-water flow and aids in the further advancements of improved nature gas recovery in volcanic reservoirs.

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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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Corrigendum to “Modified polyether gylcols supported ionic liquids for CO 2 adsorption and chemical fixation” [Mol. Catal. 492 (2020) 111008-111016]

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Molecular Catalysis 2020年 493卷

作者： Ying Liu Yan Song Jianhua Zhou Xiangping Zhang CAS Key Laboratory of Green Process and Engineering State Key Laboratory of Multiphase Complex System Beijing Key Laboratory of Ionic Liquids Clean Process Institute of Process Engineering Chinese Academy of Science Beijing 100190 China School of Chemistry and Pharmaceutical Engineering Qilu University of Technology Jinan 250353 China

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Gyrokinetic theory of turbulent acceleration and momentum conservation in tokamak plasmas

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Plasma Science and Technology 2018年第7期20卷 22-26页

作者： Lu WANG Shuitao PENG P H DIAMOND International Joint Research Laboratory of Magnetic Confinement Fusion and Plasma Physics State Key Laboratory of Advanced Electromagnetic Engineering and Technology School of Electrical and Electronic Engineering Huazhong University of Science and Technology Wuhan 430074 People's Republic of China Center for Momentum Transport and Flow Organization and Center for Astrophysics and Space Sciences University of California at San Diego La Jolla CA 92093-0424 United States of America

Understanding the generation of inmnsic rotation in tokamak plasmas is crucial for future fusion reactors such as ITER. We proposed a new mechanism named turbulent acceleration for the origin of the intrinsic parallel rotation based on gyrokinetic theory. The turbulent acceleration acts as a local source or sink of parallel rotation, i.e., volume force, which is different from the divergence of residual stress, i.e., surface force. However, the order of magnitude of turbulent acceleration can be comparable to that of the divergence of residual stress for electrostatic ion temperature gradient （ITG） turbulence. A possible theoretical explanation for the experimental observation of electron cyclotron heating induced decrease of co-current rotation was also proposed via comparison between the turbulent acceleration driven by 1TG turbulence and that driven by collisionless trapped electron mode turbulence. We also extended this theory to electromagnetic ITG turbulence and investigated the electromagnetic effects on intrinsic parallel rotation drive. Finally, we demonstrated that the presence of turbulent acceleration does not conflict with momentum conservation.

关键词： turbulent acceleration intrinsic rotation momentum conservation

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