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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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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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Numerical and experimental studies on the influences of flow field on the measurement accuracy of ultrasonic water meters

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Measurement: Sensors 2021年 18卷

作者： Jieqiang Ji Jianying Zheng GuoFu Chen Xiaojie Wu NingNing Zhang Yan Fang Leming Cheng Zhejiang Province Institute of Metrology Hangzhou 310018 China National Centre of Quality Supervision and Testing on Liquid Flow Measuring Instruments Hangzhou 310018 China State Key Laboratory of Clean Energy Utilization Institute for Thermal Power Engineering Zhejiang University Hangzhou 310027 China

CFD modelling and experiments are carried out to study the influences of flow field on the measurement accuracy of ultrasonic water meters. The swirl generator and flow disturber are selected to change the flow field distributions inside the pipe. The calculation results show that the installation of left-handed swirl generator induces a specific flow pattern of the fluid inside the pipe, while the installation of flow disturber leads to the distortion of the axial velocity distributions. The critical distance of the fluid reaching the steady flow is 10D for left-handed swirl generator and flow disturber. In the experiment part, six different ultrasonic water meters are selected for the intrinsic errors tests. The results show that the installations of swirl generator and flow disturber induce the intrinsic errors shift to negative values. Compared with the flow disturber, the swirl generator has greater impact on the measurement accuracy.

关键词： flow field Disturbance generators Ultrasonic water meters CFD

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Transient Evaporation Simulation of the Forced Circulation Hot Water Boiler

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IOP Conference Series: Materials Science and engineering 2020年第1期721卷

作者： Junjie Bao Di Wang Feng Liu Zhiguo Qu Hongtao Xu Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering School of Energy and Power Engineering University of Shanghai for Science and Technology Shanghai 200093 China Shanghai Institute of Special Equipment Inspection and Technical Research Shanghai 200062 China China Special Equipment Inspection and Research Institute Beijing 10013 China Moe Key Laboratory of Thermo-Fluid Science and Engineering Xi'an Jiaotong University Xi'an 710049 China

This paper presents a comprehensive analysis of the water vaporization in a hot water boiler system. The Computational Fluid Dynamics (CFD) technology was adopted to simulate the transient water evaporation in the boiler termed as DZL14-1.25/115/70-AⅡ under the assumption of extreme conditions such as the water pump failure. The results indicated that the average pressure in the pipeline increased from 0.57Mpa to 0.66Mpa (the setting pressure of the safety valve) within 1050s. The pressure increased rapidly with the time increase. The average temperature of hot water changed linearly with time, and the internal thermal deviation of the hot water pipeline in the boiler decreased with time. The internal vaporization phenomenon of the hot water boiler became significant under the extreme condition. The steam flowed upward and accumulated in the upper part of the boiler shell. At 1050s, the vapor volume fraction in the hot boiler was 1.05%, which indicated that the safety valve above the stream shell need to be opened in time after 1050s to ensure the safety of the boiler.

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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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Molecular Dynamics Simulation of Microscale Phase Transfer

Molecular Dynamics Simulation of Microscale Phase Transfer

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2018 7th International Conference on Advanced Materials and Computer Science(ICAMCS 2018)

作者： Zhang Longyan Xu Jinliang Lei Junpeng Beijing Key Laboratory of Multiphase Flow and Heat Transfer for Low Grade Energy North China Electric Power University

Microheat pipes occupy smaller volume than traditional heat sinks,and can be directly fitted with electronic components,which can ensure good heat dissipation *** the size of liquid film in micro heat pipe is only a few nanometers,it is difficult to estimate the time of phase transformation equilibrium by experimental method,and the existing dangerous devices can not carry out phase transformation heat transfer experiments under micro-scale ***,the simulation of liquid phase transformation under micro-scale conditions by molecular dynamics method can achieve good experimental *** paper will discuss the content of this aspect.

关键词： phase change heat transfer molecular dynamics microscale

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Pore-scale simulation of remaining oil distribution in 3D porous media affected by wettability and capillarity based on volume of fluid method

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International Journal of multiphase flow 2021年 143卷

作者： Yongfei Yang Shaobin Cai Jun Yao Junjie Zhong Kai Zhang Wenhui Song Lei Zhang Hai Sun Vadim Lisitsa 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 Institute of Petroleum Geology and Geophysics SB RAS Novosibirsk 630090 Russia

Characterizing the trapped phase in porous media is essential for many engineering applications, such as enhanced oil recovery, nuclear storage, and geological sequestration of CO 2 . This study aims to study the distribution, evolution, and influencing factors of the remaining oil in the process of water flooding at the pore scale. The single-connected pore space model was established by reconstructing the real micron CT scanned images of carbonate rocks. The VOF (volume of fluid) method using FSF (filtered surface force) formulation was adopted on OpenFOAM platform to simulate the oil-water two-phase flow process at the pore scale. Different wettability and capillary number were considered in the model. The accuracy of the model was proved by comparing with previous experimental results. The results showed that in the process of water flooding, the complex pore structure would lead to the generation of remaining oil, and the phase circulation phenomenon can be observed in the remaining oil and presents two distribution forms: co-current driven flow and lid-cavity driven flow. It also revealed that the phase recirculation increases the viscous dissipation. Further research also showed that the two forms of recirculation could be transferred by changing the wettability and that a higher capillary number was more beneficial for reducing the remaining oil saturation.

关键词： Pore-scale modeling VOF Remaining oil Phase recirculation Capillary number Wettability

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

arXiv

引用

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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Transport equation for the drift velocity in predicting the filtered Eulerian drag force: A theoretical development

arXiv

引用

arXiv 2018年

作者： Chen, Xiao Jiang, Ming Zhou, Qiang School of Chemical Engineering and Technology Xi'an Jiaotong University Xi'an710049 China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

The drift velocity has been proven to have significant relevance to the filtered Eulerian drag force by numerous correlative analyses of fully resolved simulations. It is a sub-grid quantity defined as the difference between the filtered gas velocity seen by the particle phase and the resolved filtered gas velocity. In literature, it is shown that various algebraic models for the drift velocity fail to give entirely satisfactory prediction of the filtered drag force. Unlike previous works, we theoretically derived the transport equation for the drift velocity from the standard two-fluid model (TFM) equations without any additional assumptions. The new approach, though requires additional closures for the new unresolved terms, is believed to have the potential to improve the precision of the estimation of this sub-grid quantity and hence give better prediction of the filtered drag force for gas-solid fluidization problems. Copyright © 2018, The Authors. All rights reserved.

关键词： Drag

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