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Numerical investigations on cluster characteristics in the supercritical water circulating fluidized bed riser

Particuology 2024年第11期94卷 281-293页

作者： Kenan Xi Runqing Li Xiazhi Li Mei Li Xiudong Xu Yu Zhang Hao Wang Youjun Lu Northwest Institute of Nuclear Technology Xi'an710024China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an710049China Xi'an Institute of Applied Optics Xi'an710065China

There are currently no reports about clusters in the supercritical water circulating fluidized bed(SCWCFB).Simulations were conducted to investigate the numbers,diameters,aspect ratios,circularity,and orientation angles of cluster in the riser of SCWCFB via two-fluid model across different flow velocities,solid circulation rates,pressures,and *** results show that cluster numbers are mainly between 10 and 80 per *** are more at the bottom but less at the top,and more near the wall but less at the *** diameters are mainly between 0.2 and 0.5 times the bed *** are large at the bottom but small at the top,and large at the center but small near the *** aspect ratios are mainly between 0 and 1,indicating that most clusters have shorter width than their ***-like clusters are more likely to appear near the walls,and clusters at the center of the riser are more likely to be *** circularity is mainly between 0.2 and 0.4,suggesting that the shapes of clusters are far from the *** absolute values of cluster orientation angles are mainly between 75°and 90°,indicating that most clusters move in the vertical *** fluid velocities may facilitate cluster coalescence.

关键词： Supercritical water Circulating fluidized bed Cluster Two-fluid model Riser

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Effect of partially premixed and hydrogen addition on lean burn natural gas direct injection combustion 7

Effect of partially premixed and hydrogen addition on lean b...

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7th Asia-Pacific Conference on Combustion, ASPACC 2009

作者： Wang, J.H. Huang, Z.H. Zheng, J.J. Miao, H.Y. State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

Effect of partially premixed and hydrogen addition on lean burn natural gas direct injection combustion was studied experimentally using a constant volume vessel. Flame propagating photos and pressure derived combustion parameters were analyzed at different premixed ratios (from 0% to 80%) and hydrogen fractions (from 0% to 40%) at overall equivalence ratio of 0.6 and 0.8, respectively. The results showed that the flame kernel was concentrated to the spark position with the increase of premixed ratio and/or hydrogen fraction. The flame propagating speed was increased with hydrogen addition to natural gas. The stable spark ignition of lean burn natural gas was realized with the combination of partially premixed direct injection combustion and hydrogen addition. Both the initial and main combustion durations were increased with the increase of premixed ratio, while they showed the decreasing trend with hydrogen addition to natural gas. Partially premixed direct injection combustion combing with hydrogen addition can achieve the stable spark ignition and fast combustion rate at the lean mixture condition. © 2009 Combustion Institute. All rights reserved.

关键词： Natural gas

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A Least-Squares Solution to Nonlinear Steady-state Multi-Dimensional IHCP

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Journal of Thermal Science 1996年第1期5卷 39-41页

作者： Bai Bofeng Guo Liejin Chen Xuejun (state key Lab of multiphase flow in power engineering,Xi’an Jiao Tong University,Xi’an 710049,China) State Key Lab of Multiphase Flow in Power Engineering Xi’an Jiao Tong University Xi’an China

In this paper,the least-squares method is used to solve the Inverse Heat Conduction Problem(IHCP)to determine the space-wise variation of the unknown boundary condition on the inner surface of a helically coiled tube with fluid flow inside,electrical heating and insulation *** sensitivity coefficient is analyzed to give a rational distribution of the thermocouples. The results demonstrate that the method effectively extracts information about the unknown boundary condition for the heat conduction problem from the experimental measurements. The results also show that the least-squares method converges very quickly.

关键词： helically coiled tube least-squares method IHCP.

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Evaluation of droplet drag force model on spray and atomization behaviours of R134a flashing spray 14

Evaluation of droplet drag force model on spray and atomizat...

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14th International Conference on Liquid Atomization and Spray Systems, ICLASS 2018

作者： Zhou, Zhi-Fu Lu, Guan-Yu Zhang, Lu Chen, Bin State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

Flashing spray is of great importance in a variety of engineering fields, which occurs as the pressurized liquid is released into a low-pressure environment below its saturation pressure. This paper conducts a systematically numerical study on the spray and thermal characteristics of R134a flashing spray with high volatility and low saturation temperature, using a modified sprayFoam solver in the open source tool OpenFOAM-2.4.0. key physics involved in the complex process, including droplet flash boiling, evaporation, droplet transport, breakup, heat transfer and interaction between droplet and gas phases are taken into consideration. The emphasis is put on the droplet drag force model and nozzle diameter on flashing spray including spray morphology, droplet diameter, velocity and temperature. The result indicates that most of the drag force models have little effect on droplet diameter, velocity and temperature distributions in flashing spray, except the Khan-Richardson (K-R) model. The K-R model predicts lower temperature, higher velocity and larger size of droplet, compared to other models. The nozzle diameter greatly affects R134a spray morphology and tip penetration, that smaller diameter contributes to a larger radial expansion at the near nozzle region while leading to a much smaller penetration distance. This research give a useful guidance that how people choose the appropriate drag force model for simulation of flashing spray. © 2018 Solar Turbines Incorporated.

关键词： Morphology

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Enhancing thin film boiling heat transfer through electric field and surface Macro-Structure Synergy: Insights from bubble dynamics modulation

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International Journal of Heat and Mass Transfer 2025年 249卷

作者： Changqiu He Jiameng Tian Yiqi Chen Yuchen Zhu Xin Liu Hai Wang Zhentao Wang Benan Cai Changqing Wang Junfeng Wang Zhifu Zhou Bin Chen School of Energy and Power Engineering Jiangsu University Zhenjiang 212013 PR China Laboratory of Thermo-fluid Science and Nuclear Engineering School of Energy and Power Engineering Northeast Electric Power University Jilin 132012 PR China National Key Laboratory of Marine Engine Science and Technology Shanghai 201108 PR China School of Energy and Power Engineering Chongqing University Chongqing 400044 PR China State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an 710049 PR China

Improving boiling heat transfer in thin liquid films by employing external electrical fields and macro-structured surfaces presents promising for tackling the growing difficulties related to high-heat-flux thermal management in electronic devices. In this study, six distinct macro-structured surfaces are designed and fabricated to gain insight into how liquid film thickness, structural parameters, and applied voltage affect the efficiency of boiling heat transfer with ethanol as the coolant. High-speed imaging and precise heat transfer measurements are employed to characterize the boiling performance, providing insights into the underlying fundamentals driving the observed enhancements. Results reveal that applying a 4-kV voltage increases departure frequency of bubble by 86 % and a 28 % reduction in diameter, causing a 20 % improvement in critical heat flux (CHF). CHF is positively correlated with liquid film thickness and pin height, but negatively with pin spacing, achieving a 139 % increase under optimal conditions. Liquid film thickness was found to have the most significant impact on CHF, followed by pin spacing and applied voltage. By simplifying the void fraction equation, a new CHF correlation is proposed that introduces a dimensionless characteristic length, representing the relative effects between bubble size and film thickness, while accounting for the synergy between the electric field and surface macro-structure.

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Experimental investigation on flash evaporation related to pipe leakage

Experimental investigation on flash evaporation related to p...

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作者： Cai, Benan Zhang, Qi Weng, Yu Gu, Hongfang Wang, Haijun State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

Pipelines such as the surge line and main pipe are easily subjected to thermal stratification and thermal fatigue as a result of the nonuniform temperature distribution in the nuclear power plants. When the surge line or main pipe subjected to thermal stratification and thermal fatigue keeps operating for long time, the pipe leakage may happen due to the existence of pipeline crack. When the fluids with high temperature and pressure leak in the crack, the water will evaporate quickly, which means this process belongs to spray flash evaporation process. The flash evaporation related to pipe leak was experimentally studied in the paper. The experiment was carried out under high temperature and high pressure with low spray rate. The temperature and relative humidity (T&H) variations over time were monitored in the experiment with installing T&H detectors. The T&H variations at different measurement positions and with different spray rates were analyzed, respectively. In addition, the effect of the dimensionless parameters including the Weber number and Jakob number was also investigated. Results indicated that the response speed increased with the increase of the spray flow rate. Higher Weber number and higher Jakob number led to higher evaporation rate. The slight pipe leakage can be predicted by using the (T&H) in the hazardous areas. Copyright © 2020 by ASME

关键词： Nuclear fuels

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Measurements of premixed laminar burning velocities and Markstein lengths for isooctane-air-N2 mixtures 7

Measurements of premixed laminar burning velocities and Mark...

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7th Asia-Pacific Conference on Combustion, ASPACC 2009

作者： Ran, F. Wang, X.B. Zhu, R.J. Zhang, Z.Y. Xiang, J. Huang, Z.H. State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

Experiments on the laminar burning velocities and Markstein lengths for the isooctane-air-N2 blends using a constant volume combustion chamber and a high-speed schlieren photography system have been performed under different equivalence ratios, initial pressures and temperatures, and dilution ratios to determine the effect of these parameters on the laminar burning velocities. The results suggest that an decrease in initial pressure or dilution ratio and an increase in initial temperature lead to an increase in the laminar burning velocity;an increase in initial pressure and initial temperature lead to a decrease in the Markstein length. © 2009 Combustion Institute. All rights reserved.

关键词： Velocity

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Shock Tube Experimental and Modeling Study of MTHF Ignition Characteristics at High Temperatures

Shock Tube Experimental and Modeling Study of MTHF Ignition ...

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JSAE/SAE 2015 International powertrains, Fuels and Lubricants Meeting, FFL 2015

作者： Wang, Jingshan Wang, Xibin Fan, Xiangshan Yang, Kangkang State Key Laboratory of Multiphase Flow in Power Engineering Xi'An Jiaotong University Xi'an710049 China

High temperature ignition delays of 2-methyltetrahydrofuran(MTHF) were measured behind a reflected shock tube under conditions of pressures from 1.2 to 10 atm, temperatures from 1050 to 1800 K, equivalence ratios from 0.5 to 2.0, and fuel concentrations of 0.25%, 0.5% and 1.0% diluted in argon. Results showed that the ignition delay of MTHF decreases with the increase of pressure, temperature, fuel concentration and increases with equivalence ratio. The trend is less notable at higher fuel concentrations and equivalence ratios. Based on sensitivity and pathway analysis at pressure of 10 atm, fuel concentration of 1.0%, equivalence ratio of 1.0 and temperature of 1550K, it was found that the most sensitive reaction of MTHF at high temperature is H+O2=O+OH, and the main consumption way is fuel decomposition instead of H-abstraction. Finally, ignition delays of MTHF were compared with THF both on experimental and kinetic analyses, and MTHF has lower ignition delays than THF. To our knowledge, it is the first time to present the ignition delays of MTHF under these conditions. © 2015 SAE Japan.

关键词： Shock tubes

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Large eddy simulation on the respective roles of integral length scale and turbulence intensity on turbulent premixed combustion 12

Large eddy simulation on the respective roles of integral le...

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12th Asia-Pacific Conference on Combustion, ASPACC 2019

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

The effects of integral length scale () and turbulence intensity (? ) on premixed combustion are studied using large eddy simulation. Three groups of lean CH4/air flames are carried out using the thickened flame model combined with a two-step reduced chemical mechanism. Two groups vary at constant ? and the other group increases ? from low to high while keeping unchanged. One of the cases is validated to available experimental data, showing good agreement for the flame-brush structure. The numerical results show that the increase in or ? leads to a decrease in flame-brush height and an increase in flame-brush thickness and volume. The turbulent flame speed () will be enhanced by these two factors within the scope of our study. All the flame-brush structure data, including height, thickness, volume and area, and also collapse onto a single line when the turbulent Reynolds number is used as abscissa. The probability density function distributions of filtered thickened flame front curvature show that will be increased by and ? through increasing the amount of large-scale and small-scale wrinkling structures respectively. © Asia-Pacific Conference on Combustion, ASPACC *** right reserved.

关键词： Large eddy simulation

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Multi-Objective optimization of oil–gas cyclone separators considering liquid storage in the tank bottom

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Separation and Purification Technology 2025年

作者： Lingzi Wang Wei Du Ruiyi Liu Jianmei Feng Xueyuan Peng Feng Cao School of Energy and Power Engineering Xi’an Jiaotong University Xi’an Shaanxi 710049 China The First Gas Plant of PetroChina Changqing Oilfield Company Jingbian Shaanxi 718500 China State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an 710049 China

As an efficient separation device, the gas–liquid cyclone separator has been widely used in oil injection compressor systems. It can effectively reduce the oil content in the high-pressure airflow, directly affecting the fuel consumption, operating efficiency, and exhaust quality parameters of compressors, making it crucial to enhance the separator’s performance. Given the critical role of geometric configuration in determining cyclone separator efficiency, this study comprehensively considers several influencing factors including the structure parameters. Taguchi method and analysis of variance (ANOVA) were used to quantify the contribution of three factors to the performance percentage of the separator, and the dual-objective optimization of the efficiency and pressure drop of the separator was carried out with the grey correlation analysis method. In the simulation calculation, this paper employs the DPM-to-VOF method coupled with the Euler wall film (EWF) to simulate the oil droplet particle separation process, featuring model transformation capabilities under specified conditions. The investigation culminates in the development of a parametric-performance prediction model and establishes optimal operational parameters for cyclone separators: the inlet velocity ( v in ) should be set at 24.49 m/s, the height of the inner cylinder of the separator tank (H t ) should be 1.2 times the diameter, and the buffer height between the inner cylinder and the liquid surface (H m ) should be 0.9 times the diameter.

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