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Void fraction measurement and calculation model of vertical upward co-current air-water slug flow

Chinese Journal of Chemical engineering 2022年第11期51卷 178-198页

作者： Teng Wang Miao Gui Jinle Zhao Qincheng Bi Tao Zhang State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong UniversityXi’an 710049China School of Nuclear Science and Technology Xi’an Jiaotong UniversityXi’an 710049China

The focus of this paper is on the measurement and calculation model of void fraction for the vertical upward co-current air-water slug flow in a circular tube of 15 mm inner diameter. High-speed photography and optical probes were utilized, with water superficial velocity ranging from 0.089 to 0.65 m·s^(-1)and gas superficial velocity ranging from 0.049 to 0.65 m·s^(-1). A new void fraction model based on the local parameters was proposed, disposing the slug flow as a combination of Taylor bubbles and liquid slugs. In the Taylor bubble region, correction factors of liquid film thickness Cδand nose shape CZ*were proposed to calculate aTB. In the liquid slug region, the radial void fraction distribution profiles were obtained to calculate aLS, by employing the image processing technique based on supervised machine learning. Results showed that the void fraction proportion in Taylor bubbles occupied crucial contribution to the overall void fraction. Multiple types of void fraction predictive correlations were assessed using the present data. The performance of the Schmidt model was optimal, while some models for slug flow performed not outstanding. Additionally, a predictive correlation was correlated between the central local void fraction and the cross-sectional averaged void fraction, as a straightforward form of the void fraction calculation model. The predictive correlation showed a good agreement with the present experimental data, as well as the data of Olerni et al., indicating that the new model was effective and applicable under the slug flow conditions.

关键词： Slug flow Gas-liquid flow Void fraction Measurement Optical probe Model

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Data-Driven Surrogate Model for the Dynamic Characteristics of Supercritical Units

Data-Driven Surrogate Model for the Dynamic Characteristics ...

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2024 Boao New power System International Forum - power System and New Energy Technology Innovation Forum, NPSIF 2024

作者： Dong, Shuai Zheng, An Jiang, Junyao Gao, Wei Liu, Ming Huaneng Yimin Coal-Power Co. Ltd. Hulunbuir021130 China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

ISBN: (纸本)9798331504557

Coal-fired power generation units are characterized by large inertia, strong coupling, and high delay, making dynamic characteristic modeling inherently complex and computationally intensive. To address this, this paper utilizes GSE software to explore the dynamic characteristics of supercritical units. Data-driven approaches are then employed to develop surrogate model for these dynamics, comparing neural networks and support vector regression methods in the process. The study indicates that the surrogate model achieves a relative prediction error of less than 1% for live steam temperature, reheater steam outlet temperature, and power output. For live steam pressure and reheater steam outlet pressure, the model maintains a relative error within 10%. © 2024 IEEE.

关键词： Support vector regression

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Numerical simulation on the frosting and heat transfer characteristics of plate-fin heat exchanger considering confinement effect

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Energy Storage and Saving 2022年第3期1卷 136-147页

作者： Xiaoling Yang Xue Liu Xiaojun Dong Yang Meng Yu Hou Tianwei Lai State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong UniversityXi’an710049China

In refrigerating industry,frost commonly deposits on the confined cold surfaces of heat exchangers,which affects the heat transfer *** the confined flow path of the heat exchanger,the frosting at downstream is affected by the parameters from the *** this study,a numerical model considering the confinement effect has been proposed to predict frosting characteristics in plate-fin heat ***-diffusion equations for humid air and empirical correlations for local frost density are employed in the numerical *** behavior and heat transfer in the confined channel are investigated with different humid air parameters and cold surface *** results indicate that frost thickness in the confined channel is thicker than that in open space under the same inlet *** frost layer is thicker and fluffier along the confined *** addition,the air temperature difference between inlet and outlet of the confined channel enlarges with *** the same average temperature of upper and lower surfaces,the heat and mass transfer of frosting are enhanced with diminishing temperature difference of upper and lower *** such condition,frosting is mainly influenced by the cold surface with the lower temperature.

关键词： Heat exchanger Frosting Confined channel Numerical simulation Heat transfer

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Multi-objective optimization of 200 kW air centripetal turbine based on artificial neural networks

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International Journal of Advanced Nuclear Reactor Design and Technology 2025年第2期7卷 70-80页

作者： Wang, Zideng Zhang, Yan Leng, Yuyang Lai, Jiabao Wang, Zhenzhen Chen, Weixiong State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

The air-Brayton cycle has the characteristics of safety and high efficiency, which can be used as an energy conversion system for mobile small reactors. The air turbine is one of the key components in the cycle system, and improving its performance is of great significance. In this paper, an artificial neural network model combined with a genetic algorithm was used to optimize the rotor of an air centrifugal turbine with axial thrust and efficiency as the objective. The results show that the artificial neural network model can fit the CFD numerical simulation results well, with a coefficient of determination larger than 0.97. Then, after optimizing the artificial neural network model with a genetic algorithm, the total -total efficiency of the air centrifugal turbine was improved by 1.479 %, while the axial thrust was reduced by 1.07 %. © 2025 Xi'an Jiaotong University

关键词： Genetic algorithms

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Bubble oscillation and effects of dynamic behaviors on forces and mass transfer in photoelectrochemical water splitting

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Physical Review Fluids 2024年第11期9卷 114305-114305页

作者： Yonglu She Qiang Xu Tengfei Nie Xinyi Luo Mengsha Wang Xingmiao Ye Dengwei Jing State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China

The evolution and coverage of bubbles resulting from gas evolution at the reaction interface significantly impact mass transfer and the flow field within the photoelectrochemical water splitting system, posing a significant obstacle to overcoming the efficiency bottleneck of photoelectrochemical water splitting. In situ bubble observation can be realized via a coupled experimental system combining electrochemical measurements and high-speed imaging. The results indicate that bubble growth behavior correlates with system temperature and operating voltage; that is, the bubbles grow in an oscillating state on the electrode surface at the low operating voltage and high system temperature. Besides, the deviation amplitude of oscillating bubbles increases with system temperature yet decreases with operating voltage. The results indicate that the time coefficient of the growing bubble decreases, while the growth rate and gas evolution efficiency of the bubble increase with the increase of oscillating amplitude in the horizontal direction. The study of dynamic behaviors between the oscillating bubble and the contacted electrode reveals that the bubble oscillation is characterized by the periodic contraction and extension of the triple line. The mass transfer model of concentration boundary layer and the force model of oscillating bubble are constructed based on the interaction between the bubbles and the surrounding flow field. The mass transfer model has considered the microconvection caused by single-phase natural convection, gas-liquid interface expansion, and the oscillation of bubbles. Then through the force balance model, the solutal Marangoni force is found to gradually increase as the contact line extends outward.

关键词： Bubble dynamics Contact line dynamics Marangoni convection Microbubbles multiphase flows

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Effect of H2/CO ratio on non-isothermal reduction behavior and kinetics of vanadium titanomagnetite

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International Journal of Hydrogen Energy 2025年 139卷 69-79页

作者： Shi, Jian Xu, Qiang Lu, Xuyang Cao, Zeshui Kang, Haopeng Chen, Bin Guo, Liejin State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

Hydrogen-based direct reduction of vanadium titanomagnetite is crucial for developing clean and efficient hydrogen metallurgy technology, while existing studies lack systematic research on the impact of H2/CO ratios on the reduction of vanadium titanomagnetite under non-isothermal conditions. This study examines the influence of varying H2/CO ratios on the non-isothermal reduction behavior and kinetics of vanadium titanomagnetite through thermogravimetric analysis (TGA). The results of thermogravimetric experiments show that raising the H2 ratio can significantly lower the initial reduction temperature and accelerate the reduction rate. When H2/(H2+CO) rises from 0 to 1, the initial reduction temperature can be lowered by around 150 °C at a heating rate of 10 °C/min. As the heating rate decreases, the reduction curve shifts to the low-temperature region, and the reduction reaction becomes easier to proceed. The vanadium titanomagnetite reduction activation energy was calculated using the Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) model-free kinetic methods, and the activation energy of vanadium titanomagnetite reduction under pure CO atmosphere (H2/(H2 + CO) = 0) was the highest (120.74 kJ/mol by FWO and 107.82 kJ/mol by KAS). As the H2/(H2+CO) ratio increases, the activation energy continuously decreases, effectively reducing the reduction energy barrier of vanadium titanomagnetite. In contrast to an environment of pure CO, the activation energy for the reduction of vanadium titanomagnetite was reduced by 25.47 % (FWO method) or 28.73 % (KAS method) in a pure H2 atmosphere (H2/(H2 + CO) = 1), indicating that an elevated H2 ratio significantly enhanced the reduction of vanadium titanomagnetite. XRD analysis showed that, after the non-isothermal reduction, unreduced iron oxide was still present within the vanadium titanomagnetite under a pure CO atmosphere, while the final reduction product was mainly metallic iron under different H2/CO ratios. Increas

关键词： Activation energy

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Study on startup characteristic of a supercritical carbon dioxide Brayton cycle coupled with heat pipe cooled reactor 20

Study on startup characteristic of a supercritical carbon di...

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20th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2023

作者： Wang, Zheng Zhang, Minghui Xu, Shihao Gou, Junli Shan, Jianqiang State Key Laboratory of Multiphase Flow in Power Engineering School of Nuclear Science and Technology Xi'an Jiaotong University Shaanxi Xi'an China

ISBN: (纸本)9780894487934

Nuclear energy is a viable choice for Unmanned Undersea Vehicles (UUVs) due to its high density and long operation life. However, traditional PWRs aren't suited to underwater working environments. To provide a safe and reliable power source for UUV, a new nuclear power plant coupled with the supercritical CO2 Brayton cycle and heat pipe cooled reactor is proposed. This provides the advantages of high reliability, high safety and high expansion ability. In this work, a simulation code for the new nuclear power plant is developed, which includes a reactor kinetics model, a core heat conduction model, a two-dimensional heat pipe network model, and a closeCO2 Brayton cycle model. In order to verify the accuracy of the model, the date of the experiment is compared with the model. And the design value of the new nuclear power plant has been modeled by this code. Meanwhile, the control strategies for start-up of the new nuclear power plant are proposed, including core startup, heat pipe startup and supercritical carbon dioxide Brayton loop startup. By utilizing the control strategies, the code has researched the operational characteristics of the start-up of heat pipe-cooled reactors. The development of this code provides a reference for the new nuclear power plant. © 2023 Proceedings of the 20th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2023. All rights reserved.

关键词： Brayton cycle

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Performance Analysis of Low GWP Refrigerants R1234yf and R448A in a Small High and Low-temperature Test Equipment

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Recent Patents on Mechanical engineering 2022年第3期15卷 277-284页

作者： Liqiang, Zhou Zhang, Hua Zilong, Wang Wenjing, Gao School of Energy and Power University of Shanghai for Science and Technology Shanghai200093 China Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering Shanghai200093 China

Aim: The article presents an analysis of the feasibility of R1234yf and R448A, two new low GWP refrigerants, as alternatives to R404A in the refrigeration system of small high and low-temperature test equipment. Methods: The physical properties of R448A and R404A are similar. Compared with R404A, the GWP of R1234yf and R448A reduced by 99.9% and 67.7%, respectively. The analysis is based on an experimental comparison of R404A with R448A and R1234yf, comparing the compressor discharge tempera-ture, COP, cooling capacity, and the cooling rate of three refrigeration systems at different ambient temperatures. Results: The experimental results show that the cooling capacity of R448A is better than R404A at a higher condensing temperature. Conclusion: When the charging volume is 230g, and the ambient temperature is 25°C, the COP of the R448A system is increased by about 24.63% compared with the R404A system. © 2022 Bentham Science Publishers.

关键词： Refrigerants

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A universal charge-compensating strategy for high-energy-density pseudocapacitors

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Journal of Energy Chemistry 2023年第3期78卷 333-339,I0010页

作者： Baoyi Yin Jiaqi Zhang Yuanhui Su Yu Huan Liang Hao Chen Wang Xun Hu Tao Wei School of Material Science and Engineering University of Jinan336 Nanxinzhuang West RoadJinan 250022ShandongChina School of Microelectronics Dalian University of TechnologyDalian 116024LiaoningChina Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering School of Energy and Power EngineeringUniversity of Shanghai for Science and TechnologyShanghai 200093China State Key Laboratory of ASIC and Systems School of MicroelectronicsFudan UniversityShanghai 200433China

For pseudocapacitive electrode materials(PseEMs),despite much progress having been made in achieving both high power density and high energy density,a general strategy to guide the enhancement of intrinsic capacitive properties of PseEMs remains ***,we demonstrate a universal chargecompensating strategy to improve the charge-storage capability of PseEMs intrinsically:ⅰ) in the electrolyte with anion as charge carriers(such as OH-),reducing the multivalent cations of PseEMs into lower valences could create more reversible low-to-high valence redox cou ples to promote the intercalation of the anions;ⅱ) in the electrolytes with cation as charge carriers(such as H^(+),Li^(+),Na^(+)),oxidizing the multivalent cations of PseEMs into higher valences could introduce more reversible high-to-low valence redox couples to promote the intercalation of the *** we demonstrated that the improved intrinsic charge-storage capability for PseEMs originates from the increased Faradaic charge storage sites.

关键词： Supercapacitors Universal charge-compensating strategy Changed valence state Increased Faradaic charge storage sites

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Experimental investigation on separation characteristics of axial cyclone separator

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Science China(Technological Sciences) 2023年第11期66卷 3231-3244页

作者： WANG JinZhi WANG YeChun HAN JinZai XU Qiang XIE XiangDong PAN YingXiu GUO LieJin State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong UniversityXi’an 710049China Xinjin Weihua Institute of Clean Energy Research Foshan 528216China Aero Engine Corporation of China(AECC)Shenyang Engine Research Institute Shenyang 110015China

Axial cyclone separator has been widely applied in chemical production as an efficient gas-liquid separation *** this study,a new axial cyclone separator with integrated swirler and exhaust pipe is designed to achieve the development goal of compact structure for advanced engine,and the distribution characteristics of swirling flow patterns as well as the variation in separation characteristics are investigated under slug flow *** on flow visualizations and fluctuation characteristics of pressure signals,three typical flow patterns,namely,slug flow,swirling intermittent flow,and swirling annular flow,in the horizontal swirling separation flow are *** is investigated how the inlet conditions affect the separation characteristic *** separation purity and extreme points of the air separation efficiency are independent of the inlet liquid flow *** separation pressure drop is quadratically related to the inlet air flow *** on the drift-flux model and other methods,the prediction methods for the air separation efficiency and pressure drop are proposed,and the prediction accuracy is within±20%,which may provide instructions for the practical application of axial cyclone separator.

关键词： axial cyclone separation gas-liquid two-phase flow flow pattern in the swirling flow separation characteristics

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