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Calculation of the Critical Speed and Stability Analysis of Cryogenic Turboexpanders with Different Structures

Plasma Science and Technology 2012年第10期14卷 919-926页

作者：陈双涛赵红利马斌侯予 State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University

A modularized code based on the Finite Element QZ （FEQZ） method is developed, for a better estimate of the critical speed and a more convenient method of rotor-dynamic stability analysis for a gas bearing high speed turboexpander rotor system with actual structure and application of a cryogenic turboexpander. This code is then validated by the experimental data of a gas bearing turboexpander, with a rotor diameter of 25 mm and a rated speed of 106,400 rpm. With this code, four rotors with different structures, available to the turboexpander, are parametrically analyzed by the available speed range, vibration modes and logarithmic attenuation rate. The results suggest that the rotor with a structure of two thrust collars on the system exhibits a better performance in the designed conditions.

关键词： critical speed gas bearing cryogenic turboexpander

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Experimental Investigation on Critical Heat Flux for Water flowing in a Vertical Uniformly Heated Rifled Tube under Near-critical Pressures

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Journal of Thermal Science 2018年第6期27卷 527-540页

作者： XIE Haiyan YANG Dong ZHAO Yunjie JIANG Huiqing QU Mofeng State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University

This study experimentally investigated the critical heat flux(CHF) of departure from nucleate boiling(DNB) of water flowing under near-critical pressures in a 2 m-long vertical upward rifled tube with the size of Φ35 × 5.67 mm. Operating conditions included pressures of 18–21 MPa, mass fluxes of 475–1000 kg·m^(-2)·s^(-1), inlet subcooling temperatures of 3–5°C, and wall heat fluxes of 40–960 kW·m^(-2). Tube wall temperature distribution and heat transfer performance in different test conditions were obtained. The effects of the operating parameters on CHF were analyzed. Four heat transfer coefficient correlations were evaluated against our experimental data for further investigation of the two-phase heat transfer characteristics. A heat transfer correlation based on Martinelli number utilized in two-phase region and two empirical correlations used to predict the CHF in rifled tube at near-critical pressures were proposed. Meanwhile, experimental CHF data in rifled tube were compared with six widely used correlations and a CHF look-up table. The CHF enhancement effect in rifled tube is obvious as compared with the CHF data in smooth tube. Results show that DNB occurs at low vapor quality and subcooled region in the rifled tube at near-critical pressures. The increase in pressure leads to the early occurrence of DNB and the decrease in CHF, whereas the increase in mass flux delays the occurrence of DNB and results in the increase in CHF. DNB presents a tendency to move toward the inlet of the rifled tube. At individual operating conditions, DNB and dryout coexist at different sections of the rifled tube.

关键词： critical heat flux near-critical pressure rifled tube DNB heat transfer

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Unveiling micro- and nanoscale bubble dynamics for enhanced electrochemical water splitting

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Advances in Colloid and Interface Science 2025年 343卷 103544页

作者： Lu, Xinlong Yadav, Devendra He, Baichuan Zhou, Yu Zhou, Liwu Zeng, Zilong Ma, Lijing Jing, Dengwei International Research Center for Renewable Energy & State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Shaanxi Xi'an710049 China Department of Chemical Engineering Technion - Israel Institute of Technology Haifa3200003 Israel College of Mechanical Engineering Xi'an Shiyou University Shaanxi Xi'an710065 China

Bubbles generated during electrochemical and photoelectrochemical water splitting critically influence efficiency through complex factors, including chemical reactions, species transport, mass transfer at the three-phase interface, and bubble coverage. A detailed understanding of the nucleation, growth, coalescence, and detachment of micro- and nanoscale bubbles is vital for advancing water splitting technologies. Surface-attached bubbles significantly reduce the electrocatalytically active area of electrodes, leading to increased surface overpotential at a given current density. Consequently, their effective removal is pivotal for optimizing the electrolysis process. However, the intricate interplay among single bubble evolution, mass transport, bubble coverage, and overpotential remain inadequately understood. This review explores the fundamental mechanisms underpinning bubble evolution, with an emphasis on the Marangoni effect and its influence on bubble dynamics. Furthermore, recent advancements in understanding individual bubbles on micro and nano-electrodes are highlighted, offering valuable insights into scale-dependent bubble behavior. These findings enrich our knowledge of gas-liquid interfacial phenomena and underscore their industrial significance, presenting opportunities to enhance water splitting performance through optimized bubble dynamics. © 2025

关键词： Electrolysis

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General analytical equation of state for nanoconfined gases derived from statistical physics

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Physical Review E 2025年第2期111卷 025413-025413页

作者： Chengzhen Sun Haoxuan Li Zhixiang Zhao Mehdi Neek-Amal Bofeng Bai State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an Shaanxi 710049 China School of Urban Planning and Municipal Engineering Xi'an Polytechnic University Xi'an Shaanxi 710048 China Department of Physics Faculty of Sciences Shahid Rajaee Teacher Training University 16875-163 Lavizan Tehran Islamic Republic of Iran Department of Physics University of Antwerp Groenenborgerlaan 171 2020 Antwerp Belgium

The pressure prediction of nanoconfined gases is crucial for various industrial applications, yet existing equations of state (EOS) often compromise between accuracy and usability. This study derives a theoretical EOS in analytical form, combining precision and practicality through statistical physics. It begins by examining the pressure drop mechanism due to adsorbed molecules and refines molecular pairing and potential energy interactions. The resulting EOS accurately predicts the pressure of gases in nanoconfined spaces, especially with an average prediction error of about 5% for strongly adsorbing gases like nitrogen, oxygen, and argon. Additionally, it aligns with the Van der Waals EOS under macroscopic conditions, offering a unified framework across scales. This model enhances both engineering applications and the understanding of nanoconfined EOS.

关键词： Van der Waals forces

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Occurrence and flow Characteristics of Methane in High-Temperature and High-Pressure Nanopores of Deep Shale

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Kung Cheng Je Wu Li Hsueh Pao/Journal of engineering Thermophysics 2025年第4期46卷 1200-1204页

作者： Wang, Rui Sun, Chengzhen Yang, Xu State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China Petroleum Engineering School Southwest Petroleum University Chengdu610500 China

The understanding of gas transport in deep shale nanopores is still not clear. In this study, molecular simulations of methane occurrence and flow in illite slits of deep shales under the condition of high-temperature and high-pressure was carried out. The occurrence, diffusion and flow characteristics of methane molecules were analyzed. The effects of temperature and pressure on methane occurrence and flow were elucidated. The results show that the distribution of methane density in illite slits is nonuniform, and there are density peaks near the wall. Compared with Middle and Shallow shales, more methane molecules can exist in the pores of deep shale, and the diffusion ability is limited. The methane flow flux decreases with the decrease of pressure (5∼80 MPa) and increases with the decrease of temperature (60∼120◦C). Pressure is the main dominating factor of flow flux, and the flow flux decreases gradually during depressurization. © 2025 Science Press. All rights reserved.

关键词： Nanopores

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Laser-based speciation of acetone oxidation behind reflected shock waves and chemical kinetic modeling

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International Journal of Hydrogen Energy 2025年 141卷 46-58页

作者： Congjie Hong Xin Zhang Jiabiao Zou Zuohua Huang Yingjia Zhang Aamir Farooq State Key Laboratory of Multiphase Flows in Power Engineering Xi'an Jiaotong University Xi'an 710049 People's Republic of China Clean Energy Research Platform Physical Sciences and Engineering (PSE) Division King Abdullah University of Science and Technology (KAUST) Thuwal 23955-6900 Saudi Arabia

With the growing global focus on renewable and oxygenated fuels, acetone has attracted significant attention due to its role as a key intermediate in the oxidation of alcohol-based fuels, an efficient hydrogen carrier, and a vital component in hydrogen production via catalytic reforming and biofuel synthesis. A comprehensive understanding of its pyrolysis and oxidation mechanisms is crucial for advancing clean energy technologies and optimizing its utilization in sustainable fuel applications. However, discrepancies persist in existing models regarding the time histories of key species during acetone pyrolysis. In this study, advanced laser diagnostic techniques were employed to measure the time-resolved concentration profiles of various species during acetone oxidation behind reflected shock waves, capturing the dynamic evolution of key intermediates and products such as CO, OH, and H 2 O. By integrating the latest experimental and theoretical studies, including the concentration profiles of key intermediates during pyrolysis, rate coefficient measurements, and ignition delay times, the critical reaction pathways and rate coefficients of acetone were systematically refined. Additionally, previously missing reaction pathways (i.e., CH 2 CO + CH 3 =HCCO + CH 4 ) were incorporated, leading to an improved acetone kinetic model that underwent comprehensive validation against various experimental datasets. The results indicate that the updated model accurately predicts the time-resolved concentration profiles of key species during acetone oxidation and pyrolysis over a wide temperature range, with significant improvements in predicting ignition delay times and laminar flame speeds. This study offers valuable insights for refining acetone kinetic models and establishes a research framework for investigating the complex chemical behavior of ketones and other oxygenated fuels in combustion.

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Recent advances in nanoporous graphene membrane for gas separation and water purification

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Science Bulletin 2015年第21期60卷 1807-1823页

作者： Chengzhen Sun Boyao Wen Bofeng Bai State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University

Graphene is a one-atom-thick sheet of graphite comprising sp2-hybridized carbon atoms arranged in the hexagonal honeycomb lattices. By removing the honeycomb lattices and forming nanopores with specific geometry and size, nanoporous graphene has been demonstrated as a very high-efficiency separation membrane, due to the ultrafast molecular permeation rate for its one-atom thickness. This review focuses on the recent advances in nanoporous graphene membrane for the applications of gas separation and water purification, with a major emphasis on the molecular permeation mechanisms and the advanced fabrication methods of this state-of-the-art membrane. We highlight the advanced theoretical and experimental works and discuss the gas/water molecular transport mechanisms through the graphene nanopores accompanied with theoretical models. In addition, we summarize some representative membrane fabrication methods, covering the graphene transfer to porous substrates and the pore generation. We anticipate that this review can provide a platform for understanding the current challenges to make the conceptual membrane a reality and attracting more and more attentions from scientists and engineers.

关键词： Nanoporous graphene Gas separationWater purification Molecular permeationmechanism Membrane fabrication

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A wall-temperature-independent heat transfer model and dominant dimensionless numbers for supercritical CO2 in vertical upward flow

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Journal of Supercritical Fluids 2025年 224卷

作者： Hou, Zhenghui Liao, Haifan Yang, Kuang Bai, Shaozhe Fan, Xinjiang Yang, Chaofan Wang, Haijun State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

The heat transfer coefficient is a critical parameter for the design and optimization of supercritical carbon dioxide (sCO₂) heat exchange systems. Based on 20723 data points collected from 22 published studies, existing heat transfer correlations are evaluated, and a new model with improved stability and predictive accuracy is developed. Current correlations for upward vertical sCO₂ flow typically include wall-temperature-dependent parameters, which often lead to issues such as non-uniqueness or the absence of solutions during wall temperature prediction, along with limited accuracy. To address these issues, this study integrates the Buckingham Pi theorem and constructs a wall-temperature-independent heat transfer model using a dimensionless neural network. This approach avoids the problems of multiple or no solutions and achieves high predictive performance, with mean absolute relative errors of 2.83 % for wall temperature and 5.81 % for Nusselt number predictions. Furthermore, the active subspace method is employed to identify four dominant dimensionless groups governing the heat transfer process. These groups can be decomposed into products of commonly known dimensionless numbers. During this process, a new dimensionless number—the buoyancy generation (BG) number—is proposed and defined. This study leverages data-driven dimensional analysis to explore key influencing parameters and dominant dimensionless numbers for supercritical heat transfer, offering new insights into the underlying physical mechanisms. © 2025 Elsevier B.V.

关键词： Electric heating

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Thermal and hydraulic performance of molten salt steam generation system under varying operating conditions in concentrating solar power plants

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Case Studies in Thermal engineering 2025年 72卷

作者： Jiaming Tian Bo Ren Yiran Duan Biao Li Yueshe Wang State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an 710049 China

To conduct the thermal transport characteristics and operational stability of the steam generation system (SGS) under partial load conditions in concentrating solar power (CSP), a real-scale shell-and-tube steam generator hydrodynamics predictive model is developed. This model integrates lumped parameter methods with the finite volume method to account for heat transfer and phase change. Additionally, in accordance with the prevailing water circulation mode in the CSP plant, a typical model of the natural circulation system is established, while optimal stable operating points of the maximum circulation mass flow rate under varying operating conditions are determined. The results indicate that the inherent stability of the generator strongly lies in the dynamic compromise between its thermodynamic and hydrodynamic characteristics. Under high load conditions, the natural circulation mode demonstrates excellent flow stability. Operating at lower operating pressures results in greater circulation flow and a heightened sensitivity to phase changes. Under system pressures of 13.76, 11.08, 8.39, and 6.71 MPa, the recommended circulation ratios are determined to be 5.38, 7.86, 11.95, and 16.07, respectively. Furthermore, the stability of the circulation curve is optimized by adjusting the structural dimensions of the steam generator. The sensitivity to evaporation capacity and heat exchanger effectiveness is assessed.

关键词： Molten salt storage Steam generator Natural circulation mode Concentrating solar power

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A review of engine application and fundamental study on turbulent premixed combustion of hydrogen enriched natural gas

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Science China(Technological Sciences) 2014年第3期57卷 445-451页

作者： WANG JinHua WEI ZhiLong ZHANG Meng HUANG ZuoHua State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University

The application and fundamental study on turbulent premixed combustion of hydrogen enriched natural gas is reviewed in this *** include the combustion characteristics of direct injection engine fueled with hydrogen enriched natural gas,visualization study of direct injection combustion of hydrogen enriched natural gas using a constant volume vessel,and the fundamental study of turbulent premixed combustion of hydrogen enriched natural *** effect of additional hydrogen on the combustion process of natural gas engine is investigated from the fundamental view of the interaction between combustion reaction and turbulent flow.

关键词： natural gas hydrogen direct injection combustion turbulent premixed combustion OH-PLIF engine

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