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Motion of a rigid particle in the lid-driven cavity flow

Chinese Physics B 2025年第3期34卷 448-459页

作者： Fan Yang Zhe Yan Wencan Wang Ren Shi School of Energy and Power Engineering University of Shanghai for Science and TechnologyShanghai 200093China Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering Shanghai 200093China

The motion of an elliptical rigid particle in a lid-driven cavity flow was numerically simulated using the immersed boundary lattice Boltzmann method(IB-LBM).The effects of the particle's initial orientation angle,initial position,aspect ratio,and size on the motion characteristics were *** computational results indicate that the particle's motion undergoes two distinct stages:a starting stage that involves moving from the release position to a limit cycle,and a periodic stage that involves moving on the limit *** initial orientation of the particle has a minimal impact on both stages of *** contrast,the time it takes for the particle to reach the limit cycle may vary depending on the release ***,particles with a larger aspect ratio exhibit a greater maximum velocity magnitude;an increase in particle size causes the particle trajectory to contract more toward the center of the cavity,decreasing the centrifugal force experienced by the particle.

关键词： lattice Boltzmann methods immersed boundary method elliptical rigid particle lid-driven cavity flow

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Three-dimensional numerical study on flow control of two-phase flow around a cylinder with an auxiliary miniature cylinder

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PHYSICS OF FLUIDS 2025年第4期37卷

作者： Xie, Yunqi Hu, Yu Huang, Shengxian Wang, Ying Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai Peoples R China

In ocean engineering, studying the phenomena of flow separation, vortex shedding, and particle deposition around blunt bodies is crucial, as these factors significantly affect the performance, stability, and lifespan of marine structures. This study, conducted under realistic marine conditions with a Reynolds number of Re = 2.5 x 10(5), and accounting for gravitational effects, first investigates the impact of installing auxiliary miniature cylinders at the front edge of the primary cylinder with different gap ratios, aiming to identify the optimal gap ratio. Subsequently, trailing-edge miniature cylinders are added for comparative analysis. This study also explores the effects of vibrating upstream miniature cylinders. Additionally, it examines the influence of auxiliary miniature cylinders on particle distribution in the wake region under particle-laden flow. The results indicate that miniature cylinders at specific gap ratios significantly reduce the drag and lift coefficients of the primary cylinder, suppress vortex shedding, optimize wake structures, and weaken the horseshoe vortex. While vibrating cylinders reduce vortex suppression, high-frequency vibrations contribute to greater drag reduction. Upstream miniature cylinders reduce the influence of vortex structures in the wake but increase sediment deposition. A dual-cylinder configuration is the most effective method for controlling sediment concentration distribution at the base of the primary cylinder.

关键词： Vortex flow

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Effects of pretreatment on biochar oxidation reaction and hydrogen production in lignocellulosic biochar-assisted water electrolysis

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INTERNATIONAL JOURNAL OF HYDROGEN energy 2025年 99卷 752-760页

作者： Sun, Hao Ying, Zhi Chen, Xinyue Zheng, Xiaoyuan Dou, Binlin Cui, Guomin Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

Substituting the oxygen evolution reaction in water electrolysis with the thermodynamically more favorable biochar oxidation reaction (BOR) constitutes biochar-assisted water electrolysis (BAWE), presenting a promising strategy for energy-efficient hydrogen production and high-value utilization biochar. Nevertheless, the BOR suffers from the sluggish kinetics and ambiguous selectivity with respect to ungraded biochar. Herein, we demonstrate the effects of elution treatment on pyrolytic lignocellulosic biochar concerning BOR kinetics and hydrogen production, as well as the efficiency of electrooxidized biochar in Cr(VI) removal. The original lignocellulosic biochar washed by alkali, acid, and water exhibited an improved BOR kinetics. Notably, the moderate water washing favored the removal of ash and soluble substances, thereby exposing more easily oxidizable functional groups such as C-OH and COOH, which substantially enhanced BOR kinetics. The waterwashed biochar-assisted water electrolysis achieved a Faradaic efficiency of 99.5% for hydrogen production at 50 mA cm-2, necessitating lower cell voltages compared to unwashed biochar. Water elution pretreatment also promoted the sufficient oxidation of biochar during electrolysis, with enriched oxygen-containing functional groups like C-O contributing to an increase in Cr(VI) removal rate from 20.81% to 65.10%. This work offers strategies for achieving efficient biochar upgrading and hydrogen production in the BAWE process.

关键词： Biochar-assisted water electrolysis Elution treatment Electrooxidation Hydrogen production Cr(VI) adsorption

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Meniscus-guided 3D printing with material supplied by the intrinsic capillary replenishment flow: Printing success rate, printed structure size adjustment, and microscale functional device fabrication

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JOURNAL OF MATERIALS PROCESSING TECHNOLOGY 2025年 339卷

作者： Cai, Rongze Wang, Haiyang Han, Xueqing Wang, Dongmin Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

Meniscus-guided 3D printing is a microscale ink-based 3D printing technique, which features ease of operation and can print micro/nano functional devices of multiple types of materials at a low cost. However, the customized microscale functional device fabrication challenge remains, because the critical printing conditions for successful printing are complex. Whether the printed device efficiency depends on printing conditions is unclear. Our study shows that there exist clogging and terminated critical pulling speeds in meniscus-guided 3D printing with material supplied by the evaporation-induced capillary replenishment flow, where only the pulling speed is within this range 3D printing could be successfully implemented. The printable ink viscosity can be higher than the previously reported if the pulling speed criterion is satisfied. The critical pulling speeds and the interval between them decrease with the micropipette diameter or ambient humidity. A more comprehensive formulation than the literature reported ones describing the dependence of the 3D-printed micropillar diameter on the micropipette pulling velocity and diameter is derived, which agrees well with the experimentally printed micropillar diameters under different conditions and indicates that 3D-printed micropillar diameter adjustment is governed by the meniscus shape and its evaporation rate. Based on the improved 3D-printed structure adjustment technology, the 3D microbridge humidity sensors and 3D micropillar capacitor electrodes can be fabricated with high repeatability and efficiency. The 3D-printed microscale devices' efficiencies in this study are superior to most previously reported microscale devices, with their efficiencies adjustable by the relative humidity during the printing process. Furthermore, the 3D-printed humidity sensor is demonstrated to be used as a contactless finger sensor, which shows potential application in preventing disease cross-infection in public facilities. Improveme

关键词： Meniscus-guided 3D printing Capillary replenishment flow Evaporation Nanoparticle deposition Micro humidity sensor Micro capacitor

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Theoretical study of bubble departure and lift-off diameters model for evaporation based on microlayer in flow boiling

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INTERNATIONAL JOURNAL OF THERMAL SCIENCES 2025年 214卷

作者： Dong, Wu-han Gao, Ming Shen, Zhong-xiang Dang, Meng-yuan Zhang, Li-xin Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

This study was devoted to the theory of microlayer evaporation and bubble dynamics. In subcooled flowing boiling, a theoretical study of the mechanism of heat and mass transfer in vapor bubbles during boiling heat transfer has been carried out. The forces on mononuclear boiling bubbles during subcooled flow boiling are analyzed. In addition, the effect of microlayer evaporation was considered, and microlayer evaporation force has been introduced. Evaporation of the microlayers as between the bottom of a bubble and the heated wall, evaporation of the layer of superheated liquid around the bubble, the condensation of the vapors at the top of a bubble are taken into account on the basis of the bubble dynamics. The prediction models for bubble forces, departure and lift-off diameters were improved. The influence of force on the bubble under the same working conditions was also investigated. Compared with previous experimental results, it was found that the improved model could forecast the diameters of the bubble departure and bubble lift-off well.

关键词： Bubble Microlayer flow boiling Wall temperature Theoretical model Nomenclature

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Numerical study on the effect of rim seal slot filleting on turbine endwall cooling

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AIP ADVANCES 2025年第1期15卷

作者： Li, Xinchun Wei, Na Shi, Liuliu Chen, Eryun Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

In this study, the effect of rim seal slot filleting on turbine endwall film cooling performance is numerically investigated. For comparison with the baseline case, five different fillet radius and width (R/W) ratios are adopted, i.e., R/W = 1.25, 2.5, 3.75, 5, and 6.25. The results indicate that an improvement up to 10% in overall film cooling effectiveness can be achieved with smaller fillet radii. However, this effect diminishes as the fillet radius increases and becomes negative at R/W = 6.25. By examining the contours of the film cooling effectiveness, a prominent inclined strip can be observed across the blade passage. The analysis indicates that the pressure-side leg horseshoe vortex is the primary factor contributing to the variation in the film cooling performance. Furthermore, the film cooling effectiveness can be slightly improved near the suction side of the blade leading edge as the result of the suppression of endwall separation in this region. The rim seal slot filleting eliminates the slot leakage separation, which, in turn, expedites the endwall cooling flow. Eventually, pressure-side leg horseshoe vortex is weakened and the performance of the film cooling is improved. As the fillet radius continues to increase, the through-flow area for the cooling flow enlarges, resulting in a gradual decrease in the film cooling performance. (c) 2025 Author(s).

关键词： Vortex flow

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Experimental and numerical simulation study of particles flow in the microchannel equipped with fan-shaped rib on sidewall

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PARTICUOLOGY 2025年 100卷 45-61页

作者： Yang, Zhenyu Li, Xiaolong Zhang, Weifeng Cai, Tianyi Zhou, Wu Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

Microchannels are widely used in electronic device cooling due to their efficient heat dissipation performance, but particle deposition is still a major challenge limiting their performance. To design and optimize efficient microfluidic devices, this paper proposes to introduce fan-shaped ribs within the microchannels to reduce particle deposition. The placement of fan ribs of different heights in the microchannel was first experimentally determined, and then the particle motion characteristics were further investigated by numerical simulations. The results show that the fan-shaped ribs can effectively reduce particle deposition and exhibit greater deposition inhibition with increasing rib height. The channel constriction induced by the rib structure promotes the radial diffusion of particles in the downstream, and at the same time significantly enhances the radial component of the particle flow, which is improved by 5.76 %, 7.98 %, and 10.86 %, respectively. In addition, recursive analysis revealed that the incorporation of fan-shaped ribs shifted the particle flow from a homogeneous, periodic mode to a more abrupt diffusion mode, which contributed to the improvement of particle dispersion. This study provides a new strategy without the use of surfactants, which provides a reference for the optimized design of microchannel cooling systems. (c) 2025 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI

关键词： Microchannel Fan-shaped rib Particle flow pattern Recursive analysis

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Balanced deep learning-based bubble segmentation: Model comparison, optimization, and application in microbubble detection

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flow MEASUREMENT AND INSTRUMENTATION 2025年 104卷

作者： Cai, Tianyi Tang, Ao Xu, Rixin Zhou, Jiawen Gong, Wenchao Zhou, Wu Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

The accurate segmentation and analysis of bubbles are crucial for understanding bubble generation mechanisms and improving industrial microbubble detection. This study aims to evaluate and optimize deep learning-based bubble segmentation models. Firstly, a systematic model evaluation matrix is proposed, including the general model performance, defocused bubble size prediction accuracy, and overlapping bubble segmentation. Secondly, four models, including SplineDist, StarDist, YOLOv8-seg, and Mask R-CNN, are compared. The SplineDist-M16 model demonstrates superior image processing speed (7.84 FPS) and high accuracy in bubble size prediction with minimal misdetection (6.1 %). Compared to other models, SplineDist-M16 excels in edge fitting and overlapping bubble identification. The optimized model provides rapid, accurate measurement of bubble quantity, size, and shape, offering insights into bubble formation and guiding microbubble generator design. This study paves the way for real-time microbubble detection in industrial applications and suggests further model improvements through simulated data training and enhanced overlapping bubble segmentation. Furthermore, the SplineDist-M16 model was utilized to analyse the impact of flow rate and backpressure on microbubble characteristics generated by a Venturi-tube microbubble generator. The results show that increased flow rate reduces bubble size and increases bubble circularity, while backpressure has minimal impact on bubble size distribution and shape.

关键词： Microbubbles Shadowgraphy Image segmentation Defocused bubbles Overlapping bubbles U -net

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Two-phase flow characteristics and leakage in the shaft seal of steam screw expanders

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INTERNATIONAL JOURNAL OF REFRIGERATION 2025年 172卷 214-227页

作者： Tian, Yafen Wang, Zebin Liu, Zhixiang Jiang, Ziqi Zhao, Zhaorui Zhang, Hua Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

Twin-screw expander is an efficient technology for steam pipeline pressure recovery applications. It operates at lower pressures than turbines and exhibits good performance with droplets. Leakage through the suction end face directly reduces the expander's volumetric efficiency, highlighting the significance of research on shaft seals. This study confirms that the Wet Steam Model is more accurate than the Ideal and Real Gas Models in reflecting the phase change phenomena and flow characteristics of steam after throttling. The effects of four key operating parameters were further investigated on the leakage and flow characteristics of the shaft seal, including suction pressure, superheat degree, rotating speed and liquid mass fraction. The results indicate that, within the specified pressure range, droplet condensation occurs after the final throttling when the superheat ranges from 0 to 30 K. Furthermore, leakage decreases by 1.5 % to 1.7 % with every increment of 10 K in superheat. Higher rotating speeds alter the steam flow path due to wall drag, thereby reducing leakage. An optimal liquid mass fraction of 0.1 was found for two-phase operating conditions, resulting in a 3.6 % reduction in leakage and a 20 K decrease in outlet temperature.

关键词： Steam expander Two-phase flow Labyrinth seal Leakage simulation

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Numerical investigation on the aerodynamic performance of vertical axis wind turbines utilizing a biomimetic fish tail paddle configuration

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energy 2025年 323卷

作者： Ye, Zhou Yu, Hao Wu, Hong Li, Chun Wang, Ying Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

Inspired by natural phenomena, it has been observed that fish can freely maneuver their tails while swimming, allowing them to adjust their speed and direction with precision, thus controlling their swimming state. Drawing from this insight, a fishtail-like paddle structure was designed at the trailing edge of the vertical axis wind turbine wing. The extension length and deflection angle of the paddle were controlled at different azimuth angles through user-defined functions. Using computational fluid dynamics, the lift and drag coefficients, instantaneous torque coefficients, wind energy utilization coefficients, and flow fields of biomimetic fish tail structure airfoils and corresponding vertical axis wind turbines were analyzed. The research findings indicate that the blade can increase the surface pressure difference of the airfoil while simultaneously boosting torque, resulting in improved wind energy utilization coefficients for the vertical axis wind turbine across medium and low blade tip speed ratios (TSR). At a blade TSR of 2.63, with a deflection angle of 0 degrees and an extended horizontal length of 0.4c, the biomimetic fish tail vertical axis wind turbine employing active flow control exhibited optimal aerodynamic performance, with its maximum wind energy utilization coefficient increasing by 18.9 % compared to the reference vertical axis wind turbine. This study offers valuable insights into the efficiency in practical engineering scenarios.

关键词： Vertical axis wind turbine flow control Biomimetic fish tail Aerodynamic characteristics

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