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Numerical simulation of bubble behavior in a quasi-2D fluidized bed using a bubble-based EMMS model

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Particuology 2019年第5期17卷 40-54页

作者： Hao Wang Youjun Lu State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi'an 710049 Shaanxi China

Bubbles formed during chemical processes in fluidized beds govern the bed hydrodynamics and opera-tional efficiency, thereby having a significant impact on their design and scale-up. In this study, a two-fluid model was used to simulate the bubble behavior in a quasi-two-dimensional fluidized bed within the bubble-based energy minimization multiscale (EMMS) approach. We performed experiments to verify the model and proposed a correlation of the heterogeneous index for various parameters to calculate the coefficient of drag for the bubble-based EMMS model. Moreover, the simulation results obtained from the homogeneous drag models and EMMS bubbling model were compared with experimental data and empirical correlations. The simulation results of the EMMS approach showed good agreement with the experimental data in the distribution of the vertical bubble velocity with chord length. Compared with the results from the homogeneous models, the distributions of vertical velocity and diameter of the bubbles predicted by the EMMS-bubbling model were in better agreement with empirical correlations. Moreover, the frequency distributions of bubble properties including bubble diameter, aspect ratio, and shape factor for different gas-inlet velocities were obtained.

关键词： Energy minimization multi-scale approach Heterogeneous index Fluidized bed Bubble

Interlink between Abnormal Water Imbibition in Hydrophilic and Rapid Flow in Hydrophobic Nanochannels

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Physical Review Letters 2024年第18期132卷 184001-184001页

作者： Runfeng Zhou Mehdi Neek-Amal Francois M. Peeters Bofeng Bai Chengzhen Sun State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an Shaanxi 710049 China Department of Physics Shahid Rajaee Teacher Training University 16875-163 Lavizan Tehran Iran Departement Fysica Universiteit Antwerpen Groenenborgerlaan 171 B-2020 Antwerpen Belgium Departamento de Física Universidade Federal do Ceará Fortaleza-CE 60455-760 Brazil

Nanoscale extension and refinement of the Lucas-Washburn model is presented with a detailed analysis of recent experimental data and extensive molecular dynamics simulations to investigate rapid water flow and water imbibition within nanocapillaries. Through a comparative analysis of capillary rise in hydrophilic nanochannels, an unexpected reversal of the anticipated trend, with an abnormal peak, of imbibition length below the size of 3 nm was discovered in hydrophilic nanochannels, surprisingly sharing the same physical origin as the well-known peak observed in flow rate within hydrophobic nanochannels. The extended imbibition model is applicable across diverse spatiotemporal scales and validated against simulation results and existing experimental data for both hydrophilic and hydrophobic nanochannels.

关键词： Imbibition & injection Nanofluidics Molecular dynamics Navier-Stokes equation

Degradation of Polystyrene to Aromatic Oils with Nio@C Catalyst in Supercritical Co2

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SSRN 2024年

作者： Liu, Yanbing Mao, Liuhao Kang, Xing Li, Yi Zhao, Qiuyang Jin, Hui Meng, Wei Shi, Jinwen Guo, Liejin International Research Center for Renewable Energy State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University 28 West Xianning Road Shaanxi Xi’an710049 China Hunan Provincial Key Lab of Dark Tea and Jin-Hua Departmet of Material & Chemical Engineering Hunan City University 518 East Yingbin Road Hunan Yiyang413000 China

One of the most promising ways to dispose of plastic pollution in the future is chemical recycling of plastic, and in particular supercritical fluids with excellent fluidity and transferability have shown great attraction in the disposal of plastic. Herein, catalytic degradation of polystyrene (PS) plastic in supercritical carbon dioxide (Sc-CO2) was realized with high yield of aromatic oils. NiO with simple preparation process, and high catalytic activity and stability in Sc-CO2 was doped with carbon material to prepare NiO@C catalyst with improved catalytic performance. Compared with NiO, NiO@C catalyst had rich porous structure and strong acidic sites, resulting in higher catalytic activity. The NiO@C catalyzed degradation of PS in Sc-CO2 yielded aromatic oils as high as 89.3 ± 0.6 wt% at 300oC with a reaction time of 2 h and a catalyst loading amount of 10 wt%. Moreover, the NiO@C catalyst degraded PS in Sc-CO2 for three cycles without obvious change in the catalytic performance. Sc-CO2 not only played a favorable role in swelling PS, but also inhibited the formation of coke, beneficial for the degradation of PS. Furthermore, CO2 was be consumed as an oxidant to generate new products and reduce greenhouse gas emission. The highly efficient catalytic conversion of PS to aromatic oils in Sc-CO2 via NiO@C catalyst provides a potential route for simultaneously recycling plastic and sequestering carbon. © 2024, The Authors. All rights reserved.

关键词： Carbon dioxide

Spatial artificial neural network model for subgrid-scale stress and heat flux of compressible turbulence

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Theoretical & Applied Mechanics Letters 2020年第1期10卷 27-32页

作者： Chenyue Xie Jianchun Wang Hui Li Minping Wan Shiyi Chen Shenzhen Key Laboratory of Complex Aerospace Flows Center for Complex Flows and Soft Matter ResearchDepartment of Mechanics and Aerospace EngineeringSouthern University of Science and TechnologyShenzhen 518055China School of Power and Mechanical Engineering Wuhan UniversityWuhan 430072China State Key Laboratory of Turbulence and Complex Systems Peking UniversityBeijing 100871China

The subgrid-scale(SGS)stress and SGS heat flux are modeled by using an artificial neural network(ANN)for large eddy simulation(LES)of compressible *** input features of ANN model are based on the first-order and second-order derivatives of filtered velocity and temperature at different spatial *** proposed spatial artificial neural network(SANN)model gives much larger correlation coefficients and much smaller relative errors than the gradient model in an a priori *** an a posteriori analysis,the SANN model performs better than the dynamic mixed model(DMM)in the prediction of spectra and statistical properties of velocity and temperature,and the instantaneous flow structures.

关键词： Compressible turbulence Large eddy simulation Artificial neural network

The Interaction and Activation of Fe2o3/Ceo2 Oxygen Carrier in Chemical Looping Dry Reforming of Methane

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SSRN 2024年

作者： Zhang, Jinrui Liu, Xiaozhi Pan, Yue Wang, Yuhan Yang, Tianlong Li, Peng Shen, Yuanhui Su, Dong Pan, Ying Jin, Hongguang Institute of Engineering Thermophysics Chinese Academy of Sciences Beijing100190 China University of Chinese Academy of Sciences Beijing100049 China Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing100190 China International Research Center for Renewable Energy State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University 710049 China

Chemical looping dry reforming of methane (CL-DRM) holds great promise for both CO2 utilization and syngas production with high efficiencies. The structure and component of oxygen carriers (OCs) are critical factors that influence the CL-DRM performances, such as reaction activity and production selectivity. Incorporating CeO2 is known to enhance the reactivity and stability of Fe2O3 for chemical looping reforming. However, the underlying mechanism of how CeO2 synergistically interact with Fe2O3 to enhance performances is still not clear. In this work, we comparatively investigate CeO2 supported Fe2O3 OCs in interfacial and physical Fe-Ce contact modes. The OC with sol-gel method achieves 80% CH4 conversion and 96% CO selectivity, significantly improved from OC with the mechanically mixed sample. Additionally, we found a strong interaction between Fe2O3 and CeO2 components, resulting in the formation of CeFeO3 after the first cycle. Our in-situ environmental transmission electron microscopy study shows that the Fe2O3-CeO2 interaction promotes the oxygen release during the reduction. Iron exhibited significant activity with ceria under CO2, dissolving into CeO2 lattice and forming CeFeO3. Density function theory results suggest that the improved reactivity of Fe2O3/CeO2 OC results from the enhanced oxygen ion migration in CeFeO3 © 2024, The Authors. All rights reserved.

关键词： Sol-gels

Design and Optimal Thermal Efficiency Analysis on Closed Brayton Cycle System of Fluoride-Salt-Cooled High-Temperature Advanced Reactor (Fustar)

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SSRN 2022年

作者： Li, Xinyu Zhang, Dalin Yun, Shichang Zhou, Xingguang Jiang, Dianqiang Lv, Xindi Feng, Zhenyu Wu, Wenqiang Tian, Wenxi Qiu, Suizheng Su, G.H. Zhao, Quanbin Liu, Xiuting State Key Laboratory of Multiphase Flow in Power Engineering Shaanxi Key Laboratory of Advanced Nuclear Energy and Technology School of Nuclear Science and Technology Xi’an Jiaotong University Xi’an710049 China CNNC Key Laboratory on Nuclear Reactor Thermal Hydraulics Technology Nuclear Power Institute of China Chengdu610213 China

To match the advantages of Fluoride-Salt-cooled high-Temperature Advanced Reactor (FuSTAR): the high temperature, inherent safety, compact structure, and modularization, the closed Brayton cycle system was selected as the energy conversion system, and the enthalpy analysis, conjugate gradient optimization, and exergy analysis were performed. The pinch point constraint method based on simultaneous equations was proposed to improve the calculation efficiency and ensure the unity of comparison standards, and the exergy analysis was used to quantify and optimize the exergy losses for the equipment. For the simple regenerative cycle configuration, the thermal efficiency and mass flow rate of the cycle system with various fluids (far-critical fluids: air, nitrogen, helium, and argon, near-critical fluids: carbon dioxide, sulfur hexafluoride, propane, and xenon) were analyzed, at the highest thermal efficiencies. The results of enthalpy analysis show that the thermal efficiency of the sulfur hexafluoride cycle is the highest with the simple regenerative cycle configuration. The thermal efficiency of the far-critical fluid cycle is more sensitive to turbine efficiency. The exergy analysis shows the CO2 cycle has the highest potential to improve thermal efficiency. The method and conclusion of this paper can provide references for the design and optimization of the Brayton power cycle system. © 2022, The Authors. All rights reserved.

关键词： Enthalpy

Design and Optimal Thermal Efficiency Contrastive Analysis on Closed Brayton Cycle Systems with Different Fluids of Fluoride-Salt-Cooled High-Temperature Advanced Reactor

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SSRN 2022年

作者： Li, Xinyu Zhang, Dalin Yun, Shichang Zhou, Xingguang Jiang, Dianqiang Lv, Xindi Feng, Zhenyu Wu, Wenqiang Tian, Wenxi Qiu, Suizheng Su, Guanghui Zhao, Quanbin Liu, Xiuting State Key Laboratory of Multiphase Flow in Power Engineering Shaanxi Key Laboratory of Advanced Nuclear Energy and Technology School of Nuclear Science and Technology Xi’an Jiaotong University Xi’an710049 China CNNC Key Laboratory on Nuclear Reactor Thermal Hydraulics Technology Nuclear Power Institute of China Chengdu610213 China

To match the advantages of Fluoride-Salt-cooled high-Temperature Advanced Reactor, the closed Brayton cycle system was selected as the energy conversion system, and the thermodynamic analysis, conjugate gradient optimization, and exergy analysis were performed. The pinch point constraint method based on simultaneous equations was proposed to improve the calculation efficiency and ensure the unity of comparison standards, and the exergy analysis was used to quantify and optimize the exergy losses for the equipment. For the simple regenerative cycle configuration, the thermal efficiency and mass flow rate of the cycle system with various fluids (far-critical fluids: air, nitrogen, helium, and argon, near-critical fluids: carbon dioxide, sulfur hexafluoride, propane, and xenon) were analyzed. The results of the thermodynamic analysis show that the thermal efficiency of the sulfur hexafluoride cycle is the highest and reaching 46.6% with the simple regenerative cycle configuration. The thermal efficiency of the far-critical fluid cycle is more sensitive to turbine efficiency. The results of the exergy analysis show the CO2 cycle has the highest potential to improve thermal efficiency, which has the highest improvement from 43.48% to 49.31% with the recompression process. The method and conclusion of this paper can provide references for the design and optimization of the Brayton power cycle system © 2022, The Authors. All rights reserved.

关键词： Carbon dioxide

Novel Solid-state Hydrolysis Kinetics of Nabh4 for Stable and High-Capacity On-Line Hydrogen Production

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SSRN 2024年

作者： Chen, Jiawei Wu, Zhen Zheng, Jie Shi, Yu Xie, Lei Yang, Fusheng Wang, Yuqi Zhang, Zaoxiao School of Chemical Engineering Northwest University Xi’an710069 China School of Chemical Engineering and Technology Xi’an Jiaotong University Xi’an710049 China College of Chemistry and Molecular Engineering Peking University Beijing100871 China Sunan Institute for Molecular Engineering Peking University Jiangsu 215500 China State Key Laboratory of Multiphase Flow for Power Engineering Xi’an Jiaotong University Xi’an710049 China

Solid-state hydrolysis of NaBH4 could achieve high-capacity on-line hydrogen production. However, the stability of hydrogen production in the solid-state hydrolysis process has been questioned. In this paper, a novel kinetics is proposed for the solid-state hydrolysis behavior. The acceleration factor β is introduced into the traditional shrinking core model to reveal the relationship between "dissolution" and "catalytic hydrolysis" in the solid-state hydrolysis process. The comparison results show a good agreement between the model and experiment in the temperature range of 303.15-348.15 K. Meanwhile, the kinetics conclusions and product characterization indicated that the "excessive dissolution" of NaBH4 and the "dehydration of by-products" are two important factors contributing to the uncontrolled reaction. Based on the parametric analysis and experimental verification, the optimum temperature for solid-state hydrolysis is approximately 323.15 K. Besides, the adjustment of the water intake strategy to intermittent intake reduced water consumption by 36.6%. As a result, the hydrogen release capacity could be increased to as high as 5.49 wt.% (close to the U.S. Department of Energy 2025 gravimetric hydrogen storage capacity of 5.5 wt.%), even though the weight of water is taken into account as reactant. © 2024, The Authors. All rights reserved.

关键词： Hydrolysis

ȮH insights into the interaction of hydrogen-rich methane and water: Laser absorption experiments and chemical kinetics

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Combustion and Flame 2025年 278卷

作者： Xin Zhang Zilong Feng Congjie Hong Wuchuan Sun Zuohua Huang Yingjia Zhang State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an 710049 PR China

Flue gas recirculation and steam injection are employed in hydrogen-rich gas turbines to stabilize fuel reactivity and improve cycle efficiency, introducing high water vapor content into the combustion chamber and thereby necessitating an investigation of water-fuel interactions at elevated temperatures. This study employed UV laser absorption diagnostics behind reflected shock waves to conduct in situ measurements of the ȮH concentration time-histories during the oxidation of CH 4 /H 2 /H 2 O/O 2 /Ar mixtures at pressures of approximately 1.3, 5.0, and 15.2 atm and temperatures ranging from 1225 to 1888 K with varying hydrogen blending and water addition ratios. The absorption lineshapes of the ȮH R 1 (5) transition in the A-X(0,0) vibronic band were characterized after broadening and shifting in Ar at different pressures, with diagnostic center wavelengths set at 306.6868 nm (1.3 atm), 306.6874 nm (5.0 atm), and 306.6886 nm (15.2 atm), respectively. The obtained ȮH concentration time-history data were compared in detail with predictions from eight representative reaction kinetic models, and the predictive capability of the models for ȮH behavior was quantitatively assessed using the error function method. NUIGMech1.1 exhibited superior performance in predicting ȮH behavior and was subsequently selected for kinetic analysis to elucidate stage-specific micro-mechanisms and identify key reactions driving the concentration evolution. The activating effect of H 2 on ȮH behavior during CH 4 oxidation was investigated. Results indicate that higher hydrogen levels intensify hydrogen-related reaction pathways, expanding the radical pools (H, ȮH, and Ö), thereby promoting fuel consumption through Ḣ-atom abstraction reactions. Additionally, by introducing weak collision H 2 O* and inert H 2 O**, the thermodynamic and kinetic effects of water were distinguished. The results show that under the current conditions, H 2 O primarily affects ȮH behavior through direct participatio

关键词： Hydrogen-enriched methane Kinetic models Laser absorption Water addition ȮH time-histories