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SSRN 2024年

作者： Wang, Cui Jin, Hui School of Water and Environment Chang'an University Xi’an710054 China Key Laboratory of Subsurface Hydrology and Ecological Effect in Arid Region of the Ministry of Education Chang'an University Xi’an710054 China Key Laboratory of Eco-hydrology and Water Security in Arid and Semi-arid Regions of Ministry of Water Resources Chang’an University Xi’an710054 China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi’an710049 China Ministry of Education of China Chongqing University Chongqing400044 China

Biomass energy is renewable and rich in the world, providing a solution for the shortage in fossil fuel and serious environmental pollution. Proposing efficient utilization method of biomass waste demands urgent attention. Supercritical water gasification (SCWG) process is a potential technology. In this work, a poly-generation system based on SCWG was developed to convert biomass waste to gas, biochar, heat and electricity. Firstly, mass, energy, and exergy flow were calculated at the typical condition. Subsequently, impact of various operating parameters, including gasification temperature, mass flowrate of preheated water, biomass concentration, on the hydrogen-rich syngas yield, generated electricity, thermodynamic performance of the system was investigated. The result demonstrated that the exergy loss primarily occurred on cooler, reactor, heat exchanger and preheater, accounting for more than 90% of total exergy loss under different conditions, arising from irreversible reaction, heat transfer and heat dissipation. Higher temperature, higher biomass concentration and more preheated water exerted a positive effect for hydrogen-rich gas production and supplied heat energy, while these parameters were disadvantageous to exergy efficiency. Biochar energy was primarily affected by biomass concentration. Energy efficiency increased with preheated water quantity and biomass concentration rising, and impact of biomass concentration was more significant. Conversely, evaluated gasification temperature displayed an adverse effect on energy efficiency. The maximal exergy efficiency reached about 58.3% at 550℃, biomass concentration of 33%, preheated water mass flowrate of 900 kg·h-1.© 2024, The Authors. All rights reserved.

关键词： Biomass

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Numerical study on the influence of plugging rate on the performance of adjustable steam ejector

International Journal of Fluid Engineering

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International Journal of Fluid engineering 2024年第2期1卷 50-60页

作者： Jianxiang Gao Zepeng Yuan Yuyan Hou Weixiong Chen State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong UniversityXi’an 710049People’s Republic of China

During the operation of thermal power plant systems, severe challenges to the quality and safety of the heat supply arise owing to the effects of peak regulation. Steam ejectors, widely employed in the district heating sector, often exhibit poorer performance under off-design conditions as a result of their fixed structure. This study analyzes the effects of varying plugging rate, primary pressure, and induced pressure on the performance of adjustable steam ejectors. As the plugging rate increases, the mass {1. rate of the primary fluid decrease, potentially falling below 32%, and that of the induced fluid initially experiences a minor increase, followed by a rapid decrease. Concurrently, the critical back pressure also decreases with an increase in the plugging rate, potentially falling by up to 65%. By contrast, the entrainment ratio surges with increasing plugging rate, with the maximum increase reaching up to 4.75 times. Under the same primary steam pressure and induced steam pressure, there exists an optimal entrainment ratio. Furthermore, both the critical back pressure and the optimal entrainment ratio increase as the primary steam pressure and induced steam pressure increase.

关键词： performance steam optimal

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Measurement of falling film thickness around a horizontal tube using laser-induced fluorescence technique

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Journal of Physics: Conference Series 2009年第1期147卷

作者： Xiaofei Wang Maogang He Hualiang Fan Ying Zhang State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 People's Republic of China

An optical method for the non-intrusive measurement of falling film thickness on the perimeter of the horizontal tube is described. This non-intrusive measurement method is based on the visualization of the falling film flowing around the horizontal tube and uses the laser induced fluorescence and image processing techniques. The falling film thickness around a Turbo-CII horizontal tube and a plain horizontal tube was measured when water flushed the tube vertically with a stable velocity. The results for the Turbo-CII tube are compared with those for the plain tube, and show that the film thickness around the Turbo-CII tube varies with the same trend as that around the plain tube, and the minimal values of the film thickness tend to locate at different angular position of 95°-1.0° under different conditions. The film thickness around the enhanced tube changes within a smaller range with time than that around the plain tube. The corresponding effects on flow uniformity have also been discussed.

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An efficient cellular flow model for cohesive particle flocculation in turbulence

arXiv

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arXiv 2020年

作者： Zhao, K. Vowinckel, Bernhard Hsu, T.-J. Köllner, T. Bai, B. Meiburg, E. Department of Mechanical Engineering UC Santa Barbara CA93106 United States State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China Leichtweiß-Institut für Wasserbau Technische Universität Braunschweig Braunschweig38106 Germany Center for Applied Coastal Research Department of Civil & Environmental Engineering University of Delaware NewarkDE19716 United States

We propose a one-way coupled model that tracks individual primary particles in a conceptually simple cellular flow setup to predict flocculation in turbulence. This computationally efficient model accounts for Stokes drag, lubrication, cohesive and direct contact forces on the primary spherical particles, and allows for a systematic simulation campaign that yields the transient mean floc size as a function of the governing dimensionless parameters. The simulations reproduce the growth of the cohesive flocs with time, and the emergence of a log-normal equilibrium distribution governed by the balance of aggregation and breakage. Flocculation proceeds most rapidly when the Stokes number of the primary particles is O(1.. Results from this simple computational model are consistent with experimental observations, thus allowing us to propose a new analytical flocculation model that yields improved agreement with experimental data, especially during the transient stages. Copyright © 2020, The Authors. All rights reserved.

关键词： Turbulence

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Adsorption of Dibenzofuran by Modified Biochar Derived from Microwave Gasification

SSRN

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SSRN 2024年

作者： Ren, Jiyun Zhang, Yong Wang, Hui Huang, Xiaoming Jin, Xiaoling Zhang, Kai Li, Ruiyu Yang, Kaixuan Yue, Yang Deng, Lei Che, Defu State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi’an Jiaotong University Xi’an710049 China Yantai Longyuan Power Technology Co. Ltd Yantai264000 China West Pipeline Company of PipeChina Urumchi830000 China Jinggangshan Power Plant Huaneng Power International Inc Jiangxi 343009 China Shunde Institute of Inspection Guangdong Institute of Special Equipment Inspection and Research Foshan528300 China Shanghai Power Equipment Research Institute Co. Ltd. Shanghai200240 China

Dioxins, emanating from the waste incineration, constitutes an organic pollutant that poses considerable risks to human health and environment. In this study, the corn straw char (CSC) and oak char (OC) derived from the electric heating and microwave gasification, and the coconut-shell activated carbon (AC) are employed as absorbents for the adsorption of dibenzofuran (DBF, dioxins model compound). Characterization techniques including BET, X-ray CT, SEM-EDS, FTIR, and XPS are performed to identify the DBF adsorption mechanism on biochar. The results show that the biochar prepared by the microwave gasification has a more well-developed pore structure than that of the electric heating gasification. Higher porosity (1..94%) and lower mineral content (1.75%) are responsible for the effective adsorption of DBF onto AC. The adsorption capacity of CSC is proportional to the modified concentration of KOH. It is mainly ascribed to the decrement of carboxyl and lactone groups and the enhancement of alkaline functional groups on the biochar surface, which augments the hydrophobicity and π–π electron donor–acceptor (EDA) interaction. Instead, DBF adsorption capacity on the biochar is adversely affected by HNO3 modification. For all biochar samples, the corresponding maximum adsorption ratios are AC (87.1.%) > KOH-modified CSC (77.1.%) > unmodified CSC (49.1.%) > unmodified OC (39.70%) > HNO3-modified CSC (36.09%). The adsorption mechanisms of DBF on the gasified biochar encompass pore filling, hydrophobicity, and π–π EDA interaction. A desirable adsorption capacity of DBF on the biochar prepared by the microwave gasification is attainable through augmenting the specific surface area while diminishing the oxygen-containing groups of the surface simultaneously. © 2024, The Authors. All rights reserved.

关键词： Potassium hydroxide

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Investigation of Droplet Dynamic Behavior in Pemfcs Gas Diffusion Layer and Gas Channel with Micro-Ct and Lattice Boltzmann Method

SSRN

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SSRN 2024年

作者： Lv, Xuecheng Zhou, Zhifu Wu, Wei-Tao Wei, Lei Gao, Linsong Lyu, Jizu Hu, Chengzhi Li, Yang Li, Yubai Song, Yongchen Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education Dalian University of Technology Dalian116024 China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'An710049 China School of Mechanical Engineering Nanjing University of Science and Technology Nanjing210094 China Department of Mechanical and Energy Engineering Southern University of Science and Technology Shenzhen518055 China School of Mechanical Engineering and Mechanics Xiangtan University Xiangtan411105 China School of Mechanical Engineering Guangdong Ocean University Zhanjiang524088 China

This study reconstructed the 3D structure for the gas diffusion layer (GDL) of proton exchange membrane fuel cells (PEMFCs) using the micro-CT technique and investigated the dynamic behavior of droplets inside the multi-scale space of GDL and gas channel (GC) using the lattice Boltzmann method (LBM). The prediction model for droplet detachment at the GDL-GC interface was developed. The results indicate that there is a significant difference between the breakage location of the liquid bridge and the trajectory of the liquid droplet after detaching from the GDL-GC interface in the multi-scale space of GC and GDL, compared to the single-scale GC space where GDL is ignored. The increase in gas velocity and internal contact angle of the GDL contribute to reducing the droplet detachment volume and increasing the droplet detachment frequency. At the internal contact angle of 1.0º-1.0º, GDL exhibited the most efficient removal of liquid water. A contact angle smaller than this range would hinder the detachment of droplets in the GC, while a contact angle larger than this range would lead to the accumulation of liquid water in the GDL. The surface force generated by the connection of liquid bridges in the analytical model for critical droplet detachment forms an angle with the gas flow direction, with the characteristic length determining this force being the minimum diameter at the necking of the liquid bridge. © 2024, The Authors. All rights reserved.

关键词： Contact angle

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Research on a Poly-Generation System for Gas-Biochar-Heat-Electricity by Supercritical Water Gasification of Biomass Waste

SSRN

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SSRN 2024年

Biomass energy is renewable and rich in the world, providing a solution for the shortage in fossil fuel and serious environmental pollution. Proposing efficient utilization method of biomass waste demands urgent attention. Supercritical water gasification (SCWG) process is a potential technology. In this work, a poly-generation system based on SCWG was developed to convert biomass waste to gas, biochar, heat and electricity. Firstly, mass, energy, and exergy flow were calculated at the typical condition. Subsequently, impact of various operating parameters on the hydrogen-rich syngas yield, generated electricity, thermodynamic performance was investigated. The result demonstrated that the exergy loss primarily occurred on cooler, reactor, heat exchanger and preheater, accounting for more than 90% of total exergy loss, arising from irreversible reaction, heat transfer and heat dissipation. Higher temperature, biomass concentration and preheated water exerted a positive effect for hydrogen-rich gas production and supplied heat energy, while these parameters were disadvantageous to exergy efficiency. Biochar energy was affected by biomass concentration. Energy efficiency increased with preheated water quantity and biomass concentration rising, and impact of biomass concentration was more significant. Conversely, evaluated gasification temperature displayed an adverse effect on energy efficiency. The maximal exergy efficiency reached 58.3% at 550℃, 33%, 900 kg·h-1. © 2024, The Authors. All rights reserved.

关键词： Biomass

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TiO2-SnO2:F interfacial electronic structure investigated by soft x-ray absorption spectroscopy

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Physical Review B 2012年第12期85卷 125109-125109页

作者： Coleman X. Kronawitter Mukes Kapilashrami Jonathan R. Bakke Stacey F. Bent Cheng-Hao Chuang Way-Faung Pong Jinghua Guo Lionel Vayssieres Samuel S. Mao Department of Mechanical Engineering University of California at Berkeley Berkeley California 94720 USA Environmental Energy Technologies Division Lawrence Berkeley National Laboratory Berkeley California 94720 USA Advanced Light Source Lawrence Berkeley National Laboratory Berkeley California 94720 USA Department of Chemical Engineering Stanford University Stanford California 94305 USA Department of Physics Tamkang University Tamsui Taiwan Republic of China International Research Center for Renewable Energy State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Shaanxi 710049 People's Republic of China

The electronic structure of the titanium dioxide (TiO2)-fluorine-doped tin dioxide (SnO2:F) interface is investigated by soft x-ray absorption spectroscopy using synchrotron radiation. The measurements probe the site- and symmetry-selected unoccupied density of states and reflect the interaction between an early transition-metal-oxide (d0) semiconductor and a post-transition-metal-oxide (d1.) degenerate semiconductor. The distinct interfacial electronic structure of TiO2-SnO2:F is established by contrasting spectra with those for anatase and rutile TiO2, SnO2:F, and ZnO-SnO2:F and CdO-SnO2:F interfaces. Oxygen 1. absorption spectra, which relate to the O 2p partial density of states of the conduction band, indicate that the interface is associated with a reduction in Ti d-O p orbital hybridization and an alteration of the TiO2 crystal field. These observations are consistent with measured titanium 2p absorption spectra, which in addition provide evidence for distortion of long-range order around the cation site in the interfacial TiO2. The TiO2-SnO2:F interface is a functional component of a number of optoelectronic devices, perhaps most notably within the anode structure of solar cell architectures. In nonequilibrium conditions, such as those found in operating solar cells, interfacial electronic structure directly influences performance by modifying, for instance, the quasi-Fermi level electrons and the potential distribution at the transparent electrode.

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Research on a Poly-Generation System for Gas-Biochar-Heat-Electricity by Supercritical Water Gasification of Biomass Waste

SSRN

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SSRN 2024年

Biomass energy is renewable and rich in the world, providing a solution for the shortage in fossil fuel and serious environmental pollution. Proposing efficient utilization method of biomass waste demands urgent attention. Supercritical water gasification (SCWG) process is a potential technology. In this work, a poly-generation system based on SCWG was developed to convert biomass waste to gas, biochar, heat and electricity. Firstly, mass, energy, and exergy flow were calculated at the typical condition. Subsequently, impact of various operating parameters, including gasification temperature, mass flowrate of preheated water, biomass concentration, on the hydrogen-rich syngas yield, generated electricity, thermodynamic performance of the system was investigated. The result demonstrated that the exergy loss primarily occurred on cooler, reactor, heat exchanger and preheater, accounting for more than 90% of total exergy loss under different conditions, arising from irreversible reaction, heat transfer and heat dissipation. Higher temperature, higher biomass concentration and more preheated water exerted a positive effect for hydrogen-rich gas production and supplied heat energy, while these parameters were disadvantageous to exergy efficiency. Biochar energy was primarily affected by biomass concentration. Energy efficiency increased with preheated water quantity and biomass concentration rising, and impact of biomass concentration was more significant. Conversely, evaluated gasification temperature displayed an adverse effect on energy efficiency. The maximal exergy efficiency reached about 58.3% at 550°C, biomass concentration of 33%, preheated water mass flowrate of 900 kg·h-1.© 2024, The Authors. All rights reserved.

关键词： Biomass

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Flocculation of suspended cohesive particles in homogeneous isotropic turbulence

arXiv

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arXiv 2021年

作者： Zhao, K. Pomes, F. Vowinckel, Bernhard Hsu, T.-J. Bai, B. Meiburg, E. Department of Mechanical Engineering UC Santa Barbara Santa BarbaraCA93106 United States State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China Leichtweiß-Institute for Hydraulic Engineering and Water Resources Technische Universität Braunschweig Braunschweig38106 Germany Center for Applied Coastal Research Department of Civil & Environmental Engineering University of Delaware NewarkDE19716 United States

We investigate the dynamics of cohesive particles in homogeneous isotropic turbulence, based on one-way coupled simulations that include Stokes drag, lubrication, cohesive and direct contact forces. We observe a transient flocculation phase characterized by a growing average floc size, followed by a statistically steady equilibrium phase. We analyze the temporal evolution of floc size and shape due to aggregation, breakage, and deformation. Larger turbulent shear and weaker cohesive forces yield elongated flocs that are smaller in size. Flocculation proceeds most rapidly when the fluid and particle time scales are balanced and a suitably defined Stokes number is O(1.. During the transient stage, cohesive forces of intermediate strength produce flocs of the largest size, as they are strong enough to cause aggregation, but not so strong as to pull the floc into a compact shape. Small Stokes numbers and weak turbulence delay the onset of the equilibrium stage. During equilibrium, stronger cohesive forces yield flocs of larger size. The equilibrium floc size distribution exhibits a preferred size that depends on the cohesive number. We observe that flocs are generally elongated by turbulent stresses before breakage. Flocs of size close to the Kolmogorov length scale preferentially align themselves with the intermediate strain direction and the vorticity vector. Flocs of smaller size tend to align themselves with the extensional strain direction. More generally, flocs are aligned with the strongest Lagrangian stretching direction. The Kolmogorov scale is seen to limit floc growth. We propose a new flocculation model with a variable fractal dimension that predicts the temporal evolution of the floc size and shape. © 2021. CC BY.

关键词： Flocculation

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