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Characterizations of gas-liquid interface distribution and slug evolution in a vertical pipe

Petroleum Science 2023年第5期20卷 3157-3171页

作者： Hai-Yang Yu Qiang Xu Ye-Qi Cao Bo Huang Han-Xuan Wang Lie-Jin Guo State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi’an710049ShaanxiChina

Large vertical pipes are key structures connecting subsea wells to offshore ***,existing studies mainly focus on small vertical *** a vertical acrylic pipe with 80 mm inner diameter and 11 m height,a high-speed camera was used to visually research the influences of pipe diameters,liquid properties and inlet effect on air-water co-flow *** flow regime maps of vertical pipes(diameters are in the range of 50e189 mm)were compared and the critical gas velocity of the transition boundary from bubble to slug flow tended to increase with the increase of diameters at D≥80 ***-flux models were established in different flow regimes and liquid properties have a significant effect on drift coefficients of bubble flow and slug flow(void fraction a≤0.4).The influence of inlet turbulent effect on the gas-liquid interface distribution gradually weakened and disappeared from the pipe base to 85D,where the flow was fully *** frequency has a trend of increase first and then decrease with the gas Weber numbers increasing at low liquid superficial velocities(J_(L)≤0.31 m/s).And on the basis of this law,a new slug frequency correlation was *** was found that there was an exponential relationship between the ratio of lengths of Taylor bubble to slug and the void fraction.

关键词： Void fraction flow regime Drift coefficien Slug frequency Taylor bubble length

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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

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Cyclone separation in a supercritical water circulating fluidized bed reactor for coallbiomass gasification： Structural design and numerical analysis

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Particuology 2018年第4期16卷 55-67页

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

A new concept of a supercritical water （SCW） circulating fiuidized bed reactor is proposed to produce hydrogen from coal/biomass gasification. The cyclone is a key component of the reactor system, in this paper, cyclones with a single circular inlet （SCI） or a double circular inlet （DCI） were designed to adapt to the supercritical conditions. We evaluated the separation performance of the two cyclones using numerical simulations. A three-dimensional Reynolds stress model was used to simulate the turbulent flow of the fluid, and a stochastic Lagrangian model was used to simulate the particle motion. The flow fields of both cyclones were three-dimensionally unsteady and similar to those of traditional gas-solid cyclones. Secondary circulation phenomena were discovered and their influence on particle separation was estimated. Analyzing the distribution of the turbulence kinetic energy revealed that the most intensive turbulence existed in the zone near the vortex finder while the flow in the central part was relatively stable. The particle concentration distribution was non-uniform because of centrifugal forces. The distribution area can be divided into three parts according to the motion of the particles. In addition, the separation efficiency of both cyclones increased with the inlet SCaN velocity. Because of its perturbance flow, the DCI separator had higher separation efficiency than the SCI separator under comparable simulations. However, this was at the expense of a higher pressure drop across the cyclone.

关键词： CycloneStructural design Supercritical water-solid flow Separation performance Circulating fluidized bed Computational fluid dynamics

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Investigation on a Supercritical Water Gasification System with CO_(2)as Transporting Medium

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Journal of Thermal Science 2023年第4期32卷 1614-1625页

作者： WANG Weizuo LU Bingru SHI Jinwen ZHAO Qiuyang JIN Hui State Key Laboratory of Multiphase Flow in Power Engineering(SKLMF) Xi’an Jiaotong UniversityXi’an710049China

As a benign energy vector,hydrogen has been discussed for a long *** water gasification was one of good ways to produce ***,supercritical water gasification system with H_(2)O transporting was energy consuming in the process of heating due to the high specific heat of H_(2)O.A new supercritical water gasification system was established in this paper with supercritical CO_(2)as medium *** plastics were used as the sample transported by CO_(2).Production yields,energy flow and exergy flow of the system were collected and the influence of temperature,pressure,gasification concentration and transporting concentration was *** flow of H_(2)O input into the reactor was 1000 kg/*** typical condition was as follow:temperature 923.15 K,pressure 23 MPa,and the mass ratio of water,sample and transporting medium was 100:9:*** of H_(2),CH4,CO and CO_(2)at this condition was 8.1 kg/h,39.6 kg/h,6.6 kg/h and 137.5 kg/h,*** system with H_(2)O transporting was used to compare with the supercritical CO_(2)transporting system and proved that system with CO_(2)transporting could reduce the loss of both energy and exergy while the reduce of each gas production yield was less than 0.1 mol/mol.

关键词： phenolic plastics supercritical water gasification CO_(2)-transporting system energy and exergy flow

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A computational particle fluid-dynamics simulation of hydrodynamics in a three-dimensional full-loop circulating fluidized bed: Effects of particle-size distribution

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Particuology 2020年第2期18卷 134-145页

作者： Hang Zhang Youjun Lu State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an 710049ShaanxiChina

A computational particle fluid-dynamics model coupled with an energy-minimization multi-scale(EMMS)drag model was applied to investigate the influence of particle-size distribution on the hydrodynamics of a three-dimensional full-loop circulating fluidized *** particle systems,including one monodisperse and two polydisperse cases,were *** numerical model was validated by comparing its results with the experimental axial voidage distribution and solid mass *** EMMS drag model had a high accuracy in the computational particle fluid-dynamics simulation of the three-dimensional full-loop circulating fluidized *** total number of parcels in the system(Np)influenced the axial voidage distribution in the riser,especially at the lower part of the *** numerical simulation results showed that axial segregation by size was predicted in the two polydisperse cases and the segregation size increased with an increase in the number of size *** axial voidage distribution at the lower portion of the riser was significantly influenced by particle-size ***,radial segregation could only be correctly predicted in the upper region of the riser in the polydisperse case of three solid species.

关键词： Circulating fluidized bed Computational particle fluid dynamics Particle-size distribution Energy-minimization multiscale model Three-dimensional full-loop simulation

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Fluidization of particles in SCW fluidized bed:Voidage distribution of emulsion phase

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Particuology 2022年第4期20卷 60-75页

作者： Hao Wang Youjun Lu State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an 710049ShaanxiChina

Supercritical water(SCW)fluidized bed reactors convert biomass to fuels without pollutants *** this work,experimental studies were carried out to investigate voidage distribution in an SCW fu-idized bed by capacitance *** sands with different particle sizes were fluidized by SCW under system pressure of 20-27 MPa and temperature of 410-570℃.The effect of operation conditions on voidage distributions of the emulsion phase(*** voidage and probability density)is discussed.A predicting correlation between voidage and superficial velocity in emulsion phase is *** relative error of the correlation is within+25%.These research results provide useful guidance for the optimization of supercritical water gasification technology.

关键词： Supercritical water fluidized bed Capacitance probe measurement system Voidage distribution

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Efficient One-Step Electrochemical Synthesis of Ammonia-Hydrogen Fuel for Clean Energy Applications

SSRN

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SSRN 2025年

作者： Yang, Zhongmei Wang, Xiaoyang Mu, Xiaojiang Hong, Congjie Miao, Lei Novel Battery Materials Research Center of Engineering Technology State Key Laboratory of Featured Metal Materials and Life-cycle Safety for Composite Structures School of Physical Science and Technology Guangxi University Nanning530004 China State Key Laboratory of Multiphase Flows in Power Engineering Xi’an Jiaotong University Xi’an710049 China

Ammonia-hydrogen fuel, recognized as a quintessential zero-carbon green energy source, presents significant challenges in storage and transportation due to the inherent safety risks associated with hydrogen fuel handling. Leveraging ammonia's potential as an efficient hydrogen storage medium, we focus on developing a novel technology for on-site ammonia decomposition to produce hydrogen under ambient conditions. Here, we employ a straightforward electrochemical process to catalytically decompose ammonia into hydrogen and nitrogen at standard temperature and pressure, with ammonia in its gaseous form directly volatilized from an aqueous ammonia solution. A CeO2@NiCu₃/NF electrocatalyst capable of efficient ammonia decomposition at an impressively low potential (1.27 V vs. RHE) was synthesized. This catalyst demonstrated a Tafel slope of 41.5 mV dec-1, significantly improving electrolysis efficiency. It also exhibited excellent stability during 21 hours of continuous operation. Density Functional Theory (DFT) analysis revealed that the unique composite structure of CeO2 and NiCu3 features a d-band position similar to platinum, optimizing the adsorption-desorption balance of ammonia. Furthermore, the impact of ammonia on the combustion characteristics of hydrogen under different cracking ratios was investigated from an application perspective. Combustion kinetics simulations were performed to evaluate the effects of ammonia on the ignition delay time (IDT) and laminar flame speed (LFS) of hydrogen. The results indicate that the presence of small amounts of NH3 has a negligible effect on the ignition delay time of hydrogen but significantly reduces its laminar flame *** study provides a valuable experimental foundation for advancing the practical utilization of hydrogen as a sustainable fuel while addressing the challenges associated with ammonia-hydrogen energy systems. © 2025, The Authors. All rights reserved.

关键词： Ammonia

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Instantaneous mixing characteristics of binary mixtures differing in density in a gas-solid fluidised bed

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Particuology 2020年第6期18卷 63-71页

作者： Zhen Wan Youjun Lu Hao Wang State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an 710049ShaanxiChina

Characterisations of instantaneous mixing behaviours in fluidised beds with binary mixtures has many *** studied the instantaneous mixing characteristics of binary mixtures in a 2-D quasi gas-solid fluidised bed using a capacitance probe *** method enabled the quantitative assessment of instantaneous mixing behaviours,including mixing index,rate,and *** kinds of binary mixtures of similar size but different density were used for the transient and steady fluidisation experiments in a bubbling fluidised *** mixing curves of initially segregated binary mixtures were acquired,and the instantaneous characteristics for the entire process were *** equation was proposed to describe the mixing process and predict the mixing degree over *** comparing experiments with different working conditions,the effects of superficial gas velocity and density ratio on the mixing in the centre and at the wall of the fluidised bed were *** the stable fluidisation stage,the axial concentration profiles of the mixtures were obtained,and the mechanisms of mixing were *** showed that the mixing level increased logarithmically with time and eventually reached a relatively stable *** the superficial gas velocity and reducing the density ratio promoted mixing and reduced mixing *** superficial gas velocities tended to mix the mixtures well and quickly,regardless of the density ratio of the two components.

关键词： Binary mixtures Fluidised bed Mixing Instantaneous characteristics

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Thermally induced non-coalescence of compound droplets

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Applied Thermal engineering 2025年 276卷

作者： Jianmei Zhao Xing Li Bofeng Bai State Key Laboratory of Multiphase Flow in Power Engineering School of Chemical Engineering and Technology Xi’an Jiaotong University Xi'an 710049 China

Compound droplets surrounded by a gaseous phase with different temperatures widely exist in industrial applications. Previous research has focused on thermally induced non-coalescence or delayed coalescence between two single-phase droplets or a droplet and a liquid bath. The primary mechanism is the levitated intervening pressure in the lubricating air layer between droplets, which is caused by the thermocapillary convection. In this study, the non-coalescence of two compound droplets in a cold ambient air environment is experimentally investigated. The thermocapillary mechanism manifests three distinct features. First, as the two compound droplets approach each other, the temperature of the contact side of each droplet increases because of reduced heat loss, a phenomenon termed as the contact-side heating effect. This creates a surface temperature gradient, inducing Marangoni stress and subsequent surface convection. Second, owing to the immiscibility of the two phases within each compound droplet, the thermocapillary convection develops independently in each phase, forming independent convection which cannot be observed in single-phase droplets . It was observed that the directions of the thermocapillary convection within the two droplets were correlated and always planar symmetric, which is different from the uncorrelated and opposite convection of two single-phase droplets. Third and most importantly, the thermocapillary convection in the oil phase entrains the air into the lubricating film between droplets, inhibiting their coalescence only when the oil/water interface is adjacent to the contact zone.

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Effect of the Density Difference on Fluid Distribution in Layered Rock Samples

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Energy & Fuels 2025年第9期39卷 4412-4420页

作者： Yongfei Yang Tonghui Liu Yingwen Li Weichen Sun Hai Sun Lei Zhang Junjie Zhong Kai Zhang Jun Yao State Key Laboratory of Deep Oil and Gas China University of Petroleum (East China) Qingdao 266580 P. R. China；Research Center of Multiphase Flow in Porous Media School of Petroleum Engineering China University of Petroleum (East China) Qingdao 266580 P. R. China Geosteering & Logging Research Institute Sinopec Matrix Corporation Qingdao 266071 P. R. China Research Center of Multiphase Flow in Porous Media School of Petroleum Engineering China University of Petroleum (East China) Qingdao 266580 P. R. China

During geological CO2storage, gravity segregation due to fluid density differences significantly affects the efficiency and safety of the process. This can result in premature CO2breakthrough, reduced storage efficiency, and increased leakage risks. This study aims to investigate how gas migrates in layered heterogeneous reservoirs over time due to prolonged density differences and to assess the resulting impact on fluid distribution. We use artificially layered heterogeneous sandstone cores for experimentation. After completing gas injection and water flooding experiments, the core was positioned with the low permeability layer (LPL) at the top and the high permeability layer (HPL) at the bottom for an extended period. Because the effects of density differences are not easily discernible during gas–water two-phase flow under typical driving forces, we applied micro-CT imaging technology to visualize and analyze how density differences influence gas flow within the core. The results demonstrate that during the static placement period following displacement, gas clusters exhibit different flow behaviors at the pore throats. Most gas clusters struggle to overcome the Jamin effect and enter into the upper pores; a few large-volume gas clusters, driven by density differences, partially pass through the throats into the upper pores, while the remaining portions are stranded within the throats, leading to a snap-off phenomenon; while some gas clusters successfully overcome the Jamin effect and enter the upper pores in significant numbers. The experimental findings indicate that the LPL effectively hinder the upward migration of the nonwetting phase gases from bottom and fluid density differences significantly influence gas–water distribution changes. This study provides critical insights for optimizing CO2storage and offers a new perspective on fluid behavior in layered heterogeneous reservoirs.

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