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Numerical simulation on characteristics of hydrodynamics, interphase and wall to bed heat transfer in a pseudo 2D spouted bed using supercritical CO_(2) as fluidizing agent

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Particuology 2025年第1期96卷 106-125页

作者： Kun Jiang Hui Jin State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an710049China

By employing the Eulerian-Eulerian Two Fluid Model, the effect of different particle size, supercritical CO_(2) (scCO_(2)) velocity at slit jet (U_(jet)) and initial bed height on the macroscopic characteristics (i.e., fountain morphology, profiles of particle velocity, momentum transfer characteristics among particles, transient temperature evolutions of particles, interphase heat transfer coefficient and wall to bed heat transfer characteristics) in the pseudo 2D rectangular spouted bed using scCO_(2) as fluidizing agent is numerically studied in detail herein. Considering there are currently no relevant visualized experiments reported using scCO_(2) as a fluidized agent due to the extreme operating pressure of CO_(2) (25 MPa in this paper) under supercritical conditions, present numerical model was validated with experimental data by using air as the fluidizing agent, confirming simulated instantaneous volume fraction distribution of air and transient temperature evolutions of particles basically consistent with the experiments. Numerical results reveal some of the internal relations among hydrodynamics characteristics in bed, momentum transfer characteristics among particles and relevant heat transfer behaviours. Results show larger Ujet and smaller particle size will accelerate the particles' translational motion in spout, spout core and fountain core zone. Larger particle concentration will promote inter-particle collisions while suppress the kinetic motion of particles in above zones. Decrease the particle size will enhance interphase convective heat transfer coefficient, while increasing U_(jet) results insignificant impacts. Finally, we also observe the transition zone between annular and periphery zone has a certain enhancing effect on the wall to bed heat transfer coefficient.

关键词： Spouted bed Two fluid model Kinetic theory of granular flow Supercritical CO_(2) Hydrodynamics Heat transfer

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Specific Heat Capacity and Coordination Number of Nano-Confined Transcritical Water

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Journal of Thermal Science 2025年第2期34卷 498-509页

作者： ZHANG Bowei JIANG Kun ZHANG Jie JIN Hui State Key Laboratory of Multiphase Flow in Power Engineering(SKLMF) Xi’an Jiaotong UniversityXi’an710049China

In the field of nano energy,investigating the specific heat capacity and coordination number of nano-confined water is highly significant for gaining a better understanding of the energy and microstructure of confined *** this work,we employed the method of molecular dynamics(MD)simulation to calculate the specific heat capacity at constant volume and coordination number of water molecules confined in carbon nanotubes(CNTs)under different conditions(T=600-700 K,P=21.776 and 25 MPa,CNT diameter=0.949-5.017nm).The results showed that near the critical point,the specific heat capacity at constant volume of confined water was lower than that of bulk water,and the energy fluctuation showed a trend of first increasing and then remaining unchanged with the increase of temperature and CNT *** them,the saturation point of temperature is 650 K(reduced pressure P_(r)=1)and 660 K(P_(r)=1.15),and the saturation point of CNT diameter is 2.034 ***,the pseudo-critical temperature of confined water was the same as bulk water,and it increased with the increase of critical ***,with the increase of CNT diameter,the coordination number of confined water increased rapidly,and reaches the saturation state when the CNT diameter is 2.034 *** investigation revealed the mass and energy characteristics of nano-confined water near the critical point,which could provide guidance for the critical phase transition of nano-confined water.

关键词： molecular dynamics nano-confined transcritical water specific heat capacity at constant volume coordination number

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Comparison of CO_(2)with H_(2)O as the transport medium in a biomass supercritical water gasification system

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Frontiers of Chemical Science and Engineering 2024年第11期18卷 121-133页

作者： Weizuo Wang Bingru Lu Jinwen Shi Qiuyang Zhao Hui Jin State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong UniversityXi’an 710049China

Supercritical water gasification is a clean technology for biomass conversion and *** supercritical water gasification systems,H_(2)O is often used as the transport *** in the reaction temperature at the gasification area and in the heating rate of biomass may limit the gasification rate and *** this paper,CO_(2)is used as the transport medium due to its relatively low critical point and specific heat ***,a corn stalk gasification system with different transport media is established in this paper,and the influences of various operating parameters,such as temperature,pressure and feedstock concentration,are *** results show that the gas yield in the CO_(2)-transport system decreases by no more than 5 wt%.In addition,thermodynamic analysis reveals that a system with CO_(2)as transport medium consumes approximately 25%less electricity than a system with H_(2)O as the transport *** addition,the reaction heat absorption *** results show the superiority of CO_(2)to H_(2)O as a transport medium.

关键词： biomass supercritical water gasification hydrogen production CO_(2)transport energy and exergy analyses

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Effects of physical properties of supercritical water on heat transfer characteristics of single particle within a particle cluster Author links open overlay panel

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Particuology 2024年第8期91卷 291-302页

作者： Xiaoyu Li Bowei Zhang Huibo Wang Hui Jin State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an710049China

The complex physical properties of supercritical water(SCW)make the heat transfer characteristics of particles within a particle cluster *** heat transfer characteristics of single particle within a particle cluster in SCW,influenced by surrounding particles,have not been effectively *** numerical simulations were conducted to investigate the heat transfer characteristics of particle clusters in SCW under different *** results were compared and analyzed with those from constant property *** was found that Reynolds number(Re)and the void fraction of particle cluster have no special effects on the variation trends of Nusselt number(Nu)for the focused ***,the particle temperature had a significant effect on the variation trends of *** effect of Re on the heat transfer rate exponent(η)of the focused particle can be divided into two zones:a significant effect zone and a non-significant effect *** effect of void fraction onηin the non-significant effect zone was *** the non-significant effect zone,ηdecreased with the increasing particle *** the significant effect zone,the variation trends ofηbecame more *** fundamental reason for this series of phenomena is the changes in distribution of physical properties.A model forηwas developed for the non-significant effect *** model can filter out the effects of Re and certain particle cluster spatial configurations,and it demonstrates good predictive performance.

关键词： Supercritical water Particle cluster Heat transfer characteristics Heat transfer rate exponent Physical properties correction

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Measurement,Modelling and Analysis of Residence Time Distribution Characteristics in a Continuous Hydrothermal Reactor

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Journal of Thermal Science 2024年第4期33卷 1301-1311页

作者： LI Yi ZHAI Binjiang WANG Junying WANG Weizuo JIN Hui State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong UniversityXi’an710049China

Understanding the residence time distribution(RTD)of a continuous hydrothermal reactor is of great significance to improve product quality and reaction *** this work,an on-line measurement system is attached to a continuous reactor to investigate the characteristics of *** approach that can accurately fit and describe the experimental measured RTD curve by finding characteristic values is proposed for analysis and *** RTD curves of three experiment groups are measured and the characteristic values are *** show that increasing total flow rate and extending effective reactor length have inverse effect on average residence time,but they both cause the reactor to approach a plug flow reactor and improve the materials *** branch flow rate fraction has no significant effect on RTD characteristics in the scope of the present work except the weak negative correlation with the average residence ***,the natural convection stirring effect can also increase the average residence time,especially when the forced flow is *** analysis reveals that it is necessary to consider the matching of natural convection,forced flow and reactor size to control RTD when designing the hydrothermal reactor and working conditions.

关键词： continuous reactor residence time distribution modelling

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Laminar Flame Structure-Dependent Exergy Destruction Behavior at Auto-Ignition Time Scale:A Case Study of Dimethyl Ether(DME)

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Journal of Thermal Science 2024年第4期33卷 1257-1271页

作者： WU Honghuan HUANG Wenlin ZHAO Hao SUN Wuchuan HUANG Zuohua ZHANG Yingjia State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong UniversityXi’an710049China

Hybrid deflagration/auto-ignition flame structures coexist in the combustion of advanced *** exergy destruction caused by different irreversible processes under varied flame regimes is thus important for understanding engine *** this study,the flame propagation modes for the premixed DME/air mixtures are numerically investigated under engine-relevant *** entropy generation and exergy destruction characteristics are compared under different flame *** reveal that as the typical premixed flame transition towards auto-ignition front,the exergy destruction from heat conduction and species mass diffusion gradually vanish and are dominated by chemical *** distributions of temperature and species mole fraction in the flame domain are analyzed to clarify the exergy destruction behaviors caused by heat conduction and mass ***,by dividing the DME oxidation process into four stages,the main reaction channels that contribute to the increase in exergy destruction from chemical reaction have been *** is found that the production and consumption of CH_(2)O and HO_(2) radical dominate the exergy destruction behavior during DME *** this basis,the kinetic mechanism of low-temperature chemistry causing greater exergy destruction is ***,low-temperature chemistry leads to significant exergy destruction due to(a)the large irreversibility of itself and(b)(mainly)the enhancement of H_(2)O_(2)loop reactions by low-temperature reaction *** the reduction of combustion irreversibility is promising to be achieved by reasonably regulating the fuel oxidation path.

关键词： exergy destruction flame structures entropy generation low-temperature chemistry DME

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A numerical investigation on heat transfer characteristics of a particle cluster in fluid with variable properties

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Particuology 2024年第11期94卷 327-344页

作者： Xiaoyu Li Huibo Wang Bowei Zhang Hui Jin State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an710049China

This work investigates the heat transfer characteristics of particle clusters under the effects of the complex properties of supercritical water(SCW).It analyzes the heat transfer characteristics of sub-particles and the average heat transfer characteristics of particle *** results reveal a phenomenon of shifting positions of high specific heat *** led to variations in the dimensionless heat transfer coefficient ***,the results indicate that as the heat transfer process strengthens,the effects of variations in property distribution on heat transfer tends to *** on this conclusion,the effects of variations in property distribution on heat transfer are categorized into Stable Effects Region and Non-Stable Effects *** utilizing the principles of fluid flow-heat transfer coupling and similarity,a heat transfer prediction model for particle clusters in SCW is established.

关键词： Heat transfer Supercritical water Particle cluster Modeling

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Numerical investigation on characteristics of interfacial wave of liquid film in gas-liquid two-phase flow using OpenFOAM

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Chinese Journal of Aeronautics 2024年第2期37卷 233-248页

作者： Xiaoqi MA Yueshe WANG Jiaming TIAN State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong UniversityXi’an 710049China

Liquid film cooling as an advanced cooling technology is widely used in space *** operation of liquid film along the rocket combustion inner wall is crucial for thermal protection of rocket *** stability of liquid film is mainly determined by the characteristics of interfacial wave,which is rarely investigated right *** to improve the stability of thin film has become a hot *** view of this,an advanced model based on the conventional Volume of Fluid(VOF)model is adopted to investigate the characteristics of interfacial wave in gas-liquid flow by using OpenFOAM,and the mechanism of formation and development of wave is revealed intuitively through numerical *** effects from gas velocity,surface tension and dynamic viscosity of liquid(three factors)on the wave are studied *** can be found that the gas velocity is critical to the formation and development of wave,and four modes of droplets generation are illustrated in this ***,a gas vortex near the gas-liquid interface can induce formation of wave easily,so changing the gas vortex state can regulate formation and development of ***’s more,the change rules of three factors influencing on the interfacial wave are obtained,and the surface tension has a negative effect on the formation and development of wave only when the surface tension coefficient is above the critical value,whereas the dynamic viscosity has a positive effect in this ***,the maximum height and maximum slope angle of wave will level off as the gas velocity ***,the maximum slope angle of wave is usually no more than 38°,no matter what happens to the three factors.

关键词： Interfacial wave Gas-liquid Two-phase flow VOF model OpenFOAM

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Effects of physical properties of supercritical water on coarse graining of particle cluster

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Particuology 2023年第11期82卷 166-178页

作者： Xiaoyu Li Huibo Wang Yi Li Hui Jin State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an710049China

The coarse graining of particle cluster is of great significance to the study of a fluidized bed. The effects of variations in the physical properties of supercritical water on the coarse graining of particle cluster are investigated in this work. The drag coefficient distributions of the particle cluster are not influenced by the physical properties. However, the physical properties have effects on the values of drag coefficient. The effects of physical properties are weaker in the case of large particle concentrations. Furthermore, the physical properties lead to that the effect of particle cluster wake on the drag of downstream particles being significantly different from that of constant property flow. The variation trend of drag of coarse graining particle is consistent with that of isolated particle. The physical properties lead to significant differences in the values of drag. In this paper, the dominance of the effects of physical properties in a variety of cases is confirmed. Finally, a physical properties effect model is developed accordingly.

关键词： Supercritical water Variations in physical properties Fluidized bed Coarse grain method Particle drag

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Semiempirical equations of state of H_(2)O/CO_(2) binary mixtures in graphite nanoslits

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Science China(Physics,Mechanics & Astronomy) 2023年第8期66卷 83-92页

作者： Haoxuan Li Bin Zhao Chengzhen Sun Bofeng Bai State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an 710049China

The existence of confining walls limits the prediction accuracy of nanoconfined fluids using macroscopic equations of state(EOSs);moreover,appropriate EOSs for multicomponent mixture fluids in nanoconfined spaces are ***,we derive the EOS of multicomponent mixture fluids confined in nanospaces at high temperatures and pressures,mainly considering the nanoconfinement effect and the competitive adsorption effect between different ***,the EOSs are validated through comparison with the molecular dynamics-simulated Pv T data of CO_(2)/H_(2)O mixtures in graphite *** consider the above effects,we derive two EOSs via two modeling methods:EOS I is obtained through modification of the actual component occupation volume in the Peng-Robinson equation of state(PR EOS)by fitting the binary component interaction coefficient and the number of adsorbed molecules according to a selectivity coefficient,while EOS II is obtained by considering the decreased pressure of the fluids in PR EOS by adding an attractive term between components and *** the simulation results as a benchmark,the two EOSs exhibited good prediction accuracies under low CO_(2) concentrations,and generally,EOS II was more accurate than EOS *** study fills the gap in the EOSs of nanoconfined mixture fluids,and the obtained equations can help to further describe the thermodynamic properties of confined mixture fluids.

关键词： confined fluid mixtures equation of state nanoconfined spaces molecular dynamics simulation

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