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ASME 2024 International Mechanical engineering Congress and Exposition, IMECE 2024

作者： Yang, Dong An, Ning Du, Xiaocheng Han, Lei Guo, Zerui Wei, Ziyu State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Shaanxi Xi'an China

ISBN: (纸本)9780791888667

When the boiler load varies, the operational parameters in the water wall will change, this process is called as dynamic process. Dynamic process presents unique flow and heat transfer phenomena within the water wall. To investigate the process, the research was conducted in a vertical upward smooth tube for a supercritical circulating fluidized bed (CFB) boiler. Experiments were conducted to explore the dynamic characteristics during transcritical pressure process. The results indicate that as system pressure decreases from 23 MPa to 21 MPa, the mass flux within the tube increases sharply, and the outlet fluid temperature decreases. Concurrently, a rapid rise in wall temperature was observed. As the inlet mass flux increases, the wall temperature eventually returns to the normal value. The dynamic heat transfer coefficients were calculated throughout the transcritical pressure process, revealing stages of heat transfer deterioration, subcooled boiling, and single-phase water heat transfer. In addition, experiments and numerical simulations were carried out to explore the dynamic characteristics at supercritical pressure. The dynamic response curves during the step process of heat flux and inlet enthalpy under supercritical pressure conditions were obtained. As the inlet enthalpy decreases, the system mass flux increases, and as the heat flux increases, the system mass flux decreases. And there is no rise in wall temperature during the dynamic response at supercritical pressure. Copyright © 2024 by ASME.

关键词： Water tube boilers

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Thermal-diffusive instabilities of laminar premixed CH4/H2/air flat flames 10

Thermal-diffusive instabilities of laminar premixed CH4/H2/a...

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10th Asia-Pacific Conference on Combustion, ASPACC 2015

作者： Jin, Wu Wang, Jinhua Yu, Senbin Huang, Zuohua State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

As one of the most promising clean alternative fuels, natural gas has been widely used in automobile engines. However, due to the slow burning velocity of natural gas and its poor lean-burn ability, hydrogen is often added to improve its combustion behavior. Researches on the fundamental laminar premixed flame characteristics of CH4/H2 blends are of great significance to understand the combustion process in practical combustors. The intrinsic instability of laminar flame is one of the classic issues in flame dynamics, which presents the dynamic response of laminar premixed flamelets to weak perturbations. By studying dynamic mechanism of intrinsic instability, we can estimate the burning velocity more accurately and gain a deeper insight into the turbulent combustion process in spark ignition engines. In this study, the cellular instabilities of laminar premixed CH4/H2/air flat flames were studied using McKenna burner with OH-PLIF technique. It was found that the addition of H2 can broaden the lean combustion limit on flat flame burner with which the cellular instabilities were brought. The digital and OH-PLIF images were obtained to calculate the quantitative parameters of cellular length scale, which is associated with the properties of fuel mixtures such as Lewis number, Markstein number et al. Through the theoretic analysis, we make a thorough investigation on the mechanism about how the cellular scales were determined.

关键词： Natural gas

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Performance and emission characteristics of a hydrogen-enriched compressed-natural-gas direct-injection spark ignition engine diluted with exhaust gas recirculation

Performance and emission characteristics of a hydrogen-enric...

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作者： Liu, Y.-F. Liu, B. Zeng, K. Huang, Z. Zhou, L. Sun, L. State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi'an Jiaotong University Xi'an 710049 China

Compressed natural gas (CNG) has been widely used in city buses or taxis because of its relatively low price and great abundance. Most of the CNG engines externally mix the natural gas with the intake air and utilize a lean-burn strategy to achieve low nitrogen oxide (NOx) emissions and high fuel economy. However, the well-examined external mixing of gas fuel with the intake air will result in a volumetric efficiency loss at high engine loads and may cause backfire when the natural gas is enriched with hydrogen. Also, the lean-burn technique may not sufficiently satisfy increasingly restricted future legislation. In this paper, the use of the stoichiometric equivalence ratio with exhaust gas recirculation (EGR) was investigated experimentally on a direct-injection spark ignition engine fuelled with hydrogen-natural-gas blends. Attention is focused on the advantages of combining EGR with hydrogen enrichment. The results show that hydrogen enrichment increases the brake mean effective pressure, which dramatically deteriorates under high-level EGR. Optimal efficiencies are achieved with an EGR rate of 5-10 per cent;the NO x emissions can be decreased by about 80per cent with 25 per cent EGR dilution, but the combustion variation increases simultaneously. With hydrogen enrichment, the combustion variation can be controlled under 5per cent, while the NOx, hydrocarbon, and carbon monoxide emissions are kept at a low level. Worse EGR tolerance was exhibited for the late-injection-timing case. © Author 2011.

关键词： Efficiency

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Numerical analysis of the static performance of an annular aerostatic gas thrust bearing applied in the cryogenic turbo-expander of the EAST subsystem

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Plasma Science and Technology 2017年第2期19卷 115-122页

作者： Tianwei LAI Bao FU Shuangtao CHEN Qiyong ZHANG Yu HOU State Key Laboratory of Multiphase Flow in Power Engineering Xi＇an Jiaotong University Xi＇an 710049 People＇s Republic of China Institute of Plasma Physics Chinese Academy of Sciences Hefei 230031 People＇s Republic of China

The EAST superconducting tokamak, an advanced steady-state plasma physics experimental device, has been built at the Institute of Plasma Physics, Chinese Academy of Sciences. All the toroidal field magnets and poloidal field magnets, made of NbTi/Cu cable-in-conduit conductor, are cooled with forced flow supercritical helium at 3.8 K. The cryogenic system of EAST consists of a 2 kW/4 K helium refrigerator and a helium distribution system for the cooling of coils, structures, thermal shields, bus-lines, etc. The high-speed turbo-expander is an important refrigerating component of the EAST cryogenic system. In the turbo-expander, the axial supporting technology is critical for the smooth operation of the rotor bearing system. In this paper, hydrostatic thrust bearings are designed based on the axial load of the turbo-expander. Thereafter, a computational fluid dynamics-based numerical model of the aerostatic thrust bearing is set up to evaluate the bearing performance. Tilting effect on the pressure distribution and bearing load is analyzed for the thrust beating. Bearing load and stiffness are compared with different static supply pressures. The net force from the thrust bearings can be calculated for different combinations of bearing clearance and supply pressure.

关键词： EAST helium cryogenic system aerostatic thrust beating inclination bearing load

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Study on ash fusion behaviors and physico-chemical characteristics of semi-coke and its blended fuel with coal 35

Study on ash fusion behaviors and physico-chemical character...

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35th Annual International Pittsburgh Coal Conference, PCC 2018

作者： Yuan, Maobo Wang, Chang'an Wang, Pengqian Tao, Zichen Du, Yongbo Zhao, 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

ISBN: (纸本)1890977357

With the rapid development of coal chemical industry in China, a large number of low-volatile carbon-based fuels such as semi-coke are in urgent need of combustion and utilization, and the co-combustion with high-volatile coal shows the potential to realize the large-scale utilization of semi-coke in coal-fired power plant. Because the blending coal can hardly match the design coal, it is easy to aggravate the degree of deposition and slagging on the heating surface and affect the operation of the boiler. However, the melting behavior of ash produced by blended coal with semi-coke combustion needs further study. In this paper, the ash melting behavior and physico-chemical characteristics of semi-coke and its blended fuel with coal were experimentally studied. Firstly, the relation of ash composition and ash melting behavior was observed by comparing the ash composition and ash fusion point of semi-coke and raw coal. Secondly, the influence of blending ratio and blending mode on the ash melting behavior of semi-coke blended fuel was studied by micro-computer ash melting point meter. Finally, the microstructure and physico-chemical properties of the melted ash at the softening temperature were evaluated by scanning electron microscope (SEM) technique with X-ray spectrometer (EDS) and X-ray diffractometer (XRD) technique. The experimental results showed that the mineral composition and oxide content in the semi-coke were different from the raw coal, which led to the change of coal ash fusibility. Meanwhile, the ash fusion point of semi-coke blended fuel could not be expressed linearly by the ash fusion point of its raw coal, and the influence of blending mode including in-furnace blending and out-furnace blending on the ash fusion point could be neglected. While the microstructure and physico-chemical properties were affected by the blending mode. Compared to the in-furnace blending, the carbon content was lower in out-furnace blending. Furthermore, the blending mode h

关键词： Coal

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Experimental Investigation on Ejector Performance Using R134a as Refrigerant

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Journal of Thermal Science 2019年第4期28卷 727-735页

作者： DAI Zhengshu YU Bo LIU Pengpeng CHEN Guangming ZHANG Hua School of Energy and Power Engineering University of Shanghai for Science and TechnologyShanghai 200093China State Key Laboratory of Air-conditioning Equipment and System Energy Conservation Zhuhai 519070China Institute of Refrigeration and Cryogenics Zhejiang UniversityHangzhou 310027China Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering Shanghai 200093China

Ejector refrigeration has the advantage of low capital cost,simple design,reliable operation,long lifespan and almost no *** only weakness is the low efficiency and its intolerance to deviations from design operation condition.R134 a used in ejector refrigeration system gives better performance in comparison with many other environmental friendly refrigerants as the generation temperature is from 75℃to 80℃.The present work experimentally investigated the on-design and off-design performance of the ejector with fixed geometry using R134 a as refrigerant,and cycle performance of the ejector refrigeration *** experimental prototype was constructed and the effects of primary flow inlet pressure,secondary flow inlet pressure and ejector back pressure on ejector performance and cycle performance were investigated *** operation conditions are:primary flow inlet pressure from 2.2 MPa to 3.25 MPa,secondary flow inlet pressure from 0.36 MPa to 0.51 MPa,ejector back pressure from 0.45 MPa to 0.67 *** were drawn from the experimental results,and the experimental data can be used for validation of theoretical model for both critical and subcritical mode.

关键词： ejector performance refrigeration R134a experiment

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Numerical simulations of the discontinuous progression of cerebral aneurysms based on fluid-structure interactions study

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Science China(Physics,Mechanics & Astronomy) 2010年第5期53卷 944-953页

作者： MA XiaoQi1,WANG YueShe1,YU FangJun1 & WANG GuoXiang1,2 1 State key laboratory of multiphase flow in power engineering,Xi’an Jiaotong University,Xi’an 710049,China 2 Department of Mechanical engineering,The University of Akron,Akron,OH 44325-3903,USA 1. State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an 710049 China2. Department of Mechanical Engineering The University of Akron Akron OH 44325-3903 USA

Investigations into the characteristics of hemodynamics will provide a better understanding of the pathology of cerebral aneurysms for *** this work,a steady state discontinuous-growth model of the cerebral aneurysms was *** the assumption of the fluid-structure interaction between the wall of blood vessel and blood,a fluid-structure coupling numerical simulation for this model was built using software ANSYS and *** simulation results showed that as the aneurysm volume increased,a blood flow vortex came forth,the vortex region became asymptotically larger,and eddy density became gradually stronger in *** the emergence of the vortex region,the blood flow in the vicinity of the downstream in the aneurysms volume turned into bifurcated flow,and the location of the flow bifurcated point was shifted with the aneurysm volume growing while directions of the shear stress applied to two sides of the bifurcated point were *** Von Mises stress distribution along the wall of aneurysm volume decreased in the prior period and increased gradually in the later *** maximum stress was in the neck of the volume and the minimum was on the distal end in the whole process of *** was shown that as the aneurysm increased the maximum deformation location of the aneurysm,vertical to the streamline,was transferred from the distal end of the aneurysm to its neck,then back to its distal end of the aneurysm again.

关键词： cerebral aneurysm fluid-structure interaction wall shear stress discontinuous progression

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Uncertainty analysis of molten corium In-Vessel Retention under External Reactor Vessel Cooling

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International Journal of Advanced Nuclear Reactor Design and Technology 2023年第4期5卷 159-167页

作者： Wu, Shihao Wang, Dong Zhang, Yapei Zhou, Yukun Tian, Wenxi Qiu, Suizheng Su, G.H. School of Nuclear Science and Technology Shaanxi Engineering Research Center of Advanced Nuclear Energy State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

External Reactor Vessel Cooling (ERVC) is a key measure to realize molten corium In-Vessel Retention (IVR). The uncertainty of severe accident in core leads to the uncertainty of molten pool parameters in lower head, which may threat the reliability of successful implementation of IVR. In this study, an uncertainty analysis is employed to ensure the reliability of ERVC technology to IVR with the final two-layer molten pool configuration of AP1000.600 simulations are performed to determine the effect of five key parameters. As long as parameters are within high probability density range, lower head can remain intact, and safety margin is greater than 15 %. For influence level and correlation of parameters, the order on metal layer is: Decay heat > Fe mass > UO2 mass > Zr oxidation fraction > Emissivity of metal layer. The results can provide guidance for subsequent research direction and optimal design of mitigation measures. © 2024 Xi'an Jiaotong University

关键词： Uncertainty analysis

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A two-phase non-isothermal mass transport model for direct methanol fuel cells

A two-phase non-isothermal mass transport model for direct m...

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2009 US-EU-China Thermophysics Conference - Renewable Energy, UECTC'09

作者： Miao, Zheng He, Ya-Ling Li, Xiao-Yue Zou, Jin-Qiang State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi'an Jiaotong University Xi'an Shaanxi China

ISBN: (纸本)9780791802908

A two-dimensional two-phase non-isothermal mass transport model for liquid feed direct methanol fuel cells (DMFCs) is presented in this paper. The heat and mass transfer across the membrane electrode assembly (MEA) is formulated based on the classical multiphase flow theory in the porous media. The effects of methanol crossover and non-equilibrium evaporation/condensation of methanol and water at the gas-liquid interface on the cell performance are considered. Results of this model show that the methanol feeding concentration and cell operation temperature have great effects on the cell performance. The distribution of cell temperature is non-uniform and the highest temperature appears in the cathode catalyst layer (CL). The effects of open-ratio of the flow field plate and the thermal conductivity of diffusion layers, catalyst layers and membrane are also investigated in this work. Copyright © 2009 by ASME.

关键词： Methanol

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The evaporation of nanoscale sodium liquid film on the non-ideal nanostructure surface: A molecular dynamics study

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International Journal of Advanced Nuclear Reactor Design and Technology 2023年第1期5卷 1-8页

作者： Wang, Zetao Ye, Tianzhou Guo, Kailun Tian, Wenxi Qiu, Suizheng Su, Guanghui State Key Laboratory of Multiphase Flow in Power Engineering Shaanxi Key Lab of Advanced Nuclear Energy and Technology School of Nuclear Science and Technology Xi'an Jiaotong University Xi'an710049 China

The nanoscale liquid sodium film inside the microporous wick structure is of great importance to understanding the evaporation mechanism of the sodium heat pipe. The novel optimized wick structure is made of several layers of special screen. The surface of each screen exhibits a nanostructure type. Some non-ideal nanostructures may result from experimental faults or limits. And they will have an effect on the evaporation of film. In the present study, molecular dynamics is adopted to investigate this effect. The simulation system consists of the liquid sodium film and the solid surface. The flat surface is set as the reference. Based on the three non-ideal shapes of deposition, the sinusoidal nanostructures, conical nanostructures, and spherical nanostructures are built. The results indicate that the evaporation is suppressed by the above nanostructure surfaces. The weakening effect is through three forms: the potential gradient of the liquid film is intensified and the evaporation difficulty is increased;the heat transfer in the solid-liquid contact region is impeded;the collision heat transfer inside the liquid film is affected due to the delay of the aggregation variation between liquid atoms. © 2023 Xi'an Jiaotong University

关键词： Heat pipes

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