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Evolution of nanofluid rayleigh-bénard flows between two parallel plates: A mesoscopic modeling study

Journal of Nanotechnology in engineering and Medicine 2013年第4期4卷 040905页

作者： Lu, Gui Duan, Yuan-Yuan Wang, Xiao-Dong Key Laboratory for Thermal Science and Power Engineering MOE Tsinghua University Beijing 100084 China Institute of Thermal Engineering Beijing Jiaotong University Beijing 100044 China State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources North China Electric Power University Beijing 102206 China Beijing Key Laboratory of Multiphase Flow and Heat Transfer for Low Grade Energy North China Electric Power University Beijing 102206 China

The developing and developed nanofluid Rayleigh-Bénard flows between two parallel plates was simulated using the mesoscopic thermal lattice-Boltzmann method (LBM). The coupled effects of the thermal conductivity and the dynamic viscosity on the evolution of Rayleigh-Bénard flows were examined using different particle volume fractions (1-4%), while the individual effects of the thermal conductivity and the dynamic viscosity were tested using various particle sizes (11 nm, 20 nm, and 30 nm) and nanoparticle types (Al 2O3, Cu, and CuO2). Two different heating modes were also considered. The results show that Rayleigh-Bénard cell in nanofluids is significantly different from that in pure fluids. The stable convection cells in nanofluids come from the expansion and shedding of an initial vortex pair, while the flow begins suddenly in pure water when the Rayleigh number reaches a critical value. Therefore, the average Nusselt number increases gradually for nanofluids but sharply for pure liquids. Uniform fully developed flow cells with fewer but larger vortex pairs are generated with the bottom heating with nanofluids than with pure liquid, with extremely tiny vortexes confined near the top heating plate for top heating. The number of vortex pairs decreases with increasing nanoparticle volume fraction and particle diameter due to the increasing of dynamic viscosity. The average Nusselt number increases with the increasing Rayleigh number, while decreases with the increasing nanoparticle diameters. The nanoparticle types have little effect on the Rayleigh-Bénard flow patterns. The Rayleigh-Bénard flows are more sensitive with the dynamic viscosity than the thermal conductivity of nanofluids. Copyright © 2013 by ASME.

关键词： Nanoparticles

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Experimental investigation for liquid holdup reduction of subsea riser with surfactant

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AIP Conference Proceedings 2010年第1期1207卷 119-124页

作者： C. Li L. Liu Q. B. Bao F. D. Zhou State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University China

The principal pressure drop in a subsea riser is generally the gravitational pressure drop component due to liquid holdup. Surfactant is a kind of Chemical compound related to flow improvement. Gas‐liquid two‐phase flow in subsea riser with zero and small liquid flow rates was simulated in two vertical tubes with diameters of 40 mm and 65 mm, respectively. Liquid holdup reduction of subsea riser was investigated with surfactant. The simulation was conducted at low pressure, using air as the gas phase and water as the liquid phase. Pressure drop was measured by using differential pressure transducer and holdup was obtained by trapping the liquid in the pipe section. Different trace amounts of surfactant were used in this vertical two‐phase flow system. The liquid holdups were measured at different surfactant concentrations and different gas‐liquid flow ratios. Liquid holdups with and without surfactant additives are compared and analyzed. How the foamer influences the two‐phase flow pattern was observed and the range of foamer concentration corresponding to the best holdup reduction was obtained.

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Experimental and modeling study on the influences of methanol on premixed fuel-rich n-heptane flames

Experimental and modeling study on the influences of methano...

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作者： Chen, Gen Yu, Wu Jiang, Xue Huang, Zuohua Wang, Zhandong Cheng, Zhanjun State Key Laboratory of Multiphase Flow in Power Engineering Xi'An Jiaotong University Xi'an 710049 China National Synchrotron Radiation Laboratory University of Science and Technology of China China

The structures of two laminar premixed n-heptane/O2/Ar flames (F1.60: F = 1.60, C/O = 0.51, and F1.80: F = 1.80, C/O = 0.57) and one laminar premixed n-heptane/methanol/O2/Ar flame (F1.80 M: F = 1.80, C/O = 0.51) are studied at low pressure (4000 Pa) by using synchrotron photoionization and molecular-beam sampling-mass spectrometry (PI-MBMS) techniques. Calculations are performed with a modified chemical mechanism, which satisfactorily simulates the tested flames. The results show that as equivalence ratio increases, the maximum flame temperature is reduced and the flame front is shifted away from the burner surface. The post-flame CO concentration in F1.80 M is lower than that in F1.80, which is attributed not only to the difference in inlet carbon flux but also to the variation in CO formation pathway. As methanol is added, the peak concentrations of C2-C 7 hydrocarbon intermediates are reduced substantially, and the extent of the reduction in the case of constant C/O ratio is smaller than that in the case of constant equivalence ratio. The production of formaldehyde is promoted with the addition of methanol. Reaction flux analysis indicates that the self-recombination of propargyl radical (C3H3) and the cross reaction between C3H3 and allyl radical (a-C 3H5) are the dominant pathways leading from small aliphatics to benzene for all the flames. © 2012 Elsevier Ltd. All rights reserved.

关键词： Heptane

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Reduction kinetics of SrFeO_(3−δ)/CaO∙MnO nanocomposite as effective oxygen carrier for chemical looping partial oxidation of methane

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Frontiers of Chemical Science and engineering 2022年第12期16卷 1726-1734页

作者： Xinhe Wang Liuqing Yang Xiaolin Ji Yunfei Gao Fanxing Li Junshe Zhang Jinjia Wei State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong UniversityXi’an 710049China School of Chemical Engineering and Technology Xi’an Jiaotong UniversityXi’an 710049China Institute of Clean Coal Technology East China University of Science and TechnologyShanghai 200237China Department of Chemical and Biomolecular Engineering North Carolina State UniversityRaleighNC 27695USA

Chemical looping reforming of methane is a novel and effective approach to convert methane to syngas,in which oxygen transfer is achieved by a redox *** lots of efforts have been made to develop high-performance redox materials,a few studies have focused on the redox *** this work,the kinetics of SrFeO_(3−δ)–CaO∙MnO nanocomposite reduction by methane was investigated both on a thermo-gravimetric analyzer and in a packed-bed *** the methane reduction,combustion occurs before the partial oxidation and there exists a transition between *** weight loss due to combustion increases,but the transition region becomes less inconspicuous as the reduction temperature *** weight loss associated with the partial oxidation is much larger than that with *** rate of weight loss related to the partial oxidation is well fitted by the Avrami–Erofeyev equation with n=3(A3 model)with an activation energy of 59.8 kJ∙mol^(‒1).The rate law for the partial oxidation includes a solid conversion term whose expression is given by the A3 model and a methane pressure-dependent term represented by a power *** partial oxidation is half order with respect to methane *** proposed rate law could well predict the reduction kinetics;thus,it may be used to design and/or analyze a chemical looping reforming reactor.

关键词： chemical looping reforming SrFeO_(3−δ) CaO·MnO nanocomposite reduction kinetics Avrami–Erofeyev model pressure-dependent term

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Fuel Nitrogen Evolution during Coal Pyrolysis and Gasification

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AIP Conference Proceedings 2010年第1期1207卷 56-65页

作者： Defu Che Yinhe Liu Junguang Lin State Key Laboratory of Multiphase Flow in Power Engineering X’an Jiaotong University China

The morphology of fuel nitrogen in coal and its fate during pyrolysis and the nitrogen species including N2, HCN and NH3 during coal pyrolysis and gasification have been investigated to clarify the evolution mechanism of fuel nitrogen in heat treatment process. Experimental results show that the morphology of coal nitrogen in the studied Chinese raw coals generally include pyrrolic nitrogen (N‐5), pyridinic nitrogen (N‐6), quaternary nitrogen (N‐Q) and nitrogen‐oxide (N‐X). Generally, nitrogen in char is transformed to volatile and more stable components during pyrolysis. Char‐N is the major source of NOx precursors during temperature programmed pyrolysis in 600–800° C. N‐5 and N‐X in char is converted to HCN first, and HCN is then hydrogenated to NH3. N‐Q in char is the main source of nitrogen gas. The major nitrogenous gas products during rapid coal pyrolysis are N2, HCN and NH3, amongst which N2 is dominant. The yields of N2 and NOx precursors, such as HCN and NH3, increase with increased pyrolysis temperature. The major gaseous nitrogenous products during coal gasification in steam include HCN, NH3 and N2. H2O is the main source of the groups containing hydrogen, which not only participates in the reaction as a gasification agent, but also has catalysis on the reaction.

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Investigation on surface wettability and surface structure of PTFE after remote oxygen plasma treatment

Investigation on surface wettability and surface structure o...

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2009 IEEE International Conference on Plasma Science - Abstracts, ICOPS 2009

作者： Liu, H.X. Zhang, H.J. State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China Department of Environmental Engineering Xi'an Jiaotong University Xi'an 710049 China

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The experimental study on aneurysm with PIV system

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AIP Conference Proceedings 2013年第1期1547卷 205-220页

作者： Wang Yueshe Ma Xiaoqi Li Di State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University China

Cerebral aneurysm, a local enlargement of an artery caused by weakness in the wall of a cerebral artery, has the high death rate and disability rate, and is a threat to public health. The forming mechanism of aneurysm is complex, which motivated many researchers to conduct studies in this field. The results indicated that increasing heart frequency can aggravate the oscillation of wall shear stress, and push The growth points of aneurysm along the aneurysm wall, thereby significantly affecting bthe growth and rupture mechanism of aneurysm. In addition, it is found that the curvature of the vessel is the key to induce the secondary vortex in the aneurysm; the secondary vortex increases the magnitude of WSS near the dome of aneurysm, which can cause the rupture of aneurysm dome. there is a linear relationship between the velocity of blood flow and the square root of hear frequency.

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Experimental Study on Deliquification with Atomizing Nozzle in Gas Well

Experimental Study on Deliquification with Atomizing Nozzle ...

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作者： Yutang Gao Xiaobai Li Peng Chang Lei Liu State Key Laboratory of Multiphase Flow in Power Engineering

Gas is a clean energy resource in comparison with oil and coal. Liquid-loading problem is frequently encountered in the process of gas production. It would directly cause the production of gas wells decreasing, even off production. A number of deliquification techniques have been suggested for solving this kind of problem, but the available techniques are not yet widely applicable. Based on the analysis, the method of deliquification with atomizing nozzle in gas wells was put forward. The test bench was designed for studying the atomization of nozzles and the liquid entrainment of gas flow. The size distribution of atomized droplets was measured by Malvern laser grain size analyzer. The Sauter mean diameters of atomized droplets were analysed under different two-phase flow conditions. The results indicate that the designed nozzles have good atomization performances and show potential application for reducing liquid loading in gas wells.

关键词： Gas well liquid loading deliquification atomizing nozzle two-phase flow

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Gas-liquid two-phase severe slugging in a pipeline-riser system with S-shaped flexible riser: Experiments and modeling

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AIP Conference Proceedings 2013年第1期1547卷 766-779页

作者： Nailiang Li Liejin Guo Wensheng Li State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University China

The objective of the present work is to investigate the air-water two-phase flow patterns in pipeline-riser system with an S-shaped flexible riser. The test loop with 50 mm ID consists of a horizontal pipeline with 114 m in length, a downward inclined section with 16 m in length, and an S-shaped flexible riser with 24 m in height when downward section inclined at −2° with respective to the horizontal. The inclination angle of the downward section varied from −2° to −5°. The liquid superficial velocity ranged from 0.03 to 1.5 m/s, and the gas superficial velocity from 0.4 to 6.0 m/s. Identification and characterization of flow regimes were attained by pressure at riser-base and liquid holdup at riser top. Severe slugging I, severe slugging II, transition flow and stable flows are observed to exist. flow pattern maps for each declination are presented and the transition criteria are proposed. It's found that as higher liquid and gas velocity is required for the transition of the flow in the pipeline from stratified to intermittent with increasing the declination angle, severe slugging was observed to occur over a wilder range of flow conditions. The effect of riser geometry and separator pressure on the occurrence of the flow patterns was also examined. It shows that the S-bend tends to suppress the initiation of severe slugging.

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Study of Unforced Unsteadiness in Centrifugal Pump at Partial flow Rates

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Journal of Thermal Science 2021年第1期30卷 88-99页

作者： YANG Jun XIE Tian LIU Xiaohua SI Qiaorui LIU Jun School of Energy and Power Engineering University of Shanghai for Science and TechnologyShanghai 200093China Key Laboratory of Fluid and Power Machinery(Xihua University) Ministry of EducationChengdu 610039China Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering Shanghai 200093China School of Aeronautics and Astronautics Shanghai Jiao Tong UniversityShanghai 200240China Research Center of Fluid Machinery Engineering and Technology Jiangsu UniversityZhenjiang 212013China

In order to explore the unforced unsteadiness of centrifugal pumps,a 2-D frequency domain imaging display technology was used to study the development of these unsteady flow structures at partial flow *** results showed that,the unsteady flow field was not only affected by rotor and stator interaction,but also appeared an unforced unsteadiness with fundamental frequency of St≈0.23 around the impeller throat ***,as the flow rates decreased,this unsteady flow structure gradually weakened and *** the flow rate was reduced to 0.6 times of design flow rate,another two unforced unsteady flow structures with characteristic frequencies of St≈0.0714 and St≈0.12 began to appear in the same ***,with the operating condition smaller than design flow rate,the internal flow became more and more *** addition to the forced unsteadiness,the unforced unsteadiness which is not connected with the blade passage frequency became more and more obvious.

关键词： centrifugal pumps partial flow conditions pressure pulsations unforced unsteadiness 2-D frequency domain visualization method

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