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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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Simulation of hemodynamics in portal vein hypertension using CFD

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医用生物力学 2013年第S1期28卷 99-101页

作者： Xiao Li Yansong Pu Peng Nie Zongfang Li Bin Chen State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Second Affiliated Hospital Xi'an Jiaotong University Department of Radiology Huaihe Hospital of Henan University

Introduction Liver cirrhosis generally occurs with the hemodynamic changes during the portal vein hypertension and finally leads to the atrophy of the right lobe of the liver and hepatic failure^[1].According to the hemodynamic changes,a hypothesis has been proposed that the liver volume is related to the istribution of blood from the splenic vein（SV）that involves nutrition from spleen and pancreas^[2,3].The objective of the present paper is to simulate the blood flow in real models of portal vein hypertension and validate the hypothesis using computational fluid dynamics（CFD）*** This study includes 2 patients with liver cirrhosis and a set of 4 normal subjects.

关键词： cirrhosis hemodynamic nutrition pancreas splenic atrophy hypothesis validate finally spleen

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Study on ignition delay times of dimethyl ether/propane/O2/Ar mixtures at elevated pressures

Study on ignition delay times of dimethyl ether/propane/O2/A...

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9th Asia-Pacific Conference on Combustion, ASPACC 2013

作者： Hu, Erjiang Pan, Lun Zhang, Zihang Huang, Zuohua State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University No.28 Xianning West Road Xi'an Shaanxi 710049 China

Ignition delay times of dimethyl ether (DME) and propane blends were measured in a shock tube at varied DME blending ratios (0%, 20%, 50%, 80%, 100%), equivalence ratios (0.5, 1.0, 2.0), temperatures (1100-1500 K) and pressures of 20 atm. Mechanism validations were conducted using different chemical kinetic models. A new C5 chemical model with DME sub-model was developed and it can well predict experimental ignition delay times of pure propane, DME and their blends. Experimental and numerical results show that with the decrease of temperature, the ignition delay times increase and the activation energy decreases slightly. With the increase of equivalence ratio, ignition delay times increase for propane and decrease for DME in this study. Ignition delay times decrease with the increase of DME blending ratio and the decrease rates become larger with the increase of equivalence ratio. The peak values of H and OH mole fraction increase with increasing the DME blending ratio, and they promote the ignition of DME/propane blends. Sensitivity analysis shows that the reaction rates of R1 and R353 increase with the increase of DME blending ratio and induces the decrease of the ignition delay time of DME/propane blends.

关键词： Ethers

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A study of auto-ignition of H2/CO/O2/Ar mixtures at elevated pressure and moderate temperature using shock tube

A study of auto-ignition of H2/CO/O2/Ar mixtures at elevated...

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9th Asia-Pacific Conference on Combustion, ASPACC 2013

作者： Thi, Luong Dinh Zhang, Yingjia Fu, Jin Huang, Zuohua State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University No.28 Xianning West Road Xi'an Shaanxi710049 China

Ignition delays of stoichiometric syngas mixtures (H2/CO/O 2) diluted with argon were measured behind the reflected shock wave at pressures of 0.2, 1.0 and 2.0 MPa, temperature from 896 to 1264 K, equivalence ratios of 0.3, 1.0 and 1.5. The effect of non-ideal conditions on ignition delays, determined by pressure trace behind the reflected shock wave (pressure rise rate is approximately 4.22%/ms), was used to calculate. Six available mechanisms were selected to simulate the ignition delays of syngas mixtures, the predicted results were compared with the measured ones. These results indicated that there is no mechanism can calculate accurately ignition delays over all testing conditions. The ignition delays predicted with three mechanisms (Davis 2005, USC ver 2.0, NUI nc5-49) are close to the measured ones. Using the Davis mechanism to analyse reaction kinetics, the achieved results showed that the reaction R1 dominates the ignition process of syngas. The reaction R31 plays an important promoted role in ignition process of syngas mixtures.

关键词： Shock tubes

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Simulation of a solar tower thermal power plant using TRNSYS

Simulation of a solar tower thermal power plant using TRNSYS

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26th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems, ECOS 2013

作者： Yang, Yan Zhang, Fan Cao, Fei Zhao, Liang Guo, Liejin State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an China Shanghai Electric Power Generation Group Co. Ltd. Shanghai China

The solar tower thermal power technology is a method to achieve the large-scale utilization of solar energy. A user defined TYPE of the heat receiver for the solar tower thermal power plant (STTPP) is established in the TRNSYS program with Fortran codes. Full-year simulation of the STTPP is investigated based on different input parameters, weather conditions and plant control strategies by taking Beijing as a case study. Through this case, the influences of the receiver diameter, flow form and inlet/outlet temperature on the thermal efficiency, total pump power, power efficiency and 'solar-thermal-electricity' transfer efficiency are studied. Simulation results show that the thermal efficiency of receiver rises with the decrease of pipe diameter. The lower the inlet temperature is;the lower the annual pump power consumption is, and the higher the power efficiency would be. An instantaneous increase of the receiver outlet temperature would reduce the power efficiency. The plant control strategies suggest that the "south-in-north-out" arrangement of the heat receiver working fluid holds the highest power efficiency but lowest annual pump power consumption. The annual power generation increases effectively by introducing the hot and cold molten salt storage tanks. The annual power efficiency increases with the power plant capacity.

关键词： Electric power utilization

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Modeling the evolution of aeolian sand transport in a wind tunnel

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AIP Conference Proceedings 2013年第1期1547卷 758-765页

作者： Fengjun Xiao Liejin Guo Debiao Li Yueshe Wang State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University China

An Eulerian-Lagrangian numerical simulation is performed to study aeolian sand transport in a wind tunnel. The evolutions of three parameters, sand mass flux, decay rate of sand mass flux profile and sand particle mean horizontal velocity with time, are investigated. The results show that: Sand mass flux takes more time to reach the saturated state than the last two parameters. First, we prove the evolution with time in the simulation is similar to the evolution in the length direction in a wind tunnel and then the experimental data from unsaturated wind tunnel can be used in the quantitative comparison with simulated saturated results. Second, detailed comparison is carried out. The tendency of sand mass flux is consistent with the experimental data. Decay rate of sand mass flux profile and sand particle mean horizontal velocity fit the experimental data well especially for cases of small free stream wind velocity, and the deviation is getting larger with the increasing of free stream wind velocity.

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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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Statistical analysis on the signals monitoring multiphase flow patterns in pipeline-riser system

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AIP Conference Proceedings 2013年第1期1547卷 221-229页

作者： Jing Ye Liejin Guo State Key Laboratory of Multiphase Flow in Power Engineering Xi 'an Jiaotong University China

The signals monitoring petroleum transmission pipeline in offshore oil industry usually contain abundant information about the multiphase flow on flow assurance which includes the avoidance of most undesirable flow pattern. Therefore, extracting reliable features form these signals to analyze is an alternative way to examine the potential risks to oil platform. This paper is focused on characterizing multiphase flow patterns in pipeline-riser system that is often appeared in offshore oil industry and finding an objective criterion to describe the transition of flow patterns. Statistical analysis on pressure signal at the riser top is proposed, instead of normal prediction method based on inlet and outlet flow conditions which could not be easily determined during most situations. Besides, machine learning method (least square supported vector machine) is also performed to classify automatically the different flow patterns. The experiment results from a small-scale loop show that the proposed method is effective for analyzing the multiphase flow pattern.

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Severe slugging in a flexible S-shaped riser system: Experimental studies and transient simulation

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AIP Conference Proceedings 2013年第1期1547卷 537-544页

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

Severe slugging, which could induce large-amplitude pressure and flow rate fluctuations, is a major and expensive problem in multiphase transportation systems of offshore oil production system. To avoid such problem is a basic requirement for flow assurance management. This study is an experimental and numerical investigation of severe slugging in a relatively long pipeline-riser system. A series of experiments on two-phase, air-water flow in a flexible Sshaped riser were carried out. The experimental system has a 114m long horizontal pipeline connected to a 19m long pipe which is inclined to −2degree from horizontal, followed by a 15.3m high riser operating at atmospheric end pressure. Four types of flow patterns were found and characterized by the pressure fluctuations at the bottom of the riser. A flow patter map for the prediction of severe slugging was developed based on the experimental results. The detailed characteristics of severe slugging such as pressure fluctuations, liquid holdup, under different gas-liquid superficial velocities were provided. A transient model to predict the flow behavior in the pipeline-S-shaped riser system was developed based on an existing model (OLGA). The modified model, which was tested against new experimental results obtained in this study, showed that the four types of flow patterns observed in the experiment were predicted with acceptable discrepancies. The flow pattern map was obtained using present model, as well as the detailed characteristics of severe slugging. In addition, the reasons for the difference between experimental and numerical results were analysed in this article. The motive of the numerical studies was to identify the areas that could not be reproduced by the present model and to give some suggestions for future models.

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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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