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A MODEL FOR LIQUID SLUG LENGTH DISTRIBUTION IN VERTICAL GAS-LIQUID SLUG flow

Journal of Hydrodynamics 2009年第4期21卷 491-498页

作者： XIA Guo-dong CUI Zhen-zhen LIU Qing ZHOU Fang-de HU Ming-sheng College of Environmental and Energy Engineering Beijing University of Technology Beijing 100124 China State Key Laboratory of Multiphase Flow in Power Engineering Xi＇an Jiaotong University Xi＇an 710049 China

The slug length and the trailing Taylor bubble velocity in an upward vertical slug flow were measured by using the optical probes and the EKTAPRO 1000 high speed motion analyzer. The correlation between the trailing bubble velocity and the length of liquid slug ahead of that bubble is derived from the experimental data. Based on this correlation as well as the bubble overtaking mechanism, a model for the slug length distribution at any designated locations along the pipe is proposed. The predicted results are in agreement with the experimental data.

关键词： gas-liquid two-phase flow slug flow Taylor bubble liquid slug

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Simulation of combustion in spark-ignition engine fuelled with natural gas-hydrogen blends combined with EGR

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中国高等学校学术文摘·能源与动力工程 2009年第2期3卷 204-211页

作者： Jie WANG Zuohua HUANG Bing LIU Xibin WANG State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China

A numerical simulation of the influence of different hydrogen fractions, excess air ratios and EGR mass fractions in a spark-ignition engine was conducted. Good agreement between the calculated and measured in-cylinder pressure traces as well as pollutant formation trends was obtained. The simulation results show that NO concentration has an exponential relationship with temperature and increases sharply as hydrogen is added. EGR introduction strongly influences the gas temperature and NO concentration in the cylinder. The difference in temperature will lead to even greater difference in NO concentration. Thus, EGR can effectively decrease NO concentration. NO concentration reaches its peak value at the excess air ratio of 1.1 regardless of EGR mass fraction. The study shows that natural gas-hydrogen blend combined with EGR can realize a stable combustion and low NO emission in a spark-ignition engine.

关键词： natural gas hydrogen NO exhaust gas recirculation numerical simulation

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Edge detection based on wavelet analysis with Gaussian filter and application in multiphase flow

Edge detection based on wavelet analysis with Gaussian filte...

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2008 ASME Summer Heat Transfer Conference, HT 2008

作者： Chen, Bin Yang, Fude Guo Ning, Yahui Tao State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University China

ISBN: (纸本)9780791848487

In this paper an edge detection algorithm based on wavelet transform with Gaussian filter was proposed. In this algorithm original images are firstly converted into gray images and then each pixel was analyzed using wavelet transform to find the local maximum of the gray gradient of each pixel along the phase angle direction and compared with a given threshold value, through which real edge can be kept and fake ones will be eliminated. In the computation of local maximum, the gray gradients computed in eight directions, which can improve precision of edge detection. After the investigation of influence of filter length, scale and threshold value on the edge detection and validation by comparison with N.L. Fenandez-Garcia's Minimean and Minimax methods for 100 real color images, we applied this algorithm to bubbly gas-liquid two-phase flow. Compared with Canny operator, present result is more close to real bubble shape and can distinguish very close bubbles, which indicates the algorithm is effective and can be used to study the interaction between different phases and flow field in multiphase flow. Copyright © 2008 by ASME.

关键词： Edge detection

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The dust emission law in the wind erosion process on soil surface

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Science China(Physics,Mechanics & Astronomy) 2009年第2期52卷 258-269页

作者： XING Mao1 & GUO LieJin2 1 Mining Technology Institute, Taiyuan University of Technology, Taiyuan 030024, China 2 State Key Laboratory of multiphase flow in power engineering, Xi’an Jiaotong University, Xi’an 710049, China Mining Technology Institute Taiyuan University of Technology Taiyuan 030024 China State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an 710049 China

The dust emission models to date cannot describe the relation between the transport rate of different sized grains and their grain size composition in soil surface, so Aeolian grain transport on a soil-like bed composed of fine sand and silt powder was measured in a wind tunnel. Six types of soil-like beds with different silt fractions have been tested in this experiment. The mass flux profiles of silt dust and sand grains are much different due to their different motion modes. Analysis of the vertical distribution of the powder and sand grains reveals that for a given soil bed, the ratio of the horizontal dust flux to the horizontal sand flux is directly proportional to their mass ratio in the bed. The dust flux is closely linked to the sand flux by the bombardment mechanism. For a given wind velocity and grain size of the bed, the slopes of the vertical mass flux profiles of sand grains larger than 100 μm are nearly equal in a log-linear plot and the ratio between the fraction of transport rate of each size group to the whole transport rate and the mass fraction of each size group in the bed is a constant only dependent on grain size. With this law, the transport rate of dust and different sized grains can be related with the grain size composition in the soil surface.

关键词： wind erosion dust transport rate grain size

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Measurement of laminar burning velocities and Markstein lengths for diethyl ether-air mixtures at different initial pressure and temperature 7

Measurement of laminar burning velocities and Markstein leng...

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7th Asia-Pacific Conference on Combustion, ASPACC 2009

作者： Di, Yage Huang, Zuohua Zhang, Ni Gu, Xiaolei Zheng, Bin Zhang, Zhiyuan State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an China

Measurement of laminar burning velocities and Markstein lengths were made for the diethyl ether-air mixtures at different equivalence ratios, initial temperatures and pressures by using spherically propagating flame and schlieren photography method. The results show that the stretched flame propagation speeds and unstretched laminar burning velocities are increasing with the increase of the initial temperature. While the Markstein lengths are decreased with the increase of the initial temperature. The stretched flame propagation speeds, the unstretched laminar burning velocities and Markstein lengths are decreased with the increase of the initial pressure. The Markstein lengths are decreased with the increase of the equivalence ratio. Based on the experimental data, a correlation is obtained for the unstretched laminar burning velocity versus the initial temperature and pressure over wide range of equivalence ratios. © 2009 Combustion Institute. All rights reserved.

关键词： Mixtures

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A calculation method for evaluating thermal loss of solar cavity receiver

A calculation method for evaluating thermal loss of solar ca...

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2009 Asia-Pacific power and Energy engineering Conference, APPEEC 2009

作者： Jiabin, Fang Jinjia, Wei Xunwei, Dong Yueshe, Wang State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an China

ISBN: (纸本)9781424424870

One of the most important components of solar thermal power system is the solar central receiver, which performance is in direct relation to the efficiency of the whole power generation system. The calculation of internal surface heat flux and thermal efficiency of receiver therefore plays a very important role in receiver design. A calculation method of heat loass of a cavity receiver is put forward in this paper. The first step of this method is to use the Monte Carlo method to simulate the track of solar beam and compute surface heat flux inside the receiver. The second step is to employ the correlations of flow boiling heat transfer to figure out the convective heat transfer coefficient inside the tubes and then the wall temperature of the boiling tubes laid inside the receiver. The last step is to simulate the air flow field inside the receiver to calculate convective thermal loss of the receiver. As every step can not be independently done, all steps are coupled and an iterative scheme is needed. Internal surface heat flux and thermal efficiency of the receiver can be finally gained with this method, and the result can provide theoretical guide for receiver design. © 2009 IEEE.

关键词： Monte Carlo methods

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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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Characteristics of HCN removal using cao at high temperatures

Characteristics of HCN removal using cao at high temperature...

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作者： Houzhang, Tan Xuebin, Wang Congling, Wang Tongmo, Xu State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniVersity Shaanxi 710049 China

Experimental investigation on the removal of hydrogen cyanide (HCN) using calcium oxide (CaO) was carried out in a fixed bed reactor at temperature ranging from 300 to 1173 K, and the original HCN was produced during the pyrolysis of pyridine. Effects of temperature, volume space velocity, and initial HCN concentration on HCN removal were discussed. The results of temperature-programmed experiments show that temperature is the main factor affecting HCN removal. With the formation of CO, HCN starts to decrease from 473 K, and remains unchanged from 673 to 873 K. At 873 K, there is a further decrease in HCN without CO formation, and when temperature is higher than 1023 K, HCN is removed completely. In the isothermal experiments, CaCN2 was detected at 723 K, but at higher temperatures of 923 and 1123 K, there was no CaCN2 in the solid residues, and the nitrogen in the removed HCN was equal to that in the formed N2. This indicates that at a lower temperature CaO is consumed to remove HCN, CaO + 2HCN f CaCN2 + CO + H2;but at a higher temperature, CaO acts as a catalyst for HCN removal, 2CiHj + 2HCN f N2 + (j + 1 - k)H2 + 2Ci+1Hk. The investigation on the removal efficiency shows that there is a critical temperature and a critical volume space velocity at which the HCN removal efficiency is able to reach up to 100%. © 2009 American Chemical Society.

关键词： Temperature

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Effects of hydrogen addition on cellular instabilities of the spherically expanding propane flames 7

Effects of hydrogen addition on cellular instabilities of th...

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7th Asia-Pacific Conference on Combustion, ASPACC 2009

作者： Tang, C.L. Huang, Z.H. Wang, J.H. Zheng, J.J. State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

An experimental study on the effects of hydrogen addition on the instabilities of spherically expanding propane-air flames was conducted in a constant volume combustion vessel over a wide range of mixture compositions and initial temperatures and pressures. The measured laminar burning velocities were compared with those of the calculated one dimensional freely propagating flames, using a recently developed detailed kinetic mechanism, and the agreement was excellent. The schlieren images show that for the fuel lean conditions, hydrogen addition increases the hydrodynamic instability due to the decreased flame thickness and increases diffusional-thermal instability due to the decreased Lewis number, while for the fuel rich conditions, the flame front is initially destabilized and later stabilized with the increase of hydrogen fraction as the results of the competing effects of hydrodynamic and diffusional-thermal instabilities © 2009 Combustion Institute. All rights reserved.

关键词： Propane

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Effect of partially premixed and hydrogen addition on lean burn natural gas direct injection combustion 7

Effect of partially premixed and hydrogen addition on lean b...

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7th Asia-Pacific Conference on Combustion, ASPACC 2009

作者： Wang, J.H. Huang, Z.H. Zheng, J.J. Miao, H.Y. State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

Effect of partially premixed and hydrogen addition on lean burn natural gas direct injection combustion was studied experimentally using a constant volume vessel. Flame propagating photos and pressure derived combustion parameters were analyzed at different premixed ratios (from 0% to 80%) and hydrogen fractions (from 0% to 40%) at overall equivalence ratio of 0.6 and 0.8, respectively. The results showed that the flame kernel was concentrated to the spark position with the increase of premixed ratio and/or hydrogen fraction. The flame propagating speed was increased with hydrogen addition to natural gas. The stable spark ignition of lean burn natural gas was realized with the combination of partially premixed direct injection combustion and hydrogen addition. Both the initial and main combustion durations were increased with the increase of premixed ratio, while they showed the decreasing trend with hydrogen addition to natural gas. Partially premixed direct injection combustion combing with hydrogen addition can achieve the stable spark ignition and fast combustion rate at the lean mixture condition. © 2009 Combustion Institute. All rights reserved.

关键词： Natural gas

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