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4th International Conference on Nanochannels, Microchannels and Minichannels, ICNMM2006

作者： Li, Zhuo Tang, Gui-Hua He, Ya-Ling Tao, Wen-Quan State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi'an Jiaotong University China

ISBN: (纸本)0791847608

Recently, a large number of experiments have been conducted to examine the applicability of Navier-Stokes equations to predict the friction factor for the laminar flow of polar fluids in microchannels. However, significant discrepancies still exist between various results. In order to investigate the effect of electric double layer on the pressure-driven flow of polar fluid in smooth rectangular microchannels and to reveal whether continuum model can still be applied, numerical investigations are conducted in this paper. The simulated microchannels are made of silicon engraved substrate with Pyrex cover, and the measured relative roughness of channels is less than 0.5%. Deionized water and tap water with different ion concentration and electrical conductivity are used as the working fluid. The governing equations include the two-dimensional, non-linear Poisson-Boltzmann equation, the modified N-S equation and the electric field Ez equation. The steady state electric field E z equation is coupled with the momentum equation. The FVM (finite volume method) is adopted to discretize the governing equations. The non-uniform grid systems 152×102 is applied and the Reynolds number ranges from 0.1 to 300. Good agreements are achieved between the numerical results and the experimental data available in the literature. The effects of electrical potential, fluid ion concentration, electrical conductivity and the channel dimensions on the EDL profile, and the electroviscous effect and the friction coefficient are presented in detail. The simulation results reveal that the Debye thickness depends on ion concentration greatly. Only when the ratio of Dh/δ (the ratio of channel hydraulic diameter to the Debye thickness) is low, the electroviscous effect should be considered. According to the experimental conditions, the numerical results show that if the ratio of Dh/δ is greater than 15, the predicted friction factors agree well with the macroscale classical law, and the disparities

关键词： Channel flow

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An investigation on heat transfer to supercritical water in inclined upward smooth tubes

An investigation on heat transfer to supercritical water in ...

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作者： Yin, Fei Chen, Ting-Kuan Li, Hui-Xiong National Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an China National Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China

Within the range of pressures from 23 to 30 MPa, mass velocities from 600 to 1200 kg/(m 2 s), and heat fluxes from 200 to 600 kW/m 2 , experiments have been performed for an investigation on heat transfer to supercritical water in inclined upward smooth tubes with an inner diameter of 26 mm and an inclined angle of 20° from the horizon. The results indicated that heat transfer characteristics of supercritical water are not uniform along the circumference of the inclined tube. An increase in the mass velocity of the working fluid can decrease and even eliminate the non-uniformity. Properties of supercritical fluid acutely vary with the temperature near the pseudocritical point. While the ratio of the mass velocity to the heat flux exceeded 2.16 kg/(kWs), heat transfer enhancement occurred near the pseudocritical point;conversely, heat transfer deterioration occurred while the ratio of the mass velocity to the heat flux was lower than 2.16 kg/(kWs). As the pressure increased far from the critical pressure, the amount of deterioration decreased. Correlations of heat transfer coefficients of the forced-convection heat transfer on the top and bottom of the tube have been provided, and can be used to predict heat transfer coefficient of spirally water wall in supercritical boilers.

关键词： Pipe flow

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Synthesis of a novel ZnMoS4 photocatalyst and its performance for photocatalytic production of hydrogen

Synthesis of a novel ZnMoS4 photocatalyst and its performanc...

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16th World Hydrogen Energy Conference 2006, WHEC 2006

作者： Liang, Huirong Liu, Guanjie Zhang, Yaojun Guo, Liejin State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi'an Jiaotong University 710049 Xi'an China

ISBN: (纸本)9781622765409

The production of hydrogen by photocatalytic decomposition of water using zinc tetrathiomolybdate catalyst was studied. Zinc tetrathiomolybdate catalyst was prepared by coprecipitation and hydrothermal method based on ZnSO 4 and self-prepared [NH4]2MoS4 crystal. It was characterized by XRD, XRF, BET and UV-Vis spectra. The photocatalytic activities of the catalysts were ascertained by the production of hydrogen in an aqueous Na2S-Na2SO3 solution under the ultraviolet and visible light irradiation. It was observed that the photocatalysts showed the visible-light photocatalytic activity, and the ZnMoS4 photocatalyst prepared under hydrothermal condition for about 24h had the highest activity.

关键词： Photocatalysts

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WS2 sensitized mesoporous TiO2 for efficient photocatalytic hydrogen production from water under visible light

WS2 sensitized mesoporous TiO2 for efficient photocatalytic ...

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16th World Hydrogen Energy Conference 2006, WHEC 2006

作者： Jing, Dengwei Guo, Lie-Jin Xing, Chanjuan Yan, Qiuhui State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an Shaanxi 710049 China

ISBN: (纸本)9781622765409

Nanosize WS2 sensitized mesoporous TiO2 was prepared to extend the adsorption of the wide band gap TiO2 into visible light region. Compared with nonporous particle TiO2 substrate, it was found that the existence of mesopore is important for larger amount of WS 2 loading and inhibition of the light-induced detachment of WS 2 particles from the TiO2 substrate during photocatalytic reaction, which leads to higher photocatalytic activity and stability. We also found that the rate-determining step for photocatalytic hydrogen production is the transfer of electrons from TiO2 substrate to H+ in solution, when the recombination between electrons and holes within TiO 2 could be neglected. In this case, deposition of Pt at the surface of semiconductor is indispensable for efficient hydrogen production.

关键词： Titanium dioxide

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Multiplicity Analysis in Reactive Distillation Column Using ASPEN PLUS

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Chinese Journal of Chemical engineering 2006年第3X期14卷 301-308页

作者：杨伯伦吴江赵国胜王华军路士庆 State Key Laboratory of Multiphase Flow in Power Engineering Xi＇an Jiaotong University Xi＇an 710049 China

Reactive distillation processes for synthesis of ethylene glycol （EG） and ethyl tert-butyl ether （ETBE） were modeled with the simulation package ASPEN PLUS. The input multiplicity and output multiplicity were discussed with the method of sensitivity analysis for both cases. In EG production process, steady state multiplicities were studied in terms of effective liquid holdup volume and boil-up ratio. In ETBE synthesis process, the user kinetic subroutine was supplied into ASPEN PLUS firstly, and then the composition, temperature and reaction-rate profiles within the reactive distillation column were presented in detail. A set of stable solution branches based on distinct initial guesses for a range of boil-up ratio were found in EG synthesis. Input multiplicities were observed for a range of reboiler duty at several values of reflux ratio for ETBE synthesis process. These results can be used to avoid excessive energy consumption and achieve optimum design of reactive distillation column.

关键词： reactive distillation ASPEN PLUS multiplicity ethyl tert-butyl ether ethylene glycol

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Local flow Regime Transition Criteria of Gas-Liquid Two-phase flow in Vertical Upward Tube with a Horizontal Rod

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Chinese Journal of Chemical engineering 2006年第4X期14卷 442-449页

作者：胡志华杨燕华刘磊周芳德 School of Mechanical Engineering Shanghai Jiaotong University Shanghai 200030 China State Key Laboratory of Multiphase Flow in Power Engineering Xi＇an Jiaotong Univeristy Xi＇an 710049 China

The upward multiphase cross flow and heat transfer in the vertical tube may occur in oil production and chemical facilities. In this study, the local flow patterns of an upward gas-water two phase cross flow in a vertical tube with a horizontal rod have been investigated with an optical probe and the digital high speed video system. The local flow patterns are defined as the bubble, slug, churn and annular flow patterns. Optical probe signals are ana- lyzed in terms of probability density function, and it is proved that the local flow patterns can be recognized by this method. The transition mechanisms between the different flow patterns have been analyzed and the corresponding transitional models are proposed. Finally, local flow pattern maps of the upward gas-water two-phase flow in the vertical tube with a horizontal rod are constructed.

关键词： gas-liquid two-phase cross flow local flow pattern transition

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Analysis of flow instabilities in forced-convection steam generator

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Nuclear Science and Techniques 2006年第3期000卷 185-192页

作者： WU Ge-Ping QIU Sui-Zheng SU Guang-Hui JIA Dou-Nan State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China

Because of the practical importance of two-phase instabilities, substantial efforts have been made to date to understand the physical phenomena governing such instabilities and to develop computational tools to model the dynamics. The purpose of this study is to present a numerical model for the analysis of flow-induced instabilities in forced-convection steam generator. The model is based on the assumption of homogeneous two-phase flow and thermodynamic equilibrium of the phases. The thermal capacity of the heater wall has been included in the analysis. The model is used to analyze the flow instabilities in the steam generator and to study the effects of system pressure, mass flux, inlet temperature and inlet/outlet restriction, gap size, the ratio of do /di, and the ratio of qi/qo on the system behavior.

关键词： Steam generator Forced convection flow instability

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An investigation of flow characteristics and critical heat flux in vertical upward round tube

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Nuclear Science and Techniques 2006年第3期000卷 170-176页

作者： FAN Pu QIU Sui-Zheng JIA Dou-Nan State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China

Prediction of critical heat flux (CHF) in annular flow is important for the safety of once- through steam generator and the reactor core under accident conditions. The dryout in annular flow occurs at the point where the film is depleted due to entrainment, deposition, and evaporation. The film thickness, film mass flow rate along axial distribution, and CHF are calculated in vertical upward round tube on the basis of a separated flow model of annular flow. The theoretical CHF values are higher than those derived from experimental data, with error being within 30%.

关键词： Annular flow Critical heat flux Dryout Entrainment Deposition

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Theoretical investigation on the steady-state natural circulation characteristics of a new type of pressurized water reactor

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Nuclear Science and Techniques 2006年第5期000卷 314-320页

作者： GOU JunLi QIU SuiZheng SU GuangHui JIA DouNan State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China

This article presents a theoretical investigation on the steady-state natural circulation characteristics of a new type of pressurized water reactor. Through numerically solving the one-dimensional steady-state single-phase conservative equations for the primary circuit and the steady-state two-phase drift-flux conservative equations for the secondary side of the steam generator, the natural circulation characteristics were studied. On the basis of the preliminary calculation analysis, it was found that natural circulation mass flow rate was proportional to the exponential function of the power and that the value of the exponent is related to the operating conditions of the secondary side of the steam generator. The higher the outlet pressure of the secondary side of the steam generator, the higher the primary natural circulation mass flow rate. The larger height difference between the core center and the steam generator center is favorable for the heat removal capacity of the natural circulation.

关键词： Pressurized water reactor Natural circulation characteristics Height difference

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Study of a PEMFC performance based on a novel current distribution measurement method

Study of a PEMFC performance based on a novel current distri...

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16th World Hydrogen Energy Conference 2006, WHEC 2006

作者： Zhang, Guangsheng Sun, Hong Guo, Liejin Shang, Dehua Liu, Hongtan State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an Shaanxi 710049 China Department of Mechanical Engineering University of Miami Coral Gables FL 33124 United States

ISBN: (纸本)9781622765409

With the novel and simple current distribution measurement gasket developed by MPFL, the performance of a single PEM fuel cell with serpentine flow field was investigated without modifying any of its components. Inhomogeneous current distributions were demonstrated clearly by the measurement results. Current distribution at different cell operating parameters, including reactant gas flow rate, reactant gas humidification temperature and cell operating temperature, were measured and the effects of such parameters were analyzed. Reactant gas flow rate exert effects on current distribution by influencing the reactant concentration distribution, while the critical effects of gas humidification and cell temperature is caused by their significant influence on water balance and water distribution in PEM fuel cell. To fully understand the combined effects of such factors, simultaneous measurement of current distribution, reactant distribution, temperature distribution and humidification distribution is necessary and will be helpful.

关键词： flow of gases

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