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Numerical Investigation on the Performance of Different Primary Nozzle Structures in the Supersonic Ejector

Energy Procedia 2017年 105卷 4997-5004页

作者： Kangkang Xue Kaihua Li Weixiong Chen Daotong Chong Junjie Yan State Key Laboratory of Multiphase Flow in Power Engineering Xi’an JiaotongUniversity Xi’an Shaanxi 710049 P.R. China

Computational fluid dynamics (CFD) technique is employed to investigate the effect of primary nozzle structures on the supersonic ejector performance. The performance of the supersonic ejectors with three different nozzle structures, including conical nozzle, petalage nozzle and crenation nozzle, have been compared under the same conditions. Compared with the ejector equipped with the conical nozzle, the entrainment ratio of petalage nozzle is slightly smaller, while the critical back pressure increases by 5.2%. Just the opposite, the entrainment ratio of crenation nozzle is slightly higher, and the critical back pressure would decrease by 2.1%. In addition, the effects of primary/induced fluid pressure on the flow field (pressure and Mach number along the ejector centerline) are observed and analyzed to explain the mixing process occurring inside the ejector. It finds out that the shape of the mixing layer in the supersonic ejector with different nozzles is different.

关键词： Supersonic ejector CFD Primary nozzle Entrainment ratio Critical back pressure

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Ferrites boosting photocatalytic hydrogen evolution over graphitic carbon nitride: a case study of(Co, Ni)Fe_2O_4 modification

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Science Bulletin 2016年第4期61卷 292-301页

作者： Jie Chen Daming Zhao Zhidan Diao Miao Wang Shaohua Shen International Research Center for Renewable Energy State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University

The charge cartier separation and surface catalytic redox reactions are of primary importance as elementary steps in photocatalytic hydrogen evolution. In this study, both of these two processes in photocatalytic hydrogen evolution over graphitic carbon nitride （g-C3N4） were greatly promoted with the earth-abundant ferrites （Co, Ni）Fe2O4 modification. CoFe2O4 was further demonstrated to be a better modifier for g-C3N4 as compared to NiFe2O4, due to the more efficient charge carrier transfer as well as superior surface oxidative catalytic activity. When together loading CoFe2O4 and reductive hydrogen production electrocatalyst Pt onto g-C3N4, the obtained Pt/g-C3N4/CoFe2O4 photocatalyst achieved visible-light （2 〉 420 nm） hydrogen production rate 3.5 times as high as Pt/g-C3N4, with the apparent quantum yield reaching 3.35 % at 420 nm.

关键词： Graphitic carbon nitride FerritesPhotocatalytic water splitting Solar hydrogenconversion

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Spontaneous photoelectric field-enhancement effect prompts the low cost hierarchical growth of highly ordered heteronanostructures for solar water splitting

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Nano Research 2016年第6期9卷 1561-1569页

作者： Yankuan Wei Jinzhan Su XiaokangWan Liejin Guo Lionel Vayssieres International Research Center for Renewable Energy State Key Laboratory for Multiphase Flow in Power Engineering School of Energy &Power Engineering Xi'an Jiaotong University Xi'an 710049 China

In this study, a potentially universal new strategy is reported for the large-scale, low-cost fabrication of visible-light-active highly ordered heteronanostructures based on the spontaneous photoelectric-field-enhancement effect inherent in pyramidal morphology. The hierarchical vertically oriented arrayed structures comprise an active molecular co-catalyst at the apex of a visible-light-active large band gap semiconductor for low-cost solar water splitting in a neutral aqueous medium without the use of a sacrificial agent.

关键词： bismuth vanadate co-catalysts photocatalysis solar water splitting oxygen evolution

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Prediction on bubble departure diameter of high pressure boiling water in vertical upward smooth tubes 17

Prediction on bubble departure diameter of high pressure boi...

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17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2017

作者： Guo, Kaikai Li, Huixiong Zhang, Qing Kong, Xiangfei Luo, Qing Xue, Yuqing State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi'an Shaanxi China China Huaneng Clean Energy Research Institute Beijing102209 China Xi’an Thermal Power Research Institute Co. Ltd Xi'an Shaanxi China

As one of the most important parameters of boiling phenomena, the bubble departure diameter has great influence on the vapor-liquid interfacial heat transfer and the convection heat transfer between the wall and the fluid involved. At present, the RPI wall boiling model has been often used to simulate the boiling phenomenon, however, due to the fact that the existing bubble departure diameter models embedded in the RPI wall boiling model were mostly derived from fitting of limited experimental data, there exists great limitation to the applicability of the RPI wall boiling model. Moreover, the experimental data of the bubble departure diameter was mostly obtained at low and middle pressures, and no experimental data of the bubble departure diameter was measured at high pressure (more than 10 MPa). So the effectiveness of the RPI wall boiling model at high pressures should be studied further. A series experimental investigations on the heat transfer of high pressure boiling water in vertical upward tubes has been conducted at the Hi-TaP-XJTU test loop, and wall temperatures of vertical upward tubes were acquired at pressures ranging from 1 to 19 MPa. In combinations with the experimental studies, numerical simulations were performed on the heat transfer of high pressure boiling water flow in vertical upward tubes by using the RPI wall boiling model under conditions corresponding to the experimental investigation. Then,, the reference diameter (dref) used in the Tolubinsky bubble departure diameter model was modified and selected for a specific water pressure so as to make the numerically-obtained wall temperature to satisfactorily match the corresponding experimentally-measured wall temperature at the specific pressure. It was found that the value of dref was closely related to the pressures of the boiling water, but was independent of the mass flux of the water and the heat flux on the wall at a specific pressure. Based on a correlation between the water pressures a

关键词： Heat flux

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Thermodynamic Optimization of a Double-pressure Organic Rankine Cycle Driven by Geothermal Heat Source

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Energy Procedia 2017年 129卷 591-598页

作者： Qingxuan Sun Yaxiong Wang Ziyang Cheng Jiangfeng Wang Pan Zhao Yiping Dai Institute of Turbomachinery State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi’an Jiaotong University Xi’an 710049 People’s Republic of China

Geothermal energy, as a typical low-temperature heat source, has been exploited for decades to generate electricity. Organic Rankine cycle (ORC) system has a high energy conversion efficiency due to the good performance of organic fluids under the geothermal water temperature. In this study, a double-pressure organic Rankine cycle system driven by geothermal heat source is used to generate electricity. The double-pressure ORC system achieves the cascaded utilization of energy, which can improve the efficiency of energy conversion. Mathematical model is established based on thermodynamic laws, and the overall system performance has been evaluated. A parametric analysis is conducted to examine the effects of some key thermodynamic parameters, namely turbine high-level inlet pressure, turbine low-level inlet pressure, turbine high-level inlet temperature, on the system performance. Parametric optimization is conducted by means of genetic algorithm (GA) to find the maximum system performance. At the same time, the performances of three organic working fluids are examined. Results indicate that R245fa has a better performance among the three organic fluids. The exergy efficiency of overall system exceeds 5.8% under the supply water of 120℃, and it produce more than 800kW electricity with the geothermal water at the mass flow rate of 250t/h. It is also found that the exergy efficiency has peak value under the effect of turbine high-level inlet pressure and turbine low-level inlet pressure. In addition, increasing turbine high-level inlet temperature brings a positive effect to the system performance. Exergy analysis is also conducted and the result shows that the main exergy loss occurs in high-pressure evaporator. By system optimization, the double-pressure organic Rankine cycle has a better performance in utilizing geothermal energy than single-pressure system.

关键词： Geothermal Organic Rankine cycle Double-pressure

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Lithium–Sulfur Batteries: Flexible and High‐Loading Lithium–Sulfur Batteries Enabled by Integrated Three‐In‐One Fibrous Membranes (Adv. Energy Mater. 38/2019)

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Advanced Energy Materials 2019年第38期9卷

作者： Jianan Wang Guorui Yang Jie Chen Yunpeng Liu Yuankun Wang Cheng‐Yen Lao Kai Xi Duowen Yang Christopher J. Harris Wei Yan Shujiang Ding Ramachandran Vasant Kumar Department of Applied Chemistry School of Science MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter State Key Laboratory for Electrical Insulation and Power Equipment Xi'an Jiaotong University Xi'an 710049 China Department of Environmental Science and Engineering State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China Department of Materials Science and Metallurgy University of Cambridge Cambridge CB3 0FS UK

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Multi-objective optimization of a printed circuit heat exchanger design 17

Multi-objective optimization of a printed circuit heat excha...

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17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2017

作者： Wang, L. Chen, M. Shi, S. Che, D. Sun, X. Department of Nuclear Engineering and Radiological Sciences University of Michigan 2355 Bonisteel Blvd. Ann ArborMI48109-2104 United States State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an Shaanxi710049 China

Due to their high effectiveness and compact size, printed circuit heat exchangers (PCHEs) appear promising to be employed as intermediate heat exchangers (IHXs) in High-Temperature Gas-cooled Reactors (HTGRs). In the literature, PCHEs of zigzag mini-channel designs have demonstrated superior performance in heat transfer and pressure drop. In this research, a three-dimensional numerical simulation was performed for a PCHE using computational fluid dynamics (CFD) tool ANSYS FLUENT to study the effects of the zigzag pitch and angle, and channel diameter on its thermal-hydraulic performance. The mass, momentum, and energy equations were solved using a finite volume method by considering steady-state, incompressible laminar flow. The FLUENT numerical model was validated by comparing the simulation results with the experimental data obtained in a high-temperature helium test facility. The comparison showed overall good agreement between the simulations and experiments. In addition, it was challenging to obtain accurate correlations/models for the Nusselt number and friction factor with various geometrical and operational parameters considered. In our study, two artificial neural network (ANN) models were applied by utilizing the CFD results to predict the Nusselt number and friction factor in PCHE zigzag channels with different geometrical configurations and operational parameters. Consequently, the computation time needed for the PCHE design optimization process could be significantly reduced. The comparison between the ANN predictions and CFD results showed that the ANN models could predict the numerical data with good accuracies. Furthermore, to achieve an optimal heat exchanger design, two conflicting evaluation criteria were proposed based on the capital and operational costs. Finally, the Non-dominated Sorting Genetic Algorithms (NSGA-II) and the proposed ANN models were combined and utilized to optimize the geometrical design parameters of the zigzag-channel PCHEs.

关键词： Multiobjective optimization

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Computational fluid dynamics simulation of hydrodynamics in the riser of an external loop airlift reactor

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Particuology 2016年第4期14卷 95-101页

作者： Xuedong Jiang Ning Yang Bolun Yang Department of Chemical Engineering State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China Center for Mesoscience and State Key Laboratory of Multiphase Complex Systems Institute of Process Engineering Chinese Academy of Sciences Beijing 100190 China

Local hydrodynamics in the riser of an external loop airlift reactor （EL-ALR） are identified and the performances of three drag models are evaluated in computational fluid dynamics simulation. The simulation results show that the Schiller-Naumann drag model underestimated the local gas holdup at lower superficial gas velocity whereas the Tomiyama drag model overestimated that at higher superficial gas velocity. By contrast, the dual-bubble-size （DBS）-local drag model gave more reasonable radial and axial distri-butions of gas holdup in all cases. The reason is that the DBS-local drag model gave correct values of the lumped parameter, i,e., the ratio of the drag coefficient to bubble diameter, for varying operating conditions and radial positions. This ratio is reasonably expected to decrease with increasing superficial gas velocity and be smaller in the center and larger near the wall. Only the DBS-local drag model correctly reproduced these trends. The radial profiles of the axial velocity of the liquid and gas predicted by the DBS-local model also agreed well with experimental data.

关键词： Computational fluid dynamics External loop airlift reactor Drag model Gas holdup Mnltiscale Mesoscale

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Gas and Liquid flow Rate Measurement in Wet Gas Based on Differential Pressure Signals

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Jixie Gongcheng Xuebao/Journal of Mechanical engineering 2017年第24期53卷 55-62页

作者： Bai, Bofeng Zheng, Xuebo Qiu, Lu State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China Scientific Information Division Xinjiang Oilfield Company Karamay834000 China

The basic characteristics of differential pressure signals and the limitation of flow rate metering methods based on differential pressure are studied analytically and experimentally. Through the investigation into differential pressure signals of orifice plate and V-cone, it is found that the two-phase differential pressure is mainly caused by gas phase and is slightly affected by the liquid phase. In the case of low liquid hold up, the frictional pressure drop can be decreased due to the presence of the thin liquid film on the wall, resulting in that the two-phase differential pressure, pressure loss and pressure loss ratio decrease at first and then increase as the liquid hold up increases. The fluctuation of the differential pressure is stochastic, causing the fluctuation characteristic parameters, such as the standard deviation, having the properties of poor stability and repeatability. This makes it difficult to be applied to industrial wet gas metering. The error propagation analysis demonstrates that the prediction error of liquid phase flow rate is much larger than that of the gas phase, which is a universal phenomenon of metering methods based on over-reading correlations. Finally, we recommend that for wet gas with high gas void fraction, the liquid flow rate should be measured independently. The non-monotonicity of the pressure loss ratio needs to be concerned if it is chosen as the characteristic parameter. Parameters with poor repeatability, such as standard deviation, are not recommended for wet gas metering. © 2017 Journal of Mechanical engineering.

关键词： flow rate

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Correlations of Coal Chemical Properties in China: Quantitative Analysis from Thousands of Data

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Energy Procedia 2017年 105卷 1339-1343页

作者： Chang’an Wang Song Wu Wufeng Chen Qiang Lv Defu Che State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi’an Jiaotong University No 28 Xianning West Road Xi’an 710049 China

Coal chemical properties show conspicuous impacts on its reactivity and thermal conversion. Nevertheless, the quantitative analysis of coal property indice in China is insufficient. Here, we quantitatively analyzed the correlations of various chemical properties of coals from thousands of data. Noteworthy variations were captured with some quantified expressions between coal properties obtained.

关键词： coal property quantitative analysis fuel ratio coal rank energy conversion fossil fuel

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