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Radial expansion of flash boiling jet and its relationship with spray collapse in gasoline direct injection engine

APPLIED THERMAL engineering 2019年 146卷 515-525页

作者： Guo, Hengjie Li, Yanfei Lu, Xinhui Zhou, Zhifu Xu, Hongming Wang, Zhi Tsinghua Univ State Key Lab Automot Safety & Energy Beijing 100084 Peoples R China Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

In order to mitigate spray collapse and fully utilize the advantage of flash boiling injection in gasoline direct injection (GDI) engines, it is important to understand the flashing jet behavior and its relationship with spray collapse. In this study, n-hexane sprays discharged from a modified single-hole injector and the original five-hole injector were studied. The tests were carried out in a constant volume vessel with injection temperatures from 30 to 130 degrees C and ambient pressures (P-amb) from 20 to 101 kPa. By analyzing the relationship between the jet width and different parameters including superheat level, nucleation rate, and chemical potential of phase change (Delta mu), strong correlation was found between the jet width and Delta mu.P-amb(-0.5), indicating the radial expansion of flashing jets was determined by chemical potential of phase change and ambient resistance. Beyond 20d(0), the correlation was gradually weakened along the axis, as flash boiling process was finished. Besides, it was found that the extent of single-jet radial expansion was positively related to that of multi-jet spray collapse in the transitional collapse region. Therefore, to mitigate spray collapse, it is necessary to restrict the radial jet expansion, and generating external flashing jets is proposed as a practical approach to realize it.

关键词： Gasoline direct injection Flash boiling Spray collapse Radial jet expansion Chemical potential

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(Oxy)nitride heterojunction-strengthened separation of photogenerated carriers in g-C3N4 towards enhanced photocatalytic H2 evolution

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APPLIED CATALYSIS A-GENERAL 2022年第0期643卷 1页

作者： Zhang, Yazhou Liu, Dongjie Shi, Jinwen Chen, Pengfei Zong, Shichao Cheng, Cheng Chen, Kailin Chen, Yubin Ma, Lijing Xian Jiaotong Univ XJTU Int Res Ctr Renewable Energy IRCRE State Key Lab Multiphase Flow Power Engn MFPE 28 West Xianning Rd Xian 710049 Peoples R China Xiamen Univ Coll Chem & Chem Engn State Key Lab Phys Chem Solid Surfaces 422 Siming South Rd Xiamen 361005 Peoples R China Sichuan Digital Econ Ind Dev Res Inst Integrated Energy Inst 88 Jiefang Rd Chengdu 610036 Peoples R China Power China Northwest Engn Corp Ltd 18 East Zhangba Rd Xian 710065 Peoples R China

The metal-free graphitic carbon nitride (g-C3N4) with a series of merits like low cost, favorable stability, and controllable two-dimensional graphite-like structure, has been extensively studied for photocatalytic H2 evolution. Composite engineering is regarded as one of effective strategies to adjust the kinetics of photogenerated carriers in g-C3N4 for elevating its photocatalytic performance. Herein, the composite system of g-C3N4 with oxynitride LaTiO2N was elaborately constructed for improving photocatalytic H2-evolution performance. With systematical characterizations, the partial cover of g-C3N4 nanosheets on LaTiO2N (LaTiO2N@g-C3N4) was verified and promoted the sufficient contact between g-C3N4 and LaTiO2N, accompanied by the formation of the (oxy)nitride heterojunction. Benefited by the well-matched band structures for g-C3N4 and LaTiO2N, the (oxy) nitride heterojunction strengthened the separation of photogenerated carriers and therefore enhanced the photocatalytic performance of g-C3N4. This work gives more insight in composite engineering on g-C3N4, and also provides feasible guidelines for designing g-C3N4-based photocatalysts towards improving photocatalytic performance.

关键词： Graphitic carbon nitride Oxynitride Composite Heterojunction Photocatalytic H2 evolution

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Numerical analysis of hydrodynamic fine fragmentation of corium melt drop during fuel-coolant interaction

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2019年 137卷 579-584页

作者： Li, Gen Zhang, Jun Yang, Qingzhong Duan, Guangtao Yan, Junjie Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China Waseda Univ Cooperat Major Nucl Energy Tokyo 1698555 Japan

Hydrodynamic fine fragmentation of melt drops is important in increasing melt-coolant contact area, and thus directly affects heat transfer, oxidation and solidification. The interfacial instabilities incurred by relative flow and density gradient are the dominant factors for melt drops deformation and fragmentation. In this study, we modelled melt drop breakup behavior using a meshless Lagrangian MPS method, and validated the numerical model with the experimental results. Then, the melt fragments amount, size distribution and normalized perimeter were analyzed under different Weber numbers. The results indicate that the melt drop breakup process could be divided into two phases: initial deformation and fragmentation phase governed by flow inertial force and the subsequent fragments coalescence phase under the impact of fluid surface tension. Fragments amount increased in fragmentation phase but decreased in coalescence phase. The amount of fragments with smaller size (d/d(0) < 0.04) was significantly larger at high Weber number cases, but the amount of large-scale fragments (d/d(0) > 0.05) was equivalent among different weber number cases. The maximum fragments perimeter reached 20 times of the initial melt drop perimeter for case of We = 2618, which was about 3.3 times of that at We = 291. (C) 2019 Elsevier Ltd. All rights reserved.

关键词： Fuel-coolant interaction Melt drop Fragmentation MPS method

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Upstream-flow-based mechanisms for global flow regime transition of gas/liquid two-phase flow in pipeline-riser systems

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CHEMICAL engineering SCIENCE 2021年 240卷 116542-116542页

作者： Zou, Suifeng Guo, Liejin Yao, Tian Wuhan Second Ship Design & Res Inst Wuhan 430064 Peoples R China Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China CNPC Tubular Goods Res Inst Xian 710077 Peoples R China

In order to develop the transition models for undesirable two-phase flow regimes in a pipeline-riser system in offshore oil and gas production systems, the relation between the upstream flow condition in the pipeline and the global flow regime is analysed. The transition of local flow pattern along the upstream pipeline, especially the slug dissipation behaviour, is found to be related to global flow regime transition. The mechanisms for the transition from stable flow regime to different undesirable flow regimes are proposed separately. A set of hybrid criteria is established and validated by experimental data. The proposed criteria can predict the transition to undesirable conditions which are less severe but more common than the typical cases, compared with existing uniform criteria. The findings can help for better understanding of flow regime transition in a pipeline-riser system with more complex layout of pipeline, and also the possible extension of laboratorial experimental results. (c) 2021 Elsevier Ltd. All rights reserved.

关键词： Pipeline-riser system Two-phase flow Global flow regime flow regime transition Transition criteria Slug dissipation

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Design and multi-objective optimization of low-temperature proton exchange membrane fuel cells with efficient water recovery and high electrochemical performance

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APPLIED ENERGY 2022年 324卷

作者： Yao, Jing Wu, Zhen Wang, Huan Yang, Fusheng Xuan, Jin Xing, Lei Ren, Jianwei Zhang, Zaoxiao Xi An Jiao Tong Univ Sch Chem Engn & Technol Xian 710049 Peoples R China Loughborough Univ Dept Chem Engn Loughborough LE11 3TU Leicestershire England Univ Johannesburg Dept Mech Engn Sci ZA-2092 Johannesburg South Africa Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

Water generated by electrochemical reaction in the proton exchange membrane fuel cell (PEMFC) could be used as an important resource. Several studies have been carried out to recycle the water from PEMFC emissions, which verifies the feasibility of water recovery. However, the quantitative description of the water recovery mechanism inside PEMFC is not clear and the water recovery performance could be further improved from the perspective of internal mass transfer. In this paper, a two-dimensional model is developed to present the fluid flow and mass transfer inside a PEMFC. Also, a detailed investigation into the effects of operating parameters, including pressure, temperature, and relative humidity, on both the electrochemical performance and the water recovery performance is conducted. Besides, a multi-objective optimization is carried out for the performance optimization of PEMFC. The results show that the expanded water recovery efficiency (EWRE) of PEMFC is more sensitive to pressure and relative humidity than temperature. The optimum solution at 1 atm shows that EWRE reaches 141 % with the current density of 0.7163 ***(-2). The operation strategy of decreasing the humidification temperature and increasing the relative humidity at the cathode inlet, and maintaining PEMFC working at a moderate temperature is proposed to keep the balance between the electrochemical and water recovery performance. This work contributes to the operation optimization of water recovery and to the application extension of PEMFC.

关键词： Fuel cel Water recovery Water transfer Agglomerate model Multi-objective optimization

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Investigation on drag reduction of aqueous foam for transporting thermally produced high viscosity oil

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JOURNAL OF PETROLEUM SCIENCE AND engineering 2022年第0期210卷 110062-110062页

作者： Sun, Jie Guo, Liejin Yin, Xiaoyun Jing, Jiaqiang Fu, Jiqiang Lu, Yingda Ullmann, Amos Brauner, Neima Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China Southwest Petr Univ Sch Oil & Nat Gas Engn Chengdu 610500 Peoples R China Univ Texas Austin Hildebrand Dept Petr & Geosyst Engn Austin TX 78712 USA Tel Aviv Univ Sch Mech Engn Fac Engn IL-69978 Tel Aviv Israel

An innovative idea is proposed for facilitating the transportation of thermally produced high-viscosity oil by injecting temperature tolerant aqueous foam. To this aim, experimental investigations of the flow characteristics of heated highly viscous oil flowing through a 25 mm i.d. horizontal rough-wall tempered borosilicate glass pipe were conducted. Measurements were made for the superficial oil and foam velocities in the range of 0.05-0.40 m/s and 0.04-0.39 m/s, respectively. Eccentric core annular flow configurations detected by a high-speed camera were found to be particularly dominant throughout the entire tested range. A two-fluid, three-zone mechanistic model for horizontal foam-oil flows was implemented for the case of shear thinning power-law fluid in the annulus, which is in accordance with the foam rheological behavior at the tested elevated temperature. Good agreement was achieved between the predicted and measured data over a wide range of operational conditions. When a complete foam annulus encapsulating the oil core is formed, a critical value of input foam volume fraction can be determined for the maximum drag reduction ratio. An optimal oil core-to-pipe radius ratio range was determined for the highest oil-transport operational coefficient. The drag reduction performance of the tested hot oil-foam system is better than that obtained with the oil-foam system employed at room temperature.

关键词： Highly viscous oil Aqueous foam Drag reduction Eccentric core flow Two-fluid model

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A multi-criteria comprehensive evaluation method for distributed energy system 10

A multi-criteria comprehensive evaluation method for distrib...

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10th International Conference on Applied Energy (ICAE)

作者： Dai, Haibo Wang, Jinshi Li, Gen Chen, Weixiong Qiu, Binbin Yan, Junjie Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

As the evaluation of distributed energy system (DES) is a complex problem, multi-criteria is necessary to fully evaluate the performance for different systems. In this paper, a novel multi-criteria evaluation method was established to assess the comprehensive performance of DES from economic, energy and environment criterions. Before constructing a multi-level indexes system, index correlation analysis was carried out to ensure the independence of indexes. Considering the advantages and disadvantages of subjective and objective methods, AHP-entropy method was proposed by integrating analytic hierarchy process (AHP) and information entropy method together to assign weights to the indexes. Finally, the technique for order preference by similarity to ideal solution (TOPSIS) method was applied to determine the optimal DES scheme. The case study indicated that the evaluation results of this method were in accordance with the reality, which could provide a reference for the selection of DES solutions. (C) 2019 The Authors. Published by Elsevier Ltd.

关键词： DES comprehensive evaluation AHP-entropy method TOPSIS method

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Numerical modeling and performance comparison of high-temperature metal hydride reactor equipped with bakery system for solar thermal energy storage

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INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 2020年第56期45卷 31612-31631页

作者： Ayub, Iqra Nasir, Muhammad Salman Liu, Yang Munir, Anjum Wu, Zhen Yang, Fusheng Zhang, Zaoxiao Xi An Jiao Tong Univ Sch Chem Engn & Technol State Key Lab Multiphase Flow Power Engn 28 Xianning West Rd Xian 710049 Peoples R China Xi An Jiao Tong Univ Sch Energy & Power Engn Xian 710049 Peoples R China Univ Agr Faisalabad Dept Energy Syst Engn Faisalabad 38040 Pakistan Univ Agr Faisalabad Dept Struct & Environm Engn Faisalabad 38040 Pakistan

The current study provides an optimal design strategy for the metal hydride reactor for the thermal energy storage system for solar bakery applications. The sensitivity analysis of the annular truncated hollow conical fins type reactor was conducted by using COMSOL Multiphysics 5.3a software. The gravimetric exergy output rate and exergy output of different designs were compared. It was found that the optimal geometric parameters and operating conditions for the annular truncated hollow conical fins type reactor are fin angle (theta) = 20 degrees, fin radius (R-f) = 0.07 m, number of fins (N-f)= 32 and fin spacing (S-f) = 0.02 m, fin thickness (th(f)) = 0.008 m, hydrogen supply pressure (P-in,P-H2) = 5 MPa and inlet heat transfer fluid velocity (V-HTF,V-in) = 20 m/s. Finally, it was concluded that the Deign IV is the most favorable design, which has a uniform reaction, faster reaction time (15,000 s), and higher values of gravimetric exergy output rate and exergy output (1.23 W/kg, 0.028 kW). (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

关键词： Solar thermal energy Storage (MgH2+V2O5) reactor Optimal design strategy Reduction of reaction time and non-uniform reaction An increase of gravimetric exergy output rate

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Ni coarsening and performance attenuation prediction of biomass syngas fueled SOFC by combining multi-physics field modeling and artificial neural network

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APPLIED ENERGY 2022年 322卷

作者： Zhu, Pengfei Wu, Zhen Wang, Huan Yan, Hongli Li, Bo Yang, Fusheng Zhang, Zaoxiao Xi An Jiao Tong Univ Sch Chem Engn & Technol Xian 710049 Peoples R China Xian Jiaotong Univ City Coll Dept Mech Engn Xian 710018 Peoples R China Univ Kent Sch Engn Kent CT2 7NZ England Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

Ni particle coarsening is an important factor in deteriorating the durability of solid oxide fuel cell (SOFC) operations. In order to investigate the influence of Ni coarsening on SOFC performance, the transient multi-physical field model of SOFC was developed in this paper. The high operating temperature accelerates Ni particle growth and increases the attenuation rate of SOFC current density from 0.23%/kh at 650 degrees C to 2.6%/kh at 800 degrees C. The increase in the ratio of steam to carbon also intensifies the Ni particle coarsening process and deteriorates the transient performance of SOFC. Increasing YSZ particle diameter could hinder the growth of Ni particles and slowing down the increase rate of Ni particle diameter. Within the range of preset YSZ diameter dYSZ, increasing dYSZ reduces the attenuation rate and increases the average current density. Improving Ni phase fraction helps to reduce the attenuation rate of current density. Since multi-physical field (MPF) simulation needs long calculation time and it is difficult to achieve fast prediction, artificial neural network (ANN) is trained by the database generated by MPF. The mapping relationship between operating parameters, structural parameters and attenuation indexes is obtained. Finally, the attenuation performance of SOFC is optimized by genetic algorithm (GA) through data-driven method. The absolute average relative errors of all parameters in predicting attenuation rate and average current density are as low as 0.767% and 0.248%, which indicates the reliability of the ANN prediction. After optimization, the maximum current density is 5848 A.m(-2) under operating voltage at 0.6 V when the attenuation rate requirement not exceeding 1% is satisfied. The combination of MPF simulation, ANN and GA provides a framework for fast performance prediction and optimization of strong nonlinear system.

关键词： Solid oxide fuel cell Ni coarsening Multi -physics field Artificial neural network Performance attenuation prediction

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A new simulation method for laser speckle imaging to investigate hemodynamics 12

A new simulation method for laser speckle imaging to investi...

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12th International Conference on Computational Heat, Mass and Momentum Transfer (ICCHM2T)

作者： Sang, X. Li, D. Chen, B. Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

Speckle simulation is a powerful protocol to investigate the properties of speckle and evaluate image processing method. However, only static speckle images can be simulated by available methods without considering time-integrated effect of CCD. A time-integrated dynamic speckle simulation method based on coherent imaging was developed. Through the new simulation method, the effect of speckle size on LSCI was investigated. The smaller the speckle size is, the higher the spatial resolution become. But the one-dimensional speckle size should exceed two pixels to sample the speckle pattern. The characteristics of existing speckle contrast imaging methods were studied based on spatial statistics, and optimal parameters are given to obtain accurate and less noisy image. In general, the new simulation method for laser speckle imaging is a powerful tool to monitor blood flow in vivo and lay a solid foundation for the study of hemodynamics.

关键词： Hemodynamics

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