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Hydrodynamic Pattern in Drying Saline Droplet with Suspended Nanoparticles

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Journal of Bionic engineering 2020年第4期17卷 802-808页

作者： Junheng Ren Xin Zhong Lu Shen Fei Duan School of Mechanical and Aerospace Engineering Nanyang Technological UniversitySingapore 639798Singapore State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an 710049China

Evaporation of multicomponent droplets has gained much attention nowadays because of their complex flow fields and various deposition *** we observe strong flows in evaporating sodium chloride saline droplets with suspended alumina oxide *** evolution of flow pattern was studied by tracking the trajectories of particles and the velocity field was investigated with Particle Image Velocimetry *** non-uniform evaporation rate along the droplet surface leads to a concentration gradient which induces the convection *** the evaporation process before crystallization happens,evolution of the flow can be divided into two *** Regime I,a centrosymmetric convection recirculation is formed *** RegimeⅡ,the convection recirculation migrates to the droplet edge and evolves into several small *** the late evaporation stage,crystallization could induce strong convection *** is shown that the flow tends to become more chaotic with a lower salt concentration.

关键词： convection flow concentration gradient saline droplet crystallization

Theoretical Study on Predicting the Performance of Steam Ejector by Analogy Method

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Theoretical Study on Predicting the Performance of Steam Eje...

IEEE Asia power and Energy engineering Conference (APEEC)

作者： Yiguo Mei Keneng Qian Yuyan Hou Weixiong Chen Huaxin Consulting Design and Research Institute Co. Hangzhou China State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an China

At present, it is difficult to obtain steam with high pressure under conventional laboratory conditions, and there are certain operational risks in the production of high-pressure and high-temperature steam devices. In this paper, a method to predict the critical entrainment ratio of the steam ejector by using the critical entrainment ratio of the air ejector is proposed. According to the one-dimensional calculation model of the ejector, the parameters related to the critical entrainment ratio are derived. The mathematical relationship between the entrainment ratio and each parameter is found through the mathematical tool Matlab. The performance of the ejector with different working mediums is simulated and verified by Fluent. The research results in this paper show that the entrainment ratio of air and steam ejector is linear with the pressure ratio within a certain range of pressure ratio. Under this linear relationship, the experimental entrainment ratio of the air ejector can be used to predict the entrainment ratio of the steam ejector. In a certain linear range, the relative error between the entrainment ratio predicted by the method proposed in this paper and the simulation results is within 10%.

关键词： Electrical engineering Simulation Fitting Production Media Numerical simulation Market research

Effect of Tungsten Size on Thermal Analysis and Mechanism of Lithium Perchlorate-Based Electrically Controlled Solid Propellant

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SSRN 2023年

作者： Yang, Meng Yoh, Jack J. Tang, Chenglong Huang, Zuohua State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China Department of Aerospace Engineering Seoul National University Seoul08826 Korea Republic of

Electrically controlled solid propellant (ECSP) is a novel and potential of propellant with excellent properties, which can achieve multiple ignitions and extinguishments through supplying and cutting electric power. At present, thermochemistry coupled with electrochemical reaction processes are complex and not understood clearly, especially its based thermal decomposition mechanism without electric power. In this work, the baseline ECSP was prepared using lithium perchlorate (LiClO4, LP) as oxidant, and tungsten as metal additive to obtain high energy ECSP samples. The scanning electron microscope (SEM), differential scanning calorimeter (DSC) and thermogravimetry (TGA) were used to investigate thermal analysis characteristics of ECSP and the effect of metal tungsten sizes on reaction process and mechanism. The heat release and effective activation energy (Eα) of baseline ECSP were lower than those of metalized ECSP. In addition, with W size increasing, heat release and Eα of ECSP increase. Based on thermal analysis and kinetic results, the decomposition mechanisms of ECSP main components and samples were proposed. The absorbed and crystal water evaporated, then main components molten for all cases at low temperature ( © 2023, The Authors. All rights reserved.

关键词： Thermogravimetric analysis

Experiments and predictions for severe slugging of gas-liquid two-phase flows in a long-distance pipeline-riser system

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Ocean engineering 2024年 301卷

作者： Chang, Yingjie Xu, Qiang Zou, Suifeng Zhao, Xiangyuan Wu, Quanhong Wang, Yechun Thévenin, Dominique Guo, Liejin Shaanxi Key Laboratory of New Transportation Energy and Automotive Energy Saving Chang'an University Xi'an710064 China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China Laboratory of Fluid Dynamics and Technical Flows Otto-von-Guericke-Universität Magdeburg Magdeburg39106 Germany

Experiments concerning the flow regimes observed in gas-liquid two-phase flows in a long-distance pipeline-riser system were carried out and analyzed in this paper. The test loop with 0.075 m inner diameter consisted of a 314 m horizontal pipeline, followed by a 25 m downward-inclined pipe, and finally a 21.5 m riser pipe. An industrial-scale global flow regime map including 5 flow regimes was derived from differential pressure measurements in the riser and was used as a reference for improvements. Electrical capacitance volume tomography installed in the horizontal section was used to reconstruct the phase interface and calculate the average gas void fraction (GVF). An appropriate model for this system was selected by comparing the experimental GVF with different, widely used models. The occurrence of severe slugging flow (SS) can be predicted accurately using an improved model involving additional corrections that consider pipeline length, accurate GVF calculation, and gas density. This study supports the development of a suitable SS prediction model enabling safe design, operation, and control of practical systems. © 2024 Elsevier Ltd

关键词： Pipelines

Atomic Insights into Hydrogen Peroxide Decomposition on the Surface of Pure and Pre-Treated Silver: A Reactive Molecular Dynamics Simulation Study

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SSRN 2023年

作者： Zhao, Xiao Feng, Yiming Zhang, Bowei Jin, Hui Wei, Xianggeng State Key Laboratory of Solid Propulsion Northwestern Polytechnical University Shaanxi Xi’an710072 China State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Shaanxi Xi’an710049 China

Based on ReaxFF molecular dynamics simulation, H2O2 decomposition on pure and pre-treated silver catalyst is studied at a microscopic level. The pretreatment undergoes a surface annealing with redundant H2O2 on top of catalyst. The simulation results indicate that H2O2 decomposition can be drastically accelerated by elevating temperature. The extent of decomposition is closely related to bond, hydrogen bond, and potential energy of simulation system. It is found that H2O2 decomposition follows a four-stage HO-OH bond break mechanism while it needs three times longer for pre-treated silver catalyst than pure silver catalyst. The activation energy of pre-treated silver catalyst is about 50% lower than pure silver catalyst. However, the overall reaction rate of pre-treated silver catalyst is about an order of magnitude slower than pure silver catalyst, which owes to the much smaller pre-factor. It is believed that although the pretreatment causes silver oxide to be formed on the surface, it leads to more hydrogen and oxygen atoms deposited so that most active sites for catalytic reaction are blocked for further decomposition. This may be helpful to understand the inherent mechanism of H2O2 decomposition on silver-based catalyst and provide instructional advice for further catalyst modification design. © 2023, The Authors. All rights reserved.

关键词： Catalysts

Numerical Study on the Effect of Rim Seal Slot Filleting on Turbine Endwall Cooling Performance

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SSRN 2023年

作者： Shi, Liuliu Di, Wentao School of Energy and Power Engineering University of Shanghai for Science and Technology Shanghai200093 China Key Laboratory of Power Machinery and Engineering Ministry of Education Shanghai Jiao Tong University Shanghai200240 China Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering Shanghai200093 China

In the present study, the effect of rim seal slot filleting on turbine endwall cooling performance is numerically investigated. Based on validation of the numerical method, the Reynolds-averaged Navier-Stokes (RANS) equations combined with the standard turbulence model are adopted in this study. For comparison with the baseline case, five different fillet radii are adopted, i.e. R/W=1.25, 2.5, 3.75, 5 and 6.25. The results indicate that the overall film cooling effectiveness on the turbine endwall can be improved by up to 10% with smaller fillet radii. However, this effect diminishes as the fillet radius increases and it becomes negative at R/W=6.25. By examining the contours of the endwall film cooling effectiveness in filleted cases with the baseline, a prominent strip can be observed across the blade passage. This reveals that the primary contributor to the variation of the film cooling performance is the pressure-side leg horseshoe vortex. Besides, the film cooling effectiveness is slightly improved near the suction side of the leading edge owing to the suppression of endwall separation at this area. The rim seal slot filleting eliminates the slot leakage separation, which in turn speeds up the endwall coolant flow. Ultimately, this weakens the pressure-side leg horseshoe vortex and subsequently enhances the film cooling performance. As the fillet radius continues to increase, the through-flow area for the coolant flow enlarges, resulting in a gradual decrease in film cooling performance. © 2023, The Authors. All rights reserved.

关键词： Turbulence models

Data Mining-Assisted Multi-Objective Optimization of Blade Angle Distributions for Efficiency and Stability Enhancement of a Free-Form Centrifugal Impeller

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SSRN 2024年

作者： Chen, Zhikai Chen, Ziying Sun, Jieshuai Guo, Yi Spence, Stephen Peng, Xueyuan Feng, Jianmei School of Energy and Power Engineering Xi'an Jiaotong University Xi’an710049 China School of Mechanical Manufacturing and Biomedical Engineering Trinity College Dublin Dublin 2 Ireland State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi’an710049 China

The design optimization process for a centrifugal compressors faces significant trade-offs between efficiency, pressure ratio, and stable operating range. To address this challenge, a data mining assisted-optimization combining machine learning modelling method and non-dominated sorting genetic algorithm III (NSGA-III) has been proposed to enhance efficiency and pressure ratio while considering expansion of operational stability. A validated CFD numerical model was established for data generation. A Light-GBM model with Bayesian hyperparameter tuning and a deep feedforward neural network (DNN) model were constructed, and the better one was selected for performance prediction. Data mining techniques, including Sobol sensitivity analysis and SHAP, were employed to identify the key sensitive parameters and their interactions. Finally, a NSGA-III-based multi-objective optimization was conducted to determine the optimal geometry of the free-form surface impeller. Results showed that the blade angle distributions at the leading edge of mid-span and shroud profile were the most sensitive parameters affecting isentropic efficiency at the design point, with their recommended ranges identified. The optimized impeller has an increase in total pressure ratio of 2.98% and isentropic efficiency of 0.67% at the design point, especially exhibiting excellent aerodynamic performance at higher mass flow rate conditions. The maximum improvements of total pressure ratio and isentropic efficiency were 12.91% and 9.53%, respectively, corresponding to the near choke mass flow rate at the design speed. Additionally, operating stability was expanded with a 1.22% increase in total pressure ratio at near surge mass flow rate at the design speed, which contributed to a delay in the onset of surge. © 2024, The Authors. All rights reserved.

关键词： Sensitivity analysis

Numerical and Experimental Investigation of Proton Exchange Membrane Fuel Cell with Perpendicular Gas Supply Through the Ridge

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SSRN 2023年

作者： Zhang, Yan Lu, Xinyu Su, Jinzhan School of International Trade and Economics China International Research Center for Renewable Energy State Key Laboratory of Multiphase Flow in Power Engineering School of Energy & Power Engineering Xi’an Jiaotong University Xi’an710049 China

The structural design of the cathode flow field in proton exchange membrane fuel cell (PEMFC) is essential for efficient gas supply and effective water removal. For investigating the mechanism behind the effect of gas flow direction on improving the performance of PEMFC, a novel modified serpentine flow channel with vertical inlets through the ridge for PEMFC was proposed and investigated by numerical and experimental methods. Under the operating voltage of 0.4 V, the vertical air supply mode exhibits a 7% higher current density compared to the parallel air supply mode. Compared with conventional air supply mode through the serpentine flow channel, vertical air supply mode modified serpentine through a tunnel inside the ridge exhibited higher oxygen uniformity and higher current density. Furthermore, we conducted research on the impact of physical parameters, including the porosity and thickness of the GDL, as well as the vertical gas supply pore density, on the performance of the PEMFC within the vertical gas supply mode. At an operating voltage of 0.4 V, the current density of PEMFC with a GDL thickness of 0.28 mm is 1.0009 A/cm2, which is 3.02% and 6.13% higher than that of PEMFC with vertical inlets with GDL thickness of 0.38 and 0.48 mm, respectively. With a porosity of 0.6, the current density of PEMFC reaches 1.0395 A/cm2, surpassing that of PEMFCs with porosities of 0.2 and 0.4 by approximately 24.8% and 6.6%, respectively. Moreover, higher vertical inlet densities lead to improved PEMFC performance. Simulation and experimental results demonstrate that this modified flow field effectively addresses uneven current density distribution and enhances power output at low voltage. © 2023, The Authors. All rights reserved.

关键词： Porosity

Effects of Inherent Aaems on Catalytic Gasification of Biomass with Large Particle Size Under Oxygen-Steam Atmosphere

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SSRN 2023年

作者： Ren, Jiyun Li, Yuhang Li, Yang Huang, Xiaole Jin, Xiaoling Yang, Chenglong Zhao, Hanchen Deng, Lei Che, Defu State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi’an Jiaotong University Xi’an710049 China Xi’an Thermal Power Research Institue Co. Ltd. Xi’an710032 China

Oxygen-steam gasification of biomass is a promising technology because of its ability to improve syngas quality and reduce energy consumption. In this study, a fixed-bed reactor is employed to assess the effects of inherent alkali and alkaline earth metals (AAEMs) on the catalytic gasification of candlenut wood with large particle size under oxygen-stream atmosphere. The results show that the acid-washing would remarkably remove the inherent AAEMs in biomass, which is affected by the grain direction. In terms of the gasified chars derived from acid-washed biomass, AAEMs content gradually decreases along the end surface and radial direction, which could also be observed from the 3D reconstruction of X-ray CT images. A large number of mesopores (20-30 μm) align along the grain direction in the biomass sample. Numerous micropores (10-20 μm), mesopores (20-30 μm), and macropores (30-50 μm) are present in the gasified char derived from the biomass sample. Micropores (10-20 μm) prevail in the gasified char from the acid-washed biomass sample. Inherent AAEMs facilitate an augmentation in char yield as well as BET and total pore volume of gasified char. AAEMs and grain direction have a slight effect on functional groups of gasified char. The tar component is remarkably affected by the grain direction. Acid-washing pretreatment augments the content and organic species of M2-M4 compounds (containing 2-4 benzene rings) in the tar. It also leads to a decrement in concentrations of H2, CH4, and CO2 by 14.49% and 13.35%, 0.51% and 0.89%, 2.32% and 1.37% in syngas for two-grain direction, respectively. But it raises the CO concentration by 17.1% and 15.18%, resulting in a reduction of 4.09% and 1.53% in syngas calorific value. A decrement in the volume fraction of CnHx induced from AAEMs is significantly affected by the grain direction. © 2023, The Authors. All rights reserved.

关键词： Biomass