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SSRN 2023年

作者： Zhang, Peiye Liu, Ming Mu, Ruiqi Yan, Junjie State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

The parabolic trough solar receiver-reactors of methanol decomposition reaction (PTSRR-MDR) enable efficient hydrogen production with solar energy at users' end. Solar fluctuations affect the solar-to-chemical efficiency, hydrogen yield and system stability, indicating the necessity for an appropriate control strategy. In this study, dynamic and thermodynamic models of PTSRR-MDR with Cu/ZnO/Al2O3 as catalyst were developed. Results of thermodynamic analysis show that an optimal flow rate exists for methanol to achieve the maximum solar-to-chemical exergy efficiency of the PTSRR-MDR. The temperature increases sharply and exceeds the catalyst sintering temperature when the methanol flow rate decreases under its optimal value. Then, control objectives to achieve the maximum efficiency were obtained with a temperature of 3 °C to guarantee the PTSRR-MDR safety. Control strategies based on Dynamic Matrix Control (DMC), Forward-Feedback Control (FFC) and Ramp Control (RC) were evaluated under cloud shading/recovering and real radiation processes. Results show that strategies based on DMC, FFC, and RC increase the solar-to-chemical exergy efficiency from 14.76% to 16.31%, 16.28% and 15.65%, respectively. The Integral Squared Error (ISE) for methanol conversion rate under three methods are 1.46, 0.32 and 5.28, respectively, indicating that strategy based on FFC is considered most suitable for PTSRR-MDR operation control. © 2023, The Authors. All rights reserved.

关键词： Methanol

Experimental and Kinetic Study of Methanol Reforming and Methanol-Syngas Co-Oxidation at High Pressure

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SSRN 2023年

作者： Zhan, Haochen Li, Shuming Yin, Geyuan Gao, Yibo Hu, Erjiang Huang, Zuohua State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

Using engine exhaust heat to improve efficiency by performing co-combustion after partial reforming of methanol to syngas is a favored strategy to address the challenges associated with methanol engine applications. In the present work, experiments of methanol pyrolysis and methanol-syngas oxidation were conducted using high-pressure flow reactors at 1.0-5.0 MPa. The ratio of syngas to methanol varied from 0–50%. Mech15.34 was selected as the most reliable kinetic model to further kinetic analysis, which revealed that pressure decreases the decomposition of CH3OH to CH3, enhances the H-abstraction of CH3OH to CH2OH and CH3O, and increases the yield of H2 and CO. Furthermore, high pressure inhibits CH2OH = CH2O + H, thus reducing CH2O. The effects of blending syngas can be divided into dilution and chemical effects. The dilution effect refers to the reduction of CH3OH, which directly decreases the CH2O formation. The chemical effect refers to the competition of H2 and CO for OH radicals, which decelerates the CH3OH oxidation, decreasing the CH2O generation. Meanwhile, the reaction H2O2 + H = H2 + HO2 proceeds in reverse direction with H2 blending, generating more H radicals, which enhances the CH2O consumption through the reaction CH2O + H = HCO + H2. © 2023, The Authors. All rights reserved.

关键词： Oxidation

Experimental Study on flow Boiling and Circumferential Non-Uniform Heat Transfer Characteristics in Helically-Coiled Tube Under Coupled Heat Transfer Conditions

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SSRN 2024年

作者： Wang, Hengyuan Xuan, Qiyu Lei, Hailin Li, Xi Li, Zhibin Li, Huixiong State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi’an Jiaotong University Xi’an710049 China

Because of its compact structure and high energy conversion efficiency, helically-coiled tube steam generator has been widely used in nuclear reactor, energy power, petrochemical and other systems. In the liquid metal reactor, the liquid metal on the primary side of the helically-coiled tube steam generator washes the helically-coiled tube bundles, and exchanges heat with the water on the secondary side. Due to the coupled heat transfer between liquid metal and water, the distribution of the wall temperature or heat transfer coefficient of helically-coiled tube are significant different in the circumference direction of the tube cross-section. An experimental system of helically-coiled tube steam generator was set up in this paper. The non-uniform heat transfer characteristics of secondary side fluid of helically-coiled tube steam generator were studied under the coupled heat transfer conditions between the heat transfer of primary side and secondary sides fluid. It was found the local wall temperature or local heat transfer coefficient in the circumferential direction of the tube cross-section was significantly different, and they showed different change trends with the change of the parameters such as subcooling degree, mass flux of the secondary side fluid, system pressure of secondary side fluid, heating temperature of primary side fluid, etc. Secondly, ηt and ηh were defined to represent the degree of local non-uniformity of local wall temperature or local heat transfer coefficient in the circumferential distribution of the tube cross-section, respectively. δt and δh were defined to characterize the degree of overall non-uniformity of wall temperature or heat transfer coefficient in the circumferential distribution of the tube cross-section, respectively. The variation rules of ηt and ηh, δt and δh with subcooling degree、system pressure、mass flux of primary side fluid、mass flux of secondary side fluid and heating temperature of primary side fluid were obtained.

关键词： Steam generators

Simulation Study on Hydrogen-Heating-Power Poly-Generation System based on Solar Driven Supercritical Water Biomass Gasification with Compressed Gas Products as an Energy Storage System

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Journal of Thermal Science 2020年第2期29卷 365-377页

作者： JIN Hui WANG Cui FAN Chao State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an 710049China

Supercritical water gasification driven by solar energy is a promising way for clean utilization of biomass with high moisture content, but direct discharge of liquid residual causes energy waste and decreases energy efficiency. To reduce energy waste, a poly-generation system for hydrogen-rich gas production coupling heat supply and power generation based on supercritical water gasification of biomass driven by concentrated solar energy was established in this paper, which also provided a novel energy storage method to overcome the shortcomings of solar discontinuity. Thermodynamic model of the system was proposed and life cycle assessment(LCA) of the system was conducted. Influence of different parameters(temperature of 600℃ to 800℃, outlet temperature of heat exchanger of 42℃ to 56℃, biomass slurry concentration of 5% to 6.5%) on the gasification performance, energy and exergy efficiency, energy distribution and global warming potential(GWP) was discussed. The results indicated that hydrogen yield increased as gasification temperature increased since free radical reaction was enhanced which gas production reaction was classified into. Molar fraction of hydrogen increased as gasification temperature increased and reached 65.6% at 750℃. Energy and exergy efficiency of the system reached 74.84% and 34.87% at 700℃ and 600℃ respectively and that of gas production was 18.15% at 650℃, which was the highest. Increasing reaction temperature and decreasing biomass slurry concentration were effective ways to decrease GWP. Optimal operating parameter was reaction temperature of 650℃, outlet temperature of heat exchanger of 50℃ and biomass concentration of 5%.

关键词： biomass supercritical water gasification poly-generation system thermodynamics analysis energy storage life cycle assessment

Experimental Investigation on Product and Temperature Distribution in a Continuous flow Packed-Bed Reactor for Dodecahydro-N-Ethylcarbazole Dehydrogenation

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SSRN 2024年

作者： Xue, Jingwen Li, Pengzhao Yu, Pengfei Yi, Jinhao Ma, Tao Liu, Hu Che, Defu State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi'an Jiaotong University Xi'An710049 China

The dehydrogenation of dodecahydro-N-ethylcarbazole (H12-NEC) generates enormous gas accompanied by intense heat absorption, affecting heat and mass transfer in porous catalysts. A packed-bed reactor equipped with a temperature measurement device was designed to investigate the continuous flow dehydrogenation of H12-NEC. The effects of weight hourly space velocity (WHSV), reaction temperature, catalyst particle size, and pressure were evaluated. The results reveal that the volume flow rate of hydrogen will increase with the increase of WHSV. And the generation of hydrogen enhances heat transfer by strengthening the perturbation of flow. As the temperature rises, the hydrogen yield increases along with more by-products. The decrease of catalyst particle size improves the hydrogen yield and a more uniform temperature distribution can be created within the reactor due to the weakened wall effect. 456 K and 2 mm of catalyst particle size are determined to be the optimal reaction conditions in the study, achieving the hydrogen production rate of 9.61 [[EQUATION]]. With pressure increasing, the hydrogen yield gradually decreases, but the decreased evaporation of H12-NEC results in a smaller temperature difference between the reactor and heating wall. A comparison with the thermodynamic equilibrium model reveals that the effect of pressure on chemical equilibrium may be more significant than the temperature. © 2024, The Authors. All rights reserved.

关键词： Temperature distribution

Multi-physics analysis of the galvanic corrosion of Mg-steel couple under the influence of time-dependent anisotropic deposition film

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Journal of Magnesium and Alloys 2021年第3期9卷 866-882页

作者： Kai Wang Chenpei Li Yanhui Li Jinling Lu Yueshe Wang Xingqi Luo State Key Laboratory of Eco-hydraulics in Northwest Arid Region Xi'an University of TechnologyNo.5 Jinhua South RoadXi'an 710048China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityNo.28 Xianning West RoadXi'an 710049China

The anisotropic deposit film formed during the galvanic corrosion can impede the mass transfer of the involved species,thereby affecting the electro-chemical behavior and the evolution of galvanic *** limitations of experimental studies in the spatial-temporal scales restrict a deeper understanding of the corrosion mechanism,which can be complemented by numerical simulation.A multi-physics coupled model is proposed in this work to systematically investigate the temporal and spatial evolution of galvanic corrosion of the Mg-steel couple with the growing anisotropic deposition *** utilizing the multi-physics field coupled technique,various coupled physical-chemical processes underlying the corrosion behavior are built into the model,including chemical reactions,ionic mass transfer in the bulk solution and the deposition layer,interfacial reaction,deposition of corrosion products as well as the morphological transitions caused by metal dissolution and *** particular,the anisotropic deposit film is considered to be a porous layer with a porosity varying in time and space as the corrosion *** predicted corrosion morphology by this model is better than the previous *** coupled relationship between the electrochemical behavior(e.g.,electrode reaction kinetics,current density,surface potential)and the physical processes(e.g.,ionic transport,geometric evolution of metal surface and film interface)is *** results indicate that a porous deposition layer with a denser inner layer and a loose outer layer is generated,leading to more significant inhibition of mass transfer in the inner layer than the outer *** anisotropism of the deposition layer results in a non-uniform conductivity distribution and a discontinuous current density distribution in the *** current density on the electrode surface is inhibited by the deposition layer and the variation in the cathode/anode area ratio during the corrosion *** c

关键词： Galvanic corrosion Corrosion product film Modeling Mass transport Porosity

Molecular dynamics revealing the non-monotonic variation of oil–water interfacial tension under the effect of cations and asphaltenes

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Journal of Molecular Liquids 2025年 431卷

作者： Zhang, Faxue Wen, Boyao Lu, Xi Wang, Haibo Luo, Zhengyuan Bai, Bofeng State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Shaanxi Xi'an710049 China Petroleum Exploration and Production Research Institute of Sinopec Beijing China

The cations can significantly affect the interfacial dynamics of asphaltene molecules, which greatly change the mechanics of oil–water interfaces and thus have a remarkable impact on the chemical flooding process of heavy oil. However, Due to the weak amphiphilic property of asphaltene, the effects of cations on the interfacial behaviors of asphaltene as well as the interfacial mechanics are still unclear. Here, we study the effects of different types and concentrations of cations (Na+, Ca2+ and Mg2+) on the interfacial tension of oil–water systems with different asphaltenes (C5Pe) concentrations by using molecular dynamics simulations. As asphaltene concentration rises, the stronger interactions between cation and asphaltene induce an interfacial enrichment of asphaltenes, resulting in a decrease of interfacial tension. The cations have a more prominent impact on the interfacial tension when the oil–water interfaces reach supersaturated adsorption state of asphaltene molecules. The interfacial tension shows a non-monotonic variation with cation concentration increasing, which has a minimum at intermediate cation concentrations in our simulations. We explain this non-monotonic dependence of interfacial tension on cation concentration by a coupling effect of cations and asphaltene molecules. Under low cation concentrations, the interaction between cations and asphaltenes gradually enhances with cation concentration increasing, leading to a weaker π–π interaction between asphaltenes. Consequently, the asphaltene aggregates disperse and individual asphaltene molecules can easily migrate to the interface. The surface density of asphaltene thus increases, causing a reduction in interfacial tension. At high cation concentrations, cations strongly shield the electrostatic attraction between asphaltene and water molecules, so that the adsorption ability of asphaltenes at interface will weaken or even desorb, thus the interfacial tension elevate. Our results reveal the under

关键词： Adsorption Aggregation Asphaltenes Cations Interfacial tension Molecular dynamics

Hydrodynamic Interaction of Two Droplets Covered with Insoluble Surfactant in Shear flow

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SSRN 2023年

作者： Wei, Wei Luo, Zhengyuan Bai, Bofeng State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

Despite its significance in various applications, e.g., droplet microfluidics and enhancing oil recovery, the effects of surfactants on the hydrodynamic interactions of droplets in shear flow still need to be clarified. This paper presents a systematic investigation on the hydrodynamic interaction of two droplets covered with the insoluble surfactant in a simple shear flow, which is realized by using our own three-dimensional front-tracking code. Our results indicate that surfactants significantly affect the hydrodynamic interactions of droplets, characterized by the maximum deviation in the z-direction and the shear-induced self-diffusion. Then we examine the effects of surfactant-relevant parameters, i.e., the surface Peclet number and the elasticity number. Both the maximum deviation in the z-direction and the shear-induced self-diffusion increase with the elasticity number and the surface Peclet number. Specifically, we find two mechanisms underlying the effects of surfactant on the hydrodynamic interaction of two droplets. First, Marangoni stress induced by surfactant sharply increases the maximum deviation in the z-direction when the surface Peclet number is large. It is because that Marangoni stress hinders liquid drainage from the near-contact region and thickens the liquid film between the droplets. Second, hydrodynamic interactions during crossing lead to considerable alterations of the shape and local surfactant concentration, resulting in an irreversible trajectory shift of the droplets. So, the shear-induced self-diffusion sharply rises at the high surface Peclet number. © 2023, The Authors. All rights reserved.

关键词： Surface active agents

Experimental Study on Boiling Heat Transfer Characteristics in Helical Coils with Large Coiled Diameters

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SSRN 2024年

作者： Shi, Yanggen Wu, Zhiyuan Li, Kepiao Zhang, Kui Tian, Wenxi Qiu, Suizheng State Key Laboratory of Multiphase Flow in Power Engineering Department of Nuclear Science and Technology Xi’an Jiaotong University Xi’an710049 China

The boiling heat transfer characteristics in helical coils were investigated by experimental study. Experimental results indicated that the distribution of wall temperature trended to be more uniform due to weakened influence of centrifugal force and gravity force when the bulk fluid is closed to saturation temperature. Increase in heat flux decreases the quality of ONB (onset of nucleate boiling) while increase in mass flux delay ONB. The heat transfer was dominated by nucleate boiling with quality range of 00.6 in saturated boiling region. The quality of dryou decreases with the increase of pressure and it’s scarcely affected by heat flux. Dryout rends to occur at lower quality with the increase of heat flux at high pressure since redeposition rate decreases at higher pressure and entrainment rate increases due to higher heat flux © 2024, The Authors. All rights reserved.

关键词： Heat flux

Numerical Study on Influence of Platen Super-Heaters on Heat Deviation in a 600 MW Tangentially Fired Pulverized-Coal Boiler 9th

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Numerical Study on Influence of Platen Super-Heaters on Heat...

9th International Symposium on Coal Combustion, ISCC 2019

作者： Chen, Kai Zhang, Yan Deng, Lei Che, Defu School of Mechanic Engineering Xijing University Xi’an710123 China State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

ISBN: (纸本)9789811616563

In order to investigate effects of platen super-heaters on the heat deviation in the cross-over pass, numerical simulation of a 600 MW tangentially fired pulverized-coal boiler has been studied. Two cases, building super-heaters or not, were established by FLUENT software in this study. Numerical results agree well with measured data of the utility boiler. Results show platen super-heaters break symmetry of velocity distribution at the furnace outlet. The position where peak temperature occurs is affected by platen super-heaters, while the position where peak velocity occurs is not. Platen super-heaters slightly reduce the temperature deviation at the furnace outlet, and enhances the velocity deviation at the furnace outlet. For this boiler, the velocity deviation is the main reason for the heat deviation in the cross-over pass. The simulation results in this study can provide reference for optimization of temperature deviation and velocity deviation in tangentially fired pulverized-coal boiler. © 2022, Tsinghua University Press.

关键词： Furnaces