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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

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Molecular dynamics study on bubble nucleation characteristics on rectangular Nano-Grooved surfaces

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Journal of Molecular Liquids 2025年 420卷

作者： Li, Zhibin Lou, Jiacheng Wu, Xiaoyi Li, Xujun Chang, Fucheng Wang, Hengyuan Li, Huixiong State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China National Key Lab of Aerospace Power System and Plasma Technology School of Mechanical Engineering Xi'an Jiaotong University Xi'an710049 China

The micro/nanoscale structures on metal surfaces are of significant research interest for boiling heat transfer and exhibit great application potential in the thermal management of high-power electronic devices. This study employs the molecular dynamics simulation method to investigate the boiling heat transfer characteristics of hydrophilic rectangular shallow nano-groove structures, comparing them with the smooth surface. The phase transition heat transfer characteristics of liquid films on the smooth surface, single rectangular groove (SRG) surface, and overlapping rectangular groove (ORG) surface are revealed by analyzing the variations of parameters such as energy contour diagrams, bubble volume, liquid film temperature, and average potential energy. The research results indicate that water molecules are in a solid-like state within shallow grooves, while the nucleation sites of initial bubbles form randomly outside the grooves. During the initial heating and bubble growth, the initial nucleation time and bubble growth rate of ORG are slower than those of SRG, due to the small rectangular groove on ORG that diminishes the energy transfer efficiency. During bubble formation and growth, the average kinetic energy within the liquid film fluctuates at the nucleation moment in the critical nucleation region, and the average potential energy rises from −0.083 eV. These findings provide a theoretical basis for the micro/nanoscale structure design of vapor-liquid phase transition thermal management devices. © 2024 Elsevier B.V.

关键词： Kinetic energy

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Hydrocarbon generation reaction kinetics study on supercritical water conversion of centimeter sized medium and low maturity organic-rich shale

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Petroleum Science 2025年

作者： Xie, Tian Zhao, Qiu-Yang Jin, Hui Wang, Ye-Chun Guo, Lie-Jin College of New Energy Xi'an Shiyou University Shaanxi Xi'an710065 China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Shaanxi Xi'an710049 China

Accurate prediction of the composition of pyrolysis products is the prerequisite for achieving directional regulation of organic-rich shale pyrolysis and conversion products. In this paper, the classical segmented pyrolysis kinetics model and a new refined pyrolysis kinetics model were used to forecast the composition distribution of hydrocarbon generation products co-heated by supercritical water and medium and low maturity organic-rich shale. The prediction accuracy of the two reaction kinetics models for the composition of pyrolysis products of organic-rich shale was compared. The reaction path of hydrocarbon generation in centimeter sized organic-rich shale under the action of supercritical water was identified. The results show that the prediction accuracy of the classical segmented pyrolysis kinetics model was poor at the initial stage of the reaction, and gradually increased with increasing time. The prediction error can reach less than 25% when the reaction time was 12 h. The new refined model of reaction kinetics established is better than the classical reaction kinetics model in predicting the product distribution of pyrolysis oil and gas, and its prediction error is less than 14% in this paper. The reaction paths of hydrocarbon generation in centimeter sized organic-rich shale under supercritical water conversion mainly include organic-rich shale directly generates asphaltene and saturated hydrocarbon, asphaltene pyrolysis generates saturated hydrocarbon, aromatic hydrocarbon and resin, saturated hydrocarbon, aromatic hydrocarbon and resin polymerization generates asphaltene, and saturated hydrocarbon, resin and asphaltene generates gas. The reason for the difference of centimeter sized and millimeter sized medium and low maturity organic-rich shales hydrocarbon generation in supercritical water is that the increase of shale size promotes the reaction path of polymerization of saturated hydrocarbon and aromatic hydrocarbon to asphaltene. © 2025 The Author

关键词： Crystallization kinetics

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Dissolution characteristics of mixed inorganic salts under supercritical water gasification of oily wastewater for hydrogen production

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International Journal of Hydrogen Energy 2025年 140卷 563-572页

作者： Siqi Rong Fengyuan Yang Anlan Xie Ruoyu Wang Han Jiang Pengyuan Zhao Yong Huang Yunan Chen Liejin Guo State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University No.28 Xianning West Road Xi'an 710049 China Science and Technology on Plasma Dynamics Laboratory Air Force Engineering University Xi'an Shanxi 710038 China

In this study, the solubility characteristics of mixed inorganic chloride salts in supercritical water gasification are investigated experimentally to provide theoretical guidance for the optimization of the design of anti-blockage deposition in the SCWG process of oily wastewater and other high-salt organics. At present, there is a lack of experimental studies on the solubility of mixed inorganic salts in supercritical water, so this study investigates the solubility characteristics of mixed inorganic chloride salts containing NaCl, KCl, and CaCl 2 in supercritical water through real supercritical water experimental conditions. The solubility of the mixed inorganic chloride salts in supercritical water was analyzed in the parameter ranges of 673∼823 K and 22.5–30 MPa, mainly for the experimental conditions. It is found that the solubility of mixed inorganic salts is primarily affected by the temperature, and the solubility decreases with the increase of temperature, while the solubility of each component of mixed inorganic salts has a competitive relationship with each other, and the stronger the ionic bonding ability of inorganic salt ions, the lower the solubility of the mixed supercritical water solution. Finally, the simulation of real oil-containing wastewater with high mineralization found that the non-polarity of the supercritical water system further increased under the environment containing organic matter, which made the solubility of polar inorganic salts decrease.

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Quantitative detection of alkali metal Na based on laser-induced breakdown spectroscopy technology

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Meitan Xuebao/Journal of the China Coal Society 2025年第4期50卷 2262-2270页

作者： Shen, Sijie Li, Chi Zhou, Wangzheng Wang, Zhenzhen Yan, Junjie Hou, Zongyu Wang, Zhe Deguchi, Yoshihiro School of Energy and Power Engineering Xi'an Jiaotong University Xi'an710049 China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China State Key Laboratory of Power System Operation and Control Tsinghua University Beijing100084 China Institute for Carbon Neutrality Tsinghua University Beijing100084 China Department of Energy and Power Engineering Tsinghua University Beijing100084 China Shanxi Research Institute for Clean Energy Tsinghua University Taiyuan030032 China Graduate School of Technology Industrial and Social Sciences Tokushima University Tokushima770-8506 Japan

The alkali metal compounds released from high alkali fuels such as low-quality coal during thermal utilization can affect the normal operation of thermal equipment. Therefore, rapid online detection of alkali metal content in low-quality coal is of great significance for controlling alkali metal release during combustion. The alkali metal Na element is used as the detection object, and the mixed samples of graphite and sodium chloride powder with different ratios are used as experimental samples. The influencing factors of measuring Na element in samples using laser induced breakdown spectroscopy (LIBS) technology are studied. The impact of two signal strength calculation methods on signal stability is compared. The influence of experimental parameters on signal strength and signal-to-noise ratio is analyzed. The quantitative calculation models for Na element have been established. Research has shown that the characteristic spectral lines of Na element, Na I 588.995 nm and Na I 589.592 nm, are suitable as the main analytical spectral lines. Using the area intensity of the dual line characteristic spectral lines of Na element as the signal intensity can effectively improve signal stability. When the laser energy is 60 mJ and the delay time is 1 000 ns, the relative standard deviation of spectral signal intensity is low and the signal-to-noise ratio is high. The quantitative calculation models are established using traditional calibration method, partial least squares (PLS) method, and support vector machine (SVR) with spectral signal intensity as the input and Na element addition in the sample as the output. The accuracy of each model is compared and analyzed. The results indicate that the PLS model may exhibit overfitting when the sample size is small and the input quantity is large. The fitting accuracy of the SVR model is 0.978 3, the root mean square percentage error of the training set is 13.42%, and the root mean square percentage error of the test set is 13.51

关键词： Sodium chloride

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Proposal and performance analysis on thermal energy storage systems with live and reheat steam as heat sources to co-enhance the operational flexibility and efficiency of coal-fired power plants

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Journal of Energy Storage 2025年 127卷

作者： Yang, Shuokang Liu, Ming Zhang, Kezhen Liu, Miaomiao Yan, Junjie State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China Xi'an Thermal Power Research Institute Co. Ltd. Xi'an710054 China

The high penetration of intermittent renewable power threatens the steady operation of the power grid, and the operational flexibility of schedulable power plants should be enhanced. Thermal energy storage (TES) emerges as a promising technique to enhance the operational flexibility of coal-fired power plants (CFPPs). In this study, molten salt thermal storage systems utilizing live and reheat steam as heat sources were proposed, and the steam ejectors were integrated to recover the residual pressure of exhausted steam from the TES system to co-enhance the operational flexibility and energy efficiency of coal-fired power plants. Two TES system schemes, i.e., the scheme D1 storing medium-temperature heat to heat feedwater afterwards, and the scheme D2 storing high-temperature heat to generate steam afterwards, were designed. Then, simulation models were developed, and performance indicators were defined. Results indicate that the operational flexibility of the coal-fired power plant can be enhanced by the integration of the TES system, and the adjustable minimum load ratio can be decreased from 30 % to 17.71 % and 17.83 % for the schemes D1 and D2, respectively. When the steam ejectors are integrated, the equivalent round-trip efficiency can be increased by 1.60 % and 2.43 % for schemes D1 and D2, respectively. The scheme D2 shows a higher equivalent round-trip efficiency of 46.69 %, surpassing the scheme D1. © 2025 Elsevier Ltd

关键词： Fossil fuel power plants

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Evaporation of sub-millimeter flying dinitrogen tetroxide droplet under high temperature and pressure: Experimental measurement and theoretical modeling

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Chinese Journal of Aeronautics 2025年第5期 82-93页

作者： Lihan FEI Wu ZHU Yuyuan ZHANG Peng ZHANG Zuohua HUANG Chenglong TANG State Key Laboratory of Multiphase Flow and Power Engineering Xi'an Jiaotong University Department of Mechanical Engineering City University of Hong Kong

The evaporation behaviors are crucial for the flame location estimation in liquid rocketengines. This work, for the first time, experimentally reports the sub-millimeter droplet evaporationcharacteristics of the corrosive dinitrogen tetroxide（NTO, one prevailing hypergolic oxidizer） athigh ambient pressure up to 4.5 MPa. An in-house corrosion-resistant droplet generator is usedto generate isolated flying droplets of sub-millimeter size, which are then exposed in a gas environ-ment with temperatures between 1 010 K and 1 210 K and pressures in the range between 2.0 MPaand 4.5 MPa, provided by an optical rapid compression machine. Parallelly, a theoretical modelconsidering both the droplet ambient convection and the NTO dissociation is developed. Resultsindicate that firstly, the present theoretical model that considers the transient droplet-ambient con-vection as well as the temperature and pressure dependent rate of dissociation shows good agree-ment with the experimentally observed droplet lifetime. In addition, the flying droplets velocityregress gradually due to momentum exchange with the ambient, which is more prominent at higherpressure. The evaporation caused droplet size reduction is consistent with the classical D2-law pre-diction, in the present temperature and pressure range. Finally, higher temperature and pressureaccelerate the evaporation and an empirical correlation for the temperature and pressure dependentevaporation rate constant is proposed, which shows good agreement with experiment and simula-tion results.

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Pilot-Scale Photoreforming of Hydrolyzed Polylactic Acid Waste to High-Value Chemicals and H2 via Atomic Ru Integration

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Advanced Energy Materials 2025年第0期

作者： Liu, Feng Zhang, Chunyang Lu, Kejian Yan, Xueli Wang, Yi Jing, Dengwei Guo, Liejin Liu, Maochang International Research Center for Renewable Energy & State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Shaanxi Xi'an710049 China Suzhou Academy of Xi'an Jiaotong University Jiangsu Suzhou215123 China

Photoreforming of polylactic acid (PLA) waste into valuable chemicals offers a promising approach for environmental protection and waste valorization, yet faces challenges of low yields and harsh conditions. Herein, a Cd0.5Zn0.5S nanotwin catalyst decorated with Ru single atoms and clusters is reported, enabling selective photoreforming of PLA into pyruvic acid (PA) and H2. It is demonstrated that Ru single atoms favor PA formation via hydroxyl dissociation, while the further incorporation of Ru clusters serve as active sites for H2 production. This synergistic effect significantly enhances photocatalytic performance, achieving 96.8% PA selectivity and efficient H2 production with a record-breaking apparent quantum efficiency of 83.7% at 400 nm. This approach is scalable for outdoor processes, utilizing direct 1 m2 sunlight irradiation to deliver ≈1191 mL h−1 of H2 and 47.27 mmol h−1 of PA from PLA waste, paving a viable pathway for large-scale simultaneous production of high-value chemicals and H2. © 2025 Wiley-VCH GmbH.

关键词： Photolysis

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Chromium Promoted the Efficient and Stable Catalytic Degradation of Propane Over Pt/Hzsm-5 Catalyst: Optimization and Reaction Mechanism

SSRN

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SSRN 2025年

作者： Jian, Yanfei Xu, He Wang, Yao Wang, Jingjing Xia, Lianghui Liu, Yujie Yu, Yanke He, Chi State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi'an Jiaotong University Shaanxi Xi'An710049 China National Engineering Laboratory for VOCs Pollution Control Material and Technology University of Chinese Academy of Sciences Beijing101408 China Yunnan University China

Light alkanes are a class of ubiquitous volatile organic compounds (VOCs), which bring great environmental hazards and health risks. However, low-temperature degradation of light alkanes is still a great challenge. Herein, a series of Pt/HZSM-5 catalysts without/with additives of Cr were fabricated. Catalytic performance of the catalyst for C3H8 low temperature combustion was investigated. It was found that Cr element had a significant effect on the activity of Pt/HZSM-5. Pt/Cr1/HZSM-5 performed the best activity for C3H8, excellent high temperature stability and water resistance. Characterization results of catalysts indicated that the introduction of Cr element could fix Pt site to promote the dispersion of Pt on the support. Moreover, the interaction between Cr and Pt produced more active Pt species, surface active lattice oxygen and acidic sites, which could promote the activation of C-H bonds in C3H8. Theoretical calculations showed that the interface between Pt and Cr had stronger adsorption for O2 and C3H8, which could accelerate propane oxidation. In this study, the effect of transition metal elements on the promotion of noble metal catalysts in the low-temperature degradation of light alkanes was discussed in depth, and it provided a reference for the design of efficient noble metal molecular sieve catalysts. © 2025, The Authors. All rights reserved.

关键词： Molecular sieves

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Load cycling rate of power-to-heat molten salt thermal storage and power generation system: Dynamic modeling and performance evaluation

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Journal of Energy Storage 2025年 125卷

作者： Hu, Wenting Liu, Ming Zhang, Jihong Zhang, Shunqi Yan, Junjie State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China Xi'an Thermal Power Research Institute Co. Ltd. Xi'an710054 China

To develop a low-carbon power system with high renewable energy penetration, this study proposes a novel power-to-heat energy storage and power generation (P2HES-PG) system, which utilizes molten salt thermal storage technology to achieve flexible heat-power decoupling and rapid load regulation. By establishing dynamic models, the rapid load cycling dynamic characteristics and exergy destruction evolution of the P2HES-PG system under different load ranges were investigated. The results demonstrate that, within a 25% THA amplitude, the maximum load down rates in the high, medium, and low load ranges are 15%, 12%, and 11% Pe min−1, respectively, while the maximum load up rates reach 17%, 14%, and 11% Pe min−1, exceeding the ramping rate of conventional power units. During load cycling processes, significant fluctuations in molten salt circulation flowrate were observed, directly affecting the thermal storage/release dynamics of the steam generator (SG) and the system's thermal performance. Dynamic exergy analysis indicates the condenser maintains a stable 20% exergy destruction share, while turbine and mechanical contributions increase with higher loads, and the regenerative system peaks at 13.97% during the low-load range loading down process. The SG exhibits lower exergy destruction than ideal conditions during the loading down process and higher destruction during the loading up process, providing a theoretical basis for optimizing system control strategies and improving system variable load energy efficiency. © 2025 Elsevier Ltd

关键词： Electric power plant loads

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