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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

Large contributions of emission reductions and meteorological conditions to the abatement of PM_(2.5)in Beijing during the 24th Winter Olympic Games in 2022

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Journal of Environmental Sciences 2024年第2期136卷 172-188页

作者： Yaping Jiang Shaocai Yu Xue Chen Yibo Zhang Mengying Li Zhen Li Zhe Song Pengfei Li Xiaoye Zhang Eric Lichtfouse Daniel Rosenfeld Key Laboratory of Environmental Remediation and Ecological Health Ministry of EducationResearch Center for Air Pollution and HealthCollege of Environmental and Resource SciencesZhejiang UniversityHangzhou 310058China College of Science and Technology Hebei Agricultural UniversityBaoding 071000China Chinese Academy of Meteorological Sciences China Meteorological AdministrationBeijing 100081China Aix-Marseille Univ CNRSColl FranceCNRSIRDINRAEEuropole Mediterraneen de l’ArboisAvenue Louis Philibert13100 Aix en ProvenceFrance Xi’an Jiaotong University State Key Laboratory of Multiphase Flow in Power EngineeringXi’an 710049China Institute of Earth Sciences The Hebrew University of JerusalemJerusalemIsrael

To guarantee the blue skies for the 2022 Winter Olympics held in Beijing and Zhangjiakou from February 4 to 20,Beijing and its surrounding areas adopted a series of emission control *** provides an opportunity to determine the impacts of large-scale temporary control measures on the air quality in Beijing during this special ***,we applied the WRF-CMAQ model to quantify the contributions of emission reduction measures and meteorological *** show that meteorological conditions in 2022 decreased PM_(2.5)in Beijing by 6.9 and 11.8μg/m^(3)relative to 2021 under the scenarios with and without emission reductions,*** emission reduction measures implemented in Beijing and seven neighboring provinces resulted in an average decrease of 13.0μg/m^(3)(-41.2%)in PM_(2.5)in *** the entire period,local emission reductions contributed more to good air quality in Beijing than nonlocal emission *** the emission reduction scenario,local,controlled regions,other regions,and boundary conditions contributed 47.7%,42.0%,5.3%,and 5.0%to the PM_(2.5)concentrations in Beijing,*** results indicate that during the cleaning period with the air masses from the northwest,the abatements of PM_(2.5)were mainly caused by local emission ***,during the potential pollution period with the air masses from the east-northeast and west-southwest,the abatements of PM_(2.5)were caused by both local and nonlocal emission reductions almost *** implies that regional coordinated prevention and control strategies need to be arranged scientifically and rationally when heavy pollution events are forecasted.

关键词： PM_(2.5) WRF-CMAQ Meteorological conditions Emission reductions Winter Olympic games

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

Pool Boiling Heat Transfer Enhancement on the Hybrid Surfaces Coupling Capillary Wick and Minichannels

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SSRN 2022年

作者： Zhang, Yonghai Ma, Xiang Wang, Jinyu Liu, Wanbo Wei, Jinjia School of Chemical Engineering and Technology Xi’an Jiaotong University Shaanxi Xi’an710049 China Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

Pool boiling heat transfer can fully utilize the latent heat of the vaporization, to meet the heat dissipation needs of high-power electronic components. In this study, several enhanced hybrid surfaces were designed and processed by sintering spherical copper powder on the minichannels in different ways. The coupled effects of various parameters of capillary wick and minichannels were considered to enhance the pool boiling heat transfer performance of these hybrid surfaces using HFE-7100 as the working fluid. The bubble dynamic behaviors were captured and analyzed by the high-speed camera. The results indicate that the ring groove around the minichannels and the capillary wick have a significant impact on the boiling heat transfer of these hybrid surfaces. This is because the capillary wick provide a large number of nucleation sites and large specific surface area, which can greatly reduce the contact thermal resistance between the capillary wick and the minichannels. At ΔTsub = 30 K, the critical heat flux (CHF) of hybrid surfaces coupling capillary wick and minichannels is up to 147.4 W/cm2, and its maximum heat transfer coefficient (HTC) is 2.69 W/(cm2·K). Compared with minichannels without capillary wick covered, the CHF and HTC are increase by 86.8% and 192.0%, respectively. Furthermore, a correlation for predicting CHF on these hybrid surfaces covered capillary-wick is proposed. Dimensionless parameters such as the subcooled Jakob coefficient (Jasub), the outer surface area enhancement ratio (AER), the particle distribution coefficient (PDC) and the ratio of inner to outer surface area of capillary wick (IOR) are defined to estimate the effect of different factors on the CHF. © 2022, The Authors. All rights reserved.

关键词： Heat flux

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

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 Jin, Xiaoling Huang, Xiaole Li, Yang 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. In all biomass samples and gasified chars, micropores (0-10 μm) dominate and are distributed along the grain direction. In general, pores of 20-30 μm and above 30 μm comprise a minor proportion. 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 chars. 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

Bubble Behavior and Heat Transfer of Nucleate pool boiling on Micro-Pin-Finned Surface in Microgravity

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Bubble Behavior and Heat Transfer of Nucleate pool boiling o...

Asina Microgravity Pre-Symposium——9th China-Japan-Korea Workshop on Microgravity Sciences(第九届中日韩微重力科学学术会议暨亚洲微重力科学大会)

作者： Jin-Jia Wei Jian-Fu Zhao Yong-Hai Zhang Yan-Fang Xue Yan Long Liang Zhang State Key Laboratory of Multiphase Flow in Power Engineering Xi''an Jiaotong UniversityXi''an100190China Key Laboratory of Microgravity(National Microgravity Laboratory)/CASInstitute of MechanicsChinese Academy of SciencesBeijing100190China

Optimization of crucial parameters for double-layer microchannel heat sink

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Kung Cheng Je Wu Li Hsueh Pao/Journal of engineering Thermophysics 2014年第3期35卷 567-570页

作者： Lin, Lin Chen, Yang-Yang Wang, Xiao-Dong School of Mechanical Engineering University of Science and Technology Beijing Beijing 100083 China State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources North China Electric Power University Beijing 102206 China Beijing Key Laboratory of Multiphase Flow and Heat Transfer for Low Grade Energy North China Electric Power University Beijing 102206 China

As compared with single-layer microchannel heat sink (SL-MCHS), double-layer microchannel heat sink (DL-MCHS) can significantly improve the temperature uniformity of electric elements. This work uses a three-dimensional solid-fluid conjugate model incorporated with a progressive optimization procedure to optimize the cooling performance of a water-cooled, silicon-based DL-MCHS. Four geometric parameters (channel number N, bottom channel height Hc1, upper channel height Hc2, and vertical rib width Wr) and coolant velocity ratio of upper channel to bottom channel, t, are selected as optimized variables. The results show that at a fixed pumping power of 0.05 W and a heat fluxes qw=100 W·cm-2, the optimal geometric structure and coolant velocity ratio for the DL-MCHS are Nopt=70, Hc1,opt=200 μm, Hc2,opt=650 μm, Wr,opt=71.48 μm, and topt=1.85. The thermal resistance of the optimal DL-MCHS is reduced by 11.3% compared to the SL-MCHS, and the maximum temperature difference is reduced to 0.5 K, which is far less than 4.2 K of the SL-MCHS.

关键词： Heat resistance