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Numerical Study on the Local Heat Transfer Characteristic of Supercritical Co2 in Semicircular/Circular Channel Under Cooling Condition

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SSRN 2022年

作者： Zhong, Shao-Geng Ren, Yan Wu, Weidong Yang, Ying-Ying Yang, Qi-Guo School of Energy and Power Engineering University of Shanghai for Science and Technology Shanghai200093 China Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering Shanghai200093 China

A mathematic-physical model was established to explore the local heat transfer characteristics of supercritical CO2 in semicircular and circular channels under cooling condition, which was applied in the field of supercritical CO2 Brayton cycle. The numerical method was validated by the experimental data with the average error of 3.79%, meeting the accuracy requirement. And the operation pressure, cooling heat flux, inlet velocity and hydraulic diameter were 8~9 MPa, 10~14 kW·m-2, 1.2~5 m·s-1 and 1~2 mm, respectively. The results showed that the local heat transfer coefficient of supercritical CO2 would increase at first and then decrease along the flow direction regardless of the semicircular channel and circular channel, and the peak value gradually decreased with increasing operation pressure and disappeared when the inlet velocity exceeded 3 m·s-1. Meanwhile, the heat transfer performance of the semicircular channel was weaker than that of the circular channel due to the influence of the corner area and the buoyant effect, and the latter played a dominant role. For the horizontal flow, the buoyant effect was increased, while the heat transfer was decreased with increasing hydraulic diameter of the semicircular channel. Besides, the influence of different flow directions on the heat transfer performance of the semicircular channel (about 6.2%) was greater than that of the circular channel (about 0.48%, and could be ignored). Finally, the heat transfer correlation of the supercritical CO2 cooling process in the horizontal semicircular channel was modified by considering the influence of the dimensionless buoyancy effect and hydraulic diameter, and the prediction errors of 90% correlation calculation results were within ±14% after the modification. These results will provide some theoretical guidance on the design and optimization of the cooler for the supercritical CO2 Brayton cycle system. © 2022, The Authors. All rights reserved.

关键词： Heat flux

Dense fluid transport through nanoporous graphene membranes in the limit of steric exclusion

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Physical Review Fluids 2024年第4期9卷 044202-044202页

作者： Runfeng Zhou Mathew M. Swisher Akshay Deshmukh Chengzhen Sun John H. Lienhard Nicolas G. Hadjiconstantinou Department of Mechanical Engineering Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an Shaanxi 710049 China Center for Computational Science & Engineering Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA

We investigate transport of dense fluid flow through nanoporous membranes in the limit of steric exclusion using molecular dynamics (MD) and finite element simulations. Simulation results suggest that, for simple fluids, deviations from Sampson flow are a consequence of the competition between slip and finite atomic size effects. The latter manifest themselves by introducing an effective pore size, as well as an effective membrane thickness. We propose an analytical model for the membrane permeance that accounts for all these factors. We also show how this model can be modified to describe transport of low molecular weight aromatic hydrocarbons across these membranes in the steric limit. Extensive validation of this model is conducted through MD simulations of Lennard-Jones fluids permeating single- and multilayer graphene membranes, as well as low molecular weight organic liquids permeating single-layer graphene membranes.

关键词： Nanofluidics Finite-element method Molecular dynamics

Under-Deposit Corrosion Behavior and Dynamic Deliquescence Properties of Ammonium Salts Covered on Pipelines and Components in a Crude Oil Distillation Column: Experimental and Theoretical Studies

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SSRN 2022年

作者： Li, Ruidong Chen, Jukai Wang, Yueshe State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi'An710049 China School of Chemical Engineering & Technology China University of Mining and Technology Xuzhou221116 China

Electrochemical experiments based on the interdigital electrodes of SAE 1020 steel and atomic simulation were performed to investigate the under-deposit corrosion behavior and dynamic deliquescence properties of ammonium salts. In-situ electrochemical measurements demonstrate that the deliquescence of ammonium salts affects the evolution of the interface, and the surface characterization results proved that the critical state of moisture absorption leads to the most severe corrosion. Additional ab initio molecular dynamics simulations suggest that the H transport chain impacted by the hydrolysis of NH4+ leads to a variation in the charge state of the system, which may triggering corrosion. © 2022, The Authors. All rights reserved.

关键词： Steel corrosion

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

CO2 Splitting by Solar Two-Step Thermochemical Cycles with Cr, Ni and Li Doped CeO2 Solid Solution

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CO2 Splitting by Solar Two-Step Thermochemical Cycles with C...

IUPAC 9th International Conference on Novel Materials and their Synthesis(NMS-IX) & 23rd International Symposium on Fine Chemistry and Functional Polymers(FCFP-XXIII)(IUPAC第九届新型材料和合成国际会议暨第23届国际精细化工和功能聚合物研讨会)

作者： Y.J.Lu State Key Lab.of Multiphase Flow in Power Engineering Xi''an Jiaotong University28 Xianning West Road Xi''an 710049 China

Experimental research on thermal deviation of high temperature reheater in the single tangential Π type boiler based on radiation spectroscopy analysis 7

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Experimental research on thermal deviation of high temperatu...

7th International Conference on power engineering, ICOPE 2019

作者： Xie, Jianwen Wen, Wubin Yang, Bin Yang, Fei Ping, Li Zhang, Fei Zhang, Jianwen Electric Power Research Institute Co. Ltd. Beijing100025 China Jiangsu Guohua Chenjiagang Power Generation Co. Ltd. Jiangsu Yancheng224631 China Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering University of Shanghai for Science and Technology Shanghai200093 China Shanghai Boiler Works Ltd. Shanghai200245 China

The superimposed phenomenon of thermal deviation of low and high temperature reheaters was found under the high load condition in a 660MW ultra super-critical Π type boiler. And the discharge temperature deviation between the two sides of steam were more than 15℃ in high temperature reheater. In order to reveal the thermal deviation of high temperature reheater in this boiler, a probe was designed and developed to measure the visible radiation spectrums of coal dust in the high temperature reheater zone by using the servo mechanism of soot blower. The particle concentration and temperature of coal dust were obtained by the parameter fitting method based on Planck's radiation law. The measurement result shows that the burning delay of pulverized coal caused by originally equipped one-level air staged combustion system and enrichment of coal dust under the action of inertia are the main reasons of thermal deviation of high temperature reheater. And the momentum of SOFA to eliminate the rotation is insufficient in this boiler. In order to improve the thermal balance of both sides, a new type of the two-level air staged combustion system was proposed as principle of retrofit scheme. © ICOPE 2019 - 7th International Conference on power engineering, Proceedings. All rights reserved.

关键词： Coal combustion

Investigation of Thermal Radiative Transfer Characteristics of Single Water Droplet

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SSRN 2023年

作者： Zhang, Dan Tu, Maoping Yuan, Yang Han, Wei State Key Laboratory of Multiphase Flow in Power Engineering School of Energy & Power Engineering Xi'an Jiaotong University Shaanxi Xi’an710049 China Xi'an Thermal Power Research Institute Co. Ltd Shaanxi Xi’an710054 China

Directly heat water droplet by thermal radiation was the key process of coupling solar energy to achieve green production in many industrial applications, such as desalination, carbon capture, energy storage, and so on. The radiative transfer of single water droplet for given irradiation, including reflection, absorption, transmission and their dependences on external irradiation, droplet geometry and radiative properties were investigated through a calculation model set up according to zone method. In current study, the ranges of equivalent diameter and length-width ratio of droplet were 0.1-1.0 mm, 1-10 respectively, its absorption coefficient was 10-15000 m-1 and refractive index was 1.2-2.0. Results suggested that, (1) the absorption mode of droplet could be classified into surface absorption (SA) and volumetric absorption (VA) depending on whether its optical thickness was greater than 1. In VA, droplet could get uniform and fast temperature increasing, and its absorptivity and mean temperature increase rate could be simultaneously improved by increasing absorption coefficient. (2) Scattering included reflection and transmission. Compared with incident irradiation, reflection distributed mainly on the same side of droplet's long axis, while transmission mainly on the opposite side. The overall reflectivity increased with rising refractive index, but was independent on droplet size. While its transmissivity increased with enlarging length-width ratio or reducing equivalent diameter. (3) In VA, at least 40% of incident irradiation was scattered out. The total quantity of scattering could be adjusted by changing absorption coefficient in VA or refractive index in SA. The proportion of transmission in scattering could always be increased by reducing refractive index. © 2023, The Authors. All rights reserved.

关键词： Drops

Morphology Construction of Molybdenum Doped Nickel Sulfide Electrocatalyst Induced by Nh4f to Promote Hydrogen Evolution Reaction

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SSRN 2024年

作者： Zhang, Baikai Li, Xiaohui Liu, Maochang Huadian Electric Power Research Institute Co. Ltd. Zhejiang310030 China School of Eenergy and Power Engineering Xi’an Jiaotong University Shaanxi 710049 China State Key Laboratory of Multiphase Flow in Power Engineering China

Here, by varying the mass of NH4F throughout the hydrothermal process, Mo-doped nickel-based sulfide catalysts (Mo-NiS-Fx) with various morphologies (prisms, rods, flakes, and cones) were created. Among these, the flaky Mo-NiS-F1.2 exhibited exceptional performance towards electrochemical hydrogen evolution reaction, surpassing most similar catalysts with an overpotential of 79 mV at 10 mA cm-2 and a Tafel slope of 49.8 mV dec-1. Significantly, Mo-NiS-F1.2 maintained its high activity for hydrogen evolution over 60 h at 10 mA cm-2, making it suitable for widespread commercial application. This work demonstrates the potential of morphology manipulation to enhance catalytic activity. © 2024, The Authors. All rights reserved.

关键词： Hydrogen

Stability and Emission Characteristics of Ammonia/Air Premixed Swirling Flames with Rotating Gliding Arc Discharge Plasma

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SSRN 2022年

作者： Ju, Rongyuan Wang, Jinhua Zhang, Meng Mu, Haibao Zhang, Guanjun Yu, Jinlu Huang, Zuohua State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China State Key Laboratory of Electrical Insulation and Power Equipment School of Electrical Engineering Xi’an Jiaotong University Xi’an710049 China School of Aeronautics Engineering Air Force Engineering University Xi’an710038 China

Ammonia received increased attention as a carbon-free fuel and hydrogen carrier. Poor combustion stability and high NOx emission are the main issue for ammonia combustion. Effects of rotating gliding arc (RGA) discharge plasma on the flame stability and NOx emission of NH3/air premixed swirling flames were investigated. The discharge characteristics of the RGA were studied. The flame stabilization mechanisms by plasma were revealed and analyzed according to the flame structure transition and the distribution of key intermediate OH radicals. The NOx emissions were measured by the Gasmet DX4000 Fourier Transform Infrared (FTIR) gas analyzer. Results showed that the RGA discharge plasma can enhance the stability and extend the lean blow-off (LBO) limits from 0.6 to approximately 0.43-0.57. A hysteresis phenomenon about the transition between the lift-off flame and the attached flame was observed without plasma and disappeared with plasma activation. The plasma reduces NO and NO2 emissions mainly due to the kinetic and cracking effects of plasma. Extremely low NO emission below 300 ppm can be observed for very lean ammonia flames with an equivalence ratio (f) lower than 0.6, which are stabilized by plasma, while a large amount of unburned NH3 emission is accompanied. © 2022, The Authors. All rights reserved.

关键词： Ammonia