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Characteristics of frictional pressure drop of two-phase nitrogen flow in horizontal smooth mini channels in diabatic/adiabatic conditions

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APPLIED THERMAL engineering 2019年 162卷

作者： Chen, Xingya Hou, Yu Chen, Shuangtao Liu, Xiufang Zhong, Xin Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

The two-phase frictional pressure drop of nitrogen under diabatic and adiabatic conditions is investigated experimentally in two horizontal mini channels. The effects of factors in a variety, including the channel diameter, mass flux, heat flux, inlet pressure and vapor quality are examined on the frictional pressure drop and liquid-phase multiplier of the two-phase flow. The two-phase frictional pressure drop predicted by previous correlations from other studies are compared with the experimental results of this study, and the lowest mean absolute deviation is 18.3% for adiabatic conditions and 10.9% for adiabatic conditions. Based on the experimental results of nitrogen flow, two new correlations in the form of the Chisholm-C correlation are developed to predict the two-phase frictional pressure dropby involving the effect of surface tension, and the mean absolute deviation of which is 12.3% and 10.4% for the adiabatic and diabatic conditions respectively. The new correlations are also shown able to well predict the experimental frictional pressure drop of other studies under different experimental conditions.

关键词： Frictional pressure drop Liquid nitrogen Mini channel Two-phase flow Correlation

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Effect of alkali and alkaline metals on gas formation behavior and kinetics during pyrolysis of pine wood

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FUEL 2021年 290卷

作者： Li, Jinhu Burra, Kiran G. Wang, Zhiwei Liu, Xuan Gupta, Ashwani K. Univ Maryland Dept Mech Engn Combust Lab College Pk MD 20742 USA China Univ Geosci Fac Engn Wuhan 430074 Hubei Peoples R China Henan Univ Technol Coll Environm Engn Zhengzhou 450001 Peoples R China Xi An Jiao Tong Univ Sch Energy & Power Engn State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

This study examines the acid and alkaline treatment of pine wood to help understand the effect of alkali and alkaline earth metals (AAEMs) content on the pyrolysis behavior at different temperatures. Acid and alkali pretreatment of pine wood were conducted to modify AAEMs content by ion-exchanging method. Thermal kinetic behavior of the pretreated samples was first conducted by a thermogravimetric analyzer (TGA) at different heating rates that provided activation energies of pyrolysis. Gas formation behavior of the samples for different extents of conversion was carried out in a fixed-bed reactor at two different temperatures of 823 K and 1073 K. Evolutionary behavior of the gas components during pyrolysis, including flow rate, and yield and their energy content were measured and compared. Results showed that the values of activation energies increased with the extent of conversion for all the pretreated samples examined. The effect of AAEMs on pyrolysis behavior of biomass varied with the extent of conversion. The presence of AAEMs in biomass decreased the decomposition energy at low conversion while it greatly improved under high conversion. Besides, alkali treated sample with higher AAEM content enhanced the gas and char yield while it reduced the bio-oil production at low temperature with low conversion. However, at high temperature the opposite trend was observed. Presence of AAEMs was favorable for the generation of H-2, CO, CO2 and CnHm at low temperature, while it showed an inhibition effect on CO and CnHm yield and syngas energy at high temperature. The catalytic mechanism of AAEMs on the pyrolysis behavior at different temperatures was discussed based on activation energy and gaseous formation. Results revealed decomposition of carboxylate at low temperature and formation of stable biomass-Na (BM-Na) structure at high temperature that led to the variation of activation energy and changed gaseous products yield and syngas energy. Acid washing pretreatment w

关键词： Kinetic behavior Mechanism Ion-exchanging Gas components Activation energy Syngas yield

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Study on thermal hydraulic characteristics under startup of SCWR

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PROGRESS IN NUCLEAR ENERGY 2020年 122卷

作者： Wang, Laishun Yuan, Yuan Shan, Jianqiang Zhang, Xiaoying Sun Yat Sen Univ Sino French Inst Nucl Engn & Technol Zhuhai Guangdong Peoples R China Xi An Jiao Tong Univ Sch Nucl Sci & Technol State Key Lab Multiphase Flow Power Engn Xian Shaanxi Peoples R China

To investigate the startup characteristics of the supercritical pressure water-cooled reactor (SCWR) system, a complete startup system model of the SCWR was established with the analysis code SCTRAN, based on the high-performance light water reactor (HPLWR) steam cycle and SCWR circulation startup loop. The correctness of the model was verified in comparison with the steady-state parameters of the steam cycle of the HPLWR. A sliding pressure startup procedure with a circulation loop that employs a control system was analyzed, and the transient performances of the core, steam drum, turbine, reheaters, steam extraction and heaters at each stage were obtained. The calculation results showed that the startup sequence and startup thermal parameters could fully meet the expectations: the system starts up stably and the core remains in the single phase;the inlet steam of the turbine stays superheated;the core inlet temperature can reach 280 degrees C after the adoption of the high-pressure and low-pressure heaters;and the inlet pressure of the high-pressure turbine can be kept constant. During the startup process, the maximum cladding surface temperature (MCST) remains below the limit of 650 degrees C, suggesting that the entire startup procedure is safe and reliable.

关键词： Supercritical water reactor SCTRAN Recirculation pressure startup

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Size effect of one-dimensional nanostructures on bubble nucleation in water splitting

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APPLIED PHYSICS LETTERS 2019年第10期115卷

作者： Chen, Juanwen Guo, Liejin Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

One-dimensional (1D) nanostructures have wide applications in photocatalysts for water splitting. Their surfaces may impact the gas bubble nucleation rate, thus influencing the efficiency of gas evolution. However, the effects of the 1D nanostructured surfaces on the bubble nucleation have not been studied to date. Herein, these effects are theoretically analyzed, based on the changes of free energy for a bubble nucleus forming inside/outside a nanotube. The results show that compared to flat surfaces, the inner tube wall favors the bubble nucleation, while the outer wall has an opposite effect. These differences become increasingly significant with tube radius R-t reducing when R-t<10r(*) (r(*)-bubble equilibrium radius). The size effect is further verified experimentally for bubble nucleation on TiO2 nanotube arrays. The sensitivity of bubble nucleation to nanostructure dimensions should be considered in designing high-efficient photocatalysts.

关键词： Free energy

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Experimental study of gas-liquid two-phase wavy stratified flow in horizontal pipe at high pressure

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2019年 143卷

作者： Wang, Yubo Liu, Zhigang Chang, Yingjie Zhao, Xiangyuan Guo, Liejin Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

The regimes of gas-liquid two-phase flow in horizontal pipe at high pressure were experimentally investigated, and characteristics of wave stratified flow, such as wave length, wave height and propagation speed were calculated. The pressure drop was analyzed and friction factors, such as gas-wall, liquid wall and interfacial friction factors, were calculated and new correlations were deduced. Influence of interface wave on interfacial friction factor was studied, and characteristics of interface wave were included to deduce new correlation for it, and good accuracy was proved. For the gas-water two-phase flow at 2 MPa, transition from wave stratified to annular flow appears with smaller gas superficial velocity compared with that at atmosphere, and intermittent flow appears with greater liquid superficial velocity. Regime transition models are tested, for the gas-liquid two-phase flow at atmosphere the sheltering coefficient with value of 0.01 is appropriate. However, it is promoted to be 0.06 at 2 MPa, and good performance of regime transition model was reached. (C) 2019 Elsevier Ltd. All rights reserved.

关键词： High pressure Wave stratified flow Regime transition model Interface wave Friction factor

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Nanoscale capillarity for mitigating gas bubble adhesion on arrayed photoelectrode during photoelectrochemical water splitting

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APPLIED PHYSICS LETTERS 2019年第23期114卷

作者： Chen, Juanwen Guo, Liejin Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

One-dimensional (1D) arrayed photoelectrodes usually present superior performance in photoelectrochemical (PEC) water splitting. This superiority is known to be attributed to directional transport of photogenerated charge carriers. Herein, we show that in addition to this intrinsic charge transport property, a 1D arrayed structure introduces nanoscale capillary wetting, which is also believed to contribute to the improved PEC performance. Our theoretical model predicts that this morphology-dependent capillarity leads to the formation of a liquid film between the photoelectrode surface and the adhered bubble (the generated H-2/O-2 bubble), thus largely reducing the blockage of active sites at the bubble base. This prediction has been experimentally demonstrated by taking arrayed TiO2 nanorods as a model photoelectrode, with the observation of the PEC activity within the bubble base. This work extends our knowledge toward hydrodynamic functionality involved in morphology-controlled photoelectrodes for enhanced PEC performance.

关键词： Capillarity

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Synergistic effect of nitrogen vacancy on ultrathin graphitic carbon nitride porous nanosheets for highly efficient photocatalytic H2 evolution

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CHEMICAL engineering JOURNAL 2022年 431卷

作者： Zhang, Yazhou Huang, Zhenxiong Dong, Chung-Li Shi, Jinwen Cheng, Cheng Guan, Xiangjiu Zong, Shichao Luo, Bing Cheng, Zening Wei, Daixing Huang, Yu-cheng Shen, Shaohua Guo, Liejin Xian Jiaotong Univ XJTU Int Res Ctr Renewable Energy IRCRE State Key Lab Multiphase Flow Power Engn MFPE 28 West Xianning Rd Xian 710049 Peoples R China Xiamen Univ Coll Chem & Chem Engn State Key Lab Phys Chem Solid Surfaces 422 Siming South Rd Xiamen 361005 Peoples R China Tamkang Univ Dept Phys 151 Yingzhuan Rd Tamsui 25137 Taiwan Jiangxi Acad Sci Inst Energy Res 7777 Changdong Ave Nanchang 330096 Jiangxi Peoples R China Xi An Jiao Tong Univ Sch Chem Engn & Technol Xian 710049 Peoples R China Xinjiang Tianchi Energy Co Ltd Zhundong Energy Res Inst 189 Beijing South Rd Changji 831100 Peoples R China

Nanosheets exfoliation as one of the promising modification strategies for graphitic carbon nitride (g-C3N4) nanosheets has been extensively developed for improving the photocatalytic performance. However, it was commonly found that the enhancement of photocatalytic efficiency by effective nanosheets exfoliation hardly reached the expected satisfactory level, and the corresponding photocatalytic mechanism should be further investigated. Herein, on account of the well-designed thermal exfoliation strategy, the ultrathin and porous nanosheets with the thickness of three layers were elaborately constructed and possessed abundant N vacancies in the in-plane heptazine rings. Surprisingly, the ultrathin nanosheets exhibited superior visible-light-driven photocatalytic H-2-evolution activity, with a H-2-evolution rate (5.74 mmol h(-1) g(-1)) 28.7 times that of the pristine g-C3N4, and with an apparent quantum yield (AQY) of 14.9% (420 nm) much higher than that of the previously reported ultrathin g-C3N4 nanosheets. It was confirmed by systematical characterizations and theoretical calculation that, the ultrathin and porous features in cooperation with local separation of the highest occupied molecular orbital and lowest unoccupied molecular orbital sites by N vacancy-dominated in-plane electronic structure, synergistically strengthened the separation of photo-generated carriers. Meanwhile, the incorporation of the N vacancy-induced midgap state could bring the highly efficient excitation of photo-generated carriers, and abundant photocatalytic reaction sites could be provided by the ultrathin two-dimensional (2D) microstructure. Furthermore, the ultrathin nanosheet-induced quantum confinement effect could enlarge the bandgap and then boost the driving force for water reduction. This work developed one unique synthetic route to g-C3N4 nanosheets exfoliation, and highlighted the synergistic function of nanosheets exfoliation and defect engineering for highly efficient photoc

关键词： Graphitic carbon nitride Ultrathin nanosheet Nitrogen vacancy Photocatalytic hydrogen evolution Synergistic effect

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Effects of silicoaluminate oxide and coal blending on combustion behaviors and kinetics of zhundong coal under oxy-fuel condition

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JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY 2018年第3期134卷 1975-1986页

作者： Wang, Chang'an Zhang, Yuanhang Wang, Pengqian Zhang, Jinping Du, Yongbo Che, Defu Xi An Jiao Tong Univ Sch Energy & Power Engn State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

Oxy-fuel combustion of high-alkali coal is beneficial for near-zero emission of pollutants in power plants and has the potential for extensive, efficient, and safe utilization of Zhundong coal in future. The present work was performed on oxy-fuel combustion of Zhundong coal, while the effects of silicoaluminate oxide and coal blending on oxy-fuel combustion characteristics and kinetics of high-alkali coal were further studied using thermogravimetric analysis. The thermogravimetric curves of Zhundong coals present two obvious stages but the contrastive coals are different. The increase in oxygen content weakens the impact of coal property on oxy-fuel combustion behavior of high-alkali coal. The addition of Al2O3 and kaolin results in a slight decline of the peak combustion rate, while the influences of SiO2 and diatomite additives are negligible. The additive fraction of silicoaluminate oxide gives rise to a non-monotonic impact on combustion characteristics of Zhundong coal. The interaction effect within blended coal could cause a reduction in reaction rate during the intense combustion stage, while its influence on kinetics is intensified during the later stage of oxy-fuel combustion. The impact extent of silicoaluminate oxide and coal blending on oxy-fuel combustion kinetics of high-alkali coal is highly associated with additive species and individual coals.

关键词： Zhundong coal High alkali Kinetics Thermogravimetric analysis Additive Blended coal

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Transformation and release of potassium during fixed-bed pyrolysis of biomass

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JOURNAL OF THE ENERGY INSTITUTE 2018年第4期91卷 630-637页

作者： Deng, Lei Ye, Jiaming Jin, Xi Che, Defu Xi An Jiao Tong Univ Sch Energy & Power Engn State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

To study the release and transformation of fuel K during rapid pyrolysis of biomass, wheat straw, corn stalk and rice hull are pyrolyzed in a fixed-bed reactor system during 400-1000 degrees C, and weight measurement, elemental composition analysis, and chemical fractionation analysis are performed. The effects of fuel type, pyrolysis temperature, co-pyrolysis of different fuels, and water washing pretreatment are discussed. The results show that for all biomass fuels, the released K is far less than the water-soluble K and a sudden increase occurs in the fraction of ion-exchangeable K at 400 degrees C, whereas a significant increase happens in the fraction of insoluble K above 800 degrees C. Wheat straw releases less than 5% of K at 400 and 500 degrees C. As temperature rises, the K release increases abruptly and around 40% of K enters the gas phase at 1000 degrees C. Rice hull has a slow and linear K release with increasing pyrolysis temperature. Corn stalk has the lowest K release during 400-800 degrees C. Co-pyrolysis of wheat straw and rice hull reduce the K release at 1000 degrees C, and the biggest decrement is 0.76 mg g(-1). Water washing removes all the water-soluble K of corn stalk and part of ion-exchangeable K enters the gas phase during pyrolysis of the washed sample. Water washing decreases the K release from 2.77 to 0.18 mg g(-1) at 1000 degrees C. (C) 2017 Energy Institute. Published by Elsevier Ltd. All rights reserved.

关键词： Potassium release Transformation Biomass pyrolysis Co-pyrolysis Water washing

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Rapid pyrolysis and CO₂ gasification of anthracite at high temperature

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JOURNAL OF THE ENERGY INSTITUTE 2018年第6期91卷 1143-1152页

作者： Zha, Qiongliang Zhao, Jing Wang, Chang'an Che, Defu Xi An Jiao Tong Univ Sch Energy & Power Engn State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

Anthracite could be burnt efficiently at high temperature utilizing oxy-coal technology. To clarify the effects of temperature and atmosphere on char porosity characteristics, char morphology, fuel-N conversion, and reducing products release, rapid pyrolysis and CO2 gasification of anthracite was carried out in a high temperature entrained-flow reactor to simulate the condition in a pulverized coal furnace. Developed pore structure was formed in the gasification chars, which could be contributed to char-CO2 reaction at high temperatures. More mesopores were formed in internal carbon skeleton and retained against collapse and coalescent for gasification chars than pyrolysis chars. Compared with pyrolysis char, smoother and denser surface was observed in gasification char with the irregular bulges disappeared due to the destruction of external carbon skeleton. Char-N could be oxidized to NO in CO2 atmosphere and then reduced to N-2 by (-CN) on the char surface. Char-N release was greatly promoted due to gasification reaction along with poly-condensation at high temperature;and the preact release of char-N would result in a larger portion of NOx reduction in the following reduction zone with the oxygen-staging combustion technology compared with that in air-staging combustion. Complementally, homogeneous reduction in NOx emission would play a minor effect for anthracite in oxy-coal combustion because of the deficiency of CH4 and HCN, especially at high temperature. (C) 2017 Energy Institute. Published by Elsevier Ltd. All rights reserved.

关键词： Anthracite High temperature CO2 Char porosity Fuel-N conversion

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