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Ignition delay times measurement and kinetic modeling studies of 1-heptene, 2-heptene and n-heptane at low to intermediate temperatures by using a rapid compression machine

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COMBUSTION AND FLAME 2018年第Nov.期197卷 30-40页

作者： Wu, Yingtao Liu, Yang Tang, Chenglong Huang, Zuohua Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

In this work, we have firstly investigated the auto-ignition behaviors of 1-heptene, 2-heptene and n-heptane in the low to intermediate temperature range (650-950K) over various equivalence ratios at 15 and 23 bar using a rapid compression machine. Results show that n-heptane exhibits the expected negative temperature coefficient (NTC) behavior and shows the shortest IDTs among the three fuels, while the NTC behavior for 1-heptene and 2-heptene is moderated and quasi-Arrhenius temperature dependence of the 1st stage IDTs is observed at all test conditions. As the temperature increased over 900K, the IDTs of the three fuels begin to be consistent indicating a moderated effect of the unsaturated bond. In the NTC temperature region, 1-heptene shows higher reactivity than 2-heptene, while opposite relative reactivity is observed in the temperature beyond the NTC region. The IDT data of 1-heptene, 2-heptene and n-heptane were then used to validate several kinetic models. Results show that the performance of the n-heptane models is generally good, while all the models underestimate the low temperature reactivity of 1-heptene. Finally, a model refinement has been made and the prediction shows better agreement with the present measured IDT as well as the experimental pressure evolution trace in literature. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

关键词： n-heptane 1-heptene 2-heptene Rrapid compression machine IDT

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Non-uniformity of gas/liquid flow in a riser and impact of operation and pipe configuration on slugging characteristics

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EXPERIMENTAL THERMAL AND FLUID SCIENCE 2018年 96卷 329-346页

作者： Zou, Suifeng Yao, Tian Guo, Liejin Li, Wensheng Wu, Quanhong Zhou, Hongliang Xie, Chen Liu, Weizhi Kuang, Shicai Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

A pipeline-riser system is a typical complex pipe configuration in which the non-uniformity of gas/liquid flow is observed to be significant under certain flow rates. This article interprets slugging flow, the most common flow regime in a pipeline-riser system, in the context of non-uniformity, which differs from the approaches used to characterise slugging cycles in previous studies. By comparing data collected by several transmitters positioned locally on the riser and comparing flow in a simple vertical pipe, both the temporal and spatial non-uniformity of the gas/liquid distribution in the riser is presented and interpreted;the relationship between them is also illustrated. The non-uniformity of the flow provides an effective means to quantitatively evaluate the severity of slugging in a pipeline-riser system under different operating conditions. In addition to flow uniformity, specific flow characteristics can be affected by operating conditions as well as pipe configuration. Several factors closely related to the design of experimental facilities and procedures are investigated by a case study of three experimental loops with different layouts and dimensions, and several general findings are summarised. The results may contribute to a better and more specific understanding of gas/liquid flow mechanisms in a pipeline-riser system in addition to serving as a means to evaluate the features of laboratory pipeline-riser systems and the applicability of laboratory results in industrial cases.

关键词： Pipeline-riser system Temporal and spatial non-uniformity Differential pressure Pipe configuration flow boundary condition Active flow control

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In situ decoration of g-C3N4 quantum dots on 1D branched TiO2 loaded with plasmonic Au nanoparticles and improved the photocatalytic hydrogen evolution activity

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APPLIED SURFACE SCIENCE 2020年 519卷 146208-146208页

作者： Nasir, Muhammad Salman Yang, Guorui Ayub, Iqra Wang, Silan Yan, Wei Xi An Jiao Tong Univ Dept Environm Sci & Engn State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China Xi An Jiao Tong Univ MOE Key Lab Nonequilibrium Synth & Modulat Conden State Key Lab Elect Insulat & Power Equipment Dept Appl ChemSch Sci Xian 710049 Peoples R China Xi An Jiao Tong Univ Suzhou Inst Suzhou 215123 Peoples R China Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Sch Chem Engn & Technol Xian 710049 Peoples R China Univ Agr Faisalabad Dept Struct & Environm Engn Faisalabad 38040 Pakistan Univ Agr Faisalabad Dept Energy Syst Engn Faisalabad 38040 Pakistan

The hybrid 1D branched TiO2 loaded with surface plasmonic Au and decorated with g-C3N4 QDs were successfully fabricated which played a significant role in photocatalysis. The 1D branched TiO2 prepared by electrospinning followed by an alkali-hydrothermal process. The Au particles decorated by photo deposition and after that g-C3N4 QDs were grafted over it by a chemical vapor deposition method. The composite shows great improvement in photocatalytic hydrogen evolution and evolved about 2.22 mmol g(-1) h(-1) hydrogen. The composite sample has a quantum efficiency of 19.5% for hydrogen production at 420 nm light that depicts the performance behavior of the composite. The 1D branched TiO2 fiber facilitates the fast transfer of electrons and Au reduces the charge recombination due to its surface plasmonic effect while g-C3N4 QDs facilitate the visible light absorption by improving the optical properties and reduces the bandgap. The formation of the type II heterostructure system remarkably promotes the separation and transfer of electron holes and facilitates the photo-reduction reaction.

关键词： Photocatalyst Hydrogen Quantum dots Hierarchical Plasmonic

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Experimental investigation on enhanced thermal performance of staggered tube bundles wrapped with metallic foam

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2018年 122卷 459-468页

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

Tube bundles wrapped with metallic foam can be used in air-breathing engine as the compact heat exchanger due to its low density and high specific surface area. The enhanced thermal performance of metallic foam is crucial to design of staggered tube bundles with metallic foam fins. Previous studies have shown the effects of foam-structure on entire metallic foam, and discussed the influence of tube-bundle structure on the tube bundles qualitatively. However, the thermal and flow mechanisms on coupling of metallic foam and pure fluid which could expound enhanced heat transfer process of metallic foam fins are not yet fully explored. To address this, an experimental study was conducted to investigate the effects of structure parameters of metallic foam on thermal and flow characteristics in 2 mm outer-diameter staggered tube bundles wrapped with 2 mm thickness of metallic foam. This article reveals variation trend of heat transfer rate with change of key parameters: porosity and pore density. The results indicate that: 1, with increase of porosity, Nusselt number increases because of stronger penetrating ability, and heat convection dominates the heat transfer. 2, for variation of pore density, Nusselt number of high PPI samples is lower for thermal-insulation effect at low Reynold number. However, Nusselt number of high PPI samples is higher for greater amount of penetrating air at high Reynold number. 3, a new friction factor correlation of tube bundles is proposed to describe the pressure drop by dimensionless tube pitches, Reynolds number and Darcy number with maximum +/- 20% deviation. 4, a new Nusselt number correlation of tube bundles is given to reflect the heat transfer mechanism by Darcy number. (C) 2018 Elsevier Ltd. All rights reserved.

关键词： Metallic foam Tube bundle Heat transfer Pressure drop

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Dynamics of capsules enclosing viscoelastic fluid in simple shear flow

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JOURNAL OF FLUID MECHANICS 2018年 840卷 656-687页

作者： Luo, Zheng Yuan Bai, Bo Feng Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

Previous studies on capsule dynamics in shear flow have dealt with Newtonian fluids, while the effect of fluid viscoelasticity remains an unresolved fundamental question. In this paper, we report a numerical investigation of the dynamics of capsules enclosing a viscoelastic fluid and which are freely suspended in a Newtonian fluid under simple shear. Systematic simulations are performed at small but non-zero Reynolds numbers (i.e. Re = 0.1) using a three-dimensional front-tracking finite-difference model, in which the fluid viscoelasticity is introduced via the Oldroyd-B constitutive equation. We demonstrate that the internal fluid viscoelasticity presents significant effects on the deformation behaviour of initially spherical capsules, including transient evolution and equilibrium values of their deformation and orientation. Particularly, the capsule deformation decreases slightly with the Deborah number De increasing from 0 to O(1). In contrast, with De increasing within high levels, i.e. O(1-100), the capsule deformation increases continuously and eventually approaches the Newtonian limit having a viscosity the same as the Newtonian part of the viscoelastic capsule. By analysing the viscous stress, pressure and viscoelastic stress acting on the capsule membrane, we reveal that the mechanism underlying the effects of the internal fluid viscoelasticity on the capsule deformation is the alterations in the distribution of the viscoelastic stress at low De and its magnitude at high De, respectively. Furthermore, we find some new features in the dynamics of initially non-spherical capsules induced by the internal fluid viscoelasticity. Particularly, the transition from tumbling to swinging of oblate capsules can be triggered at very high viscosity ratios by increasing De alone. Besides, the critical viscosity ratio for the tumbling-to-swinging transition is remarkably enlarged with De increasing at relatively high levels, i.e. O(1-100), while it shows little change at

关键词： biological fluid dynamics capsule/cell dynamics

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Nucleate boiling heat transfer model based on fractal distribution of bubble sizes

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2019年 128卷 1175-1183页

作者： Qi, Baojin Wang, Ya Wei, Jinjia Zhang, Yonghai Yu, Ting Xi An Jiao Tong Univ Sch Chem Engn & Technol Xian 710049 Peoples R China Xi An Jiao Tong Univ Suzhou Inst Suzhou 215123 Peoples R China Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

Scientifically and accurately predicting the distribution of the bubble sizes on the heating surface is a key step to improve the calculation accuracy of the boiling heat transfer model. In the present study, an ingenious nucleate boiling heat transfer model was developed on the basis of random fractal function of the bubble sizes distribution, and renormalization group theory was introduced to solve this distribution function. Compared to the previous correlations, the distribution function of bubbles for various sizes can be obtained by solving this random fractal distribution function with renormalization group method. Furthermore, the process of increasing the fractal dimension from 1 to 2 was first proposed in this paper to match the whole evolution of the heated liquid from natural convection to nucleate boiling, to transition boiling, and finally to film boiling. Therefore, the present model can reveal the nature of nucleate boiling more comprehensively and deeply. Through comparison, it can be found that the image of bubble distribution obtained from the random fractal model was very similar to the experimental photographs statistically, and the predictions heat transfer were in good agreement with the experimental data when the superheat AT is higher than 10 degrees C, and the deviation is less than 20%. (C) 2018 Elsevier Ltd. All rights reserved.

关键词： Bubble sizes distribution Fractal analyses Nucleate boiling Heat transfer model

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Condensation regime diagram for supersonic and subsonic steam jet condensation in water flow in a vertical pipe

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APPLIED THERMAL engineering 2018年 130卷 62-73页

作者： Xu, Qiang Ye, Shuyan Chen, Yanshuang Chen, Qiyu Guo, Liejin Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

An experimental research is performed to investigate the condensation regime diagram of supersonic and subsonic steam jet condensation in water flow in pipes. The original images of the jet plume are recorded using a visualization window and a high-speed camera. The jet condensation regimes are basically categorized into four types, including Chugging, Oscil-I, Oscil-II and Stable regimes, primarily based on the transient evolution of geometrical profile of the jet plume. And the average geometrical shape of the jet plume is found to shrink gradually with increase of ambient pressure. The stand deviation of pressure oscillation is highly correlated to jet condensation regimes, so it can be applied to quantitatively categorize different regimes. The steam mass flux, scaled by critical steam mass flux at different ambient pressure, is found to be irrelevant to the transitional lines among Chugging, Oscil-I, and "Stable or Oscil-II" regimes in the condensation regime diagram. Furthermore, the Oscil-II regime can be simply isolated from the "Stable or Oscil-II" regime via comparison of the standard deviation of pressure oscillation in this two regimes. Therefore, the jet condensation regime diagram obtained from low ambient pressure could be applied to conditions of elevated ambient pressure. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： Condensation regime diagram Regime classification Supersonic steam jet Pressure oscillation multiphase flow

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Theoretical Study of Abstraction and Addition Reactions of 2,4,4-Trimethyl-1-pentene with H and O(³P) Radical

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ENERGY & FUELS 2018年第11期32卷 11831-11842页

作者： Yin, Geyuan Hu, Erjiang Li, Xiaojie Ku, Jinfeng Gao, Zhenhua Huang, Zuohua Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

The calculation of rate constants of addition and abstraction reactions of 2,4,4-trimethyl-l-pentene with H and O(P-3) were conducted by conventional transition state theory (TST) and canonical variational transition state theory (CVT). Potential energy surfaces of reactions were calculated at the DLPNO CCSD(T)/cc-pVTZ//M06-2X/6-311G(d,p) as well as the CCSD(T)/6-311++G(d,p)//M06-2X/6-311(d,p) level. Moreover, quantum mechanical effects were determined by multidimensional small-curvature tunneling (SCT) and zero-curvature tunneling (ZCT) methods. 2,4,4-Trimethyl-l-pentene contains primary and secondary allylic, alkylic, and vinylic H atoms. It also contains addition reactions into central and terminal carbon atom channels. The results indicated that allylic H abstraction channels dominate the overall H abstractions resulting from the lower barriers. In addition, a radical added into terminal carbon dominates the addition reactions. The branching ratio is more than 72% above 1500 K for H abstraction and more than 90% below 500 K for H addition reactions.

关键词： Addition reactions Hydrogen abstraction Tunneling Energy Potential energy

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Peak shaving operational optimization of supercritical coal-fired power plants by revising control strategy for water-fuel ratio

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APPLIED ENERGY 2018年 216卷 212-223页

作者： Wang, Chaoyang Zhao, Yongliang Liu, Ming Qiao, Yongqiang Chong, Daotong Yan, Junjie Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

Electricity generated from renewable energy source fluctuates heavily and can hardly be predicted. The peak shaving (or load cycling) operation of conventional thermal power plants is an effective means to mitigate the mismatch between electricity demands and supplies. Therefore, determining how thermal power plants can operate in a flexible and effective mode is an urgent issue that should be addressed. For thermal power plants, new methods and strategies need to be proposed to face the challenge of the integrating flexibility and energy saving into transient processes. Dynamic performances of thermal power plants during load cycling processes are affected by the coupling of the thermal system and the control system. Feasible approaches from optimizing the coordinated control system (CCS) may radically enhance the peak shaving capacity of thermal power plants. The heat storage in a coal-fired power plant, including heating surface metals and work media, varies with the load rate of the plant. During cycling load operations, the real-time heat storage value of one unit differs from that of the corresponding steady state load command rate. This difference hinders the flexibility of one unit and affects its economic performances during cycling processes. In this paper, a revised water fuel ratio (WFR) control strategy based on heat storage difference was proposed and tested on established coal-fired power plant models. Results show that the accumulation deviations of load rate command and real-time load rate are considerably reduced during load cycling processes when the proposed WFR control strategy is introduced. The revised WFR control strategy diminishes the difference between the target and the actual total power output. When the load cycling rate varies from 10 to 30 MW min(-1) between 50% and 100% THA, the standard coal consumption variation rate (Delta b(s),) decreases by 0.31-1,01 g kW(-1) h(-1) during loading up processes, and decreases by 0.26-1.69 g kW(-1)

关键词： Coal-fired power plant Transient processes Operational optimization Water fuel ratio Heat storage

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Solute release from an elastic capsule flowing through a microfluidic channel constriction

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PHYSICS OF FLUIDS 2019年第12期31卷 121902-121902页

作者： Luo, Zheng Yuan Bai, Bo Feng Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

In recent years, microfluidic channels with narrow constrictions are extensively proposed as a new but excellent possibility for advanced delivery technologies based on either natural or artificial capsules. To better design and optimize these technologies, it is essential and helpful to fully understand the releasing behavior of the encapsulated solute from capsules under various flow conditions which, however, remains an unsolved fundamental problem due to its complexity. To facilitate studies in this area, we develop a numerical methodology for the simulation of solute release from an elastic capsule flowing through a microfluidic channel constriction, in which the tension-dependent permeability of the membrane is appropriately modeled. Using this model, we find that the release of the encapsulated solute during the capsule's passage through the constriction is enhanced with the increase in the capillary number and constriction length or the decrease in the constriction width. On the other hand, a large variation in the channel height, which is generally larger than the capsule diameter, generates little effect on the released amount of the solute. We reveal that the effects of the capillary number and constriction geometry on the solute release are generally attributed to their influence on the capsule deformation. Our numerical results provide a reasonable explanation for previous experimental observations on the effects of constriction geometry and flow rate on the delivery efficiency of cell-squeezing delivery systems. Therefore, we believe these new insights and our numerical methodology could be useful for the design and optimization of microfluidic devices for capsule-squeezing delivery technologies. Published under license by AIP Publishing.

关键词： Microfluidics

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