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Unsynchronized motion of inner and outer membranes of compound capsules in shear flow

PHYSICS OF FLUIDS 2020年第12期32卷

作者： Xu, Han Bai, Bo Feng Xi An Jiao Tong Univ Dept Bldg Environm & Energy Engn Xian 710049 Peoples R China Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

Despite its significance in understanding behaviors of biological cells with nucleus or designing functions of complex artificial capsules in applications, the dynamics of elastic capsules enclosing complicated internal structures in flow is still largely unexplored. In this study, by using our own three-dimensional front-tracking finite-difference model, we present a numerical investigation into the dynamics of a compound capsule in a simple shear flow whose inner and outer membranes have the same prolate ellipsoidal shape at the rest state. Particular interest is focused on the unsynchronized motion of the inner and outer membranes. Regarding the dynamical regime, both the inner and outer capsules can undergo either synchronized or unsynchronized dynamical regimes (i.e., swinging or tumbling), which strongly depends on the inner-to-outer capillary number ratio Ca-in/Ca-out, the inner-to-outer volume ratio phi, and the prolate aspect ratio a/b. Particularly, via establishing a phase diagram based on a/b and phi at Ca-in/Ca-out = 1, we find that the inner and outer membranes can exist simultaneously in different dynamical regimes, even if they have the same deformability and the same shape. More importantly, if the detailed oscillation behavior is also concerned besides the capsule's dynamical regime, such as the transient shape and the oscillating period, unsynchronization is always obvious between the inner and outer capsules. Specifically, the inner capsule exhibits a slower oscillation than the outer capsule no matter if they lie in the swinging or tumbling regime.

关键词： Shear flow

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Quantifying the sources of synergistic effects in co-pyrolysis of pinewood and polystyrene

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APPLIED ENERGY 2021年 302卷

作者： Burra, Kiran Raj G. Liu, Xuan Wang, Zhiwei Li, Jinhu Che, Defu Gupta, Ashwani K. Univ Maryland Dept Mech Engn Combust Lab College Pk MD 20742 USA Hunan Univ Coll Environm Sci & Engn Key Lab Environm Biol & Pollut Control Minist Educ Changsha 410082 Hunan Peoples R China Xi An Jiao Tong Univ Sch Energy & Power Engn State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China Henan Univ Technol Coll Environm Engn Zhengzhou 450001 Peoples R China Anhui Univ Sci & Technol Coll Safety & Engn Huainan 232001 Peoples R China

Co-processing of biomass and plastic wastes via pyrolysis and gasification for feed-flexibility revealed the presence of synergistic enhancement of H-2 and syngas yield and lowering of char and tar yields. However, an understanding of the source of these interactions and their quantification is lacking. To address this, we investigated the co-pyrolysis of pinewood (PW) and polystyrene (PS) blends at 900 degrees C using uniquely arranged sample-loading configurations in a fixed-bed reactor with online product gas and energy consumption analysis. Quantification of interactions such as volatiles-volatiles, volatiles-feedstock, and volatiles-char interactions in comparison with weighted results from individual pyrolysis of PW and PS provided deconvoluted information on the synergistic effects. Volatiles-volatiles interaction accounted for a 33% increase in H-2, while PS volatiles-PW intermediates interaction accounted for 17% increase, and inhibitive PW volatiles-PS intermediates interaction led to 8% decrease. This deconvolution also revealed another 20% increase associated with the evenly mixed copyrolysis of PW and PS that was not accounted for from the volatiles-feedstocks interaction. The co-pyrolysis of PS with PW char also revealed the catalytic activity of PW char on plastics decomposition which was found to be restricted by the capacity of PS melt to block the char's active sites during their direct contact. Cracking of PS volatiles on these catalytic active sites led to the increased yields of CH4 and H-2. These results provide quantified insight into the sources of interaction between biomass and plastics to enhance synergy, develop component compatibility, and gain prediction capability for sustainable and feed-flexible gasifier development.

关键词： Co-pyrolysis Polystyrene Synergistic effects Volatiles interaction Catalytic char Feed-flexible

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A stable dye-sensitized photoelectrosynthesis cell mediated by a NiO overlayer for water oxidation

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PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED stateS OF AMERICA 2020年第23期117卷 12564-12571页

作者： Wang, Degao Niu, Fujun Mortelliti, Michael J. Sheridan, Matthew V. Sherman, Benjamin D. Zhu, Yong McBride, James R. Dempsey, Jillian L. Shen, Shaohua Dares, Christopher J. Li, Fei Meyer, Thomas J. Univ N Carolina Dept Chem Chapel Hill NC 27599 USA Xi An Jiao Tong Univ Int Res Centre Renewable Energy State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China Florida Int Univ Dept Chem & Biochem Miami FL 33199 USA Texas Christian Univ Dept Chem Ft Worth TX 76129 USA Dalian Univ Technol State Key Lab Fine Chem Dalian 116024 Peoples R China Vanderbilt Univ Vanderbilt Inst Nanoscale Sci & Engn 221 Kirkland Hall Nashville TN 37235 USA

In the development of photoelectrochemical cells for water splitting or CO2 reduction, a major challenge is O-2 evolution at photoelectrodes that, in behavior, mimic photosystem II. At an appropriate semiconductor electrode, a water oxidation catalyst must be integrated with a visible light absorber in a stable half-cell configuration. Here, we describe an electrode consisting of a light absorber, an intermediate electron donor layer, and a water oxidation catalyst for sustained light driven water oxidation catalysis. In assembling the electrode on nanoparticle SnO2/TiO2 electrodes, a Ru(II) polypyridyl complex was used as the light absorber, NiO was deposited as an overlayer, and a Ru(II) 2,2'-bipyridine-6,6'-dicarboxylate complex as the water oxidation catalyst. In the final electrode, addition of the NiO overlayer enhanced performance toward water oxidation with the final electrode operating with a 1.1 mA/cm(2) photocurrent density for 2 h without decomposition under one sun illumination in a pH 4.65 solution. We attribute the enhanced performance to the role of NiO as an electron transfer mediator between the light absorber and the catalyst.

关键词： artificial photosynthesis water oxidation mediator core/shell NiO

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Numerical study on the thermal stratification phenomenon in the sodium-cooled fast reactor

Numerical study on the thermal stratification phenomenon in ...

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2019 Transactions of the American Nuclear Society, ANS 2019

作者： Zhang, Dalin Wang, Shibao Qiu, Suizheng Su, Guanghui School of Nuclear Science and Technology State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University No.28 Xianning West Road Xi'an710049 China

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Experimental study and similarity analysis of separation efficiency of swirl-vane separator

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NUCLEAR engineering AND DESIGN 2020年 359卷

作者： Liu, Li Bai, Bofeng Shanghai Jiao Tong Univ Sch Nucl Sci & Engn Shanghai 200240 Peoples R China Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

Swirl-vane separator in nuclear steam generator is used as primary separator for separating more than 80% of the water from the swam-water mixture to feed the qualified steam to dryers and turbines. laboratory tests are generally performed to seek alternatives for separator design and performance improvement. Though great efficiency is often obtainable in the reduced model, the performance of the full-sized prototype is not well predicted due to the lack of proven similarity analysis. In our previous study, a theoretical model for critical droplet diameter, grade efficiency and overall separation efficiency has been established to predict separator performance (Liu and Bai, 2016). Based on the model, the aim of this paper is to study the separation performance of downscaled separator and to identify important differences between small-scale and large-scale separators. Experiments are carried out on a small-sized swirl-vane separator using air and water as working fluids. Firstly, the characteristics of gas-liquid separation process are visually observed using high-speed camera to understand the operating principle of the separator. After that, the separation efficiency is measured over a wide range of flow conditions, and the gas and liquid velocities influencing the separator performance is analyzed in detail. The experimental data are then used with previous theoretical model to predict the performance of two larger separator prototypes. When model separator has a same shape but reduced size as that of prototypes, and their working pressure and gas-liquid superficial velocities are the same, the results indicate that the model separator has a significantly greater separation efficiency than the prototypes. Generally, the larger scale the prototypical separator is, the lower value the separation efficiency becomes.

关键词： Swirl-vane separator Separation efficiency Model and prototype Similarity analysis

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Isolation of bacteria capable of hydrogen production in dark fermentation and intensification of anaerobic granular sludge activity

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INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 2019年第30期44卷 15853-15862页

作者： Wang, Xueqing Dong, Tingting Zhang, Anlong Fang, Yuting Chen, Duo Zhao, Chengxin Luo, Qing Yang, Honghui Shaanxi Univ Sci & Technol Coll Environm Sci & Engn Coll Bioresources Chem & Mat Engn Xian 710021 Shaanxi Peoples R China Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

In the anaerobic biological treatment of pulp and papermaking wastewater, the gradual deposition of CaCO3 eventually leads to the inhibition of the activity of anaerobic granular sludge. In this study, a hydrogen production bacterial Raoultella DWO1 was isolated from domesticated anaerobic granular sludge. The fermentation conditions were designed using central composite design, and the optimum conditions obtained by response surface analysis encompassed an initial pH 5.77, 4.13 g/L L-glutamic acid and an inoculation amount of 15%. The H-2 production yield represented a 29.5% increase over the unoptimized conditions. Finally, the effect of adding DWO1 on the biogas production in anaerobic granular sludge with different sludge ages was investigated. The cumulative biogas yield and the max biogas production rate increased by 27.8% and 53.5% after adding DWO1 to a sludge with an age of 335 days compared with the onintensified sludge. This paper provides a way to alleviate the CaCO3 deposition by intensifying the activity of H-2- and acid producing bacteria via improving the activity of granular sludge. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

关键词： Hydrogen Biological treatment Anaerobic sludge Intensification

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Statistical characterization of gas-liquid flow in swirl vane separator with image processing technique 18

Statistical characterization of gas-liquid flow in swirl van...

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18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2019

作者： Liu, Li Bai, Bofeng School of Nuclear Science and Engineering Shanghai Jiao Tong University Shanghai200240 China State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Shaanxi710049 China

Swirl vane separator is not only used in SG for separating more than 80% of liquid water from steam-water mixture to feed qualified steam to dryers and turbines, but also applied in the thorium molten salt reactor to remove dilute dispersed bubbles from reactor coolant. The proper design and operation of swirl vane separator requires a fundamental understanding of the gas-liquid flow pattern in the system, since the mass, momentum, and energy transfer rates and processes are quite sensitive to the distribution of the phases within the flow. This paper presents a comprehensive experimental study aimed at classifying flow patterns in the condition of swirling gas-liquid flow in a downscale swirl vane separator. While a large amount of work has been done on conventional, non-swirling, two-phase flow in small pipes, investigations on swirling flow regime classification are still scarce. Here, optical and image processing techniques are used to measure gas and liquid holdup in the system through time. Detailed qualitative description of the flow regimes observed in the experiment is provided. The temporal statistics of liquid holdup (PDF and CPDF) are also analyzed to characterize and distinguish the various swirling flow regimes objectively. Based on this study, the influence of centrifugal force on phase distribution of gas-liquid flow was clarified and the general relationship between swirling gas-liquid flow and non-swirling gas-liquid flow was gained. © 2019 American Nuclear Society. All rights reserved.

关键词： Image processing

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Bubble nucleation over patterned surfaces with different wettabilities: Molecular dynamics investigation

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2019年 136卷 1-9页

作者： Zhou, Wenjing Li, Yang Li, Mingjie Wei, Jinjia Tao, Wenquan Xi An Jiao Tong Univ Sch Chem Engn & Technol Xian 710049 Shaanxi Peoples R China Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China Xi An Jiao Tong Univ Sch Energy & Power Engn Key Lab Thermofluid Sci & Engn MOE Xian 710049 Shaanxi Peoples R China

The bubble nucleation of liquid argon over patterned surfaces with different wettabilities is investigated by using molecular dynamics (MD) simulations. In order to study effects of different wall temperatures on bubble nucleation process, bubble nucleation positions and bubble dynamics behaviors are observed. Simulation results show that at low wall temperatures bubble nucleation tends to occur over the hydrophobic part of the wall. With increasing wall temperature, the bubble nucleus gradually changes its position from the hydrophobic to hydrophilic part. When the wall temperature increases to a certain value, bubble nuclei first appear on both the hydrophobic and hydrophilic parts. By analyzing heat flux and change trend of argon state points, differences in bubble nucleation process at different wall temperatures are explained. Moreover, the effect of area fraction of hydrophobic part on bubble nucleation temperature is investigated. It is found that there exists an optimal area fraction which makes the bubble nucleation temperature the lowest. (C) 2019 Elsevier Ltd. All rights reserved.

关键词： Bubble nucleation Molecular dynamics simulation Patterned surface Wettability

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Negative synergistic effects of surfactant and fluid viscoelasticity on hydrodynamic resistance of single droplet in confined microchannel

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PHYSICS OF FLUIDS 2021年第12期33卷

作者： Luo, Zheng Yuan Lu, Xi Zhao, Hong Yu Xu, Fu Gang Bai, Bo Feng Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China Petr Explorat & Prod Res Inst SINOPEC Beijing 100083 Peoples R China SINOPEC ShengLi Oilfield Petr Explorat Dept Dongying 257200 Peoples R China SINOPEC ShengLi Oilfield Hekou Oil Prod Plant Dongying 257200 Peoples R China

Polymers and surfactants are often employed simultaneously to control droplet dynamics with higher flexibility in many applications, such as droplet microfluidics and chemical enhanced oil recovery. However, the coupling effects of polymer-induced fluid viscoelasticity and surfactant have not been fully uncovered yet. To facilitate studies in this area, we present a systematic investigation on the transport of a surfactant-laden viscoelastic droplet through a confined microchannel by using our own three-dimensional front-tracking finite-difference methodology. Of particular interest is the droplet-induced additional pressure loss, which is important to deeply understand the flow rate-pressure loss relation of droplet-laden flows. We have found that either the fluid viscoelasticity or surfactant tends to enlarge the additional pressure loss, while their co-occurrence induces a further increase. Notably, negative synergistic effects are indicated between fluid viscoelasticity and surfactant;that is, their combined effect to increase the additional pressure loss is smaller than the sum of their individual effects. This synergistic effect primarily results from mutual inhibition of the viscoelastic stress and the surfactant-induced Marangoni stress to reduce the droplet surface mobility, no matter whether the surfactant is soluble or insoluble. Particularly, when the surfactant is soluble to the viscoelastic fluid phase, its transport and the consequent Marangoni stress is suppressed by the bulk viscoelastic stress via two mechanisms: the weakened surface convection by direct impact of the viscoelastic stress on the droplet surface mobility and the weakened bulk convection by the flow modification effect.

关键词： Surface active agents

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Numerical study on coal gasification in supercritical water fluidized bed and exploration of complete gasification under mild temperature conditions

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CHEMICAL engineering SCIENCE 2019年 206卷 134-145页

作者： Fan, Chao Guo, Simao Jin, Hui Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn SKLMF 28 Xianning West Rd Xian 710049 Shaanxi Peoples R China China Acad Engn Phys Inst Nucl Phys & Chem Mianyang 621900 Sichuan Peoples R China

Supercritical water fluidized bed is a promising reactor for the industrial application of the technology of supercritical water gasification of coal. In this work, a numerical model of lignite gasification in SCWFB considering flow, heat transfer and gasification reaction was established, and the Euler-Lagrange method and RNG k-epsilon model were used. Through this model, the multi-field distribution characteristics and developing rules were studied under wide temperature range. A low-temperature zone with uneven circumferential temperature distribution was found below the feed inlet, and the average residence time decreased with the increase of reactor temperature. Steam reforming of solid residual carbon was the bottleneck of complete gasification, and the alkali salt catalyst can accelerate its reaction rate and cause the reaction zone to move to the lower fluidization section. Besides, the simulated results show that the extension of the reactor length was an effective means to improve the carbon gasification efficiency, and the increase of the feed inlet height can avoid the blockage of distributor. Based on both the catalyst addition and reactor structure optimization, a scheme was proposed where the complete gasification of lignite at 750 degrees C was achieved with H-2 promotion promoted. (C) 2019 Elsevier Ltd. All rights reserved.

关键词： Supercritical water gasification Fluidized bed Field distribution Alkali salt catalyst Reactor optimization

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