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A strategy for strengthening chaotic mixing of dual shaft eccentric mixers by changing non-Newtonian fluids kinetic energy distribution

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Chinese Journal of Chemical Engineering 2024年第5期69卷 122-134页

作者： Songsong wang Tong Meng Qian Zhang Changyuan Tao Yundong wang Zequan Li zuohua Liu School of Chemistry and Chemical Engineering Chongqing UniversityChongqing 400044China State Key Laboratory of Coal Mine Disaster Dynamics and Control Chongqing 400044China Department of Chemical Engineering Tsinghua UniversityBeijing 100084China

Efficiently modulating the velocity distribution and flow pattern of non-Newtonian fluids is a critical challenge in the context of dual shaft eccentric mixers for process intensification,posing a significant barrier for the existing technologies.Accordingly,this work reports a convenient strategy that changes the kinetic energy to controllably regulate the flow patterns from radial flow to axial flow.Results showed that the desired velocity distribution and flow patterns could be effectively obtained by varying the number and structure of baffles to change kinetic energy,and a more uniform velocity distribution,which could not be reached normally in standard baffle dual shaft mixers,was easily obtained.Furthermore,a comparative analysis of velocity and shear rate distributions is employed to elucidate the mechanism behind the generation of flow patterns in various dual-shaft eccentric mixers.Importantly,there is little difference in the power number of the laminar flow at the same Reynolds number,meaning that the baffle type has no effect on the power consumption,while the power number of both unbaffle and U-shaped baffle mixing systems decreases compared with the standard baffle mixing system in the transition flow.Finally,at the same rotational condition,the dimensionless mixing time of the U-shaped baffle mixing system is 15.3%and 7.9%shorter than that of the standard baffle and the unbaffle mixing system,respectively,which shows the advantage of the U-shaped baffle in stirring rate.

关键词： Dual shaft “U-shaped”baffle Flow pattern Mixing time Power demand

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Effect of aspect ratio of elliptical stirred vessel on mixing time and flow field characteristics in the absence of baffles

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Chinese Journal of Chemical Engineering 2024年第1期65卷 63-74页

作者： Yuan Yao Peiqiao Liu Qian Zhang Zequan Li Benjun Xi Changyuan Tao Yundong wang zuohua Liu School of Chemistry and Chemical Engineering Chongqing UniversityChongqing 400044China Hubei Three Gorges Laboratory Yichang 443007China Department of Chemical Engineering Tsinghua UniversityBeijing 100084China

Elliptical tanks were used as an alternative to circular tanks in order to improve mixing efficiency and reduce mixing time in unbaffled stirred tanks(USTs). Five different aspect ratios of elliptical vessels were designed to compare their mixing time and flow field. Computational fluid dynamics(CFD) simulations were performed using the k–ε model to calculate the mixing time and simulate turbulent flow field features, such as streamline shape, velocity distribution, vortex core region distribution, and turbulent kinetic energy(TKE) transfer. Visualization was also carried out to track the tinctorial evolution of the liquid phase. Results reveal that elliptical stirred tanks can significantly improve mixing performance in USTs. Specifically, the mixing time at an aspect ratio of 2.00 is only 45.3% of the one of a circular stirred tank. Furthermore, the secondary flow is strengthened and the vortex core region increases with the increase of aspect ratio. The axial velocity is more sensitive to the aspect ratio than the circumferential and radial velocity. Additionally, the TKE transfer in elliptical vessels is altered. These findings suggest that elliptical vessels offer a promising alternative to circular vessels for enhancing mixing performance in USTs.

关键词： Mixing time CFD Stirred tank Secondary flow Mixing performance

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Laminar Flame Instability of n-Hexane,n-Octane,and n-Decane in Spherical Expanding Flames

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Journal of Thermal Science 2024年第3期33卷 1189-1199页

作者： YIN Geyuan HU Erjiang LI Xiaotian LV Xin HUANG zuohua State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong UniversityXi’an710049China United Automotive Electronic Systems Co. LtdShanghai201206China Chongqing Changan Automobile Co. Ltd.Chongqing401120China

This paper focuses on the laminar flame instability of three high molecular weight n-alkanes,namely n-hexane,n-octane,and n-decane.The experiment was carried out in a constant volume combustion bomb to get the flame images.The critical radius under different conditions was extracted using the image processing program.Combined with the existing critical Peclet number theory,the dominant factors of flame instability under current conditions for three n-alkanes can be figured out.Moreover,the average cell size(equivalent cell radius,R_(cell))was extracted to provide quantitative analysis of the flame cellular structure,based on the method developed in this work.The theoretical R_(cell)were also calculated and compared with the experimental results to validate the proposed method.

关键词： cellular instability equivalent cell radius critical Peclet number spherical flame

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Tempering mechanism of lath martensite induced in IF steel under high pressure

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Journal of Materials Science & Technology 2023年第29期160卷 148-160页

作者： zuohua wang Haidong Sun Xiaogang Guo Peng wang Ning Liu Dongli Yu Hongwang Zhang National Engineering Research Center for Equipment and Technology of Cold Strip Rolling College of Mechanical EngineeringYanshan UniversityQinhuangdao 066004China State Key Laboratory of Metastable Materials Science and Technology Yanshan UniversityQinhuangdao 066004China Liren College of Yanshan University Yanshan UniversityQinhuangdao 066004China

In this paper,low-and high-strength lath martensite(350 and 640 HV)was fabricated in an IF steel via high pressure martensitic transformation.The microstructure and the softening during their tempering from 200°C to 800°C for 1 h were systematically investigated.A carbon-irrelevant tempering process was proposed,exhibiting a three-stage structural evolution pattern depending upon the tempering de-gree(1-(HV-HV FP)/(HV NP-HV FP),where the HV is the instant hardness,HV NP is the non-tempered hard-ness and HV FP is the fully tempered hardness):(1)low tempered(50%),clearing up the remained variant laths via the migration of the triple junctions.Martensite-type microstructure is tailored by low-index lamellar variant boundaries and is thus intrinsically thermally stable,whereas the mobile terminal tips decrease the tempering resistance.The underlying mechanism for such carbon-irrelevant process was discussed and the potential effect on the tempering behavior of carbon-contained martensite was highlighted.

关键词： Tempering mechanism Lath martensite IF steel Terminal tip migration High pressure

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Laminar Flame Structure-Dependent Exergy Destruction Behavior at Auto-Ignition Time Scale:A Case Study of Dimethyl Ether(DME)

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Journal of Thermal Science 2024年第4期33卷 1257-1271页

作者： WU Honghuan HUANG Wenlin ZHAO Hao SUN Wuchuan HUANG zuohua ZHANG Yingjia State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University

Hybrid deflagration/auto-ignition flame structures coexist in the combustion of advanced engines.Decoupling exergy destruction caused by different irreversible processes under varied flame regimes is thus important for understanding engine thermodynamics.In this study,the flame propagation modes for the premixed DME/air mixtures are numerically investigated under engine-relevant conditions.Local entropy generation and exergy destruction characteristics are compared under different flame structures.Results reveal that as the typical premixed flame transition towards auto-ignition front,the exergy destruction from heat conduction and species mass diffusion gradually vanish and are dominated by chemical reaction.The distributions of temperature and species mole fraction in the flame domain are analyzed to clarify the exergy destruction behaviors caused by heat conduction and mass diffusion.Furthermore,by dividing the DME oxidation process into four stages,the main reaction channels that contribute to the increase in exergy destruction from chemical reaction have been identified.It is found that the production and consumption of CH2O and HO2radical dominate the exergy destruction behavior during DME oxidation.On this basis,the kinetic mechanism of low-temperature chemistry causing greater exergy destruction is elucidated.Specifically,low-temperature chemistry leads to significant exergy destruction due to（a） the large irreversibility of itself and（b）(mainly) the enhancement of H2O2loop reactions by low-temperature reaction intermediates.Thus the reduction of combustion irreversibility is promising to be achieved by reasonably regulating the fuel oxidation path.

关键词： exergy destruction flame structures entropy generation low-temperature chemistry DME

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{112}<111>Twins or Twinned Variants Induced by Martensitic Transformation?

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Acta Metallurgica Sinica(English Letters) 2023年第1期36卷 133-140页

作者： zuohua wang Haidong Sun Peng wang Ning Liu Pinwen Zhu Dongli Yu Hongwang Zhang National Engineering Research Center for Equipment and Technology of Cold Strip Rolling College of Mechanical EngineeringYanshan UniversityQinhuangdao 066004China State Key Laboratory of Metastable Materials Science and Technology Yanshan UniversityQinhuangdao 066004China Liren College of Yanshan University Yanshan UniversityQinhuangdao 066004China State Key Laboratory of Superhard Materials College of PhysicsJilin UniversityChangchun 130012China

Twinned substructure in lath martensite was induced in the interstitial free(IF)steel via a high pressure thermal cycle(heating up to 1100℃and holding for 30 min,cooling at 10℃/s to room temperature under a pressure of 4 GPa).Experimental observations and theoretical simulation confrm that the twinned substructure has the origin related to the twinned variants rather than the bcc{112}twins,while extra difraction spots were caused by crystal overlapping rather than any extra phase.The diferences in crystallography and electron difraction behavior between twinned variants and{112}twins were discussed in detail.

关键词： Twinned variants {112}twins Martensitic transformation Crystal overlapping Electron difraction

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Twinned Martensitic Substructure in a Water Quenched Fe–1.0 wt%C Alloy

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Acta Metallurgica Sinica(English Letters) 2022年第7期35卷 1157-1163页

作者： Haidong Sun zuohua wang Shuai Zhang Ning Liu Pinwen Zhu Dongli Yu Hongwang Zhang National Engineering Research Center for Equipment and Technology of Cold Strip Rolling College of Mechanical EngineeringYanshan UniversityQinhuangdao 066004China State Key Laboratory of Superhard Materials College of PhysicsJilin UniversityChangchun 130012China Liren College of Yanshan University Yanshan UniversityQinhuangdao 066004China State Key Laboratory of Metastable Materials Science and Technology Yanshan UniversityQinhuangdao 066004China

A Fe–1.0 wt%C alloy was quenched into water from 1100 ℃,leading to lath martensite and plate martensite of body-centered tetragonal structure.Both these two martensites have the twinned substructure that generates mirror symmetric diff raction patterns with extra diff raction spots around n/3(112).The twinned substructure has the origin from twinned martensitic variants,namely twin-related crystals separated by{110},rather than{112}deformation twins.Tetragonality eff ect on the electron double diff raction of twinned variants was discussed.

关键词： Twinned martensitic substructure Twinned variant Lath martensite Plate martensite

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Origin and the Hardening Mechanism of Twinned Lenticular Martensite in a Fe-33Ni Alloy

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Acta Metallurgica Sinica(English Letters) 2023年第6期36卷 899-905页

作者： Yong Li zuohua wang Lihua Qian Jian Zhao Wu Zhang Ping Wei Hongwang Zhang National Engineering Research Center for Equipment and Technology of Cold Strip Rolling College of Mechanical EngineeringYanshan UniversityQinhuangdao 066004China State Key Laboratory of Metastable Materials Science and Technology Yanshan UniversityQinhuangdao 066004China School of Physics Huazhong University of Science and TechnologyWuhan 430074China China Copper Huazhong Copper Cooperation Limited Huangshi 435004China College of Weaponry Engineering Naval University of EngineeringWuhan 430033China

The twinned substructure of lenticular martensite in a quenched Fe–33Ni alloy was studied.In contrary to the traditional viewpoint that the twinned laths come from{112}deformation twins and show insignificant hardening,we demonstrate that they are actually originated from the twinned Kurdjumov Sachs(KS)variants and can give rise to 3–4 times hardening up to~420 HV(~130 HV for the starting sample).The underlying mechanisms responsible for the propensity for twinned variants and the carbon-independent hardening for Fe–Ni system were discussed.

关键词： Twinned variants Midrib Lenticular martensite Hardening mechanism Fe-33Ni

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非线性拉伸对层流燃烧速度提取的影响

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中南大学学报（自然科学版） 2024年第1期55卷 399-408页

作者：蔡骁张龙凯王金华黄佐华西安交通大学动力工程多相流国家重点实验室陕西西安710049

基于理论模型推导出一种非线性NLC层流燃烧速度外推方程,并采用定容燃烧弹获取甲烷/空气、正丁烷/空气和氢气/空气的火焰发展历程。基于文献常用和本文提出的4种线性和非线性外推方程研究4种典型火焰中非线性拉伸对层流燃烧速度提取的... 详细信息

基于理论模型推导出一种非线性NLC层流燃烧速度外推方程,并采用定容燃烧弹获取甲烷/空气、正丁烷/空气和氢气/空气的火焰发展历程。基于文献常用和本文提出的4种线性和非线性外推方程研究4种典型火焰中非线性拉伸对层流燃烧速度提取的影响。研究结果表明:随着马克斯坦长度的增加,非线性拉伸的影响增加,不同方程测量的层流燃烧速度差异增加。其中,本文提出的非线性NLC模型得到的结果与实验结果吻合最好,测量层流燃烧速度精度最高;非线性LC和NLS模型表现居中,而线性LS模型明显高估层流燃烧速度。另外,可以采用高精度非线性模型并适当增加初始火焰半径的策略减小非线性拉伸的影响,从而提高层流燃烧速度的测量精度。

关键词：非线性拉伸层流燃烧速度马克斯坦长度

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Twinned substructure in lath martensite of water quenched Fe-0.2%C and Fe-0.8%C steels

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Journal of Materials Science & Technology 2020年第14期47卷 126-132页

作者： Haidong Sun Yuhui wang zuohua wang Ning Liu Yan Peng Xiujuan Zhao Ruiming Ren Hongwang Zhang National Engineering Research Center for Equipment and Technology of Cold Strip Rolling College of Mechanical EngineeringYanshan UniversityQinhuangdao066004China Liren College of Yanshan University Yanshan UniversityQinhuangdao066004China School of Materials Science&Engineering Dalian Jiaotong UniversityDalian116028China

In the present investigation,twinned substructures within lath martensite of two water quenched steels(0.2 wt.%C and 0.8 wt.%C)were studied.The lath martensite has typical hierarchical packet-block-lath with dislocation substructure.Besides,laths that are misoriented by/70.5°or/60° and bordered by{011}plane,namely twinned laths,are observed,of which the density increases and the scale decreases as more carbons were presented.Such twinned laths have body centered cubic(bcc)crystal structure,belonging to twinned variants following the classical Kurdjumov-Sachs(K-S)orientation relationship with respect to the parent austenite.Unlike bcc{112}twins,twinned variants produce strong double diffraction and in turn the extra diffraction spots that are commonly observed in the martensite in steels with wide range of carbon contents.

关键词： Twinned variant Lath martensite Double electron diffraction Orientation relationship Steels

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