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A review on thermal application of metal foam

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Science China(Technological Sciences) 2020年第12期63卷 2469-2490页

作者： chen kang GUO LieJin WANG Hui State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong UniversityXi’an 710049China Institute of Solar Engineering Technology Northwest Engineering Corporation LimitedPowerChinaXi’an 710065China School of Environmental Science and Engineering Donghua UniversityShanghai 201620China

Heat exchangers embedded with metal foam are drawing increasing attention in the thermal application field,due to the performance of low density,large ratio of surface area to volume as well as high thermal conductivity. In these applications,compact heat exchanger,solar thermal facilities and thermal energy storage are the three core components. This paper focuses on the lasted advances in thermal applications,presenting a review of theoretical and experimental progress over metal foam in thermal application. The empirical and theoretical models for pressure drop,heat transfer coefficient and performance evaluation criteria of compact heat exchangers with metal foam are reviewed and discussed,especially different optimized *** is a trade-off between heat transfer enhancement and increase of pressure drop. Some exploratory work performed by present authors are also introduced. The manufacturing,heat transfer and flow characteristics of tube bundle wrapped with metal foam are taken into account for optimization of heat exchanger. It is confirmed that the conversion mechanism of heat transfer is carried out that heat conduction is the dominative term at high dimension permeability. The correlations of heat transfer rate and pressure drop for staggered and single row tube bundle wrapped with metal foam are concluded,respectively. The effects of different bonding methods are revealed for point-contact in metal foam and base tube. The powder-sintering method can provide a stable and minimum-thickness bonding layer. Various types of solar thermal facilities utilized metal foam to improve the energy conversion efficiency from solar radiant energy to thermal energy are also reviewed and discussed,including solar collector for intermediate-low temperature utilization and solar receiver for high temperature utilization. The Last but not least,existing and future metal foam thermal application stations are overviewed.

关键词： metal foam heat transfer enhancement solar thermal facilities thermal energy storage

Failure behavior analysis of phased-mission systems considering functional and physical isolation effects

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Chinese Journal of Aeronautics 2022年第10期35卷 195-207页

作者： Ying chen Ze WANG Rui kang School of Reliablility and Systems Engineering Beihang UniversityBeijing 100083China

Phased-Mission Systems(PMS)are widely applied in aerospace,telecommunication and intelligent systems for multiple,consecutive and non-overlapping phases of *** phasedependent stresses and system structure cause some difficulties to the reliability analysis of *** this paper,we analyze the physical isolation effects on the degradation speeds and across-phase damage accumulations of failure ***,some corresponding reliability and unreliability formulas are ***,a hierarchical Binary Decision Diagram(BDD)-based modeling method is proposed for incorporating functional and physical isolation effects into BDD models,and the analytical method with phase algebras is introduced for studying the failure behavior of PMS with functional *** the case study,we evaluate the collision avoidance system of a fixed-wing unmanned aerial vehicle as an example to demonstrate the proposed modeling and analysis *** show that the physical isolation effects have significant influences on the degradations of components,which deserves detailed analysis for a more practical and realistic PMS’s failure behavior.

关键词： Failure mechanism Phase-dependent damage accumulation Phase-dependent degradation Physical isolation effect Reliability evaluation

Model-driven degradation modeling approaches:Investigation and review

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Chinese Journal of Aeronautics 2020年第4期33卷 1137-1153页

作者： Rui kang Wenjun GONG Yunxia chen School of Reliability and Systems Engineering Beihang UniversityBeijing 100083China

The second law of thermodynamics implies that any animate and inanimate systems degrade and inevitably stops *** is irreversible over time that can be labeled as‘‘the degradation arrow of time".From perspective of products’reliability design,it is essential to build appropriate models of describing the degradation arrow of *** current modeling approaches mainly include the model-driven(having assumed forms based on cognitive experience of mankind)and data-driven(using data learning techniques without form hypothesis)*** this paper,we just investigate and review the model-driven degradation approaches,hoping to provide suggestions of the model construction or selection for scholars or ***,for the single mechanism,degradation law models and stochastic process models are classified as separately depicting the tendency and fluctuation of *** the degradation law model,we propose the concept of meta-models as original types for various personal *** the stochastic process model,two main types including the non-monotonic and monotonical types are ***,four multi-mechanism degradation types are discussed,that are competitive degradation,multi-stage degradation,coexistence of degradation and impact,and coexistence of degradation and ***,for the multi-performance degradation,independent and coupling models are *** forms,connotations,applicability and insufficiency of these models are described with a series of examples from the literature and our own *** final explicit suggestions about the potential future work are provided for the development of new degradation models.

关键词： Degradation law Degradation process Meta-models Multi-mechanism Multi-performance

Review and propositions for the sliding/impact wear behavior in a contact interface

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Chinese Journal of Aeronautics 2020年第2期33卷 391-406页

作者： Yunxia chen Wenjun GONG Rui kang School of Reliability and Systems Engineering Beihang UniversityBeijing 100083China

A thermal-solid-liquid complex operational environment induces structural interface developing a typical coupling sliding/impact wear *** results in contact damage until systems fail,which may cause significant economic losses and catastrophic *** key point of solving this problem is to reveal the coupling damage mechanism of the sliding/impact behavior in typical systems and life characterization under a complicate evolving *** has been a hot topic in the area of mechanical *** main work in this paper can be concluded as ***,the main industries in which the"sliding/impact behavior"takes place have been ***,existing studies on the wear mechanism and degree analysis are presented,which includes surface morphology analysis,wear debris analysis,and wear degree ***,existing problems in theoretical modeling and experiments in current research are summarized,so as to point out a bright direction for future research on wear *** include interface contact modeling,mathematic coupling mechanism modeling,wear equation establishment,and wear life characterization,which can provide some new ideas for improving the existing studies on the sliding/impact wear behavior.

关键词： Contact interface Coupling mechanism Life prediction Sliding/impact wear behavior Wear equation

Comprehensive analysis of two-dimensional charge transport mechanism in thin-film transistors based on random networks of single-wall carbon nanotubes using transient measurements

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Nano Research 2022年第2期15卷 1524-1531页

作者： Hyeonwoo shin Sang-Joon Park Byeong-Cheol kang Tae-Jun Ha Department of Electrical Engineering and Computer Science Inter-university Semiconductor Research CenterSeoul National UniversitySeoul 08826Korea Department of Electronic Materials Engineering Kwangwoon UniversitySeoul 01897Korea

Understanding charge transport mechanisms in thin-film transistors based on random networks of single-wall carbon nanotubes(SWCNT-TFTs)is essential for further advances to improve the potential for various nanoelectronic ***,a comprehensive investigation of the two-dimensional(2D)charge transport mechanism in SWCNT-TFTs is reported by analyzing the temperature-dependent electrical characteristics determined from the direct-current and non-quasi-static transient measurements at 80-300 *** elucidate the time-domain charge transport characteristics of the random networks in the SWCNTs,an empirical equation was derived from a theoretical trapping model,and a carrier velocity distribution was determined from the differentiation of the transient ***,charge trapping and de-trapping in shallow-and deep-traps in SWCNT-TFTs were analyzed by investigating charge transport based on their trapping/de-trapping *** comprehensive analysis of this study provides fundamental insights into the 2D charge transport mechanism in TFTs based on random networks of nanomaterial channels.

关键词： single-wall carbon nanotube random networks two-dimensional(2D)charge transport time-domain transient measurements charge trapping/de-trapping shallow-/deep-traps

Base-catalyzed Formation of Enamines from β,β-Dicyanostyrene Derivatives with N-Bromosaccharin

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Chemical Research in Chinese Universities 2018年第5期34卷 751-757页

作者： kang Nan chen Zhanguo Key Laboratory of Applied Surface and Colloid Chemistry Ministry of Education Key Laboratory for Macromoleeular Science of Shaanxi ProvinceSchool of Chemistry and Chemical Engineering Shaanxi Normal UniversityXi 'an 710119 R. P China

A new method for the synthesis of functional enamines from β,β-dicyanostyrene derivatives and N-bromosaccharin（NBSA） was developed. In the presence of Na2CO3, the the reaction of β,β-dicyanostyrene derivatives with NBSA can generate the corresponding enamines smoothly in a mixed solvent of dichloromethane and N,N-dimethylformamide（DMF）（volume ratio 1：1） at 50 ℃. The reaction of 14 kinds of β,β-dicyanostyrene derivatives with NBSA was investigated. Screened olefins afforded the corresponding enamines in good to excellent yields（up to 94%）, indicating that the method has a wide adaptability for the substrate. The catalyst used is inexpen- sive and stable for storage. The amino groups of all products in their structures are on the a-position of products, revealing the reaction has an excellent regioselectivity. The possible pathway involving aminobromination of β,βdicyanostyrene derivative with NBSA first and then elimination of HBr process in one pot has been proposed. The structures of all products were confirmed by ^1H NMR, ^13C NMR and HRMS analysis.

关键词： β,β-Dicyanostyrene derivative Functional enamine Sodium carbonate N-Bromosaccharin

The Dual Iconic Features and Key Enabling Technologies of 6G

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Engineering 2023年第9期28卷 7-10页

作者： Shanzhi chen Shaoli kang National Key Laboratory of Wireless Mobile Communications China Information Communication Technology Group Co.Ltd.(CICT)Beijing 100191China

*** Since the 1980s,when the first generation(1G)of mobile networks came into being,mobile communications have been developing with the trend of a generational upgrade occurring every *** present,the fifth generation(5G)is in the commercial stage and the sixth generation(6G)is in the research *** is expected that the standardization for 6G will debut in the year 2025,and the first version for commercialization will be launched in *** the purpose of better understanding 6G.

关键词： mobile Dual networks

Exclusive enteral nutrition versus corticosteroids for treatment of pediatric Crohn's disease: a meta-analysis

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World Journal of Pediatrics 2019年第1期15卷 26-36页

作者： Yu Yu kang-chen chen Jie chen Department of Gastroenterology Children's HospitalZhejiang University School of Medicine3333 Binsheng RoadBinjiang DistrictHangzhou 310051China First Affiliated Hospital Zhejiang University School of Medicine79 Qingchun RoadShangcheng DistrictHangzhou 310002China

Background Many studies have examined the effects of exclusive enteral nutrition (EEN) in children with Crohn's disease (CD),but corticosteroids are considered a superior therapy and are frequently used in *** meta-analysis aims to compare the efficacy of EEN with corticosteroids in treating pediatric *** A comprehensive retrieval from medical databases,including PubMed,EMBASE,MEDLINE,Web of Science,Wanfang data,VIP and CNKI,was performed using the search terms 'diet therapy','exclusive enteral nutrition','Crohn's disease','inflammatory bowel diseases','child' and 'pediatrics' from January 1990 to April *** We included 18 studies from 1329 identified sources in this *** was as effective as corticosteroids in inducing remission rate of children suffering from CD (OR =1.35;95% CI 0.90,2.10;P =0.14).Nevertheless,patients who received EEN were more likely to achieve both endoscopic mucosal healing (OR =5.24;95% CI 2.06,13.37;P =0.0005)and histological mucosal healing (OR =4.78;95% CI 1.89,12.08;P=0.0009) than those who received corticosteroids;the Pediatric Crohn's Disease Activity Index was lower [mean difference (MD)=-3.67;95% CI-4.91,-2.43] and weight gain was higher (MD=1.92;95% CI 0.02,3.83;P=0.05) in those patients who received EEN than in those who received *** difference was found in relapse rate (OR =0.57;95% CI 0.25,1.29;P=0.18),height for age or body mass index between the patients treated with EEN and corticosteroids at the 1-year end *** This meta-analysis reveals that there is no significant difference between EEN and corticosteroids in the efficacy of inducing remission rate of CD in a pediatric population,but EEN is superior to corticosteroids in improving short-term mucosal inflammation and reducing the PCDAI index.

关键词： Children Corticosteroids Crohn's disease Exclusive enteral nutrition Inflammatory bowel disease Nutrition

Predicting roof-surface wind pressure induced by conical vortex using a BP neural network combined with POD

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Building Simulation 2022年第8期15卷 1475-1490页

作者： Fubin chen Wen kang Zhenru Shu Qiusheng Li Yi Li YFrank chen kang Zhou School of Civil Engineering Changsha University of Science and TechnologyChangsha410082China School of Civil Engineering Central South UniversityChangsha410083China Department of Architecture and Civil Engineering City University of Hong KongKowloonHong KongChina Hunan Provincial Key Laboratory of Structures for Wind Resistance and Vibration Control&School of Civil Engineering Hunan University of Science and TechnologyXiangtan411201China Department of Civil Engineering The Pennsylvania State UniversityMiddletownPA 17057USA

This study aims to examine the feasibility of predicting surface wind pressure induced by conical vortex using a backpropagation neural network(BPNN)combined with proper orthogonal decomposition(POD),in which a 1:150 scaled model with a large-span retractable roof was tested in wind tunnel under both laminar and turbulent flow *** distributions of mean and fluctuating wind pressure coefficients were first described,and the effects of inflow turbulence,wind direction,roof opening were examined *** the prediction of wind pressure,the POD-BPNN model was trained using measurement data from adjacent *** prediction results are overall *** root-mean-square-error(RMSE)between test and predicted data lies mostly within 10%.In particular,the prediction of mean wind pressure is found to be better than that of fluctuating wind *** outcomes in this study highlight that the proposed POD-BPNN model can be well used as a useful tool to predict surface wind pressure.

关键词： wind tunnel test-roof-surface wind pressure conical vortex proper orthogonal decomposition(POD) backpropagation neural network(BPNN)