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Effect of Graphite Layers on the Conformation and Thermal Conductivity of n-octadecane:A Molecular Dynamics Study

Journal of Thermal Science 2021年第5期30卷 1789-1802页

作者： ZHANG Tiantian XU Bo CHEN Zhenqian School of Energy and Environment Southeast UniversityNanjing 210096China Jiangsu Provincial Key Laboratory of Solar Energy Science and Technology School of Energy and EnvironmentSoutheast UniversityNanjing 210096China Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education School of Energy and EnvironmentSoutheast UniversityNanjing 210096China

To understand the thermal conductivity improvement of the paraffin and graphite composite PCMs in micro-scale,the conformation characteristics of molecules with rising temperature was studied by molecular dynamics(MD)*** then the structure and dynamics characteristics of the paraffin PCM,including the structural evolution,the self-diffusion coefficient,phase change properties and thermal conductivity,were *** results indicate that the distribution of the n-octadecane molecules is more regular in the region near the graphite layers,although the temperature is higher than the phase transition point,which means that the graphite layer has a significant absorption influence on the conformation of alkane ***,the self-diffusion coefficient of n-octadecane molecules increases with the increasing of temperature,which shows great agreement with the ***,the self-diffusion coefficient of n-octadecane molecules staying far away from the graphite layers is larger than that of the molecules in the region near the graphite *** addition,the radial distribution function(RDF)was used to analyze the molecular interaction of the system at different *** sudden increase of R(ratio of the first peak value to the first valley value of the RDF)within the temperature range from 293 K to 313 K corresponds to the phase transition point,indicating that the solid-liquid phase transition occurs at the temperature ***,the results indicate that the thermal conductivity of amorphous n-octadecane is about 2.5 times lower than that of the crystal n-octadecane with perfect *** investigation provides theoretical guidance for the study of the micro-mechanism of n-octadecane doped with graphite composite phase change materials.

关键词： phase change materials self-diffusion coefficient graphite layers thermal conductivity molecular dynamics conformation

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Azobenzene‑Based Solar Thermal Fuels:A Review

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Nano-Micro Letters 2022年第8期14卷 232-268页

作者： Bo Zhang Yiyu Feng Wei Feng School of materials Science and Engineering Tianjin UniversityTianjin 300350People’s Republic of China Tianjin Key Laboratory of Composite and Functional materials Tianjin 300350People’s Republic of China Key Laboratory of materials Processing and Mold Ministry of EducationZhengzhou UniversityZhengzhou 450002People’s Republic of China

The energy storage mechanism of azobenzene is based on the transformation of molecular cis and trans isomerization,while NBD/QC,DHA/VHF,and fulvalene dimetal complexes realize the energy storage function by changing the molecular *** as“molecular batteries,”they can exhibit excellent charging and discharging behavior by converting between trans and cis isomers or changing molecular structure upon absorption of ultraviolet *** properties determining the performance of STFs are stored energy,energy density,half-life,and solar energy conversion *** review is aiming to provide a comprehensive and authoritative overview on the recent advancements of azobenzene molecular photoswitch system in STFs fields,including derivatives and carbon nano-templates,which is emphasized for its attractive *** the energy storage performance of Azo-STFs has already reached the level of commercial lithium batteries,the cycling capability and controllable release of energy still need to be further *** this,some potential solutions to the cycle performance are proposed,and the methods of azobenzene controllable energy release are ***,energy stored by STFs can be released in the form of mechanical energy,which in turn can also promote the release of thermal energy from STFs,implying that there could be a relationship between mechanical and thermal energy in Azo-STFs,providing a potential direction for further research on Azo-STFs.

关键词： Azobenzene Solar thermal fuels Nanocarbon template Controllable energy release phase change materials

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A Review on Recent Development of Cooling Technologies for Photovoltaic Modules

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Journal of Thermal Science 2020年第6期29卷 1410-1430页

作者： ZHANG Chunxiao SHEN Chao WEI Shen WANG Yuan LV Guoquan SUN Cheng Key Laboratory of Cold Region Urban and Rural Human Settlement Environment Science and Technology Ministry of Industry and Information TechnologySchool of ArchitectureHarbin Institute of TechnologyHarbin 150090China The Bartlett School of Construction and Project Management University College London(UCL)London WC1E 7HBUK

When converting solar energy to electricity,a big proportion of energy is not converted for electricity but for heating PV cells,resulting in increased cell temperature and reduced electrical *** cooling technologies have been developed and used for PV modules to lower cell temperature and boost electric energy ***,little crucial review work was proposed to comment cooling technologies for PV ***,this paper has provided a thorough review of the up-to-date development of existing cooling technologies for PV modules,and given appropriate comments,comparisons and *** to the ways or principles of cooling,existing cooling technologies have been classified as fluid medium cooling(air cooling,water cooling and nanofluids cooling),optimizing structural configuration cooling and phase change materials *** influential factors and sub-methods were collected from the review work,and their contributions and impact have been discussed to guide future *** most cooling technologies reviewed in this paper are matured,there are still problems need to be solved,such as the choice of cooling fluid and its usability for specific regions,the fouling accumulation and cleaning of enhanced heat exchangers with complex structures,the balance between cooling cost and net efficiency of PV modules,the cooling of circulating water in tropical areas and the freezing of circulating water in cold *** be advocated,due to efficient heat transfer and spectral filter characters,nanofluids can promote the effective matching of solar energy at both spectral and spatial scales to achieve orderly energy utilization.

关键词： solar energy PV modules cooling technologies nanoparticles phase change materials

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Fabrication of form stable NaCl-Al2O3 composite for thermal energy storage by cold sintering process

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Frontiers of Chemical Science and Engineering 2019年第4期13卷 727-735页

作者： Rilvaminu Suleiman Qinghua Yu Yulong Ding Yongliang Li Birmingham Centre for Energy Storage School of Chemical EngineeringUniversity of BirminghamBirminghamB152TTUK

A form stable NaCl-Al2O3(50-50 wt-%)composite material for high temperature thermal energy storage was fabricated by cold sintering process,a process recently applied to the densification of ceramics at low temperature 300℃ under uniaxial pressure in the presence of small amount o f transient *** fabricated composite achieved as high as 98.65% of the theoretical *** NaCl-Al2O3 composite also retained the chloride salt without leakage after 30 heating-cooling cycles between 750℃-850℃ together with a holding period o f 24h at 850℃.X-ray diffraction measurements indicated congruent solubility o f the alumina in chloride salt,excellent compatibility o f NaCl with Al2O3,and chemical stability at high *** analysis by scanning electron microscope also showed limited grain growth,high density,uniform NaCl distribution and clear faceted composite structure without *** latent heat storage density o f 252.5J/g was obtained from simultaneous thermal *** strength test showed high sintered strength around 5 GPa after 50 *** composite was found to have fair mass losses due to ***,cold sintering process has the potential to be an efficient,safe and cost-effective strategy for the fabrication of high temperature thermal energy storage materials.

关键词： cold sintering process composite fabrication thermal energy storage phase change materials

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Discharging of PCM in Various Shapes of Thermal Energy Storage Systems:A Review

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Journal of Thermal Science 2023年第3期32卷 1124-1154页

作者： DHAIDAN Nabeel HASHIM Hasan ABBAS Abdalrazzaq KHODADADI Jay ALMOSAWY Wala AL-MOUSAWI Fadhel Engineering Faculty Kerbala UniversityKerbalaIraq Department of Mechanical Engineering Auburn University1418 Wiggins HallAuburnAL 36849-5341USA Al-Zahraa University for Women KerbalaIraq

Utilizing the phase change materials in different thermal storage applications attains valuable attention due to the fascinating thermal properties of these *** comprehension of the thermal behaviour of phase change materials during the melting and solidification is considered a significant priority in designing the shape of the different *** this review,analytical,computational and experimental investigations that address solidification/freezing of phase change materials within thermal energy storage systems are *** is placed on the role of the shape of adopted containers encompassing planar,spherical,cylindrical and annular *** storage for solar thermal applications,waste heat recovery,and thermal management of buildings/computing platforms/photovoltaics has been the topics that benefit from these *** all container shapes,the freezing process is controlled initially by natural convection,and a high solidification rate is ***,the conduction dominates the process,and the freezing rate *** temperature and flow of cooling heat transfer fluid affect the solidification process,but the impact of heat transfer fluid temperature is more significant than its flow ***,the freezing time increases with the container’s size and amount of contained *** aspect ratio of the planar and vertical cylindrical cavities substantially influences the discharging time and *** contrast,the orientation of the annular cavity has a lower impact on the discharging process.

关键词： containers freezing phase change materials phase transformation solidification

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Multistimuli Responsive and Thermoregulated Capability of Coaxial Electrospun Membranes with Core-sheath Structure and Functional Polypyrrole Layer

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Chinese Journal of Polymer Science 2022年第11期40卷 1380-1388页

作者： Meng-Hang Gao Wen Feng Xiao-Dong Qi Yong Wang Key Laboratory of Advanced Technologies of materials(Ministry of Education) School of Materials Science&EngineeringSouthwest Jiaotong UniversityChengdu610031China

Developing thermal management fabrics with good energy storage and multistimuli responsive properties is important for regulating the body temperature in complex ***,the intelligent nonwoven membranes were fabricated via a coaxial electrospinning method,resulting in a core-sheath structure with poly(ethylene glycol)(PEG)as core and polyurethane(PU)as ***,polypyrrole(PPy)with good light absorption ability and electrical conductivity was deposited onto the surface of the PU@PEG electrospun fibers via electrochemical *** PPy layer enabled the membranes to respond quickly to sunlight and electrical *** membranes could heat up to 86°C under simulated sunlight within 200 s or produce remarkable electrothermal effect under a low voltage input of only 1V,exhibiting efficient energy conversion and storage *** photothermal and electrothermal conversion effect could be easily adjusted by controlling the polymerization time of ***,the multifunctional membranes with high latent heat,good mechanical properties as well as excellent photothermal/electrothermal conversion ability are promising in personal thermal management applications.

关键词： phase change materials Polypyrrole Coaxial electrospinning Photothermal conversion Electrothermal conversion

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High-efficiency reflection phase tunable metasurface at near-infrared frequencies

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Chinese Physics B 2021年第5期30卷 650-654页

作者： Ce Li Wei Zhu Shuo Du Junjie Li Changzhi Gu Beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China School of Physical Sciences CAS Key Laboratory of Vacuum PhysicsUniversity of Chinese Academy of SciencesBeijing 100049China Key Laboratory of Space Applied Physics and Chemistry Ministry of Education and Department of Applied PhysicsSchool of ScienceNorthwestern Polytechnical UniversityXi'an 710129China Songshan Lake materials Laboratory Dongguan 523808China Collaborative Innovation Center of Quantum Matter Beijing 100871China

The realization of active modulation of reflection phase based on metasurfaces is of great significance for flexible control of electromagnetic wavefront,which makes metasurfaces have practical application values in polarization conversion,beam steering,metalens,*** this paper,a reflection phase tunable gap-surface plasmon(GSP)metasurface based on phase change materials Ge_(2)Sb_(2)Te_(5)(GST)is designed and experimentally *** virtue of the characteristics of large permittivities difference before and after GST phase transition and the existence of stable intermediate states,the continuous modulation of near-infrared reflection phase larger than 200°has been *** the same time,through the reasonable design of the structure sizes,the reflection has been maintained at about 0.4 and basically does not change with the GST phase transition,which improved the working efficiency of the metasurface *** addition,the coupled-mode theory(CMT)is introduced to make a full analysis of the modulation mechanism of the reflection phase,which proves that the phase transition of GST can induce the transition of metasurface working state from overcoupling mode to critical coupling *** improvement of the metasurface working efficiency has practical values for wavefront modulation.

关键词： active metasurface phase change materials phase modulation

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A Comparative Study on the Self Diffusion of N-Octadecane with Crystal and Amorphous Structure by Molecular Dynamics Simulation

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Chinese Physics Letters 2014年第1期31卷 29-32页

作者：饶中浩刘新健张瑞凯李响魏昌兴王浩东李意民 School of Electric Power Engineering China University of Mining and Technology Xuzhou 221116

The straight chain n-Mkanes and their mixture, which can be used as phase change materials （PCM） for ther- mal energy storage, have attracted much attention in recent years. We employ the molecular dynamics （MD） simulation to investigate their thermophysical properties, including self diffusion and melting of n-octadecane with crystal and amorphous structures. Our results show that, although the initial and melted structures of n-octadecane with crystal and amorphous are different, the melting behaviors of n-octadeeane judged by the self diffusion behavior are consistent. The MD simulation indicates that both the crystal and amorphous structures are effective for the property investigation of n-octadecane and the simulated conclusion can be used as reference for modeling the alkanes-based PCM system.

关键词： phase change materials HEAT storage devices MOLECULAR dynamics THERMOPHYSICAL properties CONDENSED matter -- Thermal properties ALKANES

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Transient Thermal Management Comparison of a Microprocessor Using PCMs in Various Configurations

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Journal of Thermal Science 2011年第6期20卷 516-520页

作者： Thenmozhi R Sharmeela C Natarajan P Velraj R Ganthipathy Tulsis' Engineering College AUIndia Anna University ChennaiIndia Bharathidasan Engineering college AUIndia

There has been a strong interest in the use of phase change materials (PCMs) for the transient thermal abatement of high powered *** paper presents a set of transient computational analysis for selected IC packages with the purpose of calibrating the merits of PCM in different *** transient analysis of high powered microprocessors with heat sinks was performed as a benchmark for comparison with the same microprocessors fitted with PCM in the following configurations:a) PCM imbedded into the finned region of the heat sink,b) PCM mounted between the microprocessor and heat sink,c) sealed PCM underfill to the microprocessor and d) PCM fitted to the underside of the printed circuit board directly beneath the *** analysis was performed using a commercial CFD tool together with an approximation to the phase change mechanism using the slope *** indicate the merit of each configuration.

关键词： phase change materials CFD Thermal Management Transient Latent heat

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Cavitation Simulation with Consideration of the Viscous Effect at Large Liquid Temperature Variation

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Chinese Physics Letters 2014年第8期31卷 115-118页

作者：于安罗先武季斌黄仁芳 HIDALGOVictor KIMSongHak StateKeyLaboratoryofHydroscienceandEngineering TsinghuaUniversityBeijing100084 BeijingKeyLaboratoryofCO2UtilizationandReductionTechnology TsinghuaUniversityBeijing100084

The phase change due to cavitation is not only driven by the pressure difference between the local pressure and vapor saturated pressure, but also affected by the physical property changes in the case of large liquid temperature variation. The present work simulates cavitation with consideration of the viscous effect as well as the local variation of vapor saturated pressure, density, etc. A new cavitation model is developed based on the bubble dynamics, and is applied to analyze the eavitating flow around an NACA0015 hydrofoil at different liquid temperatures from 25℃ to 150℃. The results by the proposed model, such as the pressure distribution along the hydrofoil wall surface, vapor volume fraction, and source term of the mass transfer rate due to cavitation, are compared with the available experimental data and the numerical results by an existing thermodynamic model. It is noted that the numerical results by the proposed cavitation model have a slight discrepancy from the experimental results at room temperature, and the accuracy is better than the existing thermodynamic cavitation model. Thus the proposed cavitation model is acceptable for the simulation of cavitating flows at different liquid temperatures.

关键词： CAVITATION RESEARCH HYDRODYNAMICS phase change materials THERMODYNAMICS -- Research PHYSICS research

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