The thermal conductivity of marine sediments is an important thermophysical parameter in the study of seafloor heat flow and marine engineering construction.Understanding the effect of thermal conductivity of marine s...The thermal conductivity of marine sediments is an important thermophysical parameter in the study of seafloor heat flow and marine engineering construction.Understanding the effect of thermal conductivity of marine sediments in the environment has a major engineering value and theoretical significance.In this work,a modified test method was used to measure the thermal conductivity of silt in the Yellow River Delta under different void ratios,moisture contents,temperatures,and salinities.Results showed that the thermal conductivity of silt in the Yellow River Delta decreased with the increase in the void ratio and increased with the water content.Compared with sand and clay,silt in the Yellow River Delta was the least affected by the void ratio and moisture content.Under low temperatures,the heat transfer of soil was controlled by the average velocity of the phonons;therefore,the thermal conductivity of silt in the Yellow River Estuary increased with temperature.The thermal conductivity of pore water decreased with increasing salinity.Moreover,certain salinity levels resulted in a phenomenon known as the‘compressing twin electrical layer’,which led to an increase in the contact area between soil particles.With the increase in salinity,the thermal conductivity of silt in the Yellow River Delta experiences an initial decline and a subsequent increase.The proposed thermal conductivity test method is more accurate than the existing technique,and the findings provide a basis for further study on the thermal characteristics of submarine sediments.展开更多
Highly anisotropic thermal conductive materials are of significance in thermal management applications. However,accurate determination of ultrathin composite thermal properties is a daunting task due to the tiny therm...Highly anisotropic thermal conductive materials are of significance in thermal management applications. However,accurate determination of ultrathin composite thermal properties is a daunting task due to the tiny thermal conductance,severely hindering the further exploration of novel efficient thermal management materials, especially for size-confined environments. In this work, by utilizing a hybrid measuring method, we demonstrate an accurate determination of thermal properties for montmorillonite/reduced graphene oxide(MMT/r GO) composite film with a thickness range from 0.2 μm to2 μm. The in-plane thermal conductivity measurement is realized by one-dimensional(1D) steady-state heat conduction approach while the cross-plane one is achieved via a modified 3ω method. As-measured thermal conductivity results are cross-checked with different methods and known materials, revealing the high measurement accuracy. A high anisotropic ratio of 60.5, independent of composite thickness, is observed in our measurements, further ensuring the negligible measurement error. Notably, our work develops an effective approach to the determination of ultrathin composite thermal conductivity, which may promote the development of ultrathin composites for potential thermal-related applications.展开更多
When nano-fillers are used to enhance the thermal conductivity of organic phase change materials(PCMs),the naturally formed interface is considered to hinder thermal transport of the composite PCMs.However,the effect ...When nano-fillers are used to enhance the thermal conductivity of organic phase change materials(PCMs),the naturally formed interface is considered to hinder thermal transport of the composite PCMs.However,the effect of the interface on the thermal properties of surrounding PCM has not been fully studied.In this paper,three composite PCMs(Ery@SiC,Ery@SiO_(2) and Ery@Si_(3)N_(4))were prepared by melt-blending method.The local thermal conductivity and reduced Young’s modulus(E^(*))of the erythritol at the interface and far away from the interface in the composite PCMs were simultaneously measured by scanning thermal microscopy(SThM).The results revealed significant enhancement in local thermal conductivity of erythritol at the interface and its obvious positive correlation with E^(*).For different composite PCMs,molecular dynamics(MD)simulations suggested that the increase in intrinsic thermal conductivity and E^(*)of erythritol is attributed to the increase in interaction energy between erythritol and nanoparticles,as more erythritol phonon vibrations transform from localized mode to delocalized mode and erythritol has a higher density at the interface.These findings will provide new ideas for the design of PCM for energy storage.展开更多
Raman spectroscopy-based temperature sensing usually tracks the change of Raman wavenumber,linewidth and intensity,and has found very broad applications in characterizing the energy and charge transport in nanomateria...Raman spectroscopy-based temperature sensing usually tracks the change of Raman wavenumber,linewidth and intensity,and has found very broad applications in characterizing the energy and charge transport in nanomaterials over the last decade.The temperature coefficients of these Raman properties are highly material-dependent,and are subjected to local optical scattering influence.As a result,Raman-based temperature sensing usually suffers quite large uncertainties and has low sensitivity.Here,a novel method based on dual resonance Raman phenomenon is developed to precisely measure the absolute temperature rise of nanomaterial(nm WS_(2) film in this work)from 170 to 470 K.A 532 nm laser(2.33 eV photon energy)is used to conduct the Raman experiment.Its photon energy is very close to the excitonic transition energy of WS_(2) at temperatures close to room temperature.A parameter,termed resonance Raman ratio(R3)Ω=I_(A1g)/IE_(2g) is introduced to combine the temperature effects on resonance Raman scattering for the A_(1g) and E_(2g) modes.Ω has a change of more than two orders of magnitude from 177 to 477 K,and such change is independent of film thickness and local optical scattering.It is shown that when Ω is varied by 1%,the temperature probing sensitivity is 0.42 K and 1.16 K at low and high temperatures,respectively.Based on Ω,the in-plane thermal conductivity(k)of a∼25 nm-thick suspended WS_(2) film is measured using our energy transport state-resolved Raman(ET-Raman).k is found decreasing from 50.0 to 20.0 Wm^(−1) K^(−1) when temperature increases from 170 to 470 K.This agrees with previous experimental and theoretical results and the measurement data using our FET-Raman.The R3 technique provides a very robust and high-sensitivity method for temperature probing of nanomaterials and will have broad applications in nanoscale thermal transport characterization,non-destructive evaluation,and manufacturing monitoring.展开更多
Microchannel heat sinks(MCHSs)are promising thermal solutions in miniaturized or compact devices.Lightweight aspect has been given huge emphasis in recent years.Metal-based materials are commonly used to fabricate MCH...Microchannel heat sinks(MCHSs)are promising thermal solutions in miniaturized or compact devices.Lightweight aspect has been given huge emphasis in recent years.Metal-based materials are commonly used to fabricate MCHSs due to their high thermal conductivity.Consequently,MCHSs are heavy due to the high density of these materials albeit the small footprint of MCHSs.Polymer-based materials are interesting alternatives.Despite their poor thermal conductivity,lightweight feature attracts the interest of researchers.Heat transfer is a conjugate process of heat conduction and heat convection.Poor heat conductions aspect may be compensated through enhancement of heat convection aspects.Although polymer-based materials have been used in microscale heat transfer studies,their focus was not on their feasibility.The present study aims to evaluate the feasibility of polymer-based MCHSs as thermal solutions.The effect of thermal conductivity of fabrication materials,including polymer-based PDMS,PTFE,PDMS/MWCNT,and metal-based aluminum,on the thermal performance of MCHSs was investigated and compared at various inlet flow rate,fluid thermal conductivity,and microchannel ratio at different constant heat fluxes using three-dimensional CFD approach.Results showed that the thermal performance of MCHSs was greatly affected by the heat conduction aspect in which poor heat conduction limited the thermal performance improvement due to enhanced heat convection aspects.This suggests polymer-based materials have the potential for heat transfer applications through thermal conductivity enhancement.This was confirmed in the further analysis using a recently proposed high thermal conductivity polymer-based graphite/epoxy MCHS and a hybrid-based PDMS/aluminum MCHS.展开更多
利用全局支撑径向基函数插值初始水平集函数,以水平集函数为设计变量,以结构柔度和散热弱度的加权函数为目标函数,基于参数化水平集法(Parameterized level set method,PLSM)建立了正交各向异性结构的热力耦合多目标拓扑优化模型。结合...利用全局支撑径向基函数插值初始水平集函数,以水平集函数为设计变量,以结构柔度和散热弱度的加权函数为目标函数,基于参数化水平集法(Parameterized level set method,PLSM)建立了正交各向异性结构的热力耦合多目标拓扑优化模型。结合数值算例研究了权系数、材料方向角、泊松比因子和热导率因子对PLSM多目标最优拓扑结构和目标函数的影响,并给出了相关参数的合理取值范围;在3D打印实物的基础上完成了最优各向异性拓扑结构的性能分析,并与各向同性结构进行了对比讨论。结果表明,PLSM最优拓扑结构比变密度法的拓扑结构边界更光滑、清晰,不会出现中间密度和锯齿等现象;同时正交各向异性结构的温度场、位移场和应力场比各向同性结构均有较好地改善,加权目标函数、结构柔度和散热弱度分别降低了55%、3.18%和81.1%。展开更多
A 3 D multi-scale finite element model was developed to predict the effective thermal conductivity of graphene nanoplatelet(GNP)/Al composites.The factors influencing the effective thermal conductivity of the GNP/Al c...A 3 D multi-scale finite element model was developed to predict the effective thermal conductivity of graphene nanoplatelet(GNP)/Al composites.The factors influencing the effective thermal conductivity of the GNP/Al composites were investigated,including the orientation,shape,aspect ratio,configuration and volume fraction of GNPs.The results show that GNPs shape has a little influence on the thermal conductivity of GNP/Al composites,and composites with elliptic GNPs have the highest thermal conductivity.In addition,with increasing the aspect ratio of GNPs,the thermal conductivity of GNP/Al composites increases and finally tends to be stable.The GNPs configuration strongly influences the thermal conductivity of GNP/Al composites,and the thermal conductivity of the composites with layered GNPs is the highest among the five configurations.The effective thermal conductivity is sensitive to volume fraction of GNPs.Ideally,when the volume fraction of layered GNPs reaches 1.54%,the thermal conductivity of GNP/Al composites is as high as 400 W/m K.The findings of this study could provide a good theoretical basis for designing high thermal conductivity GNP/Al composites.展开更多
基金The authors would like to thank the National Natural Science Foundation of China(Nos.U2006213,42277139,42207172)the China Postdoctoral Science Foundation(No.2022M712989)the Natural Science Foundation of Shandong Province(No.ZR2022QD103).
文摘The thermal conductivity of marine sediments is an important thermophysical parameter in the study of seafloor heat flow and marine engineering construction.Understanding the effect of thermal conductivity of marine sediments in the environment has a major engineering value and theoretical significance.In this work,a modified test method was used to measure the thermal conductivity of silt in the Yellow River Delta under different void ratios,moisture contents,temperatures,and salinities.Results showed that the thermal conductivity of silt in the Yellow River Delta decreased with the increase in the void ratio and increased with the water content.Compared with sand and clay,silt in the Yellow River Delta was the least affected by the void ratio and moisture content.Under low temperatures,the heat transfer of soil was controlled by the average velocity of the phonons;therefore,the thermal conductivity of silt in the Yellow River Estuary increased with temperature.The thermal conductivity of pore water decreased with increasing salinity.Moreover,certain salinity levels resulted in a phenomenon known as the‘compressing twin electrical layer’,which led to an increase in the contact area between soil particles.With the increase in salinity,the thermal conductivity of silt in the Yellow River Delta experiences an initial decline and a subsequent increase.The proposed thermal conductivity test method is more accurate than the existing technique,and the findings provide a basis for further study on the thermal characteristics of submarine sediments.
基金Project supported by the National Basic Research Program of China (Grant No. 2016YFA0200800)the Strategic Priority Research Program of Chinese Academy of Sciences (Grant Nos. XDB30000000 and XDB07030100)+2 种基金the Sinopec Innovation Scheme (A-527)the National Key Research and Development Program of China (Grant No. 2021YFA0715700)the National Science Fund for Distinguished Young Scholars, China (Grant No. 52125302)。
文摘Highly anisotropic thermal conductive materials are of significance in thermal management applications. However,accurate determination of ultrathin composite thermal properties is a daunting task due to the tiny thermal conductance,severely hindering the further exploration of novel efficient thermal management materials, especially for size-confined environments. In this work, by utilizing a hybrid measuring method, we demonstrate an accurate determination of thermal properties for montmorillonite/reduced graphene oxide(MMT/r GO) composite film with a thickness range from 0.2 μm to2 μm. The in-plane thermal conductivity measurement is realized by one-dimensional(1D) steady-state heat conduction approach while the cross-plane one is achieved via a modified 3ω method. As-measured thermal conductivity results are cross-checked with different methods and known materials, revealing the high measurement accuracy. A high anisotropic ratio of 60.5, independent of composite thickness, is observed in our measurements, further ensuring the negligible measurement error. Notably, our work develops an effective approach to the determination of ultrathin composite thermal conductivity, which may promote the development of ultrathin composites for potential thermal-related applications.
基金supported by the National Key R&D Program of China(No.2023YFF0612804)the National Natural Science Foundation of China(Nos.52222602,52236006,and 22293043)+3 种基金Beijing Nova Program(No.20220484170)the Fundamental Research Funds for the Central Universities(Nos.FRF-TP-22-001C1 and FRF-EYIT-23-05)Foundation of the Youth Innovation Promotion Association of CAS(No.2020048)IPE Project for Frontier Basic Research(No.QYJC-2023-08).
文摘When nano-fillers are used to enhance the thermal conductivity of organic phase change materials(PCMs),the naturally formed interface is considered to hinder thermal transport of the composite PCMs.However,the effect of the interface on the thermal properties of surrounding PCM has not been fully studied.In this paper,three composite PCMs(Ery@SiC,Ery@SiO_(2) and Ery@Si_(3)N_(4))were prepared by melt-blending method.The local thermal conductivity and reduced Young’s modulus(E^(*))of the erythritol at the interface and far away from the interface in the composite PCMs were simultaneously measured by scanning thermal microscopy(SThM).The results revealed significant enhancement in local thermal conductivity of erythritol at the interface and its obvious positive correlation with E^(*).For different composite PCMs,molecular dynamics(MD)simulations suggested that the increase in intrinsic thermal conductivity and E^(*)of erythritol is attributed to the increase in interaction energy between erythritol and nanoparticles,as more erythritol phonon vibrations transform from localized mode to delocalized mode and erythritol has a higher density at the interface.These findings will provide new ideas for the design of PCM for energy storage.
基金Support of this work by National Science Foundation(CBET1930866 and CMMI2032464 for X W)National Natural Science Foundation of China(No.52106220 for S X and No.51906161 for Y X)。
文摘Raman spectroscopy-based temperature sensing usually tracks the change of Raman wavenumber,linewidth and intensity,and has found very broad applications in characterizing the energy and charge transport in nanomaterials over the last decade.The temperature coefficients of these Raman properties are highly material-dependent,and are subjected to local optical scattering influence.As a result,Raman-based temperature sensing usually suffers quite large uncertainties and has low sensitivity.Here,a novel method based on dual resonance Raman phenomenon is developed to precisely measure the absolute temperature rise of nanomaterial(nm WS_(2) film in this work)from 170 to 470 K.A 532 nm laser(2.33 eV photon energy)is used to conduct the Raman experiment.Its photon energy is very close to the excitonic transition energy of WS_(2) at temperatures close to room temperature.A parameter,termed resonance Raman ratio(R3)Ω=I_(A1g)/IE_(2g) is introduced to combine the temperature effects on resonance Raman scattering for the A_(1g) and E_(2g) modes.Ω has a change of more than two orders of magnitude from 177 to 477 K,and such change is independent of film thickness and local optical scattering.It is shown that when Ω is varied by 1%,the temperature probing sensitivity is 0.42 K and 1.16 K at low and high temperatures,respectively.Based on Ω,the in-plane thermal conductivity(k)of a∼25 nm-thick suspended WS_(2) film is measured using our energy transport state-resolved Raman(ET-Raman).k is found decreasing from 50.0 to 20.0 Wm^(−1) K^(−1) when temperature increases from 170 to 470 K.This agrees with previous experimental and theoretical results and the measurement data using our FET-Raman.The R3 technique provides a very robust and high-sensitivity method for temperature probing of nanomaterials and will have broad applications in nanoscale thermal transport characterization,non-destructive evaluation,and manufacturing monitoring.
基金supported by The Murata Science Foundation[grant numbers 015ME0-031]。
文摘Microchannel heat sinks(MCHSs)are promising thermal solutions in miniaturized or compact devices.Lightweight aspect has been given huge emphasis in recent years.Metal-based materials are commonly used to fabricate MCHSs due to their high thermal conductivity.Consequently,MCHSs are heavy due to the high density of these materials albeit the small footprint of MCHSs.Polymer-based materials are interesting alternatives.Despite their poor thermal conductivity,lightweight feature attracts the interest of researchers.Heat transfer is a conjugate process of heat conduction and heat convection.Poor heat conductions aspect may be compensated through enhancement of heat convection aspects.Although polymer-based materials have been used in microscale heat transfer studies,their focus was not on their feasibility.The present study aims to evaluate the feasibility of polymer-based MCHSs as thermal solutions.The effect of thermal conductivity of fabrication materials,including polymer-based PDMS,PTFE,PDMS/MWCNT,and metal-based aluminum,on the thermal performance of MCHSs was investigated and compared at various inlet flow rate,fluid thermal conductivity,and microchannel ratio at different constant heat fluxes using three-dimensional CFD approach.Results showed that the thermal performance of MCHSs was greatly affected by the heat conduction aspect in which poor heat conduction limited the thermal performance improvement due to enhanced heat convection aspects.This suggests polymer-based materials have the potential for heat transfer applications through thermal conductivity enhancement.This was confirmed in the further analysis using a recently proposed high thermal conductivity polymer-based graphite/epoxy MCHS and a hybrid-based PDMS/aluminum MCHS.
文摘利用全局支撑径向基函数插值初始水平集函数,以水平集函数为设计变量,以结构柔度和散热弱度的加权函数为目标函数,基于参数化水平集法(Parameterized level set method,PLSM)建立了正交各向异性结构的热力耦合多目标拓扑优化模型。结合数值算例研究了权系数、材料方向角、泊松比因子和热导率因子对PLSM多目标最优拓扑结构和目标函数的影响,并给出了相关参数的合理取值范围;在3D打印实物的基础上完成了最优各向异性拓扑结构的性能分析,并与各向同性结构进行了对比讨论。结果表明,PLSM最优拓扑结构比变密度法的拓扑结构边界更光滑、清晰,不会出现中间密度和锯齿等现象;同时正交各向异性结构的温度场、位移场和应力场比各向同性结构均有较好地改善,加权目标函数、结构柔度和散热弱度分别降低了55%、3.18%和81.1%。
基金financially supported by the Key Research Program of Frontier Sciences,CAS(No.QYZDJ-SSWJSC015)the National Natural Science Foundation of China(Nos.51931009,51871214 and 51871215)the National Key R&D Program of China(No.2017YFB0703104)。
文摘A 3 D multi-scale finite element model was developed to predict the effective thermal conductivity of graphene nanoplatelet(GNP)/Al composites.The factors influencing the effective thermal conductivity of the GNP/Al composites were investigated,including the orientation,shape,aspect ratio,configuration and volume fraction of GNPs.The results show that GNPs shape has a little influence on the thermal conductivity of GNP/Al composites,and composites with elliptic GNPs have the highest thermal conductivity.In addition,with increasing the aspect ratio of GNPs,the thermal conductivity of GNP/Al composites increases and finally tends to be stable.The GNPs configuration strongly influences the thermal conductivity of GNP/Al composites,and the thermal conductivity of the composites with layered GNPs is the highest among the five configurations.The effective thermal conductivity is sensitive to volume fraction of GNPs.Ideally,when the volume fraction of layered GNPs reaches 1.54%,the thermal conductivity of GNP/Al composites is as high as 400 W/m K.The findings of this study could provide a good theoretical basis for designing high thermal conductivity GNP/Al composites.
