The severe dependence of traditional phase change materials(PCMs)on the temperature-response and lattice deficiencies in versatility cannot satisfy demand for using such materials in complex application scenarios.Here...The severe dependence of traditional phase change materials(PCMs)on the temperature-response and lattice deficiencies in versatility cannot satisfy demand for using such materials in complex application scenarios.Here,we introduced metal ions to induce the self-assembly of MXene nanosheets and achieve their ordered arrangement by combining suction filtration and rapid freezing.Subsequently,a series of MXene/K^(+)/paraffin wax(PW)phase change composites(PCCs)were obtained via vacuum impregnation in molten PW.The prepared MXene-based PCCs showed versatile applications from macroscale technologies,successfully transforming solar,electric,and magnetic energy into thermal energy stored as latent heat in the PCCs.Moreover,due to the absence of binder in the MXene-based aerogel,MK3@PW exhibits a prime solar-thermal conversion efficiency(98.4%).Notably,MK3@PW can further convert the collected heat energy into electric energy through thermoelectric equipment and realize favorable solar-thermal-electric conversion(producing 206 mV of voltage with light radiation intensity of 200 mw cm^(−2)).An excellent Joule heat performance(reaching 105℃with an input voltage of 2.5 V)and responsive magnetic-thermal conversion behavior(a charging time of 11.8 s can achieve a thermal insulation effect of 285 s)for contactless thermotherapy were also demonstrated by the MK3@PW.Specifically,as a result of the ordered arrangement of MXene nanosheet self-assembly induced by potassium ions,MK3@PW PCC exhibits a higher electromagnetic shielding efficiency value(57.7 dB)than pure MXene aerogel/PW PCC(29.8 dB)with the same MXene mass.This work presents an opportunity for the multi-scene response and practical application of PCMs that satisfy demand of next-generation multifunctional PCCs.展开更多
Phase-change material(PCM)is widely used in thermal management due to their unique thermal behavior.However,related research in thermal rectifier is mainly focused on exploring the principles at the fundamental device...Phase-change material(PCM)is widely used in thermal management due to their unique thermal behavior.However,related research in thermal rectifier is mainly focused on exploring the principles at the fundamental device level,which results in a gap to real applications.Here,we propose a controllable thermal rectification design towards building applications through the direct adhesion of composite thermal rectification material(TRM)based on PCM and reduced graphene oxide(rGO)aerogel to ordinary concrete walls(CWs).The design is evaluated in detail by combining experiments and finite element analysis.It is found that,TRM can regulate the temperature difference on both sides of the TRM/CWs system by thermal rectification.The difference in two directions reaches to 13.8 K at the heat flow of 80 W/m^(2).In addition,the larger the change of thermal conductivity before and after phase change of TRM is,the more effective it is for regulating temperature difference in two directions.The stated technology has a wide range of applications for the thermal energy control in buildings with specific temperature requirements.展开更多
The development of functional composites with excellent thermal management capabilities and electro-magnetic interference(EMI)shielding has become extremely urgent for keeping up with the continuous improvement of the...The development of functional composites with excellent thermal management capabilities and electro-magnetic interference(EMI)shielding has become extremely urgent for keeping up with the continuous improvement of the operating speed and efficiency for electronic equipment.In this study,the biolog-ical wood-derived porous carbon(WPC)was determined as the supporting material to encapsulating polyethylene glycol(PEG),and a series of WPC/PEG/Fe_(3)O_(4) phase change composites(PCCs)with excel-lent shape stability,EMI shielding and thermal management capabilities were prepared via a simple vac-uum impregnation method.The Fe_(3)O_(4) magnetic particles modified PCCs have greatly improved the EMI shielding effectiveness(SE).The EMI SE of WP-4(7.5 wt.% Fe_(3)O_(4) in PEG)can be up to 55.08 dB between 8.2−12.4 GHz,however,the WP-0 without Fe_(3)O_(4) addition is only 40.08 dB.Meanwhile,the absorption ratio of electromagnetic waves(EMW)has also increased from 75.02%(WP-0)to 85.56%(WP-4),which effectively prevents secondary pollution.In addition,after wrapping a thin layer of polydimethylsiloxane resin(PDMS),the obtained WP-4 can maintain a high heat storage capacity(109.52 J/g)and good wa-ter stability.In short,the prepared WPC/PEG/Fe_(3)O_(4) PCCs have great potential application value in the thermal management and electromagnetic shielding requirements for electronic devices.展开更多
With the rapid development of new generations of miniaturized,integrated,and high-power electronic devices,it is particularly important to develop advanced composite materials with efficient thermal management capabil...With the rapid development of new generations of miniaturized,integrated,and high-power electronic devices,it is particularly important to develop advanced composite materials with efficient thermal management capability and excellent electromagnetic interference(EMI)shielding performance.Herein,an innovative biomass/MXene-derived conductive hybrid scaffold,cellulose nanocrystal(CNC)-konjac glucomannan(KGM)/MXene(CKM),was prepared by freeze-drying and thermal annealing,and then paraffin wax(PW)was encapsulated in CKM using vacuum impregnation method to obtain CNC-KGM/MXene@PW phase change composites(CKMPCCs).The results show that the obtained CKMPCCs possess considerable reusable stabilities,excellent EMI shielding properties,and thermal energy management capacities.Among them,the CKMPCC-6 with 2.3 wt.%MXene exhibits excellent solar-thermal and electro-thermal conversion capabilities.In addition,the EMI shielding effectiveness value is as high as 45.0 dB at 8.2–12.4 GHz and the corresponding melting enthalpy value is 215.7 J/g(relative enthalpy efficiency of 99.9%).In conclusion,the synthesized multifunctional phase change composites provide great potential for integrating outstanding EMI shielding and advanced thermal energy management applications.展开更多
Phase change materials(PCMs)can store large amounts of energy in latent heat and release it during phase changes,which could be used to improve the freeze-thaw performance of soil.The composite phase change material w...Phase change materials(PCMs)can store large amounts of energy in latent heat and release it during phase changes,which could be used to improve the freeze-thaw performance of soil.The composite phase change material was prepared with paraffin as the PCM and 8%Class C fly ash(CFA)as the supporting material.Laboratory tests were conducted to reveal the influence of phase change paraffin composite Class C fly ash(CFA-PCM)on the thermal properties,volume changes and mechanical properties of expansive soil.The results show that PCM failed to establish a good improvement effect due to leakage.CFA can effectively adsorb phase change materials,and the two have good compatibility.CFA-PCM reduces the volume change and strength attenuation of the soil,and 8 wt.%PCM is the optimal content.CFA-PCM turns the phase change latent heat down of the soil and improves its thermal stability.CFA-PCM makes the impact small of freeze-thaw on soil pore structure damage and improves soil volume change and mechanical properties on a macroscopic scale.In addition,CFA-8 wt.%PCM treated expansive soil has apparent advantages in resisting repeated freeze-thaw cycles,providing a reference for actual engineering design.展开更多
A 1-octadecanol（OD）/1,3:2,4-di-（3,4-dimethyl） benzylidene sorbitol（DMDBS）/expander graphite（EG） composite was prepared as a form-stable phase change material（PCM） by vacuum melting method. The results of fie...A 1-octadecanol（OD）/1,3:2,4-di-（3,4-dimethyl） benzylidene sorbitol（DMDBS）/expander graphite（EG） composite was prepared as a form-stable phase change material（PCM） by vacuum melting method. The results of field emission-scanning electron microscopy（FE-SEM） showed that 1-octadecanol was restricted in the three-dimensional network formed by DMDBS and the honeycomb network formed by EG. X-ray diffraction（XRD） and Fourier transform infrared spectroscopy（FT-IR） results showed that no chemical reaction occurred among the components of composite PCM in the preparation process. The gel-to-sol transition temperature of the composite PCMs containing DMDBS was much higher than the melting point of pure 1-octadecanol. The improvements in preventing leakage and thermal stability limits were mainly attributed to the synergistic effect of the three-dimensional network formed by DMDBS and the honeycomb network formed by EG. Differential scanning calorimeter（DSC） was used to determine the latent heat and phase change temperature of the composite PCMs. During melting and freezing process the latent heat values of the PCM with the composition of 91% OD/3% DMDBS/6% EG were 214.9 and 185.9 kJ·kg-1, respectively. Its degree of supercooling was only 0.1 ℃. Thermal constant analyzer results showed that its thermal conductivity（κ） changed up to roughly 10 times over that of OD/DMDBS matrix.展开更多
This work mainly involved the preparation of a nano-scale form-stable phase change material（PCM） consisting of capric and myristic acid（CA-MA） binary eutectic acting as thermal absorbing material and nano silicon ...This work mainly involved the preparation of a nano-scale form-stable phase change material（PCM） consisting of capric and myristic acid（CA-MA） binary eutectic acting as thermal absorbing material and nano silicon dioxide（nano-SiO_2） serving as the supporting material. Industrial water glass for preparation of the nano silicon dioxide matrix and CA-MA eutectic mixture were compounded by single-step sol-gel method with the silane coupling agent. The morphology, chemical characterization and form stability property of the composite PCM were investigated by transmission electron microscopy（TEM）, scanning electron microscopy（SEM）, Fourier-transform infrared（FT-IR） spectroscopy and polarizing microscopy（POM）. It was indicated that the average diameter of the composite PCM particle ranged from 30-100 nm. The CA-MA eutectic was immobilized in the network pores constructed by the Si-O bonds so that the composite PCM was allowed no liquid leakage above the melting temperature of the CA-MA eutectic. Differential scanning calorimetry（DSC） and thermogravimetric analysis（TGA） measurement were conducted to investigate the thermal properties and stability of the composite PCM. From the measurement results, the mass fraction of the CA-MA eutectic in the composite PCM was about 40%. The phase change temperature and latent heat of the composite were determined to be 21.15 ℃ and 55.67 J/g, respectively. Meanwhile, thermal conductivity of the composite was measured to be 0.208 W·m^（-1）·K^（-1） by using the transient hot-wire method. The composite PCM was able to maintain the surrounding temperature close to its phase change temperature and behaved well in thermalregulated performance which was verified by the heat storage-release experiment. This kind of form-stable PCM was supposed to complete thermal insulation even temperature regulation by the dual effect of relatively low thermal conductivity and phase change thermal storage-release properties. So it can be formulated that the nanoscale CA-MA/SiO_2 composite PCM with the form-stable property, good thermal storage capacity and relatively low thermal conductivity can be applied for energy conservation as a kind of thermal functional material.展开更多
Graphene-based phase change composites hold significant potential for solar energy utilization,but their poor thermal conductivity hinders their practical applications.In this work,an air-dried graphene skele-ton(AGS)...Graphene-based phase change composites hold significant potential for solar energy utilization,but their poor thermal conductivity hinders their practical applications.In this work,an air-dried graphene skele-ton(AGS)with excellent thermal conductivity enhancement efficiency was constructed by the ice tem-plating method and syneresis,and the air-dried graphene phase change composite(AGP)was subse-quently obtained through vacuum-impregnating n-Docosane(C22)into AGS.The syneresis effectively re-duced the phonon scattering between graphene sheets within AGS and increased the density of AGS to 0.1701 g/cm3.Therefore,with a graphene skeleton loading of 23.82 wt.%,AGP exhibited excellent thermal conductivity of 9.867 W/(m K),outstanding electrical conductivity of 68.08 S/cm,and remarkable shape stability.Additionally,AGP demonstrated a melting enthalpy of 188.5 J/g and an outstanding solar-thermal conversion efficiency of 93.98%,showing enormous potential for the utilization of solar energy.展开更多
Electronic devices generate heat during operation and require efficient thermal management to extend the lifetime and prevent performance degradation.Featured by its exceptional thermal conductivity,graphene is an ide...Electronic devices generate heat during operation and require efficient thermal management to extend the lifetime and prevent performance degradation.Featured by its exceptional thermal conductivity,graphene is an ideal functional filler for fabricating thermally conductive polymer composites to provide efficient thermal management.Extensive studies have been focusing on constructing graphene networks in polymer composites to achieve high thermal conductivities.Compared with conventional composite fabrications by directly mixing graphene with polymers,preconstruction of three-dimensional graphene networks followed by backfilling polymers represents a promising way to produce composites with higher performances,enabling high manufacturing flexibility and controllability.In this review,we first summarize the factors that affect thermal conductivity of graphene composites and strategies for fabricating highly thermally conductive graphene/polymer composites.Subsequently,we give the reasoning behind using preconstructed three-dimensional graphene networks for fabricating thermally conductive polymer composites and highlight their potential applications.Finally,our insight into the existing bottlenecks and opportunities is provided for developing preconstructed porous architectures of graphene and their thermally conductive composites.展开更多
Thermal energy storage(TES)using phase change materials(PCMs)is a powerful solution to the improvement of energy efficiency.The application of Ammonium alum(A-alum,NH4Al(SO_(4))_(2)·12H_(2)O)in the latent thermal...Thermal energy storage(TES)using phase change materials(PCMs)is a powerful solution to the improvement of energy efficiency.The application of Ammonium alum(A-alum,NH4Al(SO_(4))_(2)·12H_(2)O)in the latent thermal energy storage(LTES)systems is hampered due to its high supercooling and low thermal conductivity.In this work,modified A-alum(M-PCM)containing different nucleating agents was prepared and further adsorbed in expanded graphite(EG)to obtain composite phase change material(CPCM)to overcome the disadvantages of A-alum.Thermal properties,thermal cycle stability,microstructure and chemical compatibility of CPCM were characterized by differential scanning calorimetry,thermal constant analysis,scanning electron microscopy,X-ray diffraction and Fourier transform infrared spectroscopy.The cold rewarming phenomenon of CPCM was established and explained.Results showed that the latent heat and melting point of CPCM were 187.22 J/g and 91.54℃,respectively.The supercooling of CPCM decreased by 9.61℃,and thermal conductivity increased by 27 times compared with pure A-alum.Heat storage and release tests indicated that 2 wt%calcium chloride dihydrate(CCD,CaCl_(2)·2H_(2)O)was the optimum nucleating agent for A-alum.The result of TG and 30 thermal cycles revealed that CPCM exhibited favorable thermal stability and reliability during the operating temperature.The prepared modified A-alum/EG CPCM has a promising application prospect for LTES.展开更多
A new potassium nitrate （KNO3）]diatomite shape-stabilized composite phase change material （SS- CPCM） was prepared by the mixing and sintering method. KNO3 served as the phase change material （PCM） for thermal en...A new potassium nitrate （KNO3）]diatomite shape-stabilized composite phase change material （SS- CPCM） was prepared by the mixing and sintering method. KNO3 served as the phase change material （PCM） for thermal energy storage, while diatomite acted as the carrier matrix to provide the structural strength and prevent the leakage of PCM. It was found that KNO3 could be retained 65 wt% into pores and on surfaces of diatomite without the leakage of melted KNO3 from the SS-CPCM. The calculated filling rate of molten KNO3 that could enter into the disc-like shape pore of diatomite verified the scanning elec- tronic microscopy images of SS-CPCM. X-ray diffraction and Fourier transform infrared spectroscopy results showed that no reaction occurred between KNO3 and diatomite, performing good compatibility. Accord- ing to the differential scanning calorimetry results, after 50 thermal cycles, the phase change temperatures for melting and freezing of SS-CPCM with 65 wt% KNO3 were changed from 330.23 ℃ and 332.90 ℃ to 330.11 ℃ and 332.84 ℃ and corresponding latent heats varied from 60.52 J/g and 47.30 J/g to 54.64 J/g and 41.25 J/g, respectively. The KNO3/diatomite SS-CPCM may be considered as a potential storage media in solar power plants for thermal energy storage.展开更多
In this paper,CPCM(Composite Phase Change Material)was manufactured with metal foam matrix used as filling material.The temperature curves were obtained by experiment.The performance of heat transfer was analyzed.The ...In this paper,CPCM(Composite Phase Change Material)was manufactured with metal foam matrix used as filling material.The temperature curves were obtained by experiment.The performance of heat transfer was analyzed.The experimental results show that metal foam matrix can improve temperature uniformity in phase change thermal storage material and enhance heat conduction ability.The thermal performance of CPCM is significantly improved.The efficiency of temperature control can be obviously improved by adding metal foam in phase change material.CPCM is in solid-liquid two-phase region when temperature is close to phase change point of paraffin.An approximate plateau appears.The plateau can be considered as the temperature control zone of CPCM.Heat can be transferred fiom hot source and be uniformly spread in thermal storage material by using metal foam matrix since thermal storage material has the advantage of strong heat storage capacity and disadvantage of poor heat conduction ability.Natural convection promotes the melting of solid-liquid phase change material.Good thermal conductivity of foam metal accelerates heat conduction of solid-liquid phase change material.The interior temperature difference decreases and the whole temperature becomes more uniform.For the same porosity with a metal foam,melting time of solid-liquid phase change material decreases.Heat conduction is enhanced and natural convection is suppressed when pore size of metal foam is smaller.The thermal storage time decreases and heat absorption rate increases when the pore size of metal foam reduces.The research results can be used to guide fabricating the CPCM.展开更多
Oleylamine （G18） and octanol （G8） were grafted onto the surfaces of the multi-walled carbon nanotubes （CNTs）. The grafted CNTs were dispersed into palmitic acid （PA） and paraffin wax （PW） to prepare phase ch...Oleylamine （G18） and octanol （G8） were grafted onto the surfaces of the multi-walled carbon nanotubes （CNTs）. The grafted CNTs were dispersed into palmitic acid （PA） and paraffin wax （PW） to prepare phase change composites. The heat storage/retrieval experiments showed that the composites kept stable after repeating melting and solidification for 80 times. The structure of the G18-CNT/PA and G8-CNT/PA was homogenous compared with the pristine CNT （P-CNT）/PA. The latent heat capacity （Ls） of solid liquid phase change of G18-CNT/PW was higher than that of PW while those of the G8-CNTI/PW and P-CNT/PW were lower than that of PW. Compared with PA, all PA based composites with both P-CNTs and grafted CNTs decreased Ls evidently. The Ls values of GI8-CNT composites in both matrices were higher than that of the counterparts of G8-CNT. The thermal conductivities of all the PA based composites in the study were higher than that of PA, as well as those of all the PW based composites. However, the thermal conductivities of the GI8-CNT composites in both matrixes were lower than those of the G8-CNT composites in both matrixes at all measured temperatures.展开更多
This paper discusses composite materials based on inorganic salts for medium- and high-temperature thermal energy storage application. The composites consist of a phase change material （PCM）, a ceramic material, and...This paper discusses composite materials based on inorganic salts for medium- and high-temperature thermal energy storage application. The composites consist of a phase change material （PCM）, a ceramic material, and a high thermal conductivity material. The ceramic material forms a microstructural skeleton for encapsulation of the PCM and structural stability of the composites; the high thermal conductivity material enhances the overall thermal conductivity of the composites. Using a eutectic salt of lithium and sodium carbonates as the PCM, magnesium oxide as the ceramic skeleton, and either graphite flakes or carbon nanotubes as the thermal conductivity enhancer, we produced composites with good physical and chemical stability and high thermal conductivity. We found that the wettability of the molten salt on the ceramic and carbon materials significantly affects the microstructure of the composites.展开更多
基金the National Natural Science Foundation of China[grant numbers 52203038,52173036 and 52073107]the National Key Technology R&D Program of China[grant number 2022YFC3901904,2022YFC3901903,and 2020YFB1709301]the Central University Basic Research Fund of China[grant number 2021XXJS035].
文摘The severe dependence of traditional phase change materials(PCMs)on the temperature-response and lattice deficiencies in versatility cannot satisfy demand for using such materials in complex application scenarios.Here,we introduced metal ions to induce the self-assembly of MXene nanosheets and achieve their ordered arrangement by combining suction filtration and rapid freezing.Subsequently,a series of MXene/K^(+)/paraffin wax(PW)phase change composites(PCCs)were obtained via vacuum impregnation in molten PW.The prepared MXene-based PCCs showed versatile applications from macroscale technologies,successfully transforming solar,electric,and magnetic energy into thermal energy stored as latent heat in the PCCs.Moreover,due to the absence of binder in the MXene-based aerogel,MK3@PW exhibits a prime solar-thermal conversion efficiency(98.4%).Notably,MK3@PW can further convert the collected heat energy into electric energy through thermoelectric equipment and realize favorable solar-thermal-electric conversion(producing 206 mV of voltage with light radiation intensity of 200 mw cm^(−2)).An excellent Joule heat performance(reaching 105℃with an input voltage of 2.5 V)and responsive magnetic-thermal conversion behavior(a charging time of 11.8 s can achieve a thermal insulation effect of 285 s)for contactless thermotherapy were also demonstrated by the MK3@PW.Specifically,as a result of the ordered arrangement of MXene nanosheet self-assembly induced by potassium ions,MK3@PW PCC exhibits a higher electromagnetic shielding efficiency value(57.7 dB)than pure MXene aerogel/PW PCC(29.8 dB)with the same MXene mass.This work presents an opportunity for the multi-scene response and practical application of PCMs that satisfy demand of next-generation multifunctional PCCs.
基金This work was supported in part by Tsinghua University-Zhuhai Huafa Industrial Share Company Joint Institute for Architecture Optoelectronic Technologies(JIAOT KF202204)in part by STI 2030—Major Projects under Grant 2022ZD0209200+2 种基金in part by National Natural Science Foundation of China under Grant 62374099,Grant 62022047in part by Beijing Natural Science-Xiaomi Innovation Joint Fund under Grant L233009in part by the Tsinghua-Toyota JointResearch Fund,in part by the Daikin-Tsinghua Union Program,in part sponsored by CIE-Tencent Robotics XRhino-Bird Focused Research Program.
文摘Phase-change material(PCM)is widely used in thermal management due to their unique thermal behavior.However,related research in thermal rectifier is mainly focused on exploring the principles at the fundamental device level,which results in a gap to real applications.Here,we propose a controllable thermal rectification design towards building applications through the direct adhesion of composite thermal rectification material(TRM)based on PCM and reduced graphene oxide(rGO)aerogel to ordinary concrete walls(CWs).The design is evaluated in detail by combining experiments and finite element analysis.It is found that,TRM can regulate the temperature difference on both sides of the TRM/CWs system by thermal rectification.The difference in two directions reaches to 13.8 K at the heat flow of 80 W/m^(2).In addition,the larger the change of thermal conductivity before and after phase change of TRM is,the more effective it is for regulating temperature difference in two directions.The stated technology has a wide range of applications for the thermal energy control in buildings with specific temperature requirements.
基金supported by the National Key Technology R&D Program of China (Grant Nos. 2020YFB1709301 and 2020YFB1709304)the National Natural Science Foundation of China (No. 52173036 and 52073107)+3 种基金the Central University Basic Research Fund of China (Grants 2021XXJS035)the Innovation and Talent Recruitment Base of New Energy Chemistry and Device (Grants B21003)the Opening Project of Key Laboratory of Polymer Processing Engineering (South China University of Technology),Ministry of Education (Grant No. KFKT2002)fund from Henan University of Science and Technology (2020-RSC02)
文摘The development of functional composites with excellent thermal management capabilities and electro-magnetic interference(EMI)shielding has become extremely urgent for keeping up with the continuous improvement of the operating speed and efficiency for electronic equipment.In this study,the biolog-ical wood-derived porous carbon(WPC)was determined as the supporting material to encapsulating polyethylene glycol(PEG),and a series of WPC/PEG/Fe_(3)O_(4) phase change composites(PCCs)with excel-lent shape stability,EMI shielding and thermal management capabilities were prepared via a simple vac-uum impregnation method.The Fe_(3)O_(4) magnetic particles modified PCCs have greatly improved the EMI shielding effectiveness(SE).The EMI SE of WP-4(7.5 wt.% Fe_(3)O_(4) in PEG)can be up to 55.08 dB between 8.2−12.4 GHz,however,the WP-0 without Fe_(3)O_(4) addition is only 40.08 dB.Meanwhile,the absorption ratio of electromagnetic waves(EMW)has also increased from 75.02%(WP-0)to 85.56%(WP-4),which effectively prevents secondary pollution.In addition,after wrapping a thin layer of polydimethylsiloxane resin(PDMS),the obtained WP-4 can maintain a high heat storage capacity(109.52 J/g)and good wa-ter stability.In short,the prepared WPC/PEG/Fe_(3)O_(4) PCCs have great potential application value in the thermal management and electromagnetic shielding requirements for electronic devices.
基金the National Natural Science Foundation of China(No.U20A20299)Y.C.acknowledges the support from Guangdong Special Support Program(No.2017TX04N371).
文摘With the rapid development of new generations of miniaturized,integrated,and high-power electronic devices,it is particularly important to develop advanced composite materials with efficient thermal management capability and excellent electromagnetic interference(EMI)shielding performance.Herein,an innovative biomass/MXene-derived conductive hybrid scaffold,cellulose nanocrystal(CNC)-konjac glucomannan(KGM)/MXene(CKM),was prepared by freeze-drying and thermal annealing,and then paraffin wax(PW)was encapsulated in CKM using vacuum impregnation method to obtain CNC-KGM/MXene@PW phase change composites(CKMPCCs).The results show that the obtained CKMPCCs possess considerable reusable stabilities,excellent EMI shielding properties,and thermal energy management capacities.Among them,the CKMPCC-6 with 2.3 wt.%MXene exhibits excellent solar-thermal and electro-thermal conversion capabilities.In addition,the EMI shielding effectiveness value is as high as 45.0 dB at 8.2–12.4 GHz and the corresponding melting enthalpy value is 215.7 J/g(relative enthalpy efficiency of 99.9%).In conclusion,the synthesized multifunctional phase change composites provide great potential for integrating outstanding EMI shielding and advanced thermal energy management applications.
基金This research was funded by the National Natural Science Foundation of China(51879166)the Open Fund of the State Key Laboratory of Frozen Soil Engineering of China(SKLFSE201909).
文摘Phase change materials(PCMs)can store large amounts of energy in latent heat and release it during phase changes,which could be used to improve the freeze-thaw performance of soil.The composite phase change material was prepared with paraffin as the PCM and 8%Class C fly ash(CFA)as the supporting material.Laboratory tests were conducted to reveal the influence of phase change paraffin composite Class C fly ash(CFA-PCM)on the thermal properties,volume changes and mechanical properties of expansive soil.The results show that PCM failed to establish a good improvement effect due to leakage.CFA can effectively adsorb phase change materials,and the two have good compatibility.CFA-PCM reduces the volume change and strength attenuation of the soil,and 8 wt.%PCM is the optimal content.CFA-PCM turns the phase change latent heat down of the soil and improves its thermal stability.CFA-PCM makes the impact small of freeze-thaw on soil pore structure damage and improves soil volume change and mechanical properties on a macroscopic scale.In addition,CFA-8 wt.%PCM treated expansive soil has apparent advantages in resisting repeated freeze-thaw cycles,providing a reference for actual engineering design.
基金Funded by Science and Technology Support Program of Hubei Province of China(No.2015BAA111)
文摘A 1-octadecanol（OD）/1,3:2,4-di-（3,4-dimethyl） benzylidene sorbitol（DMDBS）/expander graphite（EG） composite was prepared as a form-stable phase change material（PCM） by vacuum melting method. The results of field emission-scanning electron microscopy（FE-SEM） showed that 1-octadecanol was restricted in the three-dimensional network formed by DMDBS and the honeycomb network formed by EG. X-ray diffraction（XRD） and Fourier transform infrared spectroscopy（FT-IR） results showed that no chemical reaction occurred among the components of composite PCM in the preparation process. The gel-to-sol transition temperature of the composite PCMs containing DMDBS was much higher than the melting point of pure 1-octadecanol. The improvements in preventing leakage and thermal stability limits were mainly attributed to the synergistic effect of the three-dimensional network formed by DMDBS and the honeycomb network formed by EG. Differential scanning calorimeter（DSC） was used to determine the latent heat and phase change temperature of the composite PCMs. During melting and freezing process the latent heat values of the PCM with the composition of 91% OD/3% DMDBS/6% EG were 214.9 and 185.9 kJ·kg-1, respectively. Its degree of supercooling was only 0.1 ℃. Thermal constant analyzer results showed that its thermal conductivity（κ） changed up to roughly 10 times over that of OD/DMDBS matrix.
基金Funded by the National Natural Science Foundation of China(No.51308275)Natural Science Foundation of Liaoning Province(No.SY2016004)the Colleges and Universities Excellent Talents Supporting Plan Program of Liaoning Province(No.LJQ2015049)
文摘This work mainly involved the preparation of a nano-scale form-stable phase change material（PCM） consisting of capric and myristic acid（CA-MA） binary eutectic acting as thermal absorbing material and nano silicon dioxide（nano-SiO_2） serving as the supporting material. Industrial water glass for preparation of the nano silicon dioxide matrix and CA-MA eutectic mixture were compounded by single-step sol-gel method with the silane coupling agent. The morphology, chemical characterization and form stability property of the composite PCM were investigated by transmission electron microscopy（TEM）, scanning electron microscopy（SEM）, Fourier-transform infrared（FT-IR） spectroscopy and polarizing microscopy（POM）. It was indicated that the average diameter of the composite PCM particle ranged from 30-100 nm. The CA-MA eutectic was immobilized in the network pores constructed by the Si-O bonds so that the composite PCM was allowed no liquid leakage above the melting temperature of the CA-MA eutectic. Differential scanning calorimetry（DSC） and thermogravimetric analysis（TGA） measurement were conducted to investigate the thermal properties and stability of the composite PCM. From the measurement results, the mass fraction of the CA-MA eutectic in the composite PCM was about 40%. The phase change temperature and latent heat of the composite were determined to be 21.15 ℃ and 55.67 J/g, respectively. Meanwhile, thermal conductivity of the composite was measured to be 0.208 W·m^（-1）·K^（-1） by using the transient hot-wire method. The composite PCM was able to maintain the surrounding temperature close to its phase change temperature and behaved well in thermalregulated performance which was verified by the heat storage-release experiment. This kind of form-stable PCM was supposed to complete thermal insulation even temperature regulation by the dual effect of relatively low thermal conductivity and phase change thermal storage-release properties. So it can be formulated that the nanoscale CA-MA/SiO_2 composite PCM with the form-stable property, good thermal storage capacity and relatively low thermal conductivity can be applied for energy conservation as a kind of thermal functional material.
文摘Graphene-based phase change composites hold significant potential for solar energy utilization,but their poor thermal conductivity hinders their practical applications.In this work,an air-dried graphene skele-ton(AGS)with excellent thermal conductivity enhancement efficiency was constructed by the ice tem-plating method and syneresis,and the air-dried graphene phase change composite(AGP)was subse-quently obtained through vacuum-impregnating n-Docosane(C22)into AGS.The syneresis effectively re-duced the phonon scattering between graphene sheets within AGS and increased the density of AGS to 0.1701 g/cm3.Therefore,with a graphene skeleton loading of 23.82 wt.%,AGP exhibited excellent thermal conductivity of 9.867 W/(m K),outstanding electrical conductivity of 68.08 S/cm,and remarkable shape stability.Additionally,AGP demonstrated a melting enthalpy of 188.5 J/g and an outstanding solar-thermal conversion efficiency of 93.98%,showing enormous potential for the utilization of solar energy.
文摘Electronic devices generate heat during operation and require efficient thermal management to extend the lifetime and prevent performance degradation.Featured by its exceptional thermal conductivity,graphene is an ideal functional filler for fabricating thermally conductive polymer composites to provide efficient thermal management.Extensive studies have been focusing on constructing graphene networks in polymer composites to achieve high thermal conductivities.Compared with conventional composite fabrications by directly mixing graphene with polymers,preconstruction of three-dimensional graphene networks followed by backfilling polymers represents a promising way to produce composites with higher performances,enabling high manufacturing flexibility and controllability.In this review,we first summarize the factors that affect thermal conductivity of graphene composites and strategies for fabricating highly thermally conductive graphene/polymer composites.Subsequently,we give the reasoning behind using preconstructed three-dimensional graphene networks for fabricating thermally conductive polymer composites and highlight their potential applications.Finally,our insight into the existing bottlenecks and opportunities is provided for developing preconstructed porous architectures of graphene and their thermally conductive composites.
基金supported by the National key research and development plan of China(No.2022YFC3800401)the Fundamental Research Funds for the Central Universities(FRF-BD-20-09A).
文摘Thermal energy storage(TES)using phase change materials(PCMs)is a powerful solution to the improvement of energy efficiency.The application of Ammonium alum(A-alum,NH4Al(SO_(4))_(2)·12H_(2)O)in the latent thermal energy storage(LTES)systems is hampered due to its high supercooling and low thermal conductivity.In this work,modified A-alum(M-PCM)containing different nucleating agents was prepared and further adsorbed in expanded graphite(EG)to obtain composite phase change material(CPCM)to overcome the disadvantages of A-alum.Thermal properties,thermal cycle stability,microstructure and chemical compatibility of CPCM were characterized by differential scanning calorimetry,thermal constant analysis,scanning electron microscopy,X-ray diffraction and Fourier transform infrared spectroscopy.The cold rewarming phenomenon of CPCM was established and explained.Results showed that the latent heat and melting point of CPCM were 187.22 J/g and 91.54℃,respectively.The supercooling of CPCM decreased by 9.61℃,and thermal conductivity increased by 27 times compared with pure A-alum.Heat storage and release tests indicated that 2 wt%calcium chloride dihydrate(CCD,CaCl_(2)·2H_(2)O)was the optimum nucleating agent for A-alum.The result of TG and 30 thermal cycles revealed that CPCM exhibited favorable thermal stability and reliability during the operating temperature.The prepared modified A-alum/EG CPCM has a promising application prospect for LTES.
基金supported by the Program for New Century Excellent Talents in University (Grant No. NCET-08-828)the Program for the China Geological Survey (No. 1212011120323)the Fundamental Research Funds for the Central Universities (No. 2011YXL003)
文摘A new potassium nitrate （KNO3）]diatomite shape-stabilized composite phase change material （SS- CPCM） was prepared by the mixing and sintering method. KNO3 served as the phase change material （PCM） for thermal energy storage, while diatomite acted as the carrier matrix to provide the structural strength and prevent the leakage of PCM. It was found that KNO3 could be retained 65 wt% into pores and on surfaces of diatomite without the leakage of melted KNO3 from the SS-CPCM. The calculated filling rate of molten KNO3 that could enter into the disc-like shape pore of diatomite verified the scanning elec- tronic microscopy images of SS-CPCM. X-ray diffraction and Fourier transform infrared spectroscopy results showed that no reaction occurred between KNO3 and diatomite, performing good compatibility. Accord- ing to the differential scanning calorimetry results, after 50 thermal cycles, the phase change temperatures for melting and freezing of SS-CPCM with 65 wt% KNO3 were changed from 330.23 ℃ and 332.90 ℃ to 330.11 ℃ and 332.84 ℃ and corresponding latent heats varied from 60.52 J/g and 47.30 J/g to 54.64 J/g and 41.25 J/g, respectively. The KNO3/diatomite SS-CPCM may be considered as a potential storage media in solar power plants for thermal energy storage.
基金Support provided by National Basic Research Program of China(Grant No.2012CB933200)National Natural Science Foundation of China(Grant No:51161140332,Grant No.51476172)
文摘In this paper,CPCM(Composite Phase Change Material)was manufactured with metal foam matrix used as filling material.The temperature curves were obtained by experiment.The performance of heat transfer was analyzed.The experimental results show that metal foam matrix can improve temperature uniformity in phase change thermal storage material and enhance heat conduction ability.The thermal performance of CPCM is significantly improved.The efficiency of temperature control can be obviously improved by adding metal foam in phase change material.CPCM is in solid-liquid two-phase region when temperature is close to phase change point of paraffin.An approximate plateau appears.The plateau can be considered as the temperature control zone of CPCM.Heat can be transferred fiom hot source and be uniformly spread in thermal storage material by using metal foam matrix since thermal storage material has the advantage of strong heat storage capacity and disadvantage of poor heat conduction ability.Natural convection promotes the melting of solid-liquid phase change material.Good thermal conductivity of foam metal accelerates heat conduction of solid-liquid phase change material.The interior temperature difference decreases and the whole temperature becomes more uniform.For the same porosity with a metal foam,melting time of solid-liquid phase change material decreases.Heat conduction is enhanced and natural convection is suppressed when pore size of metal foam is smaller.The thermal storage time decreases and heat absorption rate increases when the pore size of metal foam reduces.The research results can be used to guide fabricating the CPCM.
基金supported by the National Natural Science Foundation of China (Nos. 50876058 and 20876042)Program for New Century Excellent Talents in University(NCET-10-883)Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning
文摘Oleylamine （G18） and octanol （G8） were grafted onto the surfaces of the multi-walled carbon nanotubes （CNTs）. The grafted CNTs were dispersed into palmitic acid （PA） and paraffin wax （PW） to prepare phase change composites. The heat storage/retrieval experiments showed that the composites kept stable after repeating melting and solidification for 80 times. The structure of the G18-CNT/PA and G8-CNT/PA was homogenous compared with the pristine CNT （P-CNT）/PA. The latent heat capacity （Ls） of solid liquid phase change of G18-CNT/PW was higher than that of PW while those of the G8-CNTI/PW and P-CNT/PW were lower than that of PW. Compared with PA, all PA based composites with both P-CNTs and grafted CNTs decreased Ls evidently. The Ls values of GI8-CNT composites in both matrices were higher than that of the counterparts of G8-CNT. The thermal conductivities of all the PA based composites in the study were higher than that of PA, as well as those of all the PW based composites. However, the thermal conductivities of the GI8-CNT composites in both matrixes were lower than those of the G8-CNT composites in both matrixes at all measured temperatures.
基金supported by the Focused Deployment Project of the Chinese Academy of Sciences(KGZD-EW-302-1)Key Technologies R&D Program of China(No.2012BAA03B03)+1 种基金Natural Science Foundation of China(Grant No.21106151)the UK Engineering and Physical Sciences Research Council(EPSRC)under grant EP/K002252/1
文摘This paper discusses composite materials based on inorganic salts for medium- and high-temperature thermal energy storage application. The composites consist of a phase change material （PCM）, a ceramic material, and a high thermal conductivity material. The ceramic material forms a microstructural skeleton for encapsulation of the PCM and structural stability of the composites; the high thermal conductivity material enhances the overall thermal conductivity of the composites. Using a eutectic salt of lithium and sodium carbonates as the PCM, magnesium oxide as the ceramic skeleton, and either graphite flakes or carbon nanotubes as the thermal conductivity enhancer, we produced composites with good physical and chemical stability and high thermal conductivity. We found that the wettability of the molten salt on the ceramic and carbon materials significantly affects the microstructure of the composites.
