Synthesis and thermal characterization of the C-S-H/paraffin composite phase change material utilizing a discontinuous two-step nucleation method

The novel calcium-silicate-hydrate(C-S-H)/paraffin composite phase change materials were synthesized using a discontinuous two-step nucleation method.Initially,the C-S-H precursor is separated and dried,followed by immersion in an aqueous environment to transform it into C-S-H.This two-step nucleation approach results in C-S-H with a specific surface area of 497.2 m^(2)/g,achieved by preventing C-S-H foil overlapping and refining its pore structure.When impregnated with paraffin,the novel C-S-H/paraffin composite exhibits superior thermal properties,such as a higher potential heat value of 148.3 J/g and an encapsulation efficiency of 81.6%,outperforming conventional C-S-H.Moreover,the composite material demonstrates excellent cyclic performance,indicating its potential for building thermal storage compared to other paraffin-based composites.Compared with the conventional method,this simple technology,which only adds conversion and centrifugation steps,does not negatively impact preparation costs,the environment,and resource consumption.This study provides valuable theoretical insights for designing thermal storage concrete materials and advancing building heat management.

Preparation and Properties of 1-octadecanol/1,3:2,4-di-(3,4-dimethyl) Benzylidene Sorbitol/Expanded Graphite Form-stable Composite Phase Change Material

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.

Design of the flame retardant form-stable composite phase change materials for battery thermal management system

Phase change materials have attracted significant attention owing to their promising applications in many aspects.However,it is seriously restricted by some drawbacks such as obvious leakage,relatively low thermal conductivity,and easily flame properties.Herein,a novel flame retardant form-stable composite phase change material(CPCM)with polyethylene glycol/epoxy resin/expanded graphite/magnesium hydroxide/zinc hydroxide(PEG/ER/EG/MH/ZH)has been successfully prepared and utilized in the battery module.The addition of MH and ZH(MH:ZH=1:2)as flame retardant additions can not only greatly improve the flame retardant effect but also maintain the physical and mechanical properties of the polymer.Further,the EG(5%)can provide the graphitization degree of residual char which is beneficial to building a more protective barrier.This designation of CPCM can exhibit leakage-proof,high thermal conductivity(increasing 400%-500%)and prominent flammable retardant performance.Especially at 3C discharge rate,the maximum temperature is controlled below 54.2℃and the temperature difference is maintained within 2.2℃in the battery module,which presents a superior thermal management effect.This work suggests an efficient and feasible approach toward exploiting a multifunctional phase change material for thermal management systems for electric vehicles and energy storage fields.

Fly Ash/Paraffin Composite Phase Change Material Used to Treat Thermal and Mechanical Properties of Expansive Soil in Cold Regions

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.

Role of Composite Phase Change Material on the Thermal Performance of a Latent Heat Storage System: Experimental Investigation

Paraffin wax is a perfect phase change material(PCM)that can be used in latent heat storage units(LHSUs).The utilization of such LHSU is restricted by the poor conductivity of PCM.In the present work,a metal foam made of aluminium with PCM was used to produce a composite PCM as a thermal conductivity technique in PCM⁃LHSU and water was used as heat transfer fluid(HTF).An experimental investigation was carried out to evaluate the heat transfer characteristics of LHSU using pure PCM and composite PCM.The study included time⁃dependent visualization of the PCM during the melting and solidification processes.Besides,a thermocouple network was placed inside the heat storage to record the temperature profile during each process.Results showed that better performance could be obtained using composite PCM⁃LHSU for both melting and solidification processes.The melting time of composite PCM⁃LHSU was about 83%faster than that of a simple PCM⁃LHSU,and the percentage decreasing in the solidification time was about 85%due to the provision of metal foam.

Preparation of Composite Phase Change Material Based on Sol-Gel Method and Its Temperature-Adjustable Textile

In this study,the sol-gel method was introduced to prepare the composite phase change material (CPCM). The CPCM was added to fabric with coating techniques and the thermal activity of modified fabric was studied. In addition,the thermal property and the microstructure of CPCM were also discussed in detail by means of polarization microscope and differential scanning calorimeter,respectively. According to the analysis of main influencial factors of the property of CPCM,the optimal preparing technique was determined. It was proved that CPCM could exhibit a good thermal property while phase transformation process took place,and a better appearance of the fabric modified with CPCM could be obtained due to the fact that in a warm circumstance,the liquid-state phase change material could be firmly enwrapped and embedded in the three-dimensional network all the time during the phase transformation. Besides,the fabric treated with CPCM had a high phase-transition enthalpy and an appropriate phase-transition temperature. As a result,a desirable temperature-adjustable function appeared.

Preparation and Characterization of CA-MA Eutectic/Silicon Dioxide Nanoscale Composite Phase Change Material from Water Glass via Sol-Gel Method

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.

Numerical Investigation of the Thermal Behavior of a System with a Partition Wall Incorporating a Phase Change Material

The work deals with the thermal behavior of a conventional partition wall incorporating a phase change material(PCM).The wall separates two environments with different thermal properties.The first one is conditioned,while the adjacent space is characterized by a temperature that changes sinusoidally in time.The effect of the PCM is assessed through a comparative analysis of the cases with and without PCM.The performances are evaluated in terms of dimensionless energy stored within the wall,comfort temperature and variations of these quantities as a function of the amount of PCM and its emplacement.

Preparation and Characterization of High-Temperature Non-Flowing Diurea/Paraffin/Oil Composites as Form-Stable Phase Change Materials

A series of form-stable phase change materials （FSPCMs） comprising paraffin as the latent heat storage material, diurea as the supporting material and base oil as the performance improvement agent were prepared. The diurea was synthesized in the system of paraffin/oil directly. A series of characterization was carried out for a deep understand- ing of shape stability and material properties of diurea-FSPCMs. The results showed that paraffin and base oil were packaged in the three-dimensional supra-molecular structures network which was formed by diurea. The dropping point of the prepared FSPCMs could reach 256 ℃ and the oil separation rate was as low as 1.19% at 100 ℃ for 30 h. The results of thermal properties tests showed that the prepared FSPCMs exhibited excellent thermal stability and the FSPCMs remained solid-like state in the temperature range from 25 to 200 ℃. This study proposes a novel method to prepare high-temperature non-flowing FSPCMs composites and methods to detect the thermal stability and shape stability of FSPCMs, which is helpful in understanding the shape stability mechanism and broadening the potential application of FSPCMs.

Experimental Approaches to Improve Thermal Stability of Organic Phase Change Properties

This study investigates the thermal behavior of Polyolefin containing Paraffin and Nano Hydrated aluminum silicate Al2Si2O5 (OH) 4 (Kaolin) particles to enhance store energy at ambient temperature. The hybrid Nano composite is based on polyolefin PE as a matrix, whereby paraffin wax and Kaolin were hot blended at varying concentrations. In addition Carbon Nanotube (CNTs) was added in different relative low concentrations to improve the thermal transition among the polymer matrix, since polymer domains are considered as isolator. The composite was prepared by melt mixing using a Brabender Plasrograph and a Two Role Mill. Thermal properties of the composite were determined using DSC and Melt flow Index. Because TES materials are subjected to melting and freezing during life time, multiple extrusion tests to simulate the degradation process of the composite were carried out. FTIR was applied to determine the degradation effect and investigate microstructure changes of the composite. The results obtained demonstrate that the blend shows a tendency to be thermally active at low temperatures. DSC tests evidenced a decrease in melt tempera-ture as a result of increasing Kaolin content and some changes in the latent heat of the compound.

Preparation and Characterization of KNO3/Diatomite Shape-Stabilized Composite Phase Change Material for High Temperature Thermal Energy Storage

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.

High density polyethylene (HDPE)--Graphite composite manufactured by extrusion:A novel way to fabricate phase change materials for thermal energy storage

Thermal energy storage (TES)has the potential to facilitate the deployment of renewable energy through addressing the demand-supply mismatch,ultimately leading to the decarbonisation of heat supply. Among the TES technologies,latent heat based TES with composite phase change materials (PCMs)has shown great potential,which has attracted significant attention in recent years.However,large scale and reliable manufacturing methods for composite PCMs are still largely lacking.Here,we present a study aimed to develop,for the first time,an extrusion process capable of fabricating high density polyethylene based graphite PCM composites at a high throughput and with enhanced thermal properties.The PCM composites were fabricated under different extrusion process parameters and characterized for their thermo-physical properties by multiple techniques including differential scanning calorimetry,thermal gravitational analyzer,and Fourier transform infrared spectroscopy.The results show that the extrusion process has the potential to fabricate PCM composite bars in a continuous fashion with a manufacturing throughput higher than traditional method;the fabricated PCM composites show enhanced properties (e.g.up to +70% increase in thermal diffusivity);and there is a clear link between extrusion process parameters and PCMs properties.Microstructural analyses show a more homogeneous structure with a lower extrusion speed;whereas a high extrusion speed gives a more microscopically heterogeneous structure with visible graphite agglomerates distributed relatively homogeneous macroscopically;and a higher graphite content gives a larger agglomerate size.The results of this work suggest that the elucidation of composition-process-property relationships is crucial:for a given formulation (composition), only through fine tuning of high throughput manufacturing process can make it possible to achieve the desired performance of the PCM composites.

Preparation and Thermal Properties of a Novel Modified Ammonium Alum/Expanded Graphite Composite Phase Change Material

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.

Processing Compressed Expanded Natural Graphite for Phase Change Material Composites

Phase change materials(PCMs)are used in various thermal energy storage applications but are limited by their low thermal conductivity.One method to increase conductivity involves impregnating organic PCMs into highly porous conductive matrix materials.Of these materials,compressed expanded natural graphite(CENG)matrices have received the most attention.Despite this attention,the effect that CENG processing has on PCM saturation and overall matrix thermal conductivity has not been fully investigated.Therefore,the effect of the heat treatment process used to expand intercalated graphite flakes is evaluated here.Higher heat treatment temperatures yielded higher saturation rates and overall saturation at similar matrix porosities.For example,increasing temperature from 300℃to 700℃resulted in approximately 60%-70%increase in pore saturation after 100 minutes of soaking.The exposure time to heat treatment had less of an effect on PCM saturation.The exposure time had negligible effect above 30 min and above 500℃heating temperatures.However,because the expanded graphite was found to oxidize around 700℃,the use of longer exposure time in manufacturing applications can be beneficial if a shortened impregnation time is needed.Heat treatment conditions did not impact thermal conductivity.The composite latent heat of fusion was also reduced approximately proportionally to the PCM mass fraction.A local maximum in axial thermal conductivity was observed at around 83%porosity,which is similar to previous studies.The observed conductivity at this maximum was a factor of 81 times greater than the conductivity of the PCM.

Thermal Analysis of Metal Foam Matrix Composite Phase Change Material

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.

Efficient Preconstruction of Three‑Dimensional Graphene Networks for Thermally Conductive Polymer Composites

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.

Carbonate-salt-based composite materials for medium- and high-temperature thermal energy storage

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.

Preparation and characterization of capric-palmitic-stearic acid ternary eutectic mixture/expanded vermiculite composites as form-stabilized thermal energy storage materials

In this study, a composite of form-stable phase change materials （FSPCMs） were prepared by the incorporation of a eutectic mixture of capric-palmitic-stearic acid （CA-PA-SA） into expanded vermiculite （EV） via vacuum impregnation. In the composites, CA-PA-SA was utilized as a thermal energy storage material, and EV served as the supporting material. X-ray diffraction and Fourier transform infrared spectroscopy results demonstrated that CA-PA-SA and EV in the composites only undergo physical combination, not a chemical reaction. Scanning electron microscopy images indicated that CA-PA-SA is sufficiently absorbed in the expanded vermiculite porous network. According to differential scanning calorimetry results, the 70 wt% CA-PA-SA/EV sample melts at 19.3 ℃ with a latent heat of 117.6J/g and solidifies at 17.1 ℃ with a latent heat of 118.3J/g. Thermal cycling measurements indicated that FSPCMs exhibit adequate stability even after being subjected to 200 melting-freezing cycles. Furthermore, the thermal conductivity of the composites increased by approximately 49.58% with the addition of 5 wt% of Cu powder. Hence, CA-PA-SA/EV FSPCMs are effective latent heat thermal energy storage building materials.

石蜡/碱改性硅藻土/膨胀石墨复合相变储热材料的制备及性能

通过碱处理,优化了硅藻土(DIA)的孔隙结构,提高了孔隙率,增加了石蜡(paraffin)负载量。通过直接浸渍法制备了新型性状稳定的石蜡/碱改性DIA/膨胀石墨(EG-alDIAP)复合材料,并研究了其结构与性能的关系。结果表明,复合相变材料的石蜡负载量从47.4%提高到了61.1%,进而提高了复合材料的储热性能;向改性DIA中添加膨胀石墨(EG)提高了复合材料的传热能力,添加质量分数10%EG时导热系数提高了113%(从0.276 W·m^(-1)·K^(-1)提高到了0.589 W·m^(-1)·K^(-1))。随着EG含量的升高,复合相变材料的相变潜热有所增加,但化学相容性、稳定性等无明显变化。含10%EG的石蜡/碱改性DIA复合材料具有可靠的储能性能、良好的温度调节性能和蓄放热能力。

棕榈酸定形复合相变材料研究进展

棕榈酸因存在热导率低和物态相变时易泄漏的缺点,限制了其在诸多领域的发展和应用。棕榈酸定形复合相变材料以支撑材料为基体,将棕榈酸分散在基体材料中,不仅有效解决棕榈酸的泄漏问题,而且基体材料的加入还能提高复合相变材料的热导率。综述了基于不同基体材料的棕榈酸定形复合相变材料的研究进展,指出了棕榈酸定形复合相变材料的不足之处,并展望了其未来研究方向。