Characterization and Thermal Conductivity of Modified Graphite/Fatty Acid Eutectic/PMMA Form-Stable Phase Change Material

We prepared and characterized a form-stable composite phase change material （PCM） with higher thermal conductivity. Capric acid（CA）-myristic acid（MA） eutectic as core, poly-methyl methacrylate （PMMA） as supportive matrix and modified graphite （MG） powders serving as the thermal conductance improver were blended by bulk- polymerization method. The composite PCMs with different MG mass fraction （2%, 5%, 7%, 10% and 15%） were characterized by FT-IR, SEM, DSC technique and mechanical tests. Thermal conductivities of the composites were measured by transient hot-wire method. The results indicate that MG powders have been successfully inserted into the CA-MA/PMMA matrix without any chemical reaction with each other. The MG/CA-MA/PMMA composites maintain good thermal storage performance while the thermal conductivity has been enhanced significantly. The composite PCM added with 15 wt% MG powders increases approximately as 195.9% in thermal conductivity. Moreover, the thermal conductivity improvement of the composite PCMs is also verified by the melting-freezing experiment, which is profitable for the heat transfer efficiency in latent heat thermal energy storage system.

Microstructure and Characterization of Capric-stearic Acid/Modified Expanded Vermiculite Thermal Storage Composites

In order to improve the thermal storage capacity of expanded vermiculite（EV） based formstable composite PCM（FS-PCM） via organic modification of EV, first, EV was modified with a sodium stearate（Na St） as surface modifier, and organic EV（OEV） with hydrophobicity and higher adsorption capacity for fatty acid was obtained. A novel capric-stearic acid eutectic（CA-SA）/OEV FS-PCM with high thermal storage capacity was then developed. OEV and CA-SA/OEV were characterized by scanning electron microscopy（SEM）, X-ray diffraction（XRD）, Fourier transform infrared spectroscopy（FTIR）, differential scanning calorimetry（DSC）, thermal gravimetry（TG）, and thermal cycling test. Results showed that OEV has obvious hydrophobicity and a higher adsorption capacity for fatty acid. Its adsorption ratio has increased by 48.71% compared with that of EV. CA-SA/OEV possesses high thermal storage density（112.52 J/g）, suitable melting temperature（20.49 ℃）, good chemical compatibility, excellent thermal stability and reliability, indicating great application potential for building energy efficiency. Moreover, organic modification of inorganic matrix may offer novel options for improving its adsorption capacity for organic PCMs and increasing heat storage capacity of corresponding FS-PCMs.

Structure,Characterization and Thermal Properties of the Form-Stable Paraffin/High-Density Polyethylene/Expanded Graphite/Epoxy Resin Composite PCMs for Thermal Energy Storage

The form-stable paraffin/high-density polyethylene/expanded graphite/epoxy resin composite phase change materials(CPCMs),exhibiting suitable thermal properties,including low melting temperature,high conductivity and high phase change enthalpy,was developed in this work.Herein,paraffin(PA)was utilized as a core PCM.High-density polyethylene(HDPE)was utilized for the shape stabilization and preventing the PCMs leakage.Expanded graphite(EG)was used to increase its thermal conductivity and act also in the porous supporting material.Epoxy resin(ER)was used to provide flexible encapsulated scaffold morphology and keep a highly tight network structure of the PCMs.However,the physical architecture,the chemical architecture and thermal behavior properties of specimens were investigated by using the spectroscopy and calorimetry techniques.The scanning electron microscope(SEM),X-ray diffraction(XRD)and fourier transform infrared spectrometer FTIR tests have shown good uniformity structure and good compatibility of components.In addition,the thermal conductivity tests revealed that the thermal conductivity of PA,initially 0.31 W/(m·K)improved up to 1.9 times by adding the 6 wt%mass fraction of EG in composite PCMs.Furthermore,the differential scanning calorimeter(DSC)measurements indicated that PA melting enthalpy,initially 231 J/g decreased up to 125 J/g with the increase of the amount of HDPE which was due to the limitation caused by the atomic network constructed by the base material.The thermogravimetric analyzer(TGA)and leakage-proof revealed the enhancement of the degradation of PA with the raise of amount of the HDPE into the CPCMs.Therefore,the proposed form-stable CPCMs are a great candidate for the thermal regulation and thermal energy storage employment.

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.

Synthesis and Characterization of Disodium Hydrogen Phosphate Dodecahydrate-Lauric-Palmitic Acid Used for Indoor Energy Storage Floor Units

Organic and inorganic phase change materials(PCMs) are considered potential materials for thermal energy storage(TES) with different phase change characteristics. In this study, a novel organic-inorganic composite phase change material(PCM) called disodium hydrogen phosphate dodecahydrate-lauric-palmitic acid(D-LA-PACM) was prepared. Expanded graphite(EG) was selected as the support material, and the novel organic-inorganic form-stable PCM called D-LA-PAPCM/EG was prepared using the vacuum adsorption method. Differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray diffraction, leakage testing, melting and solidification cycle testing, thermal conductivity testing, scanning electron microscopy observation of the micromorphology, and other characterization methods were used to study the microstructure and morphology, thermal physical parameters, thermal conductivity, stability of the PCMs, and the comprehensive material properties of D-LA-PAPCM under the composite action of EG. Results indicated that the melting and freezing temperatures and latent heats of D-LA-PAPCM/EG were measured to be 31.6℃ and 34.3℃ and 142.9 and 142.8 J/g, respectively. Although some of the lauric-palmitic acid(LA-PA) and disodium hydrogen phosphate dodecahydrate(DHPD) separated in the multiple porous structures of EG after 1000 cycles, they could still absorb and release latent heats independently, with D-LA-PAPCM/EG still exhibiting good thermal stability. The thermal conductivity of D-LA-PAPCM/EG was 1.361 W/(m·K). Therefore, the material and thermal properties of the prepared D-LA-PAPCM/EG indicate that it could be well used as a feasible material for energy-saving phase change floor units in indoor TES systems.

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.