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。     

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。     

Preparation and thermal properties of palmitic acid/expanded graphite/carbon fiber composite phase change materials for thermal energy storage

Using palmitic acid (PA), expanded graphite (EG), and carbon fiber (CF) as raw materials, PA/EG/CF composite phase change materials (CPCMs) with diverse CF contents were invented by melt blending approach. The effects of different ratios on thermal properties were studied by experimental characterization and testing. Scanning electron microscopy images displayed that PA was adsorbed in the pores of the EG surface, while CF was disorderly but uniformly embedded in the interior and surface of pores. The chemical stability and thermal decomposition stability of CPCM at low temperature were proved by Fourier transform infrared spectrometer and thermogravimetric analyzer results, respectively. According to the law of heat storage/release time and latent heat variation, the optimal ratio scheme was determined, and its heat storage/release time was 65% and 59% lower than pure PA, respectively. The form-stable materials were prepared by compression forming method, and thermal cycling experiment results demonstrated that the higher the content of CF, the stronger the inhibition of mass loss. Based on the experimental results, the PA/EG/CF CPCM has the advantages of stable phase transition, strong stability, and fast heat storage and release rate, so it has a marvelous application prospect in the field of low-temperature heat storage engineering.

     

Improvement in thermodynamic characteristics of sodium acetate trihydrate composite phase change material with expanded graphite

In this study, three different volume expansion ratios of expanded graphite (EG) are prepared and investigated to enhance the heat transfer efficiency of the sodium acetate trihydrate (SAT) composites. A series of SAT composite phase change materials (CPCMs) with EG were prepared. The influence of volume expansion ratio and mass fraction of EG on thermodynamic characteristics of SAT CPCMs was examined, including thermal conductivity, phase change temperature, enthalpy, latent heat storage and release time, and the degree of supercooling. Results showed that SAT CPCMs can be absorbed adequately by EG, and EG could enhance the heat transfer efficiency effectively. But it also brought some problems with the addition of all the three volume expansion ratios of EG, such as the poor enthalpy and serious supercooling. Particularly, the situation gets worse with the increase in mass and expansion ratio of EG. Therefore, it is better to choose the EG with proper expansion ratio or reduce the proportion of the EG which possesses higher expansion ratio. Besides, thermal cycling test and thermogravimetric analysis revealed that the SAT CPCMs with 3 mass% EG showed a good thermal stability.

     

Preparation and thermal properties of fatty acids/CNTs composite as shape-stabilized phase change materials

A series of fatty acids/carbon nanotubes (CNTs) composite shape-stabilized PCMs were prepared through infiltration method by using the eutectic mixture of capric acid, lauric acid, and palmitic acid as phase change materials, multi-walled CNTs as a supporting material. Nitrogen adsorption–desorption curves and SEM images of composite shape-stabilized PCMs indicate that the eutectic mixture was effectively absorbed into the porous structure of the CNTs. DSC thermograms show that the composite fatty acids/CNTs possess good phase change behavior. And the latent heat of the sample absorbed with 80 wt% fatty acids can achieve 101.6 J g^?1 in the melting process and its phase change temperatures and latent heat almost remain unchanged in 30 times of thermal cycling. Moreover, the thermal conductivity of the composite materials are significantly improved (up to 0.6661 W m^?1 k^?1) due to the addition of the highly thermal conductive CNTs.     

Influence of layered zinc hydroxide nitrate on thermal properties of paraffin/intumescent flame retardant as a phase change material

The thermal properties of paraffin as phase change material (PCM), combined with layered zinc hydroxide nitrate (LZHN) and intumescent flame retardant (IFR), have been studied by thermogravimetric analysis (TG), TG-Fourier transform infrared spectrometry (TG-FTIR), cone calorimeter (CONE),and differential scanning calorimetry (DSC). The TG results indicated that the thermal stabilities of the paraffin and paraffin/IFR composites could be improved when dodecyl sodium sulfate-modified LZHN (ds-LZHN) was incorporated. The TG-FTIR results indicated that ds-LZHN could reduce the release of combustible gases for paraffin and paraffin/IFR. The CONE results showed that the flame-retardant efficiency of IFR could be improved in the paraffin/IFR system owing to ds-LZHN. DSC results presented that the phase change temperatures and latent heats of the composites were determined by the dispersed paraffin with their mass percentage.     

Preparation and thermal properties of microencapsulated paraffin with polyurea/acrylic resin hybrid shells as phase change energy storage materials

Journal of Thermal Analysis and Calorimetry - Microencapsulated paraffin with polyurea/acrylic resin hybrid shells as phase change energy storage materials was obtained in situ by combining...     

Thermal energy storage properties and thermal reliability of PEG/bone char composite as a form-stable phase change material

Journal of Thermal Analysis and Calorimetry - Bone char (BC) is a promising porous material that can be used for preparing a form-stable composite phase change material (PCM). In this paper,...     

The investigation of thermal conductivity and energy storage properties of graphite/paraffin composites

Phase change materials (PCM) have been extensively scrutinized for their widely application in thermal energy storage (TES). Paraffin was considered to be one of the most prospective PCMs with perfect properties. However, lower thermal conductivity hinders the further application. In this letter, we experimentally investigate the thermal conductivity and energy storage of composites consisting of paraffin and micron-size graphite flakes (MSGFs). The results strongly suggested that the thermal conductivity enhances enormously with increasing the mass fraction of the MSGFs. The formation of heat flow network is the key factor for high thermal conductivity in this case. Meanwhile, compared to that of the thermal conductivity, the latent heat capacity, the melting temperature, and the freezing temperature of the composites present negligible change with increasing the concentration of the MSGFs. The paraffin-based composites have great potential for energy storage application with optimal fraction of the MSGFs.     

Capric acid/intercalated diatomite as form-stable composite phase change material for thermal energy storage

Journal of Thermal Analysis and Calorimetry - Leakage issue and low thermal conductivity largely restrict feasibility of fatty acid in real application of thermal energy storage (TES). In this...     

Preparation and thermal properties of palmitic acid/polyaniline/copper nanowires form-stable phase change materials

Form-stable phase change materials (PCMs) with high thermal conductivity are essential for thermal energy storage systems, which in turn are indispensible in solar thermal energy applications and efficient use of energy. In this paper, a new palmitic acid (PA)/polyaniline (PANI) form-stable PCMs were prepared by surface polymerization. The highest loading of PA in the form-stable PCMs was 80 mass% with the phase change enthalpy (ΔH _melting) of 175 J g^?1. Copper nanowires (Cu NWs) were introduced to the form-stable PCM by mixing the Cu NWs with PA and ethanol prior to the emulsifying of PA in surfactant solution. The Cu NWs would remain intact in case the ethanol was eliminated before the PA/Cu NWs mixture was mixed with surfactant solution. Otherwise, the Cu NWs would be partially oxidized under the attack of ethanol and ammonium persulfate. The ΔH _melting of the form-stable PCMs containing Cu NWs decreased linearly with the increasing of Cu NWs loading. The ΔH _melting of the form-stable PCMs doped with 11.2 mass% Cu NWs was 149 J g^?1. The thermal conductivity of the form-stable PCMs could be effectively improved by Cu NWs. By adding 11.2 mass% Cu NWs, the thermal conductivity of the form-stable PCM could attain 0.455 W m^?1 K^?1.     

Thermodynamic and thermal energy storage properties of a new medium-temperature phase change material

Journal of Thermal Analysis and Calorimetry - Phase change materials (PCMs) that can store the heat energy obtained from intermittent solar irradiation are very important for solar energy...     

Preparation and characterization of a novel form-stable phase change material for thermal energy storage

Journal of Thermal Analysis and Calorimetry - A series of novel polymeric form-stable phase change materials (FSPCMs) composed of poly(trimethylolpropane trimethacrylate-stearyl methacrylate) (PTS)...     

Preparation and characterization of anode materials using expanded graphite/pitch composite for high-power Li-ion secondary batteries

Expanded graphite was prepared by the intercalation of natural graphite using ammonium peroxodisulfate as an oxidizing agent and a high purity of sulfuric acid as an intercalate. The amounts of oxidizing agent and intercalate were changed to determine the preparation conditions of expanded graphite as the anode material for high-power Li-ion batteries. The expanded graphite was tested as the anode material and further composited with the different amounts of petroleum pitch to improve the electrochemical properties. Although the expanded graphite anode showed the improved electrochemical properties such as initial reversible capacities of around 400 mAh/g and a charge capacity at 5 C-rate of 83 mAh/g as compared with those for the natural graphite anode of 378 and 19.4 mAh/g, respectively, it still had some weak points for a high-power anode material such as low initial efficiency and potential plateaus with the stage characteristic. The anode composites with high performance could be obtained by compositing the expanded graphite and the petroleum pitch at the ratio of 1:2, showing an improved initial efficiency of 78 % and decreased potential plateaus with 389 mAh/g of the initial reversible capacity.     

Synthesis of a paraffin phase change material microencapsulated in a siloxane polymer

The coemulsification method suitable for the formulation of microcapsules of n-eicosane coated with a polysiloxane is developed. This method allows to synthesize core–shell microcapsules of paraffin which have the shape of spheres or distorted spheres and are designed for the use as phase change materials. The microcapsules are formed in aqueous phase by the precipitation of n-eicosane together with modified polyhydromethylsiloxane from a common solvent which is miscible with aqueous media. The polysiloxane is modified by the attachment of silylvinyl and alkoxy functions before coemulsification with the paraffin. It also contains the Pt(0) Karstedt catalyst. The microcapsules formed by coemulsification are stabilized by the in situ cross-linking of the polysiloxane shell. The shell is additionally modified by the in situ generation of silanol groups which provide colloidal stabilization of microspheres in aqueous phase. Microcapsules were studied by DSC, SEM, optical polarized microscope, and by thermooptical analysis (TOA).     

ASA/SEBS/paraffin composites as phase change material for potential cooling and heating applications in building

Phase change material (PCM) is able to melt and crystalize with a high heat of phase change at constant temperature, which provides new and green cooling and heating strategies for buildings. In this work, PCMs for buildings composed of acrylonitrile‐styrene‐acrylate copolymer (ASA), polystyrene‐b‐poly(ethylene/butylene)‐b‐polystyrene triblock copolymer (SEBS) and paraffin were fabricated by melt blending. The results of the accelerated leakage test indicated an excellent ability of PCMs to keep paraffin from leakage. Thermal properties suggested that the phase change enthalpy of PCMs increased with the increasing content of paraffin and their phase change temperature was close to the comfortable sensible temperature of human body, which made it quite suitable for building cooling and heating. Besides, PCMs presented excellent stability and reusability after several thermal cycling tests. The temperature test conducted with self‐designed cylindrical devices gave a more sufficient and direct demonstration of the cooling and heating effect. Remarkably, excellent cooling and heating performance (both as high as 15°C) of the composites could be obtained with the addition of paraffin. And the time span of the cooling and heating process was as long as 5 and 7.5 hours, respectively. Owing to its excellent cooling and heating capabilities, the ASA/SEBS/paraffin composites are of great potential to be applied in building temperature control.     

Graphene oxide improved thermal and mechanical properties of electrospun methyl stearate/polyacrylonitrile form-stable phase change composite nanofibers

In the present work, a novel PAN-based form-stable composite phase change materials with the methyl stearate (MES) encapsulated in the supporting matrices of polyacrylonitrile (PAN) nanofibers were fabricated through electrospunning for the storage and retrieval of thermal energy. Influences of graphene oxide (GO) addition on the chemical properties, structural morphologies, mechanical properties, thermal energy storage properties, thermal stability, and thermal energy storage/retrieval rates of electrospun MES/PAN/GO phase change composite nanofibers were systematically investigated by FT-IR, FE-SEM, tensile testing, DSC, TG, and measurement of melting/freezing times, respectively. The results revealed that the incorporation of GO effectively enhanced the mechanical properties, thermal stability, as well as heat storage and release rates of the phase change composite nanofibers. The averaged tensile strength of electrospun MES/PAN/GO phase change composite nanofibers increased significantly by 573 % with 10 mass% loading of GO, while elongation at break had a maximum 107 % increment when adding 3 mass% of GO. The DSC results indicated that the electrospun PAN-based phase change composite nanofibers with various GO loadings had suitable phase transition temperatures with the latent heat ranging from about 92 to 109 kJ kg^?1 and exhibited good thermal reliability in terms of DSC measurements during 50 melting-freezing cycles. Moreover, the melting and freezing time were significantly decreased about 44 and 43 % for the MES/PAN/GO5, as well as 59 and 64 % for the MES/PAN/GO10 after introducing the GO into the composite nanofibers systems.