相变储能材料研究进展

综述了固-固相变储能材料（s-S PCMs：sofid-solid phase change materials）、固-液相变储能材料（s-1 PCMs：solid—liquid phase change materials）的主要优缺点，并主要介绍了以下2种封装方式：（1）PCMs与基体材料复合制成定型PCMs，包括：与有机高分子材料机械共混、用无机多孔材料封装；（2）PCMs微囊化。此外，还分析了PCMs的主要应用领域及PCMs的主要研究方向。     

Thermal Conductivity and Viscosity of Nanofluids Having Nanoencapsulated Phase Change Material

In this study, the thermal conductivity and viscosity of nanofluids, composed of a base fluid and nanoencapsulated phase change material (NEPCM), were investigated experimentally. The NEPCM was prepared by the encapsulation of n-nonadecane as phase change material with diethylenetriamine and toluene-2,4-diisocyanate using interfacial polymerization method. The NEPCM was characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC) analyses. In the preparation of the nanofluids containing NEPCM, two different base fluids, water and ethylene glycol (EG), were used. The concentration of NEPCM and the working temperature were selected as the main parameters. It was found that the viscosity of the nanofluids decreases with increasing temperature and increases with increasing solid concentration. The viscosity was also expressed as a function of the solid concentration and temperature. The thermal conductivity of the nanofluids was found to increase with increasing temperature. Thermal conductivity exhibited an increasing tendency with increasing solid concentration, but the changes in thermal conductivity according to base fluid are in the range of uncertainty of the measurement for both nanofluids with a solid volumetric fraction lower than 1.68%.     

Improving the performance of air conditioning systems by using phase change materials: A review

This paper reviews the application of phase change materials (PCMs) for improving the performance of air conditioning systems. The different methods of integrating PCMs into air conditioning systems are presented. Moreover, the effects of PCM geometry, flow, and heat transfer characteristics on the performance of air conditioning systems and the potential use of PCMs in increasing the energy savings and coefficient of performance of air conditioning systems are also discussed. Recent studies on the thermodynamic (energy and exergy), economic, and environmental benefits of integrating PCMs into air conditioning systems are reviewed. Several methods for the preparation and optimal selection of PCMs are proposed to improve the performance of air conditioning systems, and then the challenges relating to PCM properties, optimal thickness, and PCM containers are highlighted. The economic aspects, humidity effect, life cycle assessment, and use of solid‐solid PCMs are cited as potentially important topics for future research.     

Rapid visualization of the potential residential cost savings from energy storage under time-of-use electric rates

Buildings feature a prominent role in electric grid loading, as they use about 75% of the total electricity generated in the United States and are main drivers of electric peak demand in the summer due to electrically driven air conditioning systems. Energy storage is a key technology that can increase energy cost savings, and add flexibility to the grid. However, cost is an important factor to consider. This study proposes a rapid approach that allows for visualization of potential cost savings by introducing energy storage as a peak load control for residential buildings in California. A combination of EnergyPlus load data generation, Matlab post-processing, and Google Fusion Tables data presentation analyses the potential cost savings when energy storage is implemented and TOU rates are applied. The study presents potential annual cost savings of $420 per home with storage capacities of 24?kWh.     

Effect of graphene and its derivatives on thermo-mechanical properties of phase change materials and its applications: a comprehensive review

Phase change materials (PCMs) play a leading role in overcoming the growing need of advanced thermal management for the storage and release of thermal energy which is to be used for different solar applications. However, the effectiveness of PCMs is greatly affected by their poor thermal conductivity. Therefore, in the present review the progress made in deploying the graphene (Gr) in PCMs in the last decade for providing the solution to the aforementioned inadequacy is presented and discussed in detail. Gr and its derivatives ((Gr oxide (GO), Gr aerogel (GA) and Gr nanoplatelets (GNPs)) based PCMs can improve the thermal conductivity and shape stability, which may be attributed to the extra ordinary thermo-physical properties of Gr. Moreover, it is expected from this review that the advantages and disadvantages of using Gr nanoparticles provide a deep insight and help the researchers in finding out the exact basic properties and finally the applications of Gr can be enhanced.In this work, Gr and its derivatives based PCMs was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction spectroscopy (XRD), and scanning electron microscopy (SEM) by which crystal structure was known, phase was identified along with the knowledge of surface structure respectively. The increase in the mass fraction (%) of the filler (Gr and its derivatives) led to even better thermo-physical properties and thermal stability. The thermal characterization was also done by differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA) and thermal conductivity tests. The enthalpy of freezing and melting showed that Gr and its derivatives based PCMs had a very high energy storage capability as reflected in its various applications.     

相变材料在建筑节能中的研究及应用

相变材料是一类高效的储能物质,通过与传统的建筑材料复合可提升建筑材料功能、降低建筑能耗和调整建筑室内环境舒适度,近年来发展迅速、受到愈来愈广泛的重视,并已在建筑节能中得到了多种应用。叙述了相变材料与建筑材料复合的制备方法、研究和应用进展,对现阶段相变材料在建筑节能中的研究及其存在的问题进行了总结与分析,并指出了其进一步的研究方向。     

Developing microencapsulated 12‐hydroxystearic acid (HSA) for phase change material use

Phase change materials (PCM) have an increasingly more important role as a thermal energy storage (TES) media. However, leakage problem of PCM causes limitation during their integration in TES systems. Therefore, the encapsulation of PCMs is attracting research interest to extend usage of PCMs in real TES applications in recent years. In this study, hydroxystearic acid (HSA) was encapsulated with polymethyl methacrylate (PMMA) and different PMMA comonomer shells via emulsion polymerization method for the first time in literature. HSA with high melting temperature range (74–78°C) can widen the scope of using PCMs, and the encapsulated form can make it more versatile. The chemical structures, morphologies, and thermophysical properties of capsules were determined by FT‐IR, SEM, DSC, TGA, and thermal infrared camera. Among the produced HSA capsule candidates, PMMA‐HEMA is the most promising with latent heat of 48.5 J/g with melting range of 47 to 85°C. SEM analysis indicated that the capsules have spherical shape with compact surface at nano‐micro (100–440 nm) size range; however, some capsules exhibited agglomeration.     

Lipid‐derived monoamide as phase change energy storage materials

One of the major shortcomings of current organic phase change materials (PCMs) is their relatively low melting points, typically below 80°C, which limits their integration into thermal energy storage (TES) systems. The present work was aimed at developing lipid‐derived PCMs with increased melting points which would be suitable for TES applications requiring higher melting points without compromising other key properties such as enthalpy. The introduction of an amide group into the structure of linear saturated fatty acids was used as a means to increase intermolecular interactions and therefore crystallization and melting points. A series of six linear monoamides with differing chain length and symmetry about the amide group were investigated for thermal stability, thermal transition, flow behavior, and crystal structure to establish the structure‐property relationships relevant to TES. The presence of the highly polar amide group in the aliphatic fatty acid–derived molecules resulted in notable improvement in performance compared with the analogous monofunctional molecules: Increases in melting points (79°C‐96°C) and high enthalpies of fusion (155‐201 J/g) were recorded. Fundamental relationships between structure, processing, and macroscopic physicochemical properties, never before elucidated, were revealed in the study. The study revealed a step‐like variation of macroscopic properties: a surprising outcome of the competition between intermolecular attractions, symmetry effects, and mass transfer limitations. The predictive structure‐function relationships established in this work will allow the straightforward engineering of monoamide architectures that can extend the range of organic PCMs and deliver thermal properties desirable for TES applications.     

石墨纳米片尺寸对复合相变材料储热特性的影响

为了探究二维纳米材料的尺寸对复合相变材料储热特性的影响, 将膨胀石墨分别超声振荡10、30和90 min, 得到3种不同尺寸的石墨纳米片:GNS-10、GNS-30、GNS-90, 添加到十六醇中制备出纳米复合相变材料。利用SEM、XRD和Hot Disk等方法对其微观结构和性能进行表征和测试的同时, 对比研究了Maxwell、Bruggeman及Nielsen模型对热导率的计算结果。结果显示, 石墨纳米片尺寸越大, 对复合相变材料热导率的提升幅度越大。当GNS-10添加量为10%(质量分数)时, 热导率提升了约517%。Nielsen模型在形状因子A取100~180时可以较好地预测实验值。与大幅增长的热导率相比, 复合相变材料相变温度、相变焓的变化可忽略不计。此外, 石墨纳米片的加入明显缩短了储热材料的凝固速率, 有效热导率的提高是产生这种效果的主要原因。     

Preparation and textile application of poly(methyl methacrylate-co-methacrylic acid)/n-octadecane and n-eicosane microcapsules

In this study, a series of microencapsulated phase change materials with poly(methyl methacrylate-co-methacrylic acid) P(MMA-co-MAA) shell and n-octadecane or n-eicosane core were synthesized by emulsion polymerization method. The aim was to produce microencapsulated n-alkanes having functional groups on their outer surface, so that functional groups would help increasing physical interactions between microcapsules and fiber surface. Therefore, methyl methacrylate (MMA), ethylene glycoldimethacrylate (EGDM), and methacrylic acid (MAA) were copolymerized in oil phase of n-alkane. FT-IR results proved the successful synthesis of P(MMA-co-MAA) shell of microencapsulated n-alkanes. The DSC results indicated that the microencapsulated n-alkanes have considerable latent heat storage capacity in a range of 58–145 J/g. The average melting and freezing temperatures of the microencapsulated n-alkanes were measured as 27 and 26 °C for n-octadecane and 36 and 35 °C for n-eicosane, respectively. The microcapsules were of spherical and compact shape with particle sizes between 15 and 32 μm. The microcapsules on the cotton fabric applied by pad-dry-cure method were found highly durable and they showed sufficient stability upon several washings and rub fastness. Thermo-regulating properties of the fabrics were declared as a result of thermal history measurements.