Study on preparation and thermal properties of binary fatty acid/diatomite shape-stabilized phase change materials

The choice of fatty acids as shape-stabilized phase change materials (PCMs) will increase the feasibilities of PCMs in practical applications due to the low price of the fatty acids. Compounding different fatty acids for each other is an effective way to obtain a PCM with a suitable phase-transition temperature. In this study, a series of binary fatty acids composed by capric acid, lauric acid, palmitic acid and stearic acid for each other were prepared using the phase diagram thermal dynamics calculation method. Then these binary fatty acids are absorbed in four kinds of diatomites with different specific areas, which act as a supporting material, to prepare shape-stabilized PCMs. The prepared shape-stabilized PCMs are characterized by the Scanning electron microscope (SEM) and the differential scanning calorimetry (DSC) analysis method. The results show that there is an optimum absorption ratio between binary fatty acids and the diatomite. The latent heat of capric-lauric acid/diatomite decreases to 57% of that of capric-lauric acid, and the phase-transition temperature rises from 16.36 to 16.74 °C when the capric-lauric acid is absorbed in the diatomite. The prepared capric-lauric acid/diatomite composite PCM has proper melting temperatures and latent heat for thermal energy storage application in buildings.     

A novel polynary fatty acid/sludge ceramsite composite phase change materials and its applications in building energy conservation

The preparation and characteristics of a composite phase change material (PCM) produced by incorporating polynary fatty acid eutectic mixture into sludge ceramsite were studied. According to Schröeder–Van Laar equation, five different kinds of polynary fatty acid eutectic mixture were prepared, and one of them, suitable for regulating room temperature, was absorbed into sludge ceramsite by vacuum impregnation method. The microstructures were observed by scanning electron microscope (SEM). The thermal properties and chemical structures were analyzed by differential scanning calorimetry (DSC) and Fourier transform infrared (FT-IR) spectrometer, respectively. The durability or stability of the composite PCM was determined by heating–cooling cycles test, and the temperature regulation effect was tested by building models. The results indicated that polynary fatty acid eutectic mixture can be retained by 46 wt.% into the pores of sludge ceramsite without seepage. The melting temperature of composite PCM was 26.66 °C, and the corresponding melting enthalpy was 47.1 J/g, suitable to regulate building room temperature. The preparation of composite PCM was just a physical combination, and its chemical structures can remain stable in application process. In addition, model experiments showed that the prepared composite PCM can significantly reduce indoor temperature fluctuation, suitable for building energy conservation.     

Preparation and performances of palmitic acid/diatomite form-stable composite phase change materials

Using palmitic acid (PA) as an organic phase change material (PCM), a series of PA/diatomite composite PCMs (CPCMs) composed of PA absorbed into diatomite mesopores with different mass contents were made through direct impregnation method. Nitrogen adsorption-desorption curves indicated the porous structure of diatomite with the specific surface area and the mesopore peak at 40 m²/g and 3 to 5 nm, respectively. The form-stability measurement indicated that the maximum mass loading capacity of PA was 55 wt%. The melting temperature and fusion enthalpy of the PA/diatomite CPCM (55 wt%) were calculated from DSC at 63°C and 88 J/g, respectively. The thermal cycle test implied that the PA/diatomite CPCM with 55-wt% PA loading showed excellent thermal reliability after 1000 thermal cycles. Moreover, the composite has thermal conductivity at 0.5810 W/m·K and enhanced thermal storage/release rate. PA/diatomite CPCM (55 wt% PA) was a suitable candidate for modern building energy saving and industrial solar energy.     

High-chain fatty acid esters of myristyl alcohol with even carbon number: Novel organic phase change materials for thermal energy storage—1

High-chain fatty acid esters have not been investigated for their thermal properties as phase change materials (PCMs) in thermal energy storage. A series of high-chain fatty acid esters of myristyl alcohol (1-tetradecanol) were synthesized via esterification of lauric, myristic, palmitic, stearic and arachidic acids under vacuum and in the absence of any catalyst. The esterification reactions were studied by FT-IR spectroscopy. A differential scanning calorimeter (DSC) and a thermo-gravimetric analyzer (TGA) were intensively used to determine the thermal properties of the introduced thermal storage materials. The thermal properties were given in terms of phase change temperature, enthalpy, specific heat (C_p) and thermal decomposition temperature with related statistical data. The thermal reliability of the novel organic PCMs was investigated by thermal cycling with 1000 thermal cycles with respect to the thermal properties of the original synthesized PCMs. In addition to the synthesized esters, one commercial product was also investigated. The DSC analyses indicated that the melting points of the novel organic PCMs were between 38 and 53 °C with phase change enthalpy above 200 kJ/kg. The effect of chemical structure of the materials on thermal properties was also discussed. The results showed that these materials were favorable for low temperature heat transfer applications with superior thermal properties and reliability.     

High-chain fatty acid esters of myristyl alcohol with odd carbon number: Novel organic phase change materials for thermal energy storage—2

A series of high-chain fatty acid esters of 1-tetradecanol (myristyl alcohol) were synthesized via esterification of 1-tridecanoic, 1-pentadecanoic, 1-heptadecanoic and 1-nonadecanoic acids under vacuum and in the absence of catalyst. The esterification reactions were controlled by FT-IR spectroscopy. Differential scanning calorimeter (DSC) and thermo-gravimetric analyzer (TGA) were intensively used to determine the thermal properties of the presented novel organic phase change materials (PCM). The thermal properties were given in terms of phase change temperature, enthalpy, specific heat (C_p) and thermal decomposition temperature with related statistical calculations. The thermal reliability of the synthesized PCMs, which is an important property for utilization, was determined via measuring the change in thermal properties after 1000 thermal cycles. The DSC analyses indicated that the melting points of the novel organic PCMs were between 40 and 50 °C with phase change enthalpy above 200 kJ/kg. The results showed that these thermal storage materials were favorable for low temperature heat transfer applications with superior thermal properties and reliability among the known PCMs.     

Electrospun ultrafine composite fibers of binary fatty acid eutectics and polyethylene terephthalate as innovative form‐stable phase change materials for storage and retrieval of thermal energy

In this study, four fatty acids of lauric acid (LA), myristic acid (MA), palmitic acid (PA), and stearic acid (SA) were selected to prepare six binary fatty acid eutectics of LA‐MA, LA‐PA, LA‐SA, MA‐PA, MA‐SA, and PA‐SA; thereafter, electrospun ultrafine composite fibers with the binary fatty acid eutectics encapsulated in the supporting matrices of polyethylene terephthalate (PET) were prepared as innovative form‐stable phase change materials for storage and retrieval of thermal energy. The morphological structures and thermal energy storage properties of the ultrafine composite fibers were characterized by scanning electron microscope (SEM) and differential scanning calorimeter (DSC), respectively. The SEM results indicated that the fibers had the cylindrical morphology with diameters of 1–2 µm; some had smooth surfaces, while others had wrinkled surfaces with grooves. The DSC results indicated that the phase transition temperatures of binary fatty acid eutectics were lower than those of individual fatty acids; the enthalpy values associated with melting and crystallization for the eutectics encapsulated in the composite fibers were considerably reduced, whereas there were no appreciable changes on the phase transition temperatures. Copyright © 2012 John Wiley & Sons, Ltd.     

Morphology and thermal properties of electrospun fatty acids/polyethylene terephthalate composite fibers as novel form-stable phase change materials

The ultrafine fibers based on the composites of polyethylene terephthalate (PET) and a series of fatty acids, lauric acid (LA), myristic acid (MA), palmitic acid (PA), and stearic acid (SA), were prepared successfully via electrospinning as form-stable phase change materials (PCMs). The morphology and thermal properties of the composite fibers were studied by field emission scanning electron microscopy (FE-SEM) and differential scanning calorimetry (DSC), respectively. It was found that the average fiber diameter increased generally with the content of fatty acid (LA) in the LA/PET composite fibers. The fibers with the low mass ratio maintained cylindrical shape with smooth surface while the quality became worse when the mass ratio is too high (more than 100/100). Moreover, the latent heat of the composite fibers increased with the increase of LA content and the phase transition temperature of the fibers have no obvious variations compared with LA. In contrast, both the latent heat and phase transition temperature of the fatty acid/PET composite fibers varied with the type of the fatty acids, and could be well maintained after 100 heating-cooling thermal cycles, which demonstrated that the composite fibers had good thermal stability and reliability.     

Preparation, physical property and thermal physical property of phase change microcapsule slurry and phase change emulsion

Phase change microcapsule slurry and phase change emulsion are two novel two-phase heat transfer fluids. Compared with a conventional single-phase heat transfer fluid such as water, their apparent specific heats in the phase change temperature range are greatly increased. Due to this, the heat transfer ability and energy transport ability can be obviously improved. Therefore, they have many potentially important applications in fields such as heating, ventilating, air-conditioning, refrigeration and heat exchangers. In this paper, a phase change emulsion was prepared by mixing film synthesis, and a phase change microcapsule slurry was prepared by in situ polymerization with polystyrene, polymethyl methacrylate, polyethyl methacrylate as encapsulation material, respectively. Physical properties, such as viscosity, diameter and its distribution of microcapsule and emulsion were investigated. The relationship between the concentration of tetradecane and physical properties have been discussed in detail. Meanwhile, the thermal physical properties of these two fluids were determined by DSC. Also, the influence of tetradecane concentration on phase change temperature and phase change heat has been discussed.     

Recent progress in diatomite based composite phase change materials for thermal energy storage

硅藻土是一种含量丰富的非金属矿,具有较高的孔隙率,良好的表面结构和热物理性能,因而可作为复合储热材料的载体.本文综述了复合储热材料的种类和制备工艺,并介绍了硅藻土的结构,性能和以硅藻土为载体的复合相变储热材料的研究及应用现状.     

Preparation of capric acid/halloysite nanotube composite as form-stable phase change material for thermal energy storage

A novel form-stable composite as phase change material (PCM) for thermal energy storage was prepared by absorbing capric acid (CA) into halloysite nanotube (HNT). The composite PCM was characterized by TEM, FT-IR and DSC analysis techniques. The composite can contain capric acid as high as 60 wt% and maintain its original shape perfectly without any CA leakage after subjected to 50 melt-freeze cycles. The melting temperature and latent heat of composite (CA/HNT: 60/40 wt%) were determined as 29.34 °C and 75.52 J/g by DSC. Graphite (G) was added into the composite to improve thermal storage performance and the thermal storage and release rates were increased by 1.8 times and 1.7 times compared with the composite without graphite, respectively. Due to its high adsorption capacity of CA, high heat storage capacity, good thermal stability, low cost and simple preparation method, the composite can be considered as cost-effective latent heat storage material for practical applications such as solar energy storage, building energy conservation and agricultural greenhouse in the near future.     

Thermal properties of a modified MOF-stearic acid composite phase change materials

以ZIF-67作为金属有机框架（MOF）,通过原位沉淀法生长在膨胀石墨片上对膨胀石墨进行改性,经过煅烧后形成Co₃O₄/EG分级多孔混合结构。为了优化硬脂酸的充放热性能,将Co₃O₄/EG与硬脂酸通过熔融共混和真空吸附法复合,制备出具有优异充放热性能的SA/Co₃O₄/EG复合相变材料。表征SA/Co₃O₄/EG复合相变材料的微结构、物相、相变焓值、相变温度和充放热时间等热物理性能,分析添加物Co₃O₄/EG的微结构对硬脂酸相变储热材料微结构和热性能产生的影响。添加物Co₃O₄/EG对SA/Co₃O₄/EG复合相变材料的相变温度影响较小,相变温度与Co₃O₄/EG添加量没有依赖关系。而复合储热材料的相变潜热随Co₃O₄/EG量的增加而减少,但与理论计算相差较少。Co₃O₄/EG分级多孔结构可以阻止Co₃O₄的团聚并提供高比表面积和孔体积吸附硬脂酸,多孔隙结构Co₃O₄和高热导率膨胀石墨（EG）的协同作用可以增加硬脂酸相变储热材料的热传递,缩短充放热时间,提高充放热效率。     

Adipic acid-silica composite phase change materials for thermal energy storage:Preparation and characterization

以己二酸为相变材料,二氧化硅溶胶为基体,采用水热法制备己二酸/二氧化硅复合相变储热材料.应用X射线衍射仪(XRD),红外光谱分析(FT-IR),场发射扫描电子显微镜(FE-SEM),同步热分析仪(TG)和差示扫描量热仪(DSC)测试所制备复合材料的显微结构,相变温度和相变焓.结果表明:当反应条件为pH=5,反应温度为150 ℃,反应时间为4 h时,己二酸与二氧化硅之间是简单的物理嵌合关系,复合材料粒径较均匀,平均粒径在1~2 μm;当己二酸的质量分数为30%时,复合材料相变温度峰值为139.0 ℃,相变焓为48.82 J/g;当己二酸的质量分数为50%时,复合材料相变温度峰值为140.5 ℃,相变焓为71.89 J/g.     

Fatty acid eutectic/polymethyl methacrylate composite as form-stable phase change material for thermal energy storage

This work is focused on the preparation and characterization of fatty acid eutectic/polymethyl methacrylate (PMMA) form-stable phase change material (PCM). Capric acid (CA), lauric acid (LA), myristic acid (MA) and stearic acid (SA) were selected to prepare binary fatty acid eutectic for the sake of decreasing the phase change temperature. Using the method of self-polymerization, CA–LA, CA–MA, CA–SA and LA–MA eutectics acting as the heat-absorbing materials and PMMA serving as the supporting material were compounded in the ratio of 50/50 wt.%. The relations between mass fraction of LA–MA eutectic and latent heat and compressive strength of LA–MA/PMMA composite were discussed, and the feasible maximum mass fraction of LA–MA eutectic was determined to be 70%. CA–LA/PMMA, CA–MA/PMMA, CA–SA/PMMA and LA–MA/PMMA composites were examined to investigate their potential application in building energy conservation. Scanning electron microscope and polarizing optical microscope observations showed that fatty acid eutectic was coated by PMMA thus the composite remained solid when the sample was heated above the melted point of the fatty acid. Fourier-transform infrared results indicated that fatty acid and PMMA had no chemical reaction and exhibited good compatibility with each other. According to the differential scanning calorimetry results, phase change temperatures of CA–LA/PMMA, CA–MA/PMMA, CA–SA/PMMA and LA–MA/PMMA composites were 21.11 °C, 25.16 °C, 26.38 °C and 34.81 °C and their latent heat values were determined to be 76.3 kJ/kg, 69.32 kJ/kg, 59.29 kJ/kg and 80.75 kJ/kg, respectively. Moreover, thermal stability and expansibility of the form-stable PCMs were characterized by thermogravimetric analysis and volume expansion coefficient respectively, and the results indicated that the composites were available for building energy conservation.     

Application of phase change materials in thermal management of electronics

Application of a novel PCM package for thermal management of portable electronic devices was investigated experimentally for effects of various parameters e.g. power input, orientation of package, and various melting/freezing times under cyclic steady conditions. Also, a two-dimensional numerical study was made and compared the experimental results. Results show that increased power inputs increase the melting rate, while orientation of the package to gravity has negligible effect on the thermal performance of the PCM package. The thermal resistance of the device and the power level applied to the PCM package are of critical importance for design of a passive thermal control system. Comparison with numerical results confirms that PCM-based design is an excellent candidate design for transient electronic cooling applications.     

Thermal properties of 3-hydroxy fatty acids and their binary mixtures as phase change energy storage materials

In the present work, we describe the chemical synthesis of 3-HFAs as prominent derivatives of fatty acids and assess if they could be applied as phase change materials (PCM). In addition, 3-HFAs were obtained by depolymerization of a bacterial biopolymeric material, polyhydroxyalkanoate. Thermal properties of 3-hydoxyoctanoic, decanoic, and dodecanoic acids are reported for the first time. These materials showed the potential to be applied as PCM in temperature range from 33°C to 66°C. In order to expand the temperature range for application of 3-HFAs as PCM, eutectic mass ratios of three kinds of binary mixtures of 3-HFAs were calculated, and their properties were predicted using the Schröder-van Laar equation. Thermal properties of these mixtures were validated by differential scanning calorimetry (DSC) analysis. These results showed that eutectics considerably expanded the scope of applications of 3-HFAs as PCMs. 3-HFAs originating from biotechnologically obtained polyhydroxyalkanoates also showed potential to be applied in development of PCMs.     

Hexamethylene dilauroyl, dimyristoyl, and dipalmytoyl amides as phase change materials for thermal energy storage

Hexamethylene dilauroyl, dimyristoyl, and dipalmytoyl amides have been produced as solid-liquid phase change materials via condensation of hexamethylene diamine with the respective acyl chlorides (lauroyl chloride, myristoyl chloride, and palmytoyl chloride) and were characterized by FT-IR, NMR, DSC, and TG analysis. Hexamethylene dilauroyl, dimyristoyl, and dipalmytoyl amides crystallized due to structural symmetry and flexibility of long alkyl groups. They were characterized by DSC and FT-IR spectroscopy before and after thermal cycling to determine their thermal reliability. Phase change enthalpies were found 110.1 and −103.3 J g⁻¹ for hexamethylene dilauroyl amide (N,N′-hexamethylene didodecanamide), 116.9 and −110.4 J g⁻¹ for hexamethylene dimyristoyl amide (N,N′-hexamethylene ditetradecanamide), and 144.5 and −140.5 J g⁻¹ for hexamethylene dipalmytoyl amides (N,N′-hexamethylene dihexadecanamide) by DSC. The endurance of hexamethylene dilauroyl, dimyristoyl, and dipalmytoyl amides was studied by TG analysis.     

The experimental exploration of carbon nanofiber and carbon nanotube additives on thermal behavior of phase change materials

In this study, thermal properties of carbon nanofiber (CNF) and carbon nanotube (CNT) filled phase change materials (soy wax and paraffin wax) were studied experimentally, aiming to improve their thermal conductivities. The composite phase change materials (PCMs) were prepared by the stirring of CNF or CNT in liquid wax at 60 °C, with CNF and CNT doping levels of 1, 2, 5, and 10 wt%. The experimental results show that the thermal conductivity of composite PCMs increases as CNF or CNT loading contents. Both CNF and CNT can improve the thermal conductivity of the composite, while CNF is shown to be more effective than CNT as the thermal conductive filler because of its better dispersion in the matrix.     

Form-stable phase change materials for thermal energy storage

The present paper considers the state of investigations and developments in form-stable phase change materials for thermal energy storage. Paraffins, fatty acids and their blends, polyethylene glycol are widely used as latent heat storage component in developing form-stable materials while high-density polyethylene (HDPE), styrene-butadiene-styrene (SBS) triblock copolymer, Eudragit S, Eudragit E, poly (vynil chloride) (PVC), poly (vynil alcohol) (PVA) and polyurethane block copolymer serve as structure supporting component. A set of organic and metallo-organic materials with high transition heat in solid-solid state is considered as perspective for-stable materials to store thermal energy. Another perspective class of form-stable materials are the materials on the basis of such porous materials as expanded perlite and vermiculite impregnated with phase change heat storage materials. The technology of producing new form-stable ultrafine heat storage fibers is developed. It opens availability to produce the clothers with improved heat storage ability for extremely cold regions. The perspective fields of application of form-stable materials are discussed. The further directions of investigations and developments are considered.     

Properties of stearic acid/modified carbon nanotube composite phase change materials

使用混酸氧化和球磨处理制备改性碳纳米管,并与硬脂酸复合制备相变储热材料。X射线衍射结果显示,球磨处理对碳纳米管的结构有一定影响,混酸氧化后的碳纳米管物相没有发生改变。红外光谱分析表明,球磨处理和混酸氧化对碳纳米管有纯化作用,酸化碳纳米管出现羟基、羰基等官能团,有助于碳纳米管的分散。扫描电镜照片显示,改性碳纳米管在硬脂酸中的分散性为酸化碳纳米管 > 球磨碳纳米管 > 碳纳米管,热导率测试结果也与此符合,说明碳纳米管分散性增加,对硬脂酸热导率有较大的提高。     

二元有机复合相变材料相变过程热特性实验研究

二元有机复合相变材料因其无腐蚀性、过冷度低、价格低廉和可循环性的优点,在电子器件散热过程中极具发展潜力。通过差示扫描量热法(DSC)测得 4 种脂肪酸和 4 种脂肪醇相变温度与潜热,然后利用准共晶相变理论计算脂肪酸/醇二元有机复合相变材料共晶点,确定 4 种相变温度在 33～37 ℃ 范围内的复合体系,并通过 DSC 实验测量二元体系相变特性。实验结果表明,筛选出的二元有机复合相变材料相变温度分布在 33.08～36.63 ℃,与理论相变温度偏差在0.30%～4.61%;相变潜热分布在 138.5～215 kJ·kg^-1,与理论相变潜热偏差在 0.4%～27%;十二酸与十八醇复合相变材料具有最高的相变潜热(215 kJ·kg^-1),相变温度为 36.5 ℃。研究结果可为有机复合相变材料在电子器件热管理中的应用提供技术参考。