Preparation and thermal energy storage properties of poly(n‐butyl methacrylate)/fatty acids composites as form‐stable phase change materials

This work is focused on the preparation, characterization, and determination of thermal energy storage properties of poly(n‐butyl methacrylate) (PnBMA)/fatty acid composites as form‐stable phase change material (PCM). In the composite materials, the fatty acids act as latent heat storage material whereas PnBMA serves as supporting material, which prevents the leakage of the melted fatty acids. The maximum encapsulation ratio for all fatty acids was found to be 40 wt%. The composites that do not allow PCM leakage in melted state were identified as form‐stable PCMs. The compatibility of fatty acids with PnBMA is investigated by optical microscopy (OM) and Fourier Transform Infrared (FT‐IR) spectroscopy. Thermal properties and thermal reliability of the form‐stable composite PCMs were determined using differential scanning calorimetry (DSC). DSC analysis revealed that the form‐stable composite PCMs had melting temperatures between 29.62°C and 53.73°C and latent heat values between 67.23 J/g and 87.34 J/g. Thermal stability of the composite PCMs was studied by thermal gravimetric (TG) analysis and the results indicated that the form‐stable PCMs had good thermal stability. In addition, thermal cycling test showed that the composite PCMs had good thermal reliability with respect to the changes in their thermal properties after accelerated 5,000 thermal cycling. On the basis of all results, it was also concluded that the prepared form‐stable composite PCMs had important potential for many thermal energy storage applications such as solar space heating of buildings by using wallboard, plasterboard or floors integrated with PCM. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Preparation and properties of novel ceramic composites based on microencapsulated phase change materials (MEPCMs) with high thermal stability

Ceramic composites are widely used in medium/high temperature thermal energy storage (TES) and catalysis. Due to the high latent heat of phase change materials (PCMs), it is an effective method to improve the TES capacity by combining PCMs with ceramic materials. However, PCMs are easy to leak after being heated, so they need to be microencapsulated. Furthermore, for porous ceramic catalytic composites, the leakage of PCMs will block the pores, which seriously hinders their application. In this paper, a novel microencapsulated phase change material (MEPCM) with thermal expansion void was prepared using “double-layer coating, sacrificing inner layer” method. Based on that, two kinds of ceramic composites have been prepared. One is a TES material which composed of alumina, glass frit (GF) and MEPCMs. Thermal analysis results showed that the composite can still maintain stable heat storage performance after 200 melting-solidification cycles with little latent heat loss. Another is a multifunctional porous composite phase change material (CPCM) by loading Ce and Mn as catalyst via solution combustion synthesis (SCS) method, which can be used in low temperature SCR catalysis and other catalytic fields (100–300 °C). Based on MEPCMs with thermal expansion void, the two ceramic composites show great potential in energy storage and catalysis.     

Particle Technology in the Formulation and Fabrication of Thermal Energy Storage Materials

This article reviews the state of the art of the formulation and fabrication of sensible, latent, and thermochemical thermal energy storage (TES) materials with special focus on the role of particle technology in enhancing the performance of these materials. Molten salt-based sensible TES materials have been intensively studied, particularly the use of doped nanoparticles for enhancing specific heat capacity and thermal conductivity. For latent TES, the inclusion of property enhancers is among the most effective approaches to address the low thermal conductivity and supercooling issues of phase change materials (PCMs), whereas the encapsulation of PCMs and structurally stabilized composite PCMs are the favorable methods to address leakage and chemical incompatibility challenges. Thermochemical TES materials are often incorporated with an inert or an active host matrix for structural stabilization.     

组合相变材料强化固液相变传热可视化实验

采用高清相机和红外热像技术，对组合相变材料融化-凝固循环过程与传热特性开展了可视化实验研究。以填充三种石蜡的相变蓄热腔体为研究对象，追踪了腔体内固液相界面的动态演化过程和温度分布的变化规律。在此基础上，考察了相变材料布置顺序对蓄热腔体热性能的影响，分析了组合相变材料蓄热腔体的相变行为及强化传热特性。结果表明，相变温度较高的相变材料应靠近加热壁面布置；组合相变材料蓄热腔体存在多个固液相界面现象，不同相变材料可同时融化/凝固；与单一相变材料相比，组合相变材料的应用改善了蓄热腔体各单元相变速率的均匀性，提高了平均相变速率；组合相变材料虽然降低了蓄热腔体的显热蓄热量，但减小了温度变化速率，增强了系统的稳定性，并显著增加了潜热蓄热量，有效提高了相变蓄热腔体的总蓄热量。     

Sustainable lignin-based polyols as promising thermal energy storage materials

Six lignin-based polyols (LBPs) have been prepared by cationic ring opening polymerization of an oxirane in the presence of an organosolv lignin in tetrahydrofuran (THF) as reaction media and co-monomer. The prepared LBPs have been characterized and tested for the first time as phase change materials (PCMs) for thermal energy storage (TES) at low temperature. It was found a strong influence of the LBPs composition on their performance to storage thermal energy. Thus, LBPs with higher THF wt% content and lower oxirane/THF mass ratio exhibit the highest latent heats. Furthermore, a clear inversely proportional trend between the oxirane/THF mass ratio and the melting temperatures of the prepared LBPs was noticed. Among the prepared LBPs, the highest obtained latent heat was 53.7 J/g demonstrating the potential application of lignin as feedstock for PCMs preparation. To the best of our knowledge, this is the first time that a biomass derived PCM based on lignin has been studied and considered for TES applications at low temperature. LBPs show energetic solid–liquid transitions that point out their promising potential as bio-PCMs. This work paves the way to introduce new bio-based PCMs from lignin in TES systems, for example, in a more sustainable construction sector.     

Poly(styrene‐co‐maleic anhydride)‐graft‐fatty acids as novel solid–solid PCMs for thermal energy storage

A solid–solid phase change material (S‐SPCM) can store and release a specific amount of latent heat during its phase transition. In this regard, poly(styrene‐co‐maleic anhydride) (SMA)‐graft‐fatty acids (FA) copolymers were synthesized as novel S‐SPCMs for thermal energy storage (TES). The chemical structures of the SMA‐g‐FA copolymers were characterized by proton nuclear magnetic resonance (¹H NMR) and Fourier transform infrared (FT‐IR) spectroscopy techniques. The phase transformations of the copolymers form crystalline phase to amorphous phase were monitored using polarized optical microscopy (POM). The latent heat TES (LHTES) properties, thermal cycling reliability, and thermal stability of the S‐SPCMs were investigated by differential scanning calorimetry and thermogravimetric analysis methods. The SMA‐g‐FA copolymers produced as S‐SPCMs showed solid–solid phase transitions at about 40°C–60 °C range and had latent heat storage and release ability between 84 and 127 J/g, respectively. The S‐SPCMs had stable chemical structures and reliable LHTES characteristics even after 5,000 thermal cycling. They had reasonable thermal conductivity value changed in the range of 0.15–0.19 W/mK. Furthermore, it was concluded that the SMA‐g‐FA copolymers can be considered as promising S‐SPCMs for TES utilizations. POLYM. ENG. SCI., 59:E337–E347, 2019. © 2019 Society of Plastics Engineers     

Synthesis and characterization of polyethylene glycol acrylate crosslinking copolymer as solid–solid phase change materials

A kind of crosslinking copolymer as solid–solid phase change material (PCM) is synthesized by copolymerization. The scope of PCM applications is often severely limited by their heat stablility and phase transition state. The solid–solid phase change materials we obtained retain basic state during phase change transitions. The crosslinking polymer is heat stable under 300° and the latent heat of crystalline and latent heat of melting is on the average of 120 J/g and 140J/g, respectively. The property of thermal stability and heat storaged is related to crosslinking density of the gel. The property of thermal stability and high latent heat may expand the scope of PCMs applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39755.     

Porous silica matrices infiltrated with PCM for thermal protection purposes

In this work, numerical and experimental studies are proposed to predict and investigate the thermal absorption characteristics of porous silica infiltrated with phase change materials (PCM) for thermal protection applications. Several types of different solid–liquid phase change composites were introduced into a cylindrical enclosure while it was heated on the left of the enclosure. The numerical simulation was performed using a volume-averaging technique, and a finite volume modelling (FVM) was used to discretise the heat diffusion equation. The phase change process was modelled using the enthalpy–porosity method. The results are portrayed in terms of the temperature distribution and liquid fraction, and the numerical and experimental results showed good agreement. The results indicated that a higher latent heat storage capacity meant a more stable thermal performance of the phase change composite.     

Preparation of erythritol–graphite foam phase change composite with enhanced thermal conductivity for thermal energy storage applications

Three-dimensional interconnected graphite composite foam as a heat conductive matrix was fabricated by using low cost polymeric precursors and polyurethane (PU) foam as carbon source and sacrificial macroporous template, respectively. Erythritol–graphite foam as a stable composite phase change material (PCM) was obtained by incipient wetness impregnation method. The thermophysical properties such as thermal diffusivity, specific heat, thermal conductivity and latent heat of the erythritol–graphite composite foam were measured. From the results, it was found that the thermal conductivity of the erythritol–graphite composite foam (3.77 W/mK) was enhanced 5 times as compared with that of pristine erythritol (0.72 W/mK). This enhancement can significantly reduce the charging and discharging times of the PCM storage system. There is no chemical reaction between erythritol and graphite as confirmed by X-ray diffractometer (XRD). The PCM/foam composite has a melting point of 118 °C and latent heat of 251 J/g which corresponds to the mass percentage (75 wt.%) of the erythritol within the composite foam. The obtained results confirmed the feasibility of using erythritol–graphite foam as a new phase change composite for thermal energy storage (TES) applications, thus it can contribute to the efficient utilization and recovery of solar heat or industrial waste heat.     

纳米材料/十四酸混合相变蓄热材料的制备与特性

选用纳米金属Cu和碳素材料石墨烯纳米片（GnPs）为改性剂分别添加至十四酸（MA）中,制备出Cu质量分数为1%、2%、3%和4%的Cu/MA混合相变蓄热材料及GnPs质量分数为1%、2%和3%的GnPs/MA混合相变蓄热材料,并对混合相变材料性能进行表征。结果表明：Cu/MA固态和液态热导率随Cu质量分数增加呈线性提高,1%（质量）GnPs/MA固态热导率较纯MA显著提高101.51%,随GnPs质量分数增加,热导率增幅减缓;FT-IR谱图表明Cu与MA及GnPs与MA间的混合均为物理作用;DSC结果显示添加Cu或GnPs可降低MA的过冷度和相变潜热,且随质量分数增加,相变潜热逐渐降低;4%（质量）Cu/MA和3%（质量）GnPs/MA放热时间相比于纯MA分别减少了23.4%和38.7%;4%（质量）Cu/MA和3%（质量）GnPs/MA在经历300次快速热循环试验后,晶体结构和相变温度基本保持不变,相变潜热分别降至168 J·g^-1和181 J·g^-1左右,仍满足蓄放热要求,两种材料均具有良好的热循环稳定性。     

硬脂醇/膨胀石墨复合相变材料的制备及储热性能

相变储热技术是解决热量在时空上分配不平衡问题的有效手段之一,研制高性能的复合相变材料（phase change material, PCM）成为当前研究者关注的重点。硬脂醇（stearyl alcohol, SAL）等有机PCM目前主要存在热导率偏低以及循环稳定性较差等问题而限制了实际应用。以SAL作为PCM,膨胀石墨（expanded graphite, EG）为高导热多孔基质,采用吸附定形工艺制备了16种SAL/EG复合PCMs[EG含量为7%、14%、21%、28%（质量）;样品密度为700kg/m³、800kg/m³、900kg/m³、1000kg/m³]。对复合PCMs样品的微观结构、储热能力、导热性能、循环稳定性及充放热性能进行研究与分析。结果表明：SAL完全填充于EG的多孔网络。当样品密度为900kg/m³,EG质量分数为28%的水平热导率最高,其值为28.58W/(m ? K),相比于纯SAL[0.38W/(m ? K)]提高了74倍,该值大约是相对应垂直热导率[5.99W/(m ? K)]的4.8倍。另外在构建的充放热性能试验台上研究了样品中心位置的储/放热性能,结果显示样品密度为900kg/m³,EG质量分数为28%的样品充放热速率最大,固-液潜热吸热和放热阶段所经历的时间分别为53min和20min。与此同时验证了样品的导热性能和熔化-凝固特性,说明SAL/EG复合PCMs具有稳定可靠的储/放热性能。     

二维纳米片基复合相变储热材料研究进展

相变材料（PCMs）作为潜热储存和释放的介质,能够解决热能供需矛盾,从而缓解能源危机。纯相变材料具有能量密度高、温度范围广、能量输出稳定性强等优点,但其热导率低和在相变过程发生渗漏的缺点阻碍了其广泛的应用和发展。通过将PCMs与二维纳米片复合,PCMs热导率低和渗漏问题被有效解决。通过在导热机理方面进行详细阐述的基础上,综述了近几年来有关碳基二维纳米片、六方氮化硼（h-BN）纳米片、二硫化钼等复合储热材料的研究进展,为高性能二维纳米片基复合PCMs的设计提供一定的研究思路。     

Eudragit S (methyl methacrylate methacrylic acid copolymer)/fatty acid blends as form‐stable phase change material for latent heat thermal energy storage

By composing (Eudragit S) with fatty acids (stearic acid (SA), palmitic acid (PA), and myristic acid (MA)), form‐stable phase change materials (PCMs), which can retain the same shape in a solid state even when the temperature of the PCMs is over the melting points of the fatty acids, are prepared. The compatibility of fatty acids with the Eudragit S is proved by microscopic investigation and infrared (FTIR) spectroscopy. The melting and crystallization temperatures and the latent heats of melting and crystallization of the form‐stable PCMs are measured by Differential Scanning Calorimetry (DSC) method. The maximum mass percentage of all fatty acids in the form‐stable PCMs is found as 70%, and no leakage of fatty acid is observed at the temperature range of 50–70°C for several heating cycles. Thermal properties obtained from the DSC analysis indicate that the Eudragit S/fatty acid blends as form‐stable PCM have great potential for passive solar latent heat thermal energy storage (LHTES) applications in terms of their satisfactory thermal properties and utility advantage. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1402–1406, 2006     

The use of lipids as phase change materials for thermal energy storage

Phase change materials (PCMs) are substances capable of absorbing and releasing large amounts of thermal energy (heat or cold) as latent heat at constant temperature as they undergo a change in state of matter (phase transition), commonly, between solid and liquid phases. Since the late 1940s, researchers have recognized the potential for phase change materials to play an essential part in energy storage systems and the search for suitable substances has received increasing interest. Currently, the global PCM market is estimated to grow from $ 460 million in 2013 to approximately $ 1.15 billion by 2018. Fats, oils, and their derivatives are diverse in their structures and among the few renewable feedstocks available that have melting and enthalpy profiles among other properties comparable to those of commercial paraffin waxes currently used in PCM applications. This has led to the investigation of triglycerides, fatty acids, esters, alcohols, and other lipid‐based derivatives as potential PCMs and much research examining lipid‐based materials as PCMs has been published. This article gives a brief overview of phase change materials, highlights the various types of lipid substances examined for PCM applications, and suggests potential future areas of study.     

多熔点相变材料堆积蓄热床蓄热性能分析

对采用多种不同熔点相变材料（PCM）构成的堆积蓄热床进行了数值分析。热水作为换热流体（HTF）自上而下流经蓄热床,熔化相变材料、蓄积相变潜热。石蜡作为相变材料被注射入聚碳酸酯球壳内形成相变胶囊,根据熔点高低依次排放在蓄热床的不同位置,熔点越高距离热水进口越近。假定流场稳定,采用一维Schumann模型计算HTF温度,相变模拟采用显热容法。分别对两种排列方式下采用2种、3种以及4种相变材料的蓄热床的蓄热过程进行了基于热力学第一及第二定律的性能分析,并将结果与单相变材料蓄热床进行比较。基于热力学第一定律分析结果表明,采用多种相变材料构成的蓄热堆积床蓄热速度更快,能量效率更高。基于热力学第二定律分析表明,平均熔点更高的蓄热床能够储存更高的火用。结果表明采用多熔点相变材料构成的堆积蓄热床能够显著地缩短蓄热时间,改进蓄热性能。     

Reliable phase-change polyurethane crosslinked by dynamic ionic-bond crosslinking for thermal energy storage

The fabrication of phase-change materials (PCMs) for thermal energy storage is of great significance, since they combine the sustainable development of energy and human comfortable. Herein, a dynamically crosslinked PCM was successfully fabricated by the blending of complementary polyurethanes bearing carboxylic acid and tertiary amine through reversible ionic bonds via the acid–base reaction. The resultant PCM exhibited good crystalline property, which was confirmed by wide-angle X-ray diffraction and polarizing optical microscopy. Differential scanning calorimetry characterizations suggested that the prepared PCMs could reversibly store and release latent heat during heating and cooling process. The presence of physical crosslinks in PCM could maintain shape stable and had no deteriorate effect on the value of latent heat. Therefore, a high latent heat of 70 J/g was obtained within the temperature range of 13.2–45.4 °C. This good thermal storage ability remained constant even after 100 consecutive heating/cooling cycles. Thermogravimetric analysis results provided distinct evidence that the prepared PCM has an outstanding thermal stability with the onset decomposition temperature higher than 250 °C. The combined thermal storage ability and thermal reliability endow the PCM promising application as solar energy storage, waste heat utilization, and thermal protection coatings or adhesives. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48213.     

Form-Stabilized Polyethylene Glycol/Palygorskite Composite Phase Change Material: Thermal Energy Storage Properties,Cycling Stability,and Thermal Durability

In this work, polyethylene glycol (PEG) as a phase change material (PCM) was incorporated with palygorskite (Pal) clay to develop a novel form-stable composite PCM (F-SCPCM). The Pal/PEG(40 wt%) composite was defined as F-SCPCM and characterized using SEM/EDS, FT-IR, XRD, DSC, and TGA techniques. The DSC results revealed that the F-SCPCM has a melting temperature of 32.5°C and latent heat capacity of 64.3 J/g for thermal energy storage (TES) applications. Thermal cycling test showed that the F-SCPCM had good cycling thermal/chemical stability after 500 cycles. The TGA data proved that that both cycled and non-cycled F-SCPCMs had considerable high thermal durability. Consequently, the created F-SCPCM could be considered as an additive material for production of green construction components with TES capability. POLYM. ENG. SCI., 60:909–916, 2020. © 2020 Society of Plastics Engineers     

Novel phase change materials based on fatty acid eutectics and triallyl isocyanurate composites for thermal energy storage

In this study, a series of dimension‐stabilized fatty acid eutectics and triallyl isocyanurate (TAIC) composite phase change materials were prepared via in situ reaction by blending the fatty acids and TAIC, in which the fatty acids were introduced as a phase change material (PCM), and TAIC performed as a supporting material by self‐crosslinking. Fourier transform infrared spectroscopy, X‐ray diffraction, differential scanning calorimetry, scanning electron microscopy (SEM), and thermogravimetric analysis were applied to investigate the chemical structure, crystalline properties, phase transition behavior, microstructure, and thermal stability of the composites. The results indicated that the composite possessed excellent thermal reliability and heat storage durability even after 300 heating–cooling cycles. Moreover, the composites had applicable phase transition temperatures in the range of 26–40 °C and satisfying latent heat storage capacities of higher than 110 J/g. The SEM images showed that the particle size of the nanoparticles of the composites was about 200 nm after treatment. The dimensional measurement of the composites proved a high service temperature of 100 °C, indicating that the composites were promising for thermal energy storage materials. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44866.     

(准)共晶系相变储能材料的研究进展

节能技术的发展是当今非常现实的问题,这些技术的发展方向之一是各行业的热能储存。相变储能材料由于其较大的潜热和恒温性,被广泛应用于潜热储能系统和热管理系统中。然而,单一相变材料的相变温度和潜热比较固定,难以同时满足多种储能应用对各种潜热、相变温度等性质的要求。因此,人们开展了关于二元或多元共晶相变体系的研究。本文介绍了近年来国内外（准）共晶相变储能材料及其复合材料的研究进展,探讨了（准）共晶相变储能材料的理论设计机理,指出了（准）共晶相变储能材料存在的不同问题并提出建议,最后指出了（准）共晶系相变储能材料在实际应用领域的局限,提出未来在寻找新型相变储能材料,建立传热理论模型,对（准）共晶系复合相变储能材料的力学性能、耐老化性能、储能密度低和高温条件下的耐久性差等方面需要进一步探索。     

多孔纳米基复合相变材料在建筑节能中的应用进展

近年来相变材料的开发和应用受到广泛的关注,研究表明,纳米和多孔基复合相变材料可以显著提高材料热导率和热稳定性,同时可以有效防止相变材料在熔融和凝固过程中发生的泄漏问题。本文主要介绍了建筑领域的纳米和多孔基复合相变材料的选择和制备、材料的表征及热物性测量研究,简述了掺入复合相变材料的砂浆、石膏板、混凝土和砖块的热性能情况,通过实验和数值模拟分析了建筑系统中的复合相变材料的应用情况,对采用了储热相变材料的建筑系统进行成本分析和节能研究。最后说明应根据地区气候和使用需求选择不同相变点和热导率的相变材料,添加相变墙体可提高热舒适性,并有效减少能耗。同时指出如何将相变墙体更好地与主动式技术结合,以及探究降低相变墙体的可回收年限和长时间使用相变墙体后的热性能是今后的主要研究方向。