Thermal stability of composite phase change material microcapsules incorporated with silver nano-particles

This paper reports a study on the thermal stability of phase change material microcapsules that are incorporated with silver nano-particles (Ag-NPs). The novel microcapsules were fabricated by the technique of in situ polymerization, with aminoplast as the wall and phase change material bromo-hexadecane (PCM BrC16) as the core. Thermal gravimetry (TG) analysis was applied to measure the thermal stability of these microcapsules and surface morphology of the microcapsules was observed by means of scanning electron microscopy (SEM) after an application of curing treatment at 130 °C. Comparing with conventional phase change material microcapsules (PCMMs), nano-composite phase change material microcapsules (NCPCMMs) have higher thermal stability. This can be attributed to nano-composite structure of the microcapsules, in which metal Ag-NPs distributed on the surface to increase wall toughness and strength. The possible reinforcement mechanisms of the nano-composite structure are explored.     

Polymer-derived silicon nitride aerogels as shape stabilizers for low and high-temperature thermal energy storage

This work presents a new skeleton material for thermal energy storage (TES), a silicon nitride aerogel obtained through the pyrolysis of a pre-ceramic polymer. Silicon nitride offers a good combination of thermal conductivity, high-temperature resistance, and chemical inertness. The aerogel porosity can be spontaneously infiltrated with molten NaNO₃, which is a typical phase change material (PCM) in high-temperature TES. The Si₃N₄/NaNO₃ composite exhibits excellent thermal properties with a thermal energy storage efficiency of 82 %, a limited molten salt leakage, and good stability to thermal cycling. The aerogel withstands oxidation up to high temperature and is chemically inert even in contact with salts. This novel aerogel shows also a notable paraffin absorption ability (used in room temperature TES) with negligible leakage even when in contact with absorbent paper. The so-obtained composite reached ≈ 82.4 vol % of organic PCM and a thermal energy storage efficiency of ≈ 62 % compared to neat paraffin.     

THERMAL PROPERTIES OF MULTICOMPONENT FATTY ACIDS AS SOLID-LIQUID PHASE CHANGE MATERIALS FOR COOLING APPLICATIONS

Solid-liquid phase change materials (PCMs) consisting of multicomponent fatty acids have been developed. The thermodynamic properties of PCMs were investigated in detail with a differential scanning calorimeter (DSC). PCMs were prepared using two saturated fatty acids. The phase transition temperature of the binary system composed of capric and lauric acids was able to be freely controlled. In addition, the additive effect of surfactants with fatty acid properties (sodium oleate or sodiumlaurate) was investigated. In particular, the addition of more than 15 wt% sodium oleate or sodiumlaurate to the binary system was a very effective means of suppressing the supercooling and controlling the temperature of the phase change between 4° and 7°C. Furthermore, the phase transition behavior on a large scale was constant in 200 heating-cooling cycle tests using handmade experimental apparatus. Physicochemical degradation of PCMs was not observed after repeated tests by FT-IR.     

Microencapsulation of stearic acid with polymethylmethacrylate using iron (Ⅲ) chloride as photo-initiator for thermal energy storage

Aiming to identify the validity of fabricating microencapsulated phase change material (PCM) with polymethylmethacrylate (PMMA) by ultraviolet curing emulsion polymerization method using iron (Ⅲ) chloride as photoinitiator,SA/PMMA microcapsules were prepared and various techniques were employed to determine the ignition mechanism,structural characteristics and thermal properties of the composite.The results shown that the microcapsules containing SA with maximum percentage of 52.20 wt％ formed by radical mechanism and only physical interactions existed in the components both in the prepared process and subsequent use.The phase change temperatures and latent heats of the microencapsulated SA were measured as 55.3 ℃ and 102.1 J.g-1 for melting,and 48.8 ℃ and 102.8 J.g-1 for freezing,respectively.Thermal gravimetric analysis revealed that SA/PMMA has good thermal durability in working temperature range.The results of accelerated thermal cycling test are all shown that the SA/PMMA have excellent thermal reliability and chemical stability although they were subjected 1000 melting/freezing cycles.In summary,the comparable thermal storage ability and good thermal reliability facilitated SA/PMMA to be considered as a viable candidate for thermal energy storage.The successful fabrication of SA/PMMA capsules indicates that ferric chloride is a prominent candidate for synthesizing PMMA containing PCM composite.     

硬脂酸脂肪酯作为温室控温相变材料的制备及性能研究

相变材料可对室内温度进行调控,采用酰氯醇解法将硬脂酸及直链脂肪醇合成系列硬脂酸酯(18-8,18-10,18-12,18-14)作为温室控温相变材料,并通过傅里叶变换红外光谱(FT—IR)、核磁共振(1H NMR)、差示扫描量热仪(DSC)、热重分析仪(TGA)、导热仪等对其结构、热性能及导热性能等进行了测定。结果表明:该系列硬脂酸酯的相变温度为22.2~44.8oC,相变焓为138.7~155.7 kJ·kg~(-1),并具有良好的热稳定性和导热性能,适于作为温室控温相变材料。     

改善石蜡相变材料导热性能的研究进展

近年来石蜡作为一种相变储能材料受到越来越多的关注,由于石蜡PCM本身的导热系数偏低,导致储能系统在吸热或放热过程中的有效热率极低,热量无法快速有效地进行存储和释放。因此,提高石蜡PCM的导热系数成为了近年来的研究重点。主要从翅片结构、组合相变材料、复合相变材料、相变材料微胶囊化这几个方面总结了在改善石蜡PCM导热性能方面的国内外研究状况。     

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.     

Storage composites for the optimisation of solar water heating systems

Composite materials based on expanded natural graphite (CENG) and various phase change materials (PCM) have been developed for low temperature solar applications (323–373 K). The integration of such composite materials directly into the solar collector could allow new storage functionality. A numerical model has been developed to describe the materials behaviour. Composites properties are presented and discussed.     

十八烷/PSt相变微胶囊的制备及其热性能研究

细乳液法制备了十八烷/聚苯乙烯(PSt)相变微胶囊,用TEM、DLS和DSC等对微胶囊进行了表征。研究了十二烷基硫酸钠(SDS)的加入量、亲水性单体丙烯酸的加入量、引发剂类型以及苯乙烯与十八烷的加料比对产物形态的影响。研究表明:低的SDS浓度有利于微胶囊结构的形成,产物粒子的平均粒径随SDS加入量的增大而减小;加入亲水性共聚单体丙烯酸可以改善微胶囊的形态,但产物中PSt均相微球增多;使用油溶性引发剂AIBN比使用KPS更加有利于微胶囊的形成;苯乙烯与十八烷的投料比为1∶1时,制备的微胶囊相变焓为111.6 J/g。     

复合蓄热材料的研制与应用

以KAl(SO4)2·12H2O为相变材料,以多孔陶瓷为基体,采用熔融浸渍法制备了复合相变蓄热材料。此复合相变材料结合了潜热蓄热材料与显热蓄热材料的优点,并克服了无机盐相变材料相变过程无定型的缺点及陶瓷蓄热显热小的缺点。将自制的复合蓄热材料实际应用于咖啡壶加热设备中,实验结果表明加入复合蓄热材料后的咖啡壶每小时节能率达38.8%。     

相变储热的传热强化技术研究进展

相变储热技术具有储热密度大、相变温度稳定以及过程容易控制等优点,具有广泛应用前景。相变储热技术在应用中需完成热能的储存与释放过程,其传热特性直接决定应用效果。储热技术的传热强化主要包括三个方面：一是相变材料本身的导热强化;二是潜热型功能热流体的对流传热强化;三是储热器的传热强化。本文综述了国内外在相变储热技术的传热强化研究方面的进展,主要介绍了膨胀石墨、泡沫金属等复合相变材料的导热强化,相变微胶囊及相变微、纳米乳液潜热型功能热流体传热强化以及管壳式储热器、板式储热器、螺旋盘管储热器等储热器的传热强化。文章指出,膨胀石墨基复合相变材料具有高热导率、大储热密度以及良好的定型特性,且价格低廉,极具应用前景。纳米乳液功能热流体具有表观比热容大、流阻较小等优势,但存在稳定性较差、过冷度大等问题。板式储热器具有较大的传热面积、较高的传热功率,适宜应用于相变材料传热系统。但应用背景不同,针对不同场景提供不同储热器的选型及指导值得作进一步的研究。     

一种蜜胺树脂为壁材的相变储热微胶囊致密性研究

采用原位聚合法用蜜胺树脂包覆了一种相变点为24℃,相变热为225 5J/g的有机复合相变材料,并对所制备的相变储热微胶囊的致密性进行了研究。利用扫描电子显微镜对微胶囊的表面形态进行了观察;用722型分光光度计对不同工艺条件下所得微胶囊在密度为0.79g/mL乙醇中的渗透性进行了研究;采用压力法观察微胶囊在受压后的表面形貌,对其强度进行了评价。结果表明:相变储热微胶囊呈均匀的球形,表面光滑且致密,平均粒径110μm;由于蜜胺树脂有大的交联密度,微胶囊在乙醇中渗透缓慢,证明芯材包覆效果好,同时发现双层壁材微胶囊的致密性优于单层壁材的微胶囊;平均粒径为10μm的优于平均粒径为1μm的;随着壁材用量的增大,渗透性减弱,但为了保证相变储热微胶囊的储热效果,芯材与壁材质量比以3为好。所制备的微胶囊可以承受1 96×105Pa的压力而不破损。