Preparation and thermal properties of form-stable palmitic acid/active aluminum oxide composites as phase change materials for latent heat storage

Form-stable palmitic acid (PA)/active aluminum oxide composites as phase change materials were prepared by adsorbing liquid palmitic acid into active aluminum oxide. In the composites, the palmitic acid was used as latent heat storage materials, and the active aluminum oxide was used as supporting material. Fourier transformation infrared spectroscope (FT-IR), X-ray diffractometer (XRD) and scanning electronic microscope (SEM) were used to determine the chemical structure, crystalloid phase and microstructure of the composites, respectively. The thermal properties and thermal stability were investigated by a differential scanning calorimeter (DSC) and a thermogravimetry analyzer (TGA). The FT-IR analyses results indicated that there is no chemical interaction between the palmitic acid and active aluminum oxide. The SEM results showed that the palmitic acid was well adsorbed into porous network of the active aluminum oxide. The DSC results indicated that the composites melt at 60.25 °C with a latent heat of 84.48 kJ kg⁻¹ and solidify at 56.86 °C with a latent heat of 78.79 kJ kg⁻¹ when the mass ratio of the PA to active aluminum oxide is 0.9:1. Compared with that of the PA, the melting and solidifying time of the composites CPCM5 was reduced by 20.6% and 21.4% because of the increased heat transfer rate through EG addition. The TGA results showed that the active aluminum oxide can improve the thermal stability of the composites.     

Preparation and characterization of gypsum-based materials used for 3D robocasting

In this study, gypsum-based materials (GM) comprising mainly α-hemihydrate gypsum, polycarboxylate, hydroxypropyl methyl cellulose and starch ether were prepared and used for 3D robocasting (3DR). The setting time and rheological properties of the GM slurry and the physical properties of the GM sample, including bulk density, porosity and mechanical strength, were investigated. The results indicate that the GM slurry exhibits an obvious shear thinning behavior and a good shape fidelity. The measured dynamic yield stress, final viscosity and initial storage modulus of the GM slurry are as high as 420.73 Pa, 7.29 Pa s and 273.86 kPa, respectively. Meanwhile, the GM slurry presents an adequate initial setting time of 68 min compared with a printing time of 14 min. In addition, the GM sample prepared by 3DR has a high compressive strength of 64.96?±?5.98 MPa and a bending strength of 15.24?±?1.58 MPa. These mechanical strengths are comparable with those of the GM and pure gypsum plaster sample prepared by traditional molding. Generally, the 3DR of GM is a promising method to improve the mechanical strength of printed gypsum products and presents great application prospects in the building of complex large-scale structures.     

The effect of impurities on the melting temperature and the heat of fusion of latent heat storage materials

Thermophysical properties of four normal paraffins (tetradecane, hexadecane, octadecane, eicosane) and three fatty acids (lauric acid, palmitic acid, stearic acid) were determined experimentally using a modified differential-thermoanalysis technique. For calibration of the measuring device, literature data in the temperature range from 5 to 70°C of six of these substances of at least 99% purity were used. Melting temperature, heat of fusion, and specific heat of a number of these pure and technically pure organic compounds were measured and compared to determine the effect of impurities and to give values of the application range of the properties required for the construction of thermal storage equipment.     

Mass and heat transfer in building materials

A system of differential equations is proposed for mass and heat transfer in capillary-porous bodies. The principal thermophysical characteristics of mass and heat exchange in relation to building materials and structures are discussed.     

Efficiency of free cooling using latent heat storage integrated into the ventilation system of a low energy building

This article presents the results of an investigation into the free cooling efficiency in a heavyweight and lightweight low energy building using a mechanical ventilation system with two latent heat thermal energy storages (LHTESs), one for cooling the fresh supply air and the other for cooling the re-circulated indoor air. Both LHTESs contain sphere encapsulated PCM (paraffin RT20). Using a developed and experimentally verified numerical model of the LHTES, the temperature response functions, based on the heat storage size, the air flow rates and the PCM's thermal properties, are established in the form of a Fourier series and empirical equations and used in the TRNSYS building thermal response model. Several mechanical ventilation, night cooling and free cooling operation modes were analysed and compared. It was found that the free cooling technique enables a reduction in the size of the mechanical ventilation system, provides more favourable temperatures and therefore enables better thermal comfort conditions, and in our studied case also fresh air for the occupants.     

基于太阳能供热的石墨烯/石蜡复合相变材料蓄放热特性实验研究

由于太阳能间歇性和不稳定性的缺点,给其在供热方面的应用带来了局限,采用相变储能法可改善太阳能供热应用的缺点。对此以石蜡为基液,向其中添加石墨烯通过"两步法"制备出石墨烯质量分数分别为0.1%、0.3%和0.5%的复合相变材料,搭建复合相变材料蓄放热实验台并记录数据。结果表明:在相同的实验条件下,石墨烯/石蜡复合相变材料随着石墨烯质量分数的增加,熔化速率也随之增加,在添加量为0.5%时增加了14.15%;凝固速率也随石墨烯质量分数的增加而增加,但效果不如熔化速率明显;复合相变材料在圆管外的蓄放热过程中,位于圆管底部的材料熔化与凝固效果均不理想。     

Preparation and characterization of a series of diol di-stearates as phase change heat storage materials

A series of solid-liquid phase change materials, diol di-stearates, were prepared via esterification of stearyl chloride with the respective diol (1,2-ethanediol, 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol and 1,10-decanediol) using pyridine as acid absorbent, and were then characterized by FT-IR, WAXD, POM, DSC and TGA measurements. All of the resulting diol di-stearates were apt to crystallize due to structural symmetry and flexibility of long alkyl groups. The DSC results indicated that the melting point of the prepared diol di-stearates varied from 38.5 °C to 56.4 °C, and phase change enthalpy lies in the range 134 kJ/kg-189 kJ/kg.     

新戊二醇/皂土复合储能材料的制备

为了解决有机储能材料中液相流动问题,利用液相插层法制备有机/无机复合储能村料.皂土经过十六烷基三甲基溴化铵(CTAB)改性后,用离子交换法将新戊二醇(NPG)嵌入改性皂土层间,采用小角X射线衍射、红外测试和差热分析表征皂土改性前后层间距、层间结构的变化和制备的复合储能材料的储热性能.实验结果表明:改性皂土的层间距随CTAB量的增加而变宽,新戊二醇/皂土复合储能材料相变温度为56.4 ℃,相变焓为66.18 J/g.     

聚苯乙烯基相变微胶囊储热复合材料的制备及性能研究

以苯乙烯、偶氮二异丁腈(AIBN)和硬脂酸丁酯相变微胶囊(MCPCM)为原料,采用本体聚合法制备聚苯乙烯基相变微胶囊(MCPCM/PS)储热复合材料。研究了MCPCM含量对MCPCM/PS复合材料储热性能、传热性能及宏观力学性能的影响。结果表明,MCPCM/PS复合材料具有储热功能,随MCPCM含量增加相变潜热增大,导热系数减小,传热速率变缓,玻璃化转变温度(Tg)降低,断裂强度减小,伸长率增大,当MCPCM为25%(质量分数)时,相变温度为25~28℃,相变潜热为31.8J/g,导热系数为0.0210W/(m·K),Tg=59.13℃。     

潜热储能石膏基建筑材料的制备及其储(放)热行为研究

以膨胀石墨为吸附介质,硬脂酸丁酯为吸附对象,可以制得有机/无机复合相变材料,将这种复合材料掺入石膏中制备潜热储能石膏建材.DSC的测试结果显示,复合相变材料的相变焓值与纯硬脂酸丁酯的相变焓值基本相当,体现了良好的热物理性能.考虑到浆体的和易性,复合相变材料在石膏试样中的掺量不宜超过5%.在石膏硬化浆体中,复合相变材料与石膏浆体间的界面具有一定的缺陷,但是对石膏试样的强度影响不大.温度循环试验显示,复合相变材料掺量5%的潜热储能石膏具有良好的储(放)热效果,这种特性将有助于增加环境温度波动的惰性,实现热量在不同时间上的迁移,从而在建筑节能领域中加以应用.     

相变储能材料的制备与研究

选择了几种脂肪酸,依据二元低共熔原理,制备出适合建筑材料使用的二元有机相变储能材料。通过DSC分析了复合储能材料的相变温度、相变焓等热性能,结果表明:当CA∶LA;CA∶MA;CA∶PA的质量比分别为53.45∶46.55∶60.2∶39.8∶61.6∶38.4时,其相变焓和相变温度分别为CA-LA:120.7J/g;20.82℃,CA-MA:120.3J/g;19.15℃,CA-PA:142.9J/g;22.05℃,适合于民用建筑对相变材料的要求。通过SEM分析检测了珍珠岩吸附相变材料后的表面微观变化,结果表明:有机羧酸均匀吸附在多孔基体中,此种材料可以应用于夹心节能建筑围护结构中。     

Reproducibility of solidification and melting processes in a latent heat thermal storage tank

This study analyzes the reproducibility of solidification and melting tests in a tank containing 181 kg of paraffin for cold storage at around 8 °C. Firstly, an experimental campaign of 10 identical tests was carried out. The performance is practically the same in terms of PCM temperatures and thermal power, with a maximum deviation of 2% in the capacity of all tests. In a second campaign, the impact of the initial conditions was studied. The results indicate that fixing a same mean PCM temperature at the beginning of the tests is insufficient to ensure an accurate reproducibility. Depending on the heat transfer rate during the preparation tests, the capacity differed in up to 33%. In tanks with such quantities of PCM, fixing a uniform initial PCM temperature is hardly possible, thus it is important to prepare the tank with same operation conditions.     

Performance enhancement of a household refrigerator by addition of latent heat storage

This paper studies the effect of adding a phase change material (PCM) slab on the outside face of a refrigerator evaporator. A dynamic model of the vapour compression cycle including the presence of the phase change material and its experimental validation is presented. The simulation results of the system with PCM show that the addition of thermal inertia globally enhances heat transfer from the evaporator and allows a higher evaporating temperature, which increases the energy efficiency of the system. The energy stored in the PCM is yielded to the refrigerator cell during the off cycle and allows for several hours of continuous operation without power supply.     

Ti基准晶材料制备和贮氢性能研究进展

Ti基准晶材料具有热力学稳定的正二十面体构造，表现出特殊的传输特性、贮氢特性和力学特性等，相关研究受到广泛关注。近年，作者所在研究组在Ti基准晶的制备和贮氢性能研究方面取得了一些新进展。综合报道了Ti-Zr-Ni-Cu系准晶相及其复合相材料的制备和贮氢性能。     

CA-SA/蒙脱土复合相变贮能材料的制备、结构与性能

用差式扫描量热(DSC)技术研究了癸酸(CA)和硬脂酸(SA)二元混合物的热性能,确定了CA-SA二元低共熔物的组成和相变温度;在此基础上,研究了CA-SA二元低共熔物与蒙脱土复合贮能材料的制备方法,并用XRD、IR、DSC等方法对复合材料的结构和性能进行了表征与测试.研究结果表明:CA-SA被有效地包封在蒙脱土层间,制得复合材料的相变温度为20.21℃,相变焓为120.43J/g.     

基于生物质吸附效应的石膏基多功能化复合材料制备与性能

采用废弃核桃壳制备生物质多孔活性炭（PC）,利用真空吸附法将癸酸（CA）封装于PC的孔结构中,形成癸酸-多孔活性炭（CA-PC）。然后将CA-PC与硅藻土（Di）、石膏（Gy）进行复合制备CA-PC/Di-Gy多功能化复合材料,并对其热性能、湿性能以及吸附性能进行测试。采用BET、FTIR、SEM以及DSC等技术对CA-PC/Di-Gy多功能化复合材料进行表征,并分析其结构。结果表明:以废弃核桃壳制备的PC具有发达的孔隙结构,不仅能够包裹CA,而且可以吸附甲醛。CA-PC/Di-Gy多功能化复合材料具有良好的调温调湿性能与吸附率,即在32℃附近出现温度平台,在相对湿度40%~60%的平衡含湿量为0.0859~0.2310 g/g,经过4 h对甲醛气体的吸附率接近40%。     

复合相变储冷材料的制备及性能研究

以十二烷基苯磺酸钠(SDBS)作为分散剂,多层石墨烯、TiO₂/石墨烯(m(TiO₂):m(石墨烯)=25∶75)和TiO₂颗粒作为导热添加剂,加入到二元复合有机储冷材料中(m(壬酸):m(葵醇)=60:40),制备了复合相变储冷材料。通过吸光度、DSC和热导率测试等手段,对复合相变储冷材料的稳定性、相变温度、相变潜热及热导率进行了评价分析。结果表明,分散剂和导热添加剂的加入,对储冷材料的相变温度和相变潜热影响不大,但对热导率影响较大。当分散剂SDBS浓度为0.2 g/L,导热添加剂(分别为TiO₂/石墨烯和TiO₂颗粒)浓度为0.5 g/L时,复合相变储冷材料具有较好的稳定性,其热导率分别为为0.2211和0.2096 W/(m·K),相比没有加入任何导热添加剂的储冷材料的热导率(0.1738 W/(m·K)),分别提高了27.22%和20.61%;当分散剂SDBS浓度为0.3 g/L,导热添加剂多层石墨烯浓度为0.3 g/L时,复合相变储冷材料处于稳定状态,其热导率为0.2...     

纳米胶囊潜热型功能流体制备及强化沸腾换热的实验研究

采用溶胶凝胶法制备了以软脂酸为芯材,二氧化硅为壳材的纳米相变胶囊,分析测试表明所合成的胶囊呈现为核壳结构分明的规则球形结构,且具有良好的储热能力。选用聚二甲基硅氧烷疏水改性,制备了稳定分散的丙酮基纳米胶囊潜热型功能流体,热导率及粘度测试表明其可以应用于强化换热。微小通道过冷流动沸腾实验研究发现,纳米相变胶囊的加入不但可以阻止气泡的合并,而且可以加速沸腾气泡的破裂,揭示了除提升热导率及提供潜热之外的另一强化沸腾换热的原因。