相变储热研究进展(2)组合相变材料储热与应用潜力

本文从两个方面总结了相变储热（ＬＴＥＳ）的研究现状：①ＬＴＥＳ在太空太阳能动力（ＤＢＰ）发电系统和建筑物围护结构中的应用;②组合相变材料储热系统的研究历程和最新进展。     

含碳二元系相变储热材料储热性能分析选择北大核心CSCD

相变储热技术与聚光太阳能发电技术相结合可以提高太阳能的利用率,减缓化石燃料燃烧带来的环境压力。本文通过分析相变储热材料的选择标准,对筛选出具有研究价值的含碳二元系相变储热材料的性能特别是热物理性能进行分析。研究发现,硅、硼、铝、铬、铁单质材料与碳元素形成的二元化合物或固溶体具有较高的熔点,形成的含碳二元系相变储热材料在高温相变储热领域应用前景广阔。在含碳二元系相变储热材料中,Fe-C二元合金可满足高温相变储热系统1100~1500℃的相变储热要求,当合金为含碳4.3%的Fe-C共晶成分时,Fe-C二元合金的相变潜热理论值为611 kJ/kg,热导率约为(40±16)W/(m·K),相变温度为1148℃,具有相对其他合金成分更为优异的综合储热性能可用于聚光太阳能热发电系统储热。     

陶瓷基复合相变储热材料的冷热循环性能研究

通过探讨材料烧成温度和无机盐质量分数的影响,发现NaNO3/SiO2和Na2CO3-Li2CO3/MgO的烧成温度分别在330℃和520℃、无机盐质量分数均达到70%时冷热循环性能较好。同时研究了冷热循环测试对这两种储热材料机械性能的影响,探索出在长期使用过程中材料力学性能的变化规律。     

铝硅合金用作相变储热材料的研究

本文针对铝合金相变储热材料（ＰＣＭ）的高温氧性能、热循环特性以及与容器材料的相容性进行了实验研究。结果表明，铝硅合金由于相变潜热大，熔点适中，而且性能稳定，是一种较为理想的中高温相变储热材料。     

高温复合相变材料储热电暖器的储热性能CSCD

本文研究了基于高温复合相变材料的相变储热电暖器,对其储热性能、内部流场和温度分布及温度调控机制进行了实验和模拟研究,并与镁砖显热电暖器的储热性能进行对比。结果表明这类相变储热电暖器的储热平均温度高、平均温差小、出风口温度高,整体性能要优于镁砖显热电暖器。相同体积下两种电暖器储热量相当,但相变储热电暖器的重量可减轻1.6倍;在相同储热时间和储热温度下,同等重量的相变储热电暖器较镁砖电暖器可多储热68%。结果也展示了这类储热电暖器温度控制测点选择的重要性,当选取距离加热单元10 mm处的测点作为温度调控点时,电暖器内的平均温度和储热砖体的最高温度均能满足安全要求,而且加热单元电源在谷电8 h储热过程中只需启停两次。     

石蜡高岭土相变储热材料的制备及表征

为克服太阳能不连续与不稳定引起的建筑物室内温度波动的现象,文章以石蜡与高岭土为试验原料,制备一种用于建筑墙体隔热保温的新型高岭土基相变储热材料。采用XRD,SEM,FTIR和DSC测试方法研究了相变储热材料的结构与性能。结果表明：高岭土具有良好的吸附性能,能物理吸附大量的石蜡至其孔隙结构;石蜡高岭土相变储热材料的熔融和冷凝温度分别为27.5,25.3℃,熔融和冷凝相变潜热值分别为33.5,32.9J/g;服役期间,石蜡未从储热材料中泄露,也未与高岭土化学键合;经1 000次循环试验后,储热材料的相变温度与相变潜热值变化不显著。高岭土优异的吸附能力赋予了该储热材料优异的吸储热能力。高岭土与石蜡较好的物理化学相容性使储热材料具有优良的化学稳定性。     

Na_(2)CO_(3)/电石渣复合相变储热材料制备与性能北大核心CSCD

为循环利用工业固体废弃物,降低储热系统成本,以工业固废电石渣替代传统骨架材料,采用冷压烧结法创新制备7种不同配比的Na_(2)CO_(3)/电石渣复合相变储热材料,利用差示扫描量热法、恒速增压法、电子显微法、高温热冲击法、X射线衍射法、红外吸收光谱法等方法研究其储热性能、力学性能、微观结构、热循环稳定性和化学兼容性。结果表明,电石渣与碳酸钠结合可形成性能优异的复合相变储热材料;电石渣与碳酸钠质量比为52.5∶47.5时制备的复合相变储热材料(NC5)综合性能最佳,储热密度在100~900℃内达到993 J/g,抗压强度达到22.02 MPa,最高导热系数为0.62 W/(m·K);样品NC5中不同组分均匀分布,组分间具有良好的兼容性;样品NC5经100次加热/冷却循环后仍具有优异的储热性能,可为固废资源化利用和低成本储热材料研发提供技术支持。     

用于太阳能热发电站的Na_2SO_4基相变储热材料的制备研究

膨胀珍珠岩具有较好的吸附性能,利用膨胀珍珠岩作为封装基体能够降低Na_2SO_4的泄漏风险。文章以膨胀珍珠岩和Na_2SO_4为原料,制备了一种新型的相变储热材料,然后通过实验分析了该相变储热材料的储热性能、热稳定性等。分析结果表明:膨胀珍珠岩能够吸附大量的Na_2SO_4,并且可以将Na_2SO_4输送至其空腔结构内,形成相变储热材料;热循环期间,相变储热材料中的Na_2SO_4不会泄露,也不会与膨胀珍珠岩发生反应;热循环1 000 h后,相变储热材料的质量、相变潜热分别仅减少了4.60%,7.70%。     

高温相变储热材料制备与应用研究进展北大核心CSCD

面向工业领域蒸汽供热需求,大力发展高温相变储热技术,有效调节电网峰谷负荷,有力促进电能替代,助力实现“碳达峰、碳中和”目标。本文通过对近期相关文献的回顾,首先介绍了相变材料优选原则与方法,其次介绍了高温相变材料的分类,着重阐述了盐基高温复合相变材料的最新研究动态,包括金属泡沫/无机盐、石墨泡沫/无机盐、膨胀石墨/无机盐、多孔陶瓷/无机盐复合相变材料和黏土矿物/无机盐相变复合材料,指出高温复合相变材料可以改善无机盐低热导率和热稳定性、腐蚀密封材料等问题。然后总结了高温相变材料的制备方法,指出浸渗法、溶胶-凝胶法、冷压烧结法在实际应用中各有利弊,相比之下,冷压烧结法是制备盐基复合材料最具成本效益的方法。最后重点介绍了高温复合相变材料在工业过程余热回收、电力调峰、太阳能热发电三个领域的应用现状,为研究不同场景下蒸汽型高温相变储热系统容量配置和经济评估方法提供了理论基础。     

应用于太阳能热发电站的高岭土基相变储热材料的制备

由于高岭土具有优异的吸附性和包覆性,文章以高岭土为载体,硬脂酸钠为相变材料,制备出一种新型的高岭土/硬脂酸钠相变储热材料,并利用XRD,SEM,FTIR和DSC现代测试技术对该相变储热材料的结构和各项性能进行研究。分析结果表明:高岭土和硬脂酸钠之间存在吸附关系,二者未发生化学反应;高岭土基相变储热材料的熔融、冷凝温度分别为252.86,256.91℃,熔融、冷凝相变潜热值分别为109.25,109.01 J/g;经500次热循环后,高岭土基相变储热材料的储热性能没有明显降低,高岭土与硬脂酸钠之间的结合方式也没有发生变化。     

Microencapsulation of phase change material with poly(ethylacrylate) shell for thermal energy storage

Microcapsules containing caprylic acid and polyethylacrylate shells were prepared using an emulsion polymerization technique for thermal energy storage applications. Ethylene glycol dimethacrylate was used as a crosslinking agent. The influence of the crosslinking agent concentration on the phase change properties of microcapsules was examined. The caprylic acid microcapsules (MicroPCMs) were analyzed by Fourier transform infrared spectroscopy, thermal gravimetric analysis, scanning electron microscopy, and differential scanning calorimetry. The results showed that microcapsules were synthesized successfully and that the best shell material:crosslinking agent concentration ratio was 1:0.2. The melting and freezing temperatures were measured through differential scanning calorimetry analysis and found to be 13.3 and 7.1°C, respectively. The melting and crystallization heats were determined to be 77.3 and ?77.0 kJ/kg, and the mean particle diameter was 0.64 μm. The thermal cycling tests of the microcapsules were performed for 400 heating/cooling cycles, and the results indicate that the synthesized microcapsules have good thermal reliabilities. Air stability test proved that the thermal properties and physical form of microcapsules were not affected by air. We recommend the prepared thermal, air, and chemically stable caprylic acid microcapsules for thermal energy storage applications as novel microPCM with latent heat storage capacities and properties. Copyright © 2014 John Wiley & Sons, Ltd.     

PolyHIPE composite based-form stable phase change material for thermal energy storage

A novel shape-stabilized n-hexadecane/polyHIPE composite phase change material (PCM) was designed and thermal energy storage properties were determined. Porous carbon-based frameworks were produced by polymerization of styrene-based high internal phase emulsions (HIPEs) in existence of the surface modified montmorillonite nanoclay. The morphological and mechanical properties of the obtained polyHIPEs were investigated by scanning electron microscopy analysis and the compression test, respectively. The polyHIPE composite with the best pore morphology and the highest compression modulus was determined as a framework to prepare the form stable n-hexadecane/polyHIPE composite phase change material using the one-step impregnation method. The chemical structure and morphologic property of composite PCM was investigated by FT-IR and polarized optical microscopy analysis. Thermal stability of the form-stable PCM (FSPCM) was examined by TG analysis. The n-hexadecane fraction engaged into the carbon foam skeleton was found of as 55 wt% from TG curve. differential scanning calorimetry analysis was used for determining melting temperature and latent heat storage capacity of FSPCM and these values were determined as (26.36°C) and (143.41 J/g), respectively. The results indicated that the obtained composite material (FSPCM) has a considerable potential for low temperature (18°C-30°C) thermal energy storage applications with its thermal energy storage capacity, appropriate phase change temperatures and high thermal stability.     

Numerical analysis of latent heat thermal energy storage using encapsulated phase change material for solar thermal power plant

Thermal energy storage improves the load stability and efficiency of solar thermal power plants by reducing fluctuations and intermittency inherent to solar radiation. This paper presents a numerical study on the transient response of packed bed latent heat thermal energy storage system in removing fluctuations in the heat transfer fluid (HTF) temperature during the charging and discharging period. The packed bed consisting of spherical shaped encapsulated phase change materials (PCMs) is integrated in an organic Rankine cycle-based solar thermal power plant for electricity generation. A comprehensive numerical model is developed using flow equations for HTF and two-temperature non-equilibrium energy equation for heat transfer, coupled with enthalpy method to account for phase change in PCM. Systematic parametric studies are performed to understand the effect of mass flow rate, inlet charging system, storage system dimension and encapsulation of the shell diameter on the dynamic behaviour of the storage system. The overall effectiveness and transient temperature difference in HTF temperature in a cycle are computed for different geometrical and operational parameters to evaluate the system performance. It is found that the ability of the latent heat thermal energy storage system to store and release energy is significantly improved by increasing mass flow rate and inlet charging temperature. The transient variation in the HTF temperature can be effectively reduced by decreasing porosity.     

Thermal energy storage using a phase change material

A two-dimensional melting process of a solid phase change material is investigated theoretically. The material contained in a rectangular enclosure heated from one side, while all the other sides are assumed to be adiabatic ones. In this study convection mode was considered to be the dominant mode of heat transfer within the melted region, except within the region very close to the solid surface at the bottom where conduction mode was only taken into considerations. It was found that the obtained results are in good agreement with previous ones. Finally the present analysis was used to predict the melted fraction of the phase change material and hence the amount of stored energy.     

Performance evaluation of a solar thermal energy storage system using nanoparticle-enhanced phase change material

This paper presents a numerical investigation on the thermal performance of a solar latent heat storage unit composed of rectangular slabs combined with a flat-plate solar collector. The rectangular slabs of the storage unit are vertically arranged and filled with phase change material (PCM: RT50) dispersed with high conductive nanoparticles (Al₂O₃). A heat transfer fluid (HTF: water) goes flow in the solar collector and receives solar thermal energy form the absorber area, then circulates between the slabs to transfer heat by forced convection to nanoparticle-enhanced phase change material (NEPCM). A numerical model based on the finite volume method and the conservation equations was developed to model the heat transfer and flow processes in the storage unit. The developed model was validated by comparing the obtained results with the experimental, numerical and theoretical results published in the literature. The thermal performance of the investigated latent heat storage unit combined with the solar collector was evaluated under the meteorological data of a representative day of the month of July in Marrakesh city, Morocco. The effect of the dispersion of high conductive nanoparticles on the thermal behavior and storage performance was also evaluated and compared with the case of base PCM without additives.     

Solar thermal storage systems using phase change materials

Using Fourier series expansion of the involving temperatures and the forcing parameters i.e. the solar radiation and the ambient temperature, an iterative procedure has been developed to solve the heat transfer problem with moving boundaries. Calculations specific to a typical summer and winter day in Delhi have been presented for a numerical appreciation of the developed analysis. Experiments have been performed to validate the developed theoretical analysis. A good agreement is seen between theoretical and experimental results with in the domain of the applicability of theory.     

Microencapsulated n-octacosane as phase change material for thermal energy storage

This study deals with preparation and characterization of polymethylmetracrylate (PMMA) microcapsules containing n-octacosane as phase change material for thermal energy storage. The surface morphology, particle size and particle size distribution (PSD) were studied by scanning electron microscopy (SEM). The chemical characterization of PMMA/octacosane microcapsules was made by FT-IR spectroscopy method. Thermal properties and thermal stability of microencapsulated octacosane were determined using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The melting and freezing temperatures and the latent heats of the microencapsulated octacosane as PCM were measured as 50.6 and 53.2 °C, 86.4 and −88.5 J/g, respectively, by DSC analysis. TGA analysis indicated that the microencapsulated octacosane degrade in two steps and had good chemical stability. Thermal cycling test shows that the microcapsules have good thermal reliability with respect to the accelerated thermal cycling. Based on the results, it can be considered that the microencapsulated octacosane have good energy storage potential.     

Preparation, characterization, and thermal properties of microencapsulated phase change material for thermal energy storage

This study is focused on the preparation, characterization, and determination of thermal properties of microencapsulated docosane with polymethylmethacrylate (PMMA) as phase change material for thermal energy storage. Microencapsulation of docosane has been carried out by emulsion polymerization. The microencapsulated phase change material (MEPCM) was characterized using scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. Thermal properties and thermal stability of MEPCM were measured by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). DSC analysis indicated that the docosane in the microcapsules melts at 41.0 °C and crystallizes at 40.6 °C. It has latent heats of 54.6 and −48.7 J/g for melting and crystallization, respectively. TGA showed that the MEPCM degraded in three distinguishable steps and had good chemical stability. Accelerated thermal cycling tests also indicated that the MEPCM had good thermal reliability. Based on all these results, it can be concluded that the microencapsulated docosane as MEPCMs have good potential for thermal energy storage purposes such as solar space heating applications.     

三水合乙酸钠/蛭石复合相变蓄热材料性能优化研究

采用真空浸渍法将三水合乙酸钠（sodium acetate trihydrate,SAT）吸附在膨胀蛭石（expanded vermiculite,EV）微孔内,选择EV吸附SAT能力最佳的质量比为1:6。通过扫描电子显微镜（scanning electron microscopy,SEM）观察复合相变材料（composite phase change material,CPCM）的微观结构,显示EV微孔几乎完全被SAT填充。X射线衍射（X-ray diffraction,XRD）表明SAT与EV化学相容性较好,二者仅发生物理相互作用。通过差式扫描量热法（differential scanning calorimetry,DSC）测试EV在最大吸附能力下,复合材料的相变温度为57.6℃,接近SAT理论相变温度58.1℃;相变潜热为238.8kJ/kg。热重分析（thermogravimetric analysis,TG）结果显示复合材料热稳定性良好。因为EV负载体将SAT间隔为无数微单元,有效改善SAT相变过程中过冷和相分离现象,起到成核剂和悬浮剂的作用。实验研究结果表明,制备的CPCM具有较好的热物性以及稳定的热循环性能,有望成为相变蓄热材料应用于冬季供暖。     

Microencapsulation of coco fatty acid mixture for thermal energy storage with phase change material

Thermal energy storage systems provide several alternatives for efficient energy use and energy conservation. Microcapsules of natural coco fatty acid mixture were prepared to be used as phase change materials for thermal energy storage. The coacervation technique was used for the microencapsulation process. Several alternatives for the capsule wall material were tried. The microcapsules were characterized according to their geometric profiles, phase transition temperatures, mean particle sizes, chemical stabilities, and their thermal cycling. The diameters of microcapsules prepared in this study were about 1 mm. Coco fatty acid mixtures have kept their geometrical profiles even after 50 thermal cycles for melting and freezing operations in temperature range from 22 to 34°C. It was found that gelatin+gum Arabic mixture was the best wall material for microencapsulating coco fatty acid mixtures. Copyright © 2005 John Wiley & Sons, Ltd.