超声波辅助制备超细粒径双壳相变储湿胶囊及其性能

采用超声波技术辅助制备以正十八烷为核材、甲基丙烯酸甲酯为内壳、壳聚糖为外壳的超细粒径双壳相变储湿胶囊,考察乳化剂、引发剂、交联剂对超细粒径双壳相变储湿胶囊的粒径分布、相变调温性能、储湿调湿性能与微观形貌的影响。结果表明:超细粒径双壳相变储湿胶囊的最佳工艺参数:正十八烷(N-O)用量5.0 g、司盘-80用量1.0 g、吐温-80用量0.5 g、十六烷基三甲基溴化铵(CTAB)用量0.2 g、十二烷基硫酸钠(SDS)用量0.3 g、苯乙烯(St)用量5.0 g、偶氮二异丁腈(AIBN)用量0.3 g、甲基丙烯酸甲酯(MMA)用量3.5 g、壳聚糖(C)用量3.0 g、二乙烯基苯(DVB)用量0.2 g、四乙烯五胺(TEPA)用量0.2 g、超声波功率700 W。超细粒径双壳相变储湿胶囊的粒径分布为124.60～389.10 nm,其中d_(50)=217.63 nm;超细粒径双壳相变储湿胶囊具有良好的相变调温性能与储湿调湿性能,即相变温度为26.75～29.53℃、相变焓为70.67～72.84 J/g、渗透率为6.45%～7.52%,相对湿度35%～65%的平衡含湿量为0.0583～0.1276 g/g、损耗率为5.71%～6.90%。     

高温相变胶囊梯级储热系统实验研究北大核心CSCD

中高温相变储热及再利用的方式是低碳经济与工业生产的有效手段。为了更高效地实现工业高温废热的利用,本工作设计搭建并测试了一套高温相变胶囊梯级储热系统,采用了两种不同相变温度的多元碳酸盐材料作为储热材料,对换热工质空气的不同进口温度和进口流量的储放热过程进行了实验研究,研究内容主要包括储热罐中的温度变化、储热量以及储放热过程完成时间。实验结果表明在进口温度为500℃的工况下,系统的储热量可以达到30000 kJ,系统进口流量的提高会缩短储热时间,对系统总储热量影响较小,并分析了不同工况下储热罐体内相变材料平均液相率对系统总储热量的影响。同时测试发现系统中设置的空气预热器使得系统的高温尾气与常温进气进行热量交换,可以有效实现高温尾气的余热利用。相变实验的研究结果为高温相变储热技术的实际应用提供了系统运行参数的影响规律和优化准则,具有很高的参考价值。     

脂肪酸类二元储能材料的相变特性与配比调节北大核心CSCD

针对单一脂肪酸相变温度固定,与实际需求匹配性差的问题,提出以癸酸(CA)、月桂酸(LA)、十四酸(MA)、软脂酸(PA)和硬脂酸(SA)五种常见的脂肪酸作为相变材料,将其两两复合,利用低共融理论计算10种二元复合体系的最低共融点和理论质量配比,通过熔融共混法制备二元低共融复合体系并在其低共熔点上下3%~6%调节质量配比,借助DSC测试二元低共融复合体系的相变特性。结果表明,二元低共融体系的理论相变温度范围为21.58~53.90℃,理论相变潜热范围为157.64~191.85 J/g,与五种单一脂肪酸的热性能相比,相变温度降低了约10~15℃,相变潜热值无明显变化;制备的10种二元低共融体系的相变温度范围为19.94~56.49℃,与理论相变温度偏差为1.93%~14.72%;相变潜热为125.78~181.45 J/g,与理论相变潜热偏差为0.18%~19.86%;其中CA二元体系的理论相变温度范围为21.58~30.11℃,适用于建筑节能领域;LA二元体系的理论相变温度范围为35.87~41.15℃,适用于电子器件热管理或调温纺织品领域;MA和PA二元体系的理论相变温度范围为46.05~53.9℃,适用于大体积混凝土温控领域;在低共熔点附近调节配比发现最佳配比与理论计算的低共熔配比偏差在4%以内,验证理论计算的准确性和可行性。本研究结果可为脂肪酸类二元复合相变材料的具体使用范围提供技术参考。     

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。     

静电纺丝用于制备有机相变储热纤维的研究进展

相变储热材料是指由于材料相转变吸热或放热过程而本身温度不变,从而实现储能的一类功能材料。有机相变材料如石蜡类、多元醇类及硬脂酸类因无腐蚀、无毒、无过冷等优点已成为重要的低温相变储热材料。这类材料通过固-液相变调节微环境温度,可用于服装、建筑及军事等方面,市场前景广阔。但相变过程易泄漏及热导率低等限制其了实际应用。静电纺丝是有效解决该问题的方法之一,高分子在高压静电作用下形成纤维,相变材料被高分子作为支撑材料所固定,很好地解决了泄漏问题。此外,通过加入高热导率材料可提高相变材料的吸放热速率,改善有机相变材料热导率低的问题。本文总结了近年来静电纺丝用于制备相变调温纤维的研究报道,分析了目前该类材料的研究现状,并讨论未来研究方向。为储热相变材料的进一步研究提供参考。     

二醋酸纤维素脱盐膜制备及耐污染性能研究

膜法脱盐技术在电厂水处理中的广泛应用受到膜污染的限制。为此本研究选用二醋酸纤维素为制膜材料,采用相转化法制备脱盐膜,通过对溶剂的选择,优化膜的分离性能与耐污染性能。以蛋白质(BSA)、腐殖酸(HA)、十二烷基硫酸钠(SDS)、十二烷基三甲基溴化铵(DTAB)等为模型污染物,以水渗透通量回复率与脱盐率为指标,详细考察所制备脱盐膜的抗污染性能。研究发现以丙酮和N-甲基吡咯烷酮为混合溶剂时,二醋酸纤维素膜表现出较好的分离性能与耐污染性能,通量回复达到了95%左右,脱盐率几乎不受影响,具有缓解水处理过程中膜污染产生的潜力。     

列管式相变储热单元的优化模拟CSCD

列管式换热器具有结构牢固、传热面积大、材料使用适应性强等优点,是相变储热领域应用较为广泛的一种换热器。但由于大部分相变材料热导率偏低,导致换热器的换热性能较差,因此提高相变储热器的储热效率,是目前国内外研究的热点。本工作对列管式相变储热单元进行了二维非稳态模拟优化,研究了换热器结构、翅片数目及中心距3种参数对储热性能的影响,并探讨了熔化过程中相变材料的温度和液相率变化趋势。研究结果表明,与圆形换热器结构相比,正方形换热器储热性能更优;相比于无翅片的储热换热器,添加翅片后储热性能得到显著提升,相变材料熔化时间缩短66％;对中心距而言,在一定范围内,随中心距减小进出口降压增大,但储热性能相应提高。     

相变蓄热材料微胶囊制备工艺的正交试验分析

以常低温相变蓄热材料作为芯材,脲醛树脂作为壳材,通过原位聚合法合成了常低温相变蓄热材料微胶囊。采用正交试验优化,确定了微胶囊的最佳制备工艺。利用SEM分析了乳化剂的种类对微胶囊微观形貌的影响,并结合FTTR和DSC等测试仪器考察了通过最佳制备工艺得到的微胶囊化学结构及热性能。实验结果表明:在乳化转速为3000r/min下使用由吐温60和司盘60组成的混合型乳化剂,用量为芯材质量5%,所制备的微胶囊具有良好的热稳定性、球体表面光滑、粒径均一。在吸热过程中,相变温度为30.10℃,相变潜热为63.85J/g。     

热适应复合相变材料的制备与热性能

根据电子器件散热技术领域对热适应复合材料的性能要求,选取导热系数高且密度低的膨胀石墨作为无机支撑材料,石蜡作为有机相变材料,制备出高导热系数和储热密度的热适应复合相变材料.采用扫描电镜(SEM)、差示扫描量热仪(DSC)、偏光显微镜(POM)和Hot Disk热常数分析仪等多种测试技术,对复合相变材料进行分析研究;通过储/放热实验和1000次热循环实验研究了复合相变材料的传热性能和热稳定性.实验结果说明该复合相变材料具有形状稳定、导热率高、储热密度大等特点,并具有良好的热稳定性和使用寿命.     

膨胀石墨/多壁碳纳米管基共晶盐复合相变材料的制备及热特性北大核心CSCD

单一水合盐作为相变蓄热材料使用时常常由于过冷、相分离、易泄漏以及其相变温度而受到限制,因此迫切需要制备出一种储热密度高、相变温度适宜、热导率大的复合相变材料。本工作采用熔融共混法在NH_(4)Al(SO_(4))_(2)·12H_(2)O(AASD)中掺入不同质量分数的MgSO_(4)·7H_(2)O(MSH),成功制备了AASD-MSH共晶盐相变材料,其质量比为55∶45,相变温度为76.4℃,相变潜热为189.4 J/g。共晶盐的X射线衍射图谱和傅里叶红外光谱表明其为物理混合。引入质量分数1%成核剂CaCl_(2)·2H_(2)O及1%增稠剂可溶性淀粉降低共晶盐过冷度,过冷度从34.9℃降低至28.0℃。引入改性膨胀石墨(MEG)与多壁碳纳米管(MWCNTs)制备复合相变材料,改善共晶盐易泄漏及热导率低等问题,当MWCNTs质量分数为0.5%时,复合相变材料的热导率高达8.185 W/(m·K),为共晶盐的19.98倍,其中共晶盐占比为75.6%,相变温度为74.3℃,相变焓值为133.5 J/g,过冷度进一步降低至22.2℃。热重实验表明与MEG-MWCNTs的复合增加了共晶盐的热稳定性,且经过100次冷热循环后复合相变材料的相变焓值基本不变,具有良好的循环稳定性。本工作制备得到的AASD-MSH/MEG-MWCNTs复合相变材料是一种相变温度适合、相变焓值较高、热导率较大的相变材料,且具有良好的热循环稳定性,应用潜力极大。     

Electrospun polyethylene glycol/cellulose acetate phase change fibers with core–sheath structure for thermal energy storage

The ultrafine phase change fibers (PCFs) with core–sheath structure based on polyethylene glycol/cellulose acetate (PEG/CA) blends were fabricated successfully via coaxial electrospinning for thermal energy storage. SEM and TEM images show that cylindrical and smooth phase change fibers are obtained and PEG as a phase change ingredient is encapsulated completely by CA sheath. The morphology of the composite fibers before and after thermal treatment indicates that the prepared fibers are form stable phase change materials (PCMs). The results from DSC demonstrate that the composite fibers impart balanced and reversible phase change behaviors, and phase transition enthalpies of the composite fibers increase with the increasing of PEG content in the fibers, while the phase transition temperatures of the fibers are similar with those of pure PEG. The stress–strain curves show that the ultimate strength and ultimate strain of the composite fibers are lower than those of CA fibers, and they decrease with the increase of PEG content. The PEG/CA composite fibers have extensive applications as a smart material for thermal energy storage and temperature regulation.     

Electrospun phase change fibers based on polyethylene glycol/cellulose acetate blends

Ultrafine phase change fibers based on polyethylene glycol (PEG)/cellulose acetate (CA) blends in which PEG acts as a model phase change material (PCM) and CA acts as a supporting material, were successfully prepared via electrospinning. The effect of PEG content on the morphology, crystalline properties, phase change behaviors and tensile properties of the composite fibers was studied systematically by field-emission scanning electron microscopy (FE-SEM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and a tensile tester, respectively. The SEM observation indicates that maximum PEG content in the fibers could reach up to 70 wt%, and the morphology and average diameter of the composite fibers vary with PEG content. Thermal analysis results show that the latent heats of the phase change fibers increase with the increasing of PEG content in the fibers, and the PEG/CA fibers with high enthalpies have a good capability to regulate their interior temperature as the ambient temperature alters. Therefore, the developed phase change fibers have enormous applicable potentials in thermal energy storage and temperature regulation.     

Recent progress about expanded graphite matrix composite phase change material for energy storage

膨胀石墨基复合相变材料具有导热系数高,储能密度大以及相变过程无液体泄漏等优点,是近年来储能科学领域的研究热点.本文探讨了应用于储热系统的相变材料的性能及分类,并对膨胀石墨及其复合相变材料的制备方法进行了简要分析,最后综述了石蜡类,脂肪酸类,共晶混合物类,聚乙二醇以及乙酰胺等膨胀石墨基复合相变材料的国内外研究进展.     

多孔基无机玻璃-熔盐复合相变材料蓄热性能的实验研究

基于熔融浸渗法和黏结封装法,以多孔基作为基体材料,分别采用无机玻璃粉与熔盐作为相变材料开展实验,探究储热样本的最佳制备工艺流程。考察了复合相变蓄热体的显微结构及物相组成特征,分析了复合相变蓄热材料的质量损失率,并对蓄热体进行蓄热性能分析及高温抗压强度测试。实验结果表明,采用黏结封装法,以氯化钠作为相变材料,加盖圆柱形三角孔蜂窝陶瓷基体作为载体,设定6.5℃/min的升温速率,烧结温度至800℃,保温30 min,可制备蓄热性能较为优异的复合相变蓄热材料。复合相变蓄热材料的蓄热密度为445.5 kJ/kg,该蓄热体在800℃条件下高温抗压强度达到75.9 MPa,具有良好的蓄热性能和力学性能。     

Fabrication and characterization of electrospun fatty acid form-stable phase change materials in the presence of copper nanoparticles

Latent heat storage system using phase change materials (PCMs) has been recognized as one of the most useful technologies for energy conservation. In this study, a novel type of fatty acid eutectic of methyl palmitate (MP) and lauric acid (LA)/polyacrylonitrile (PAN) composite phase change fiber is prepared by single electrospinning method. Additionally, copper nanoparticles (CNPs) with different mass ratio are combined for improving the thermal conductivity of the PCM. The structure and morphology of the fabricated composite PCMs are observed by scanning electron microscopy (SEM), and the thermal properties and performance are also characterized. SEM results show that the liquid fatty acid has been fully stabled by the three-dimensional structure of the fibers. Good compatibility among the components of the composites is also demonstrated. Besides, the addition of nanoparticles leads to an improved thermal conductivity by over 115.2% and a phase transition temperature 21.24 °C as well as a high latent heat of 85.07 J/g. Moreover, excellent thermal reliability of the phase change fiber is confirmed by multiple thermal cycles. Hence, the composite PCM prepared in this study shows a promising potential for thermal energy system such as building insulating and thermal mass regulating textiles.     

Thermal performance of shape-stabilized phase change paraffin wallboard

This paper presents thermal performance of shape-stabilized phase change material (PCM) wallboards and common wallboard. Shape-stabilized PCMs consist of paraffin and high-density polyethylene as support materials. The wallboards were prepared by shape-stabilized PCMs and grout with the building materials in mass proportions of 5%, 10%, and 15%. The phase change temperature of the shape-stabilized paraffin was 27.5 °C and the maximum content of paraffin in the shape-stabilized PCM was 70%. The energy-saving effect and feasibility of shape-stabilized PCM wallboard were compared with those of ordinary wallboards. The results showed that prepared PCM wallboard has good thermal performance and thus it has high potential for the cooling of buildings.     

石蜡/膨胀石墨复合相变储热材料的研究

以膨胀石墨为基体,石蜡为相变储热介质,利用膨胀石墨对石蜡良好的吸附性能,制备出了石蜡／膨胀 石墨复合相变储热材料。由于毛细作用力和表面张力的作用,石蜡在固-液相变时,很难从膨胀石墨的微孔中渗 透出来。实验结果表明,石蜡/膨胀石墨复合相变储热材料没有改变膨胀石墨的结构和石蜡的固-液相变温度, 且其结合了石墨高的导热系数和石蜡大的相变潜热,因而储热密度较高,导热性能好。其相变潜热与对应质量 分率下的石蜡相当,储/放热时间比石蜡明显减少。     

墙体储能用定形相变石蜡储热性能的实验研究

实验配制并研究了以高密度聚乙烯为支撑材料的定形相变石蜡.所使用的石蜡为由液体石蜡分别与46#石蜡、48#石蜡配制的两种适于墙体中使用低熔点混合物,相变温度分别为26.6、25.5℃,相变潜热较大.利用DSC实验研究了两种石蜡混合物分别与高密度聚乙烯按40%～90%比例配制成的定形相变材料的相变温度、相变潜热、均匀性和稳定性.定形相变材料在低温区的相变温度与石蜡的相变温度基本一致,在26～28℃之间,定形材料相变潜热近似等于石蜡的相变潜热与石蜡百分含量的乘积.定形相变材料中石蜡的最佳含量为70%,此时相变潜热约为100J/g.     

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.     

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.