【作者】 王毅；

【导师】 夏天东；

【作者基本信息】 兰州理工大学 ， 先进材料及其制备技术， 2014， 博士

【摘要】 复合相变储热材料利用相变物质相变过程中的相变潜热来实现能量的储存与利用,不仅可解决相变物质的腐蚀性、相变过程中的流动性等自身缺陷,而且可解决能量供求在时间、空间上的不匹配,有助于提高能效和开发可再生能源。本文利用层次分析法和多准则妥协解排序法对常用相变材料的综合性能进行了优选排序,以优选的硬脂酸为相变储热主体,分别以高分子聚合物和无机载体对其进行了封装,测试了胶囊型相变储热材料和负载型相变储热材料的结构和性能,分析了自组装机理,研究了制备工艺对复合相变储热材料结构和性能的影响,讨论了界面作用与相变行为间的关系。将层次分析法和多准则妥协解排序法引入相变材料的多属性决策中,根据影响相变材料实际应用的关键性能参数,构建了三个层次六个属性的相变材料评价体系,建立了基于层次分析法和多准则妥协解排序法的相变储热材料评价模型,指出了评价方法和步骤。在此基础上,对十种备选相变材料的综合性能进行了优选排序。通过与文献选用频次的比较,证明了层次分析法和多准则妥协解排序法在相变储热材料优选排序中具有有效性、实用性和统一性,筛选出的综合性能最优的有机相变储热材料为硬脂酸。以优选的硬脂酸为芯材,以甲基丙烯酸甲酯为壁材单体,通过紫外光引发单体聚合制备了硬脂酸／聚甲基丙烯酸甲酯微胶囊相变储热材料,应用差示扫描量热仪、热重分析仪、扫描电子显微镜、傅立叶红外光谱仪和加速热循环实验等手段研究了微胶囊相变储热材料的结构和性能,讨论了硬脂酸／聚甲基丙烯酸甲酯微胶囊的形成机理。结果发现,硬脂酸／聚甲基丙烯酸甲酯微胶囊相变储热材料具有明显的核-壳结构,核壳间仅存在氢键作用,其芯材含量为51.8%,粒径为2-3μm,熔融相变温度和结晶相变温度分别为60.4℃和50.6℃,对应的相变潜热分别为92.1J·g-1和95.9J·g-1。硬脂酸／聚甲基丙烯酸甲酯微胶囊相变材料具有良好的稳定性,热循环次数对其相变行为无明显影响。研究结果同时表明,采用紫外光引发单体聚合工艺可获得与传统热引发工艺相媲美的微胶囊相变储热材料。以硬脂酸-二十酸共晶混合物为包封对象,采用紫外光引发甲基丙烯酸甲酯乳液聚合自组装合成了硬脂酸-二十酸／聚甲基丙烯酸甲酯纳米胶囊相变储热材料,研究了乳化剂种类、乳化速率、引发剂浓度和交联剂等因素对胶囊粒径分布和储热性能的影响。研究结果表明,乳化剂类型和乳化速率对硬脂酸-二十酸／聚甲基丙烯酸甲酯的储热能力和粒径分布影响显著。随着乳化速率和引发剂浓度的增加,以及交联剂的加入,硬脂酸-二十酸／聚甲基丙烯酸甲酯胶囊的粒径逐渐减小、粒径分布变窄,并且在乳化速率达到5000rpm和单体浓度达到0.15mo1·L-1时趋于恒定。同时,单体浓度和引发剂浓度的增加,将会导致聚合速率加快,进而导致粒子间聚集的速率增加,胶囊的储热能力下降。硬脂酸-二十酸／聚甲基丙烯酸甲酯纳米相变胶囊的最佳制备工艺条件为核壳比1：0.7；乳化速率5000rpm,单体浓度O.15mol·L-1、引发剂浓度O.1Ommol·L-1,使用聚乙二醇辛基苯基醚为乳化剂、乙二醇二甲基丙烯酸酯为交联剂。在该制备条件下,纳米胶囊相变储热材料的平均粒径为46nm,硬脂酸-二十酸共晶混合物的含量为68.8%,熔融和结晶温度分别56.9℃和54.5℃,相应的相变潜热分别为126.4J·g-1和128.3J·g-1,且具有良好的稳定性。纳米胶囊的形成使得共晶混合物的过冷度显著减小。以硬脂酸为相变基质,采用化学氧化法制备了具有储热、导电功双重功能的硬脂酸/聚苯胺复合材料。通过对硬脂酸/聚苯胺复合材料组装工艺的优化、结构的表征和性能的测试发现,聚合温度对硬脂酸/聚苯胺复合材料的形貌和储热能力影响显著,掺杂酸的种类仅影响硬脂酸/聚苯胺的形貌而对储热能力影响不大,引发剂种类的不同则不会改变硬脂酸/聚苯胺的形貌但影响其储热能力,通过聚合温度、掺杂剂种类的选择可调控硬脂酸/聚苯胺复合材料的形貌。组装机理分析表明,片状硬脂酸/聚苯胺复合材料的组装作用力为氢键,而球形硬脂酸/聚苯胺复合材料的组装力为静电引力。制备具有良好稳定性、较高储热能力的硬脂酸/聚苯胺复合材料的最佳工艺为：在室温条件下,使用氨基磺酸为掺杂剂、过硫酸铵和过氧化苯甲酰为混合引发剂,制备的片状硬脂酸/聚苯胺复合材料中硬脂酸的含量为53.8%、导电能力为0.4336S-cm-1,熔融和结晶温度分别为55.6℃和50.7℃,对应的相变潜热为98.0J·g-1和97.5J·g-1。硬脂酸/聚苯胺复合材料的形成,赋予了相变材料导电性能,拓展了应用领域。以硬脂酸为相变基质,以甘肃平凉工业蒙脱土为载体,采用真空热熔注入法和溶液浸渍法制备了两种硬脂酸/蒙脱土复合相变储热材料,采用FTIR、XRD、DSC和SEM等手段进行了结构表征和性能测试,并将真空热融注入法获得的相变储热材料添加到泡沫水泥中,研究了相变储热泡沫水泥的隔热性能。结构分析结果表明,制备方法对材料的结构和形貌不会产生影响,两种材料具有相似的形貌和结构,硬脂酸均以物理作用吸附于蒙脱土表面,且两者之间不存在任何化学键合。性能分析结果表明,在热熔法和浸渍法制备的复合储热材料中硬脂酸的负载率分别为47.5wt.%和46.9wt.%,其熔融相变温度和结晶相变温度分别为59.9℃、58.2℃和55.1℃、54.6℃,对应的相变潜热分别为84.4J·g-1、88.5J·g-1和83.6J-g-1、86.8J/g,均具有较好的储热能力,且复合相变储热材料的储热能力和硬脂酸在蒙脱土表面的负载率成正比,但加速热循环实验表明浸渍法制备的复合相变储热材料的热稳定性较差,真空熔融注入法更适合制备稳定性良好的负载型复合相变储热材料。模拟隔热实验研究表明,添加3.3wt.%硬脂酸/蒙脱土的相变储热泡沫水泥具有明显的隔热调温作用,其表面温度从20℃升高到70℃的时间比普通水泥增加了172%。更多还原

【Abstract】 The rapid development of global economy leads to energy demand increase quickly. However, conventional fossil energy sources are limited and their uses are restricted due to the emission of harmful gases which are responsible for climate changes and environmental pollution. Composite phase change materials (PCM) can be used for energy storage and utilization due to it can absorb or release large latent heat during the melting or solidifying process when surrounding temperature increases and decreases, which is helpful to improve energy efficiency and develop new renewable energy and can prevent PCM from leaking and harmful interaction with the environment when phase change occurs. In this work, we have determined the ranks of important PCMs using Analytic Hierarchy Process (AHP) and VlseKriterijumska Optimisacija IKompromisno Resenje (VIKOR) technique. Stearic acid is found to be the best PCM for latent heat thermal energy storage systems within the range of our reseach and it also encapsulated with the polymer wall or inorganic carrier. The structure and properties of capsules and loaded phase change materials were studied, and the self-assembly mechanism of the composites were analyzed. Also, the effects of fabricated technology on particle size distribution, thermal properties and structures were stuied and the relationship between the phase transiton behavior with surface interreaction of PCM and matrix was explored.Selection of an optimal PCM according to engineering requirements, such as high sensible heat, latent heat, heat of conduction and light weight, is a crucial and tedious task. It depends upon various thermo-physical properties including latent heat of fusion, density, thermal conductivity, specific heat capacity. Therefore, Analytic Hierarchy Process and VlseKriterijumska Optimisacija IKompromisno Resenje, the approach of multi-attribute decision making, are employed for PCMs selection. Based on the characteristics of PCM, the valuation system of three level and six different attributes was constructed and the evaluation model based on AHP and VIKOR method were established. At last, the VIKOR and AHP method were used to sort the attributes of alternative PCMs comprehensively. The results show that the two methods are effective and practical for selecting PCMs and stearic acid is the optimal PCM within the candidants for thermal energy storage.In order to identify the validity of fabricating microencapsulated phase change material by ultraviolet irradiation-initiated method, the stearic acid/polymethyl methacrylate (PMMA) microcapsules were prepared. The structural characteristics and thermal properties of the microcapsules were also determined by various techniques. The results show that the form-stable microencapsulated PCM with core/shell structure is formed and the maximum encapsulated proportion of SA in the composite is51.8wt.%without melting PCM seepage from the composite. In the shape stabilized microencapsulated PCM, the polymer acts as supporting material to form the microcapsule cell preventing the leakage of PCM from the composite and the SA acts as a PCM encapsulated in the cell of PMMA resin. The oxygen atom of carbonyl group of skeleton is interacted with the hydrogen atom of hydroxyl group of SA. The melting and freezing temperatures and the latent heats of the composite PCM are measured as60.4℃,50.6℃and92.1J-g-1,95.9J-g-1, respectively. The results of hermal cycling test show that the thermal reliability of the composite PCM has an imperceptible change.In order to further optimize the preparation technology and reduce the particle size of capsules, the polymethyl methacrylate encapsulated eicosanoic-stearic acid (EA-SA) eutectic nanocapsules were prepared by ultraviolet photoinitiated emulsion polymerization and various characterization techniques were employed to investigate the influence of preparation methods on thermal properties and particle size distribution (PSD). The results show that the particle size decreases and PSD narrows with the increase of agitation speed, reduction of initiator and monomer concentration, existence of cross-linking agent and stabilized at agitated speed higher than5000rpm and monomer concentration lower than0.15mol-L-1. However, latent heats of the capsules decreases with the increase of monomer and initiator concentration. Type of emulsifier in emulsion has significant effects on PSD and phase change properties of EA-SA/PMMA and nonionic emulsifier is suitable for reducing particle size and enhancing heat storage ability. Morphology and chemical characteristic analysis indicate that spherical nanocapsules with average diameter of46nm were successfully fabricated and its maximum encapsulation ratio is68.8wt.%without leakage of core material. The melting and crystallizing temperatures and latent heats of capsules are determined as56.9℃and54.5℃,126.4J-g-1and128.3J-g-1, respectively. Accelerated thermal cycling test shows that the nanocapsules have good thermal and chemical reliability after repeated thermal cycling. Besides, the super-cooling problem of PCMs is reduced dramatically by forming nanocapsules.In order to entrust electrical conductivity for phase change materials, the composite phase change material using SA as core material and polyaniline (PANI) as wall materials were perapared though chemical oxidation method. The structure, thermal properties, thermal reliability, thermal conductivity, heat storage or release performance and electrical conductivity of the dual-functional compsosite were also determined. The results show that the polymerization temperature has significant effects both on the morphology and phase change properties of SA/PANI, but the type of the doping acid and the type of initiator are only effect the morphology or thermal performance respectively. In addition, the the type of doping acid has negligible effects on thermal performance and the type of initiator has ignore effects on morphology. Self-assembly mechanism analysis show that the assembly forces of flaky composite is hydrogen bond and the assembly force in spherical composite is electrostatic force. The optimal technology for preparation SA/PANI composite which has high thermal storage capacity and excellent stability is using sulfamic acid as doping agent, APS and BPO as mixed initiator and polymerized at room temperature. The maximum encapsulated proportion of SA in the flake SA/PANI composite is53.8wt.%and the melting and crystallization temperature is55.6℃and50.7℃respectively, corresponding phase transition enthalpy is98.0J-g-1and97.5J-g-1. The conductive ability of the composite is determined as0.4336S-cm-1. All of the conclusions indicate that the composite has a better thermal conductivity, good stability and conductive ability.In order to stuied the effect of preparation methods on the structure and thermal properties fully, two kinds of phase change materials using SA as PCM and activated montmorillonite as matrix were prepared. The composite PCM was characterized using scanning electron microscope, Fourier transformation infrared analysis technique and the thermal properties, thermal reliability and heat storage/release performance were determined by differential scanning calorimetry, FT-IR and thermal cycling test. Also, the pahse change foam cement containing composite PCM which synthesized by melting impregnation method was prepared and the temperature adjusting performance was also studied. The results show both composites have similar morphology, structure and comparable latent heats with SA intercalated into a-MMT gallery. Thermal reliability and thermal cycling test obviously indicate that preparation technology affects the thermal properties. Latent heat of the composite prepared by melting impregnation method changs by-0.59%for fusion and-1.01%for solidification, whereas, it decline by39.71%and40.89%for the composite prepared by solution immersed technology after600thermal cycling. In other words, the melting impregnation method is a potential candidate for preparing reliable composite PCMs. The result of temperature adjusting test show that the time of phase change cement increased172%when temperature increasing from20℃to70℃.更多还原