相变微胶囊储能过程传热与流动特性研究

发布时间：2018-09-02 06:26

【摘要】：随着全球工业和经济的飞速发展,各国对能源的需求量越来越多,煤炭和石油等传统不可再生能源的消耗逐渐增加,能源短缺和环境污染问题日益加剧,因此,节能减排、提高能源利用率迫在眉睫。相变储能材料能够解决热能供求在时间和空间上不匹配的问题,可以有效地提高能源的利用率,在工业余热回收、太阳能热利用、建筑节能、电子元器件的热管理、动力电池热管理等方面具有广阔的应用前景。通过微胶囊技术对相变储能材料进行封装制备出相变微胶囊,能够有效解决相变储能材料的泄漏对环境和设备造成污染的问题。但是目前相变微胶囊芯材大多为石蜡类等有机相变材料,导热性能普遍较低,致使热能的存储和运输效率不高,从而限制了相变储能技术在实际中的应用。本论文针对上述问题开展了相变微胶囊强化传热、潜热型功能热流体的传热与流动特性研究和无机水合盐相变微胶囊的制备及其热物性研究等相关方面的工作。主要研究内容与结论如下:(1)采用纳米铜、石墨烯和膨胀石墨三种高导热材料对石蜡/密胺树脂相变微胶囊进行了传热强化研究,并分析了高导热材料的种类及质量分数对相变微胶囊的热物性和储热/释热性能的影响。结果表明,当纳米铜、石墨烯和膨胀石墨的含量均为2.5 wt.%时,相变微胶囊的导热系数分别提高了8.72%、28.27%、39.62%。在储热/释热测试中,膨胀石墨对相变微胶囊储热/释热效率的提升也明显高于纳米铜和石墨烯。当膨胀石墨添加含量为2.5 wt.%时,膨胀石墨/Micro EPCM复合材料的储热和释热效率与相变微胶囊相比分别提高了14.98%和26.63%,并且储热/释热效率随着膨胀石墨添加含量的提高而增大。(2)以石蜡/密胺树脂相变微胶囊为基材,制备了不同微胶囊质量分数下的相变微胶囊悬浮液作为潜热型功能热流体,并对其热物性和管内的传热与流动特性进行了研究。结果表明,潜热型功能热流体的密度、导热系数随着相变微胶囊含量的增大而减小,而相变潜热则随着相变微胶囊质量分数的增大而增大。其粘度也随着相变微胶囊质量分数的增大而升高,当相变微胶囊的含量为20 wt.%、30 wt.%和40 wt.%时,潜热型功能热流体的粘度迅速增加。通过搭建对流换热实验平台,对潜热型功能热流体在管内的传热性能进行了研究,结果表明潜热型功能热流体的对流换热系数随着相变微胶囊含量的增大而增大。当相变微胶囊的添加含量为5 wt.%和10 wt.%时,其对流换热系数分别约为基液的2倍和3倍。(3)以七水合硫酸镁为芯材,脲醛树脂为壁材,采用乳液聚合法制备出了相变微胶囊。并对不同工艺条件下制备的相变微胶囊微观形貌、物性参数进行了研究。结果表明,乳化剂的含量对相变微胶囊的微观形貌和粒径分布有很大的影响。当乳化剂的含量为0.5 g时,微胶囊呈现规则的球状结构,且表面光滑紧凑、粒径相对均匀,此时微胶囊的平均粒径为34.99μm,其包覆率为36.5%。(4)以五水合硫代硫酸钠为芯材,聚苯乙烯为壁材,采用溶剂挥发法制备出了相变微胶囊。并对不同乳化剂含量和搅拌速率下制备的微观形貌、热稳定性等进行了分析。研究表明,所制备的相变微胶囊均成规则的球状结构,且表面光滑紧凑。随着乳化剂含量的增加和搅拌速率的加快,微胶囊的粒径呈现出减小的趋势。随着乳化剂含量的增大,微胶囊的相变温度也随之降低;而微胶囊的相变潜热则随着乳化剂天机含量的增加先增大后减小。五水合硫代硫酸钠经聚苯乙烯包覆后,热稳定性也明显的提高。微胶囊中五水合硫代硫酸钠的包覆率为26.4%。(5)以五水合硫代硫酸钠为芯材,二氧化硅为壁材,采用溶胶凝胶法制备出了相变微胶囊。并对不同乳化剂含量、芯材与壁材质量比、搅拌速率下制备的相变微胶囊微观形貌、热物性等进行了分析。结果表明,乳化剂含量、芯材与壁材质量比、搅拌速率对胶囊的微观形貌和粒径分布均有很大的影响。当芯材、壁材、乳化剂的质量比为1:0.4:0.04时,相变微胶囊呈规则的球形结构,表面光滑紧凑,且粒径分布最为均匀。芯壁比对相变潜热影响较大,随着芯壁比的减小相变微胶囊的相变潜热逐渐增大。所制备的相变微胶囊相变潜热最大为199.47k J/kg,包覆率为94.65%。五水合硫代硫酸钠经二氧化硅包覆后,其过冷度和导热系数均有所改善,热稳定性也明显提高,同时解决了芯材熔化后流动造成泄漏的问题,从而延长了无机水合盐在实际应用中的循环寿命。综上,本文针对相变微胶囊的强化传热、潜热型功能热流体的流动与传热和无机水合盐相变微胶囊的制备及其热物性分析三方面开展了相关的研究工作,研究结果和方法在储能过程传热与流动的强化、新型无机盐类相变微胶囊材料的制备等方面具有一定的参考价值。
[Abstract]:With the rapid development of global industry and economy, more and more countries are demanding energy, the consumption of traditional non-renewable energy such as coal and oil is increasing, energy shortage and environmental pollution are becoming increasingly serious. Therefore, it is urgent to save energy, reduce emissions and improve energy efficiency. Phase change microcapsules can be prepared by encapsulating phase change energy storage materials with microcapsule technology. However, most of the core materials of phase change microcapsules are organic phase change materials, such as paraffin wax. Their thermal conductivity is generally low, resulting in low thermal energy storage and transport efficiency, which limits the practical application of phase change energy storage technology. The main research contents and conclusions are as follows: (1) Paraffin/melamine resin was prepared by using nano-copper, graphene and expanded graphite as high thermal conductive materials. The heat transfer enhancement of phase change microcapsules was studied, and the effects of the kinds and mass fraction of high thermal conductivity materials on the thermal properties and heat storage/release properties of phase change microcapsules were analyzed. The results showed that the thermal conductivity of phase change microcapsules increased by 8.72%, 28.27% and 39.62% respectively when the contents of nano-copper, graphene and expanded graphite were 2.5 wt%. When the content of expanded graphite was 2.5 wt.%, the thermal storage and release efficiency of expanded graphite / micro EPCM composites were 14.98% and 26.63% higher than that of phase change microcapsules, respectively. (2) Phase change microcapsule suspensions with different mass fractions of microcapsules were prepared as latent functional thermal fluids, and their thermophysical properties and heat transfer and flow characteristics in tubes were studied. The density and thermal conductivity of the fluid decrease with the increase of the content of phase change microcapsules, while the latent heat increases with the increase of the mass fraction of phase change microcapsules. The results show that the convective heat transfer coefficient of latent functional heat fluids increases with the increase of the content of phase change microcapsules. When the content of phase change microcapsules is 5 wt.% and 10 wt.%, the convective heat transfer system is established. The number is about 2 times and 3 times that of the base solution. (3) with seven hydrated Magnesium Sulfate as core material and urea formaldehyde resin as wall material, phase change microcapsules were prepared by emulsion polymerization. The micromorphology and physical parameters of phase change microcapsules prepared under different technological conditions were studied. When the content of emulsifier was 0.5 g, the microcapsules showed regular spherical structure, smooth and compact surface, and the particle size was relatively uniform. At this time, the average diameter of microcapsules was 34.99 micron, and the coating rate was 36.5%. (4) Sodium thiosulfate pentahydrate was used as core material, polystyrene as wall material, and solvent evaporation method was used to prepare microcapsules. The phase change microcapsules were prepared. The morphology and thermal stability of the microcapsules prepared under different emulsifier content and stirring rate were analyzed. The results showed that the phase change microcapsules had regular spherical structure and smooth and compact surface. With the increase of emulsifier content, the phase transition temperature of microcapsules decreases, while the latent heat of microcapsules increases first and then decreases with the increase of emulsifier content. 4%. (5) Phase change microcapsules were prepared by sol-gel method with sodium thiosulfate pentahydrate as core material and silica as wall material. When the mass ratio of core material, wall material and emulsifier is 1:0.4:0.04, the phase change microcapsules have regular spherical structure, smooth and compact surface, and most uniform particle size distribution. The latent heat of phase change increases gradually. The maximum latent heat of phase change microcapsules is 199.47kJ/kg and the coating rate is 94.65%. The supercooling and thermal conductivity of sodium thiosulfate pentahydrate coated with silica are improved, and the thermal stability is also improved obviously. The leakage problem caused by the flow of core material after melting is solved, thus the coating rate is prolonged. In summary, this paper focuses on the enhanced heat transfer of phase change microcapsules, the flow and heat transfer of latent functional heat fluids, the preparation and thermophysical properties analysis of phase change microcapsules of inorganic hydrate salts. It has a certain reference value in strengthening the preparation of new inorganic salt phase change microcapsule materials.
【学位授予单位】：中国矿业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TK124

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