金属氧化物/聚苯乙烯双壳层纳米相变胶囊蓄冷流体的制备及其传热特性

Phase change cool storage technology is effective means of improving the efficiency of air conditioning and refrigeration, achieving peak load shifting. In this project，using n-tetradecane(Tet)as core, polystyrene(PS) as inner shell and metal oxides (SiO2,TiO2,Al2O3) with high thermal conductivity as outer shell, the metal oxides and polystyrene double-shell nanoencapsulated phase change materials as cool storage media were synthesized by Sol-Gel and ultrasonically initiated miniemulsion polymerization. The influences of the sorts and amount of the modifying metal oxides with coupling agent, ultrasound condition such as power,time and temperature, hydrophilic co-monomer, emulsifier and the shell-core ratio on polymerization process were systematically investigated.The composition, particle size,morphology and the thermo-physical property of namocapsules were characterized using particle size analyzer, scan and transmission electron microscope (SEM,TEM), fourier transform infrared and near infraed spectroscopy (FTIR,FTNIR),polarizing microscopy(POM), differential scanning calorimeter (DSC),X-ray photoelectron spectroscopy(XPS)，thermalconductivity measurer and thermogravimetric analyzer (TG). The mechancial,thermal and resistence freezing-traw stability of the synthesized latex was also tested. The heat transfer behavior of the novel latent nanofluid was discussed, and the relationship of the heat transfer performance was also established. The intrinsic essence between the structure of the nanocapsules and the thermal-physical performance of the new nanofluid was revealed .It will provide theoretical guidance for the preparation of high performance latent heat nanofluid for cool storage.

相变蓄冷技术是提高空调制冷效率、实现"移峰填谷"的有效手段。本项目以正十四烷为囊芯，聚苯乙烯为内壳层，高导热性金属氧化物（SiO2,TiO2,Al2O3）为外壳层，采用溶胶-凝胶工艺、超声辐射细乳液聚合法，制备出金属氧化物/聚苯乙烯双壳层纳米相变胶囊蓄冷流体。系统考察偶联剂改性金属氧化物种类及用量、超声条件(功率、时间、温度)、亲水性共聚单体、乳化剂以及芯壳比等因素对聚合性能的影响；采用纳米粒度仪、扫描（透射）电镜、傅立叶红外、（近红外）、偏光显微镜、差示扫描量热、X-射线光电子能谱、导热系数仪以及热失重等手段对纳米胶囊的组成、形貌以及热物性等进行表征，并测试其浮液的机械、热及抗冻融稳定性；研究新型潜热型纳米蓄冷流体的传热特性，并建立其传热性能关系式。揭示纳米胶囊粒子的结构与新型纳米流体热物性之间的内在联系，为制备高性能潜热型纳米蓄冷流体提供理论指导。

本论文以建筑节能、空调蓄冷为背景，开展新型潜热型功能蓄冷流体的合成及传热性能的研究，具体如下：.以正十四烷(Tet)为芯材， SiO2和聚苯乙烯(PS)为复合壳层，采用溶胶-凝胶工艺、细乳液原位聚合法，制备出Tet @ PS-SiO2复合纳米相变胶囊（NEPCM）蓄冷乳液。系统考察合成聚合条件对NEPCM性能的影响；探讨了抗冻剂乙二醇质量分数对新型蓄冷流体冰点及稳定性的影响；并测量其相变蓄冷流体的热物性。采用纳米粒度仪、扫描电镜、透射电镜、傅立叶红外、X-射线光电子能谱仪、差示扫描量热仪、热失重以及热常数分析仪等对纳米胶囊的组成、形貌以及热物性进行表征，并测试了蓄冷流体的热物性包括粒径大小及分布、导热系数、表观比热容、粘度及机械稳定性和密度等。在自行建立的新型蓄冷流体传热性能实验台开展了复合壳层NEPCM蓄冷流体的对流换热特性实验研究；分析影响其释冷/蓄冷过程强化换热的因素。.合成NEPCM的最佳配比为：RTet/St为1:1，水油比为5:1，共聚单体MMA为4%，复合乳化剂（SDS:OP-10=1:1）为3%，引发剂AIBN含量为0.4%，改性二氧化硅用量为7%。TEM及粒径分析表明，新型Tet @ PS-SiO2 NEPCM具有规则球形核壳结构，其平均粒径为151.3 nm；XPS分析表明，复合纳米相变胶囊的Si含量为3.27%；DSC显示胶囊熔融焓值达到83.38 kJkg-1，具有良好的储能能力。TG数据显示复合壳层高于没改性胶囊，具有良好的热稳定性。以添加15%的乙二醇与水组成的混合液为基液，当Tet @ PS-SiO2 NEPCM的质量分数为5%时，新型蓄冷流体的导热性能和表观比热容，均高于未用改性PS@Tet NEPCM蓄冷流体，且新型蓄冷流体具有较低的粘度、较高的机械稳定性。 .实验平台测试结果表明：在释冷过程中，质量分数为5%的复合壳层NEPCM流体，其对流换热系数较未用SiO2改性的提高了8%，较基液提高了50%；对应地，在蓄冷过程中，其提高分别为6%和30%。在释冷/蓄冷过程中，随着雷诺数的增加，复合壳层 NEPCM流体的对流换热系数增大，但是其强化换热的程度随之降低；随着复合壳层NEPCM质量分数的增加及管外换热介质流量的增大，新型蓄冷流体强化换热的效果均有所增强。