新型无机—有机复合壳层纳米胶囊相变蓄冷流体的热物性及传热性能

发布时间：2018-04-21 14:51

  本文选题：无机-有机复合壳层 + 纳米胶囊相变蓄冷流体　； 参考：《华南理工大学》2015年硕士论文

【摘要】：潜热型蓄冷流体是一种集蓄冷和强化传热为一体的功能流体。传统的有机相变微胶囊蓄冷流体存在流动阻力大、导热系数低等不足。基于无机纳米粒子的高导热性及纳米胶囊相变流体的低流动阻力,研究新型无机-有机复合壳层的纳米胶囊相变蓄冷流体,具有重要的理论指导意义和实际应用价值。本文开展以聚苯乙烯(PS)和二氧化硅(Si O2)作复合壳层,正十四烷(Tet)作芯材的新型纳米胶囊相变蓄冷流体热物性及传热性能的实验研究。采用细乳液原位聚合法合成了新型PS-Si O2@Tet纳米胶囊相变材料(Nano-encapsulated phase change material,NEPCM)及其乳液;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;对复合壳层纳米胶囊的热性能进行差示扫描量热(DSC)、热失重(TG)表征,并测量其相变蓄冷流体的热物性,包括粒径大小及分布、导热系数、表观比热容、粘度和密度等。测试结果表明:制备的新型PS-Si O2@Tet NEPCM的平均粒径为151.3 nm,相变潜热达83.38 k J·kg-1,具有较高的热稳定性;以质量分数为15%的乙二醇和OP-10/SDS复合乳化剂以及水组成的混合液为基液,当PS-Si O2@Tet NEPCM的质量分数为5%时,新型蓄冷流体的导热性能(5℃时导热系数为0.4035 W·m-1·K-1)和表观比热容(6.79℃时比热容峰值达8.842 J·g-1·℃-1),均高于未用Si O2改性的PS@Tet NEPCM蓄冷流体,且新型蓄冷流体具有较低的粘度(5℃时粘度为2.76 c P)、较高的机械稳定性,适合作为潜热型蓄冷功能流体。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。实验结果表明: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Si O2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。
[Abstract]:Latent heat storage fluid is a kind of functional fluid which integrates cold storage and enhanced heat transfer. The traditional organic phase change microencapsulated cold storage fluid has many disadvantages, such as high flow resistance and low thermal conductivity. Based on the high thermal conductivity of inorganic nanoparticles and the low flow resistance of phase change fluids in nano-capsules, it is of great theoretical significance and practical application value to study the novel inorganic / organic composite shell phase change cold storage fluids. In this paper, the thermal properties and heat transfer properties of phase change storage fluid with polystyrene (PS) and silica (SiO2) as composite shell and tetradecane (Tet) as core material were studied. A novel phase change material PS-Si O2@Tet phase change material material NEPCM and its emulsion were synthesized by in-situ polymerization of fine emulsion, and the effects of the mass fraction of ethylene glycol, an antifreeze, on the freezing point and stability of the new cold storage fluid were investigated. The thermal properties of composite shell nanocapsules were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). The thermal properties of phase change cold storage fluid, including particle size and distribution, thermal conductivity, apparent specific heat capacity, viscosity and density, were measured. The results show that the average particle size of the new PS-Si O2@Tet NEPCM is 151.3 nm, the latent heat of phase transition is 83.38 kJ / kg -1, and it has high thermal stability, and the mixture of 15% mass fraction of ethylene glycol and OP-10/SDS and water is used as the base solution. When the mass fraction of PS-Si O2@Tet NEPCM is 5, the thermal conductivity of the new cold storage fluid is 0.4035 W m-1 K 1 at 5 鈩，

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