相变纳米胶囊悬浮液在微通道内的流动与传热特性

In view of low specific heat of nanoparticle suspensions and low thermal conductivity of microencapsuled phase change materials, nanoencapsuled phase change material (NEPCM) suspensions were proposed to enhance heat transfer in microchannels for heat dissipation of high heat flux apparatus. A two-step Pickering emulsification procedure was designed to creat NEPCM particles. Surface-modified amphiphilic zirconium phosphate nanoplatelets were fabricated as the Pickering smulsifiers, nonadecane was chosen as the core phase change material, and polystyrene, the shell material. Carbon nanomaterials were used in capsule shell synthesis to prepare thermal-mechanical enhanced high-performance NEPCM particles. The convective heat transfer for laminar flows in a microchannel subjected to an external uniform heat flux was studied as well as the thermophysical properties of NEPCM suspensions. The effects of particle diameter and concentration were investigated to reveal mechanisms controlling the laminar flow and heat transfer behaviors of NEPCM suspensions. Nusselt number and friction factor calculation formulas were derived from experimental test, which will provide us the theory basis and the key preparation technology for developing a new high-performance working fluid used in microchannel coolers. It has some advantages such as high heat transfer rate and low power consumption..At present, the research about the laminar flow and heat transfer of NEPCM suspensions in microchannels has not been reported yet. The study to proceed can develop the utilization of NEPCM particles. It will be expected to solve the problem of conventional fluid with low thermal conductivity and specific heat. There is no doubt about its important academic value and application purpose.

针对纳米颗粒悬浮液的低比热、相变微胶囊悬浮液的低导热系数问题，提出采用相变纳米胶囊悬浮液强化微通道换热能力，以解决高热流密度器件的散热问题。采用皮克林乳化方法，利用双亲性磷酸锆纳米碟片作界面稳定粒子，掺入高导热系数碳纳米材料优化囊壁结构和性能，制备导热和机械性能优良的石蜡纳米胶囊。研究相变微胶囊悬浮液的热物性及在微通道中的对流传热特性，重点考察胶囊浓度、粒径的影响及其规律，探索相变纳米胶囊对流传热和流动的影响机理，获得流动阻力系数与换热系数的拟合式，为开发传热能力强、功耗小的新型高性能传热工质提供理论依据与关键制备技术。.目前，有关纳米胶囊悬浮液在微通道中对流传热的研究还未见报道，开展该领域的研究可大大的拓展纳米胶囊的使用范围，有望解决现有传热工质导热能力小、比热低的问题。这无疑具有重要的学术价值与明确的应用。

研究关注石蜡相变材料的包裹技术和控制条件，提出“皮克林乳化+原位聚合”方法制备聚甲基丙烯酸甲酯壳层的石蜡相变纳米胶囊，“溶胶凝胶+无水溶剂”方法制备二氧化钛无机壳层的石蜡相变纳米胶囊，“微流控单重乳化+界面聚合”制备聚脲有机壳层的石蜡相变微胶囊，“微流控双重乳化+光固化”制备己二醇二丙烯酸酯壳层的石蜡相变微胶囊，获得的石蜡相变微/纳米胶囊结构可控、粒径均一、性能稳定。在此基础上开展的石蜡相变微/纳米胶囊的固液相变和成核特性研究证实，精准控制胶囊粒径大小和均匀性是准确定义和调控相变胶囊成核过冷的重要前提；以二氧化钛纳米颗粒作成核剂，利用球/片状颗粒混合方式改善其在石蜡相变材料中的分散稳定性，能够有效缓解相变胶囊发生凝固时存在的过冷问题。相变微/纳米胶囊能够在传热工质中稳定分散是其实际应用的重要前提，本研究通过阴离子型表面活性剂十二烷基苯磺酸钠的静电位阻作用实现石蜡相变纳米胶囊在水工质中的悬浮稳定；通过精准控制石蜡相变微胶囊的结构尺寸，利用等密度法既能得到分散稳定的水基石蜡相变微胶囊悬浮液。为提升石蜡相变微/纳米胶囊悬浮液的综合热物性能，研究加入高导热系数固体纳米颗粒配制二元混合水基悬浮液，进一步获得了性能优良的氧化石墨烯/相变纳米胶囊混合悬浮液、二氧化钛/相变微胶囊混合悬浮液的优化配制方案。本研究设计了一种基于微通道强化换热及热电制冷的散热装置，分别以微米级和纳米级的一元石蜡相变胶囊悬浮液、二元纳米颗粒/相变胶囊混合悬浮液作传热工质，对其在微通道中流动传热的研究证实纳米级二元混合悬浮液具有最强的强化散热冷却能力，且其强化传热能力随相变胶囊和纳米颗粒浓度的增加而增强。综上，本研究提出的石蜡相变微/纳米胶囊及其悬浮液的制备方法和优化方案，解决了目前相变微/纳米胶囊悬浮液研究所采用对象不一致的先天缺陷问题，同时能够提升相变微/纳米胶囊悬浮液的强化传热性能，对于推广相变微/纳米胶囊悬浮液在强化传热技术中的应用具有实际意义。

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