异形同种粒子间排空作用下的混合纳米流体分散稳定性及热物性

The dispersion stability of nanofluid is the main bottleneck restricting the industrial application of nanofluids. It is necessary to find means to effectively improve and evaluate dispersion stability through physical mechanism. A new method is proposed in this project to improve the dispersion stability of nanofluid by employing the depletion interaction between mixed nanoparticles. The physical mechanism of preparing stable nanofluid by dispersing nanoparticles of different shapes and of the same material into the same base liquid will be analyzed. The depletion interaction between nanoparticles will be measured by laser tweezer and atomic force microscopy to reveal the effects of nanoparticle concentration and size ratio on stability. In theory, the space distribution of nanoparticles in base liquid will be evaluated using parameters of mixing entropy and system’s free energy to quantitatively describe the dispersion stability of nanofluid. That is, through balance of depletion force, van der Waals force and electrostatic force and calculations of nanoparticle mixing entropy and system’s free energy, the dispersion stability of nanofluid can be quantitatively analyzed from mechanical and thermodynamic point of view. Then criterions for dispersion stability will be obtained. On this basis, the relationship between thermophysical properties of mixed nanofluid and nanoparticle mixing entropy will be studied and the variation of thermophysical properties of mixed nanofluid influenced by the nanoparticle depletion interaction will be revealed. It is hopeful that the this project will provide a simple effective way to prepare stable nanofluid without affecting chemical property and it will promote the practical application of nanofluid.

纳米流体的分散稳定性是约束其工业应用的主要瓶颈，亟需从分散稳定的物理机制入手发现有效的分散稳定性调控和定量评价方法。本项目提出一种利用混合粒子间的排空作用提高纳米流体分散稳定性的方法，分析不同形状同种纳米粒子混合分散于相同基液形成稳定纳米流体的物理机制，通过激光光镊和原子力显微镜测试纳米粒子间的排空作用，揭示粒子浓度和粒径比对稳定性的作用。理论方面，采用混合熵和系统自由能参数来描述纳米粒子在基液中的空间排布，定量刻画纳米流体的分散稳定性，即通过粒子间的排空力、范德华力和静电力的平衡及计算粒子混合熵和系统自由能参数，分别从力学和热力学角度定量分析混合纳米流体的分散稳定性，提出分散稳定性的判据。在此基础上，研究混合纳米流体的热物性与粒子混合熵的关系，揭示粒子排空作用影响下混合纳米流体热物性的变化规律。本研究有望开拓一种简单有效且不影响化学性质的稳定纳米流体的制备方法，促进纳米流体的实际应用。

纳米流体在能源、化工、建筑、微电子等领域具有巨大的应用前景。纳米流体的分散稳定性对其应用至关重要。关于纳米流体分散稳定性的两个传统机制是静电稳定和空间位阻稳定作用，通常通过调节基液的性质或使用分散剂等方法改善纳米粒子与基液的相容性从而提高分散稳定性。本项目从纳米流体分散稳定的物理机制入手，考虑混合粒子纳米流体的分散稳定性，通过混合球状、片状和管状纳米二氧化钛粒子分散于水中制备纳米流体，讨论了纳米粒子的浓度和混合比等参数对分散稳定性的影响，探讨了不同形状纳米粒子混合的排空作用和混合熵的协同效应，揭示了混合纳米流体的分散稳定机制，提出了混合纳米流体分散稳定性相图。研究了混合纳米流体的分散稳定性对其热物性、固液相变特性和光催化特性等的影响，探讨了纳米粒子长径比、混合比和浓度等参数的影响规律。研究工作揭示了纳米流体的分散稳定机理，提供了一种提高纳米流体分散稳定性的新方法，有利于促进纳米流体的应用。