纳米流体中碳纳米管的热泳及取向性研究

Due to its special structure, carbon nanotube has many excellent properties , including the very high thermal conductivity, thus it has potential applications in the aerospace , machinery, electronics and other fields. Thermophoresis has significant impact on the orientation of carbon nanotubes and then on the thermal conductivity of nanofluids. The project aims to use the thermomass theory of the heat flow to explain the unified mechanism of thermophoresis, based on the present of temperature gradient along with the heat flow , which can be described by the thermomass theory, the physical nature and its inherent laws of the relationship between the three-phase thermophoresis and thermal conductivity of particles will be revealed. The thermophoretic lift force will be raised which is related to thermophoresis but distinct from thermophoretic force, the direction of force will be pointed out as vertical to the local average temperature gradient, the expression of its relationship with the thermal conductivity and the change rate of the temperature gradient will be given and validated; the role of thermophoretic related forces and inertial effects of heat flow on the orientation change of carbon nanotubes in the fluid will be analyzed. For the uncertainty of the nanotube axis direction, the control strategy for external fields and surface modification will be proposed, numerical simulation will be used for the design first, then experimental will be performed to validate, with the purpose of increasing the collaboration between the orientation of the axis and the direction of the temperature gradient, making full use of the high thermal conductivity of carbon nanotubes, increasing the thermal conductivity of nanofluids. The project will provide basis and reference for improving the heat transfer performance of nanofluids and the related engineering applications.

由于其特殊的结构，碳纳米管具有很多优异性能，在航空航天、机械电子等领域均有广阔的应用前景。热泳对于碳纳米管在纳米流体中的取向进而对导热性能有着重要的影响。本项目旨在运用热质理论中的热流运动规律解释热泳现象的统一机理，基于温度梯度伴随热流，热流可用热质理论描述的观点，探讨三相热泳与粒子热导率等的关联特性和物理本质，揭示其内在规律；提出与热泳相关但区别于热泳力的热泳升力，指出其方向与局部平均温度梯度垂直，给出随热导率和温度梯度变化率的关系表达式并进行验证；揭示热泳相关力和热流惯性效应对碳纳米管在流体中取向变化的作用规律；针对碳纳米管主轴方向不确定性的问题，结合外场控制和表面修饰等措施，参照数值模拟进行设计，然后实验观测给予验证，以提高主轴取向和温度梯度二者的协同程度，充分发挥碳纳米管高热导率的特点，优化纳米流体的导热性能，从而为纳米流体的强化传热和相关工程应用提供依据和参考。

由于碳纳米管具有热、电等优异性能，它在能源动力、生物医学等领域都有潜在的应用价值。热泳过程对于碳纳米管在流体中的取向，进而对整体导热和集热性能有着重要的影响。本项目基本按照计划研究内容开展，获得的结果包括：(1) 提出与实际温度梯度的剪切相关的热泳升力。获得了热泳升力的表达式，指出该力与流体平均温度梯度垂直。结合碳纳米管热驱动和暖气片熏墙的例子，验证了热泳升力的存在并分析了作用特征，并将其拓展到光泳现象的研究; (2) 给出碳纳米管在流体内部做热泳运动时受到的热泳力表达式，发现存在碳纳米管的临界长径比，揭示两种转动平衡态的稳定性截然不同的原因; (3)提出含有介观尺度团簇点的模拟方法，可用于分析纳米颗粒两相流; (4)提出旋转颗粒在具有温度梯度的流体中会受到热泳张力的作用，结合前人热泳和光泳的实验研究验证了理论的合理性; (5)指出温度的非定常特征的影响包括无粘和粘性两部分; (6)比拟摩擦力的原理，给出了三相统一热泳力的初步分析和表达式。该研究可以为冷却调控和太阳能集热等领域提供重要的参考价值。