摘 要

液体对流换热作为工业生产中常用的散热制冷的方式，过去一直使用单一液体作为传热介质。在近几年的研究中，人们发现一种纳米粒子和液体介质混合而成的悬浮液，对原基液的导热系数会有一定的提升。在工业生产中，将有效地提高能源的利用效率，具有广泛的应用前景。然而，纳米流体传热性能增强的机理至今没有明确的结论。

本文通过测试氧化铝纳米流体的导热系数，并建立纳米流体导热系数计算模型。实验主要测试不同体积分数下的铝基纳米流体的导热系数，发现在体积分数较低时，导热系数与体积分数呈线性变化，在0.005g/ml时增加量为2.28%，在0.01g/ml时增加量为5.35%。随着体积分数持续增大，其导热系数增长速度放缓，在体积分数0.05g/ml时，导热系数增加量仅为10.41%。针对此现象，参考文献中的观点，认为颗粒沉降、团聚将影响纳米流体导热系数。

根据实验提出的观点，以有限元为基础，使用COMSOL Multiphysics的传热模块，模拟了纳米流体在相同体积分数下不同粒径、颗粒沉降、颗粒团聚的场景。通过仿真，证实单考虑纳米颗粒均匀分布情况，体积分数与导热系数成正比.当纳米流体发生团聚现象时，导热系数会随聚合而成的粒径的增大而降低。当纳米流体发生沉降现象时，导热系数会随着沉降的严重而降低。

关键词：纳米流体 导热系数 传热仿真

Experimental and Simulation Study on Heat Conduction Mechanism of Nanofluids

Abstract

Liquid convective heat transfer, as a commonly used way of heat dissipation and refrigeration in industrial production, has been used as a single liquid as heat transfer medium in the past. In recent years, it has been found that a suspension composed of nanoparticles and liquid medium will improve the thermal conductivity of the original solution to a certain extent. In industrial production, it will effectively improve the efficiency of energy utilization, and has a wide range of application prospects. However, there is no clear conclusion on the mechanism of enhancing the heat transfer performance of nanofluids.

In this paper, the thermal conductivity of alumina nanofluid is measured, and the calculation model of thermal conductivity of nanofluid is established. The thermal conductivity of aluminum-based nanofluids with different volume fraction was tested. It was found that the thermal conductivity increased linearly when the volume fraction was low, and 2.28% at 0.005g/ml. The increase is 5.35% at 0.01g/ml. With the continuous increase of volume fraction, the increase rate of thermal conductivity slows down. When the volume fraction 0.05g/ml is used, the increase of thermal conductivity is only 10.41%. In view of this phenomenon, it is pointed out that particle settlement and agglomeration will affect the thermal conductivity of nanofluids.

According to the viewpoint put forward by the experiment, based on the finite element method, using the heat transfer module of COMSOL Multiphysics, the scene of different particle sizes, particle sedimentation and particle agglomeration of nano-fluid under the same volume fraction is simulated. Through simulation, it is confirmed that considering the uniform distribution of nanoparticles, the volume fraction is directly proportional to the thermal conductivity. When nanofluids agglomerate, the thermal conductivity decreases with the increase of particle size resulting from polymerization. When nano-fluid subsides, the thermal conductivity will decrease with the severity of sedimentation.

Key words: Nanofluid ； Thermal conductivity； Heat transfer simulation

目录

摘 要 I

Abstract II

第一章 绪论 1

1.1课题研究背景及研究意义 1

1.2国内外研究现状 4

1.3存在的问题 5

1.4本文的研究内容 5

第二章 采用3ω法测量纳米流体的导热系数 6

2-1试验台介绍 6