【作者】 管延祥；

【导师】 赵蔚琳；

【作者基本信息】 济南大学 ， 材料学， 2010， 硕士

【摘要】 随着纳米科技的快速发展,纳米材料已被应用到传热领域中,孕育而生了“纳米流体”的概念。纳米流体是指以一定的方式和比例在液体中添加纳米级金属、非金属或聚合物固体粒子以构成一种新型的传热工质,这种新传热工质可用于换热设备中替代传统的工质。热管作为换热设备中的一种高效传热元件,将纳米流体应用于其中可显著改善传热性能。因此,对应用于热管的纳米流体热物性参数的研究是将纳米技术应用于热能工程的创新性研究,具有重要的工程应用价值。本文以Al₂O₃-水纳米流体作为热管的工作介质,通过测试其各种热物性参数,来研究Al₂O₃纳米颗粒的加入如何改变工作介质的热物性参数以及对热管传热能力的影响。其主要研究内容为:首先,通过透射电子显微镜、X射线衍射仪对Al₂O₃纳米颗粒进行了表征,采用两步法制备了两种粒径（40nm、65nm）、五种体积分数（0.1%～0.5%）的Al₂O₃-水纳米流体。为了制备悬浮稳定的纳米流体,采用L9（3⁴）正交试验进行分析,得出了最佳工艺参数为:pH值为8、超声振动时间为3h、不添加分散剂、磁力搅拌时间为30min。并通过Zeta电位分析仪、激光粒度分析仪等分析了超声振动时间、分散剂、pH值等对Al₂O₃-水纳米流体悬浮稳定性的影响,得出:pH值为8、超声振动时间为3h、分散剂添加量为0.02%时,Al₂O₃-水纳米流体的悬浮稳定性最好。并对其悬浮稳定性作用机理进行了一定的理论分析。其次,采用旋转粘度计、全自动界面张力仪、KD 2 Pro导热系数仪、热重差热联用仪等仪器对Al₂O₃-水纳米流体在不同条件下的粘度、表面张力系数、导热系数、热重、汽化潜热、密度、沸点等热物性参数进行了测量,结果发现:Al₂O₃-水纳米流体的粘度随着纳米颗粒体积分数的增加而增加,随着温度的升高而减小,随着颗粒尺寸的减小而增大;Al₂O₃-水纳米流体的表面张力系数随着体积分数的增加而减小,随着颗粒粒径的减小而减小,随着温度的升高而减小;Al₂O₃-水纳米流体的导热系数随着体积分数的增加而增加,随着颗粒粒径的减小而增大,随着温度的升高而增大;Al₂O₃-水纳米流体的相变速率随着颗粒体积分数的增加而增大,而颗粒粒径对其基本没影响;Al₂O₃-水纳米流体的汽化潜热随着颗粒体积分数的增加而减小;Al₂O₃-水纳米流体的密度随着颗粒体积分数的增加而增大;Al₂O₃-水纳米流体的沸点随着颗粒体积分数的增加而减小。并对各热物性参数的作用机理进行了一定的理论分析。最后,分析了应用于热管的Al₂O₃-水纳米流体工作介质的综合热物理性质。结果表明Al₂O₃-水纳米流体具有较好的综合热物理性质,适合做热管的工作介质;与水相比,其传输因素提高了3.2%¹4.9%,具有较好的传热性能。更多还原

【Abstract】 With the rapid development of nanotechnology, nanomaterials have been applied into the heat transfer areas, breded as "nano-fluid". Nanofluid is a new type of heat working fluid, which is formed by adding nano-level metal, non-metallic or polymer solid particles into the liquid in a certain way and ratio. This kind of new heat transfer working substance may substitute traditional working substance in the heat exchange equipment. Heat pipe as one kind of highly effective heat transfer part in heat exchange equipment, nano-fluid may obviously improve the heat-transfer property, when it was applied in the heat pipe. Therefore, the research of nanometer class volumetric heat natural parameter used in heat pipe is innovative research of appling nanotechnology in the thermal engineering, it has the important project application value.In this paper, the Al₂O₃-water nanofluid was used to the heat pipe working medium, and through testing its various thermal parameters, the effects of the addition of Al₂O₃ nanoparticles on the thermal parameters of working fluid and heat transfer ability of heat pipe were studied. The main research contents are as follows:Fristly, the Al₂O₃ nanoparticles were characterized by transmission electron microscopy, X-ray diffraction, two particle sizes （40nm,65nm） and five volume fractions （0.1% 0.5%） of Al₂O₃-water nanofluids were prepared by the two-step method. In order to prepare stable nanofluids suspended, the L9（34） orthogonal experiment was employed to analysis, the optimum process parameters are: pH value of 8, ultrasonic vibration time of 3h, not add the dispersing agent, magnetic stirring time of 30min. By using Zeta potential analyzer, laser particle size analyzer, the influences of the time of the ultrasonic vibration, dispersing agent, pH value on the suspension stability Al₂O₃-water nanofluids were studies, the obtained results are: the suspension stability of Al₂O₃-water nanofluid is best when the pH value was 8, ultrasonic vibration time was 3h, dispersion agent was 0.02%. The mechanism of the suspension stability was theoretically analyzed as well.Secondly, viscosity, surface tension, thermal conductivity, heat weight, latent heat of vaporization, density, boiling point and other thermal parameters for Al₂O₃-water nanofluids under different conditions were measured by rotating viscometer, automatic surface tension meter, KD 2 Pro thermal conductivity meter, thermogravimetric differential thermal spectrometer and other instruments. The results showed that: the viscosity of Al₂O₃-water nanofluid increases with increasing the volume fraction of nanoparticles, decreases with increasing temperature, increases with decreasing particle size; the surface tension coefficient of Al₂O₃-water nanofluid decreases with increasing volume fraction, decreasing particle size, and increasing temperature, respectively; the thermal conductivity of Al₂O₃-water nanofluid increases with increasing volume fraction, decreasing particle size, and increasing temperature, respectively; the phase transition rate of Al₂O₃-water nanofluid increases with increasing the particle volume fraction, the particle size did not affect its basic; the latent heat of evaporation of Al₂O₃-water nanofluid increases with decreasing the particle volume fraction; the nanofluids density of Al₂O₃-water increases with increasing the volume fraction of particles; the boiling point of Al₂O₃-water nanofluid decreases with increasing volume fraction of particles. The mechanism of the every thermal parameter was theoretically analyzed as well.Lastly, analyzed synthesis hot physical property of Al₂O₃-water nanofluid working substance which has applied in heat pipe. The result indicated that Al₂O₃-water nanofluid has the good synthesis hot physical property, suitable to make heat pipe’s working substance; Its transmission factor enhanced 3.2%¹4.9% compared to water, has the good heat-transfer property.更多还原