【作者】 徐淼；

【导师】 白敏丽；

【作者基本信息】 大连理工大学 ， 工程热物理， 2010， 硕士

【摘要】 随着科学技术的发展,能源问题日益突出,如何降低工业装备的能量消耗、提高热交换设备的换热效率就变得十分重要。传统的低导热系数的纯液体换热工质已经很难满足一些特殊条件下的换热要求,因此需要研制出导热系数高、传热性能好的新型换热工质。为了解决这一问题,有学者提出一个全新的概念—纳米流体：即以一定的方式和比例,将纳米级的金属或非金属粒子添加到液体介质中形成的一类新型传热工质。本文对纳米流体的制备及稳定性进行了探索性研究,采用两步法制备出多种具有较好悬浮稳定性的纳米流体。在此基础上,详细研究了纳米流体的热物性参数,通过实验方法测量了纳米流体的导热系数、粘度和比热容；总结归纳了近年来国内外学者对纳米流体热物性参数理论模型的研究成果,并将实验值与理论预测值进行比较,确定出最有效的纳米流体热物性参数理论模型。为了研究纳米流体的流动特性,将不同体积浓度的SiO2-水纳米流体应用于波壁管中进行实验研究,由于波壁管自身的结构特点,使得流体能够在较小雷诺数下达到湍流状态,可以方便测出流体在层流、过渡流、湍流区的特点。通过纳米流体在波壁管内沿程阻力特性实验发现：SiO2-水纳米流体的摩擦系数在层流区和过渡流区内随着纳米粒子浓度的增加而增大,在湍流区其摩擦系数随浓度的变化不大。通过流动可视化实验,拍摄到了不同体积浓度的SiO2-水纳米流体在波壁管内流动的照片,可以看出纳米流体的浓度越高,流动就越显得活跃,这是由于内部纳米粒子的微运动促使流体均匀性更好。实验测量了波壁管内纳米流体的质量传递系数,结果表明：SiO2-水纳米流体的质量传递系数无论在层流、过渡流还是湍流区都比去离子水的质量传递系数有显著提高。采用FLUENT软件并基于标准k-ε计算模型,假定纳米流体为均匀、单相、不可压缩流体,分别对去离子水和体积浓度为2％的SiO2-水纳米流体在波壁管内的流动特性进行数值模拟,得到了两种流体在相同雷诺数及相同入口流速条件下的流线图,从图中看出体积浓度为2％的SiO2-水纳米流体的数值模拟结果与可视化实验结果并不一致,并分析了产生这种现象的原因,为进一步研究纳米流体的流动特性和传热传质机理提供了更多还原

【Abstract】 With the development of science and technology, the problem of energy sources is getting more and more serious than ever. It is very important to reduce power consumption and enhance the heat transfer rate in heat tansfer capabilities. Nowadays, the traditional pure liquid heat-transfer medium can’t meet the requirements in some special work condition. It is necessary to prepare a higher thermal conductivity and more efficient heat-transfer medium. To solve this problem, a new concept of heat transfer fluids called "nanofluids" has been proposed. It refers to a new kind of heat transfer medium created by suspending nanoscaled metallic or nonmetallic particles in the base fluids.This research focuses on the preparation and stability of nanofluids. Two steps method is used to prepare many kinds of nanofluids with better stability. On this basis, research on thermophysical characteristic of nanofluids and measure the conductivity, viscosity and specific heat of nanofluids through the experimental method; generalize the research achievement of thermophysical characteristic proposed by researchers in the recent years; confirm the effective thermal property models of nanofluids after comparison between the experimental data and the calculated results.Experiments are carried on flow behavior of different volume concentration SiO2-water nanofluids in a wavy-walled tube. Because of the structural characteristics of the wavy-walled tube, the SiO2-water nanofluids can be in a turbulent area in smaller Reynolds numbers and the flow structural characteristics can be easily measured in the laminar, transitional and turbulent flow regimes. The result of resistance tests shows that the friction factor of SiO2-water nanofluids increases with the concentration of nanoparticles in the laminar and transitional flow regimes, but it is almost unchanged in the turbulent flow regimes. The photos of flow visualization show that the SiO2-water nanofluids have better uniformity due to the micro-movements of the nanoparticles. The result of mass transfer tests show that the mass transfer of SiO2-water nanofluids is higher than pure water in the laminar, transitional and turbulent flow regimes.The flow behavior of pure water and SiO2-water nanofluids(2%) in a wavy-walled tube is simulated by using FLUENT software based on the standard k-εmodel. The flow line pictures of pure water and SiO2-water nanofluids(2%) are achieved, which is under the condition of the same Reynolds number and the same inlet velocity. It is found that the simulation results of SiO2-water nanofluids(2%) are not entirely consistent with the experimental results and the reasons for this phenomenon are analyzed. The software provides a new method for further research on the flow behavior as well as the heat and mass transfer mechanisms of the nanofluids.更多还原