【作者】 朱爱军；

【导师】 凌智勇；

【作者基本信息】 江苏大学 ， 机械电子工程， 2010， 硕士

【摘要】 随着MEMS技术的发展,纳米流体因其独特的热物理性质而成为当今研究的热点。纳米流体是指将一定量的纳米级(＜100nm)固体颗粒均匀分散在传统流体(水、酒精、乙二醇等)中制得的稳定的悬浮液。论文以纳米流体为研究对象,对其制备方法、稳定性及其粘度、微管道中的流动特性、及其对流传热特性进行了研究。首先,本文采用“两步法”制备了含有不同质量分数的Cu-水纳米流体。研究了分散剂(SDBS)的用量对纳米流体稳定性的影响。实验结果表明在基液中添加与Cu纳米颗粒质量分数相当的SDBS而制得的纳米流体较稳定。同时,并对Cu-水纳米流体的粘度进行研究。研究发现纳米流体的粘度随着颗粒质量分数的增加而增加。其次,采用实验与数值模拟相结合的方法对微管道中压力驱动下质量分数为1%的Cu-水纳米流体的流动特性进行了研究。研究发现纳米流体的流量-压力特性基本呈线性关系,其流动特性符合单相流体的假设,并且随着驱动压力的增大流量增大。但模拟结果与实验结果之间存在一定的差异,主要是由于基液中颗粒的团聚结构、纳米流体粘度的变化、尺度效应、分散剂的使用和边界滑移等因素所致。最后,通过数值模拟的方法研究了层流状态下雷诺数、体积分数、颗粒和基液种类以及颗粒粒径对纳米流体对流传热特性的影响。研究结果表明纳米流体的对流传热系数明显高于基液,并且与基液和颗粒的性质、颗粒的体积分数及颗粒粒径密切相关。纳米流体的对流传热系数随着颗粒和基液热导率的增加、颗粒体积分数的增加以及颗粒粒径的减小而增大。研究发现对于一定体积分数的Cu-水纳米流体,在层流状态下对流传热系数的提高程度基本保持一致,与雷诺数大小无关。更多还原

【Abstract】 With the rapid development of MEMS, Nanofluids have become today’s research focus for the predominant thermophysical properties. Nanofluids are the stable suspensions prepared by dispersing nanometer-sized particles (<100nm) in the conventional fluid such as water, alcohol or glycol. In the present study, the preparation methods、stability、viscosity、flow characteristics in micro-channels and convective heat transfer characteristics have been studied.Firstly, the two-step method was adopted to prepare the Cu-Water nano-fluid with different mass faction of particles. In this article, the effect of SDBS dispersant concentrations on the stability of nanofluids has been investigated. The result shows that nanofluid has better stability when the mass faction of Cu particles is the same as SDBS dispersant concentrations. At the same time, the viscosity of Cu-Water nano-fluid has been studied. We found that the viscosity of nanofluids increases with an increase in the mass faction of Cu particles.Secondly, both numerical simulations and experimental study have been performed on the flow characteristics of Cu-water nanofluids including 1% mass faction of Cu nanoparticles. The results show that the mass flow of nanofluids is in line with the driven pressure, and the mass flow of nanofluids increases with increasing the driven pressure, and we found that single-phase hypothesis can be successfully applied to nanofluids. However, the numerical results are different from the experimental date, which is due to the cluster of nanoparticles in based fluids、changes in viscosity of nanofluids、the size effect、the concentrations of SDBS and the boundary slip.Finally, the effects of the Reynolds number、volume fraction and type of based fluid and nanoparticles on the convective heat transfer characteristics of nanofluids under the laminar flow conditions have been numerical studied by using single phase model. The computed results show that the convective heat transfer coefficient of nanofluids is higher than that of the based liquid, however, which is closely related to properties of the based liquid, nanoparticles, and its volume fraction. The heat transfer coefficient of nanofluids increases with increasing the thermal conductivity of nanoparticles and base fluid, and increases with an increase in the volume fraction of nanoparticles. The heat transfer coefficient of nanofluids almost keeps constant for Cu-water nanofluids with a fixed volume fraction, which has nothing to do with the Reynolds number.更多还原