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摘要纳米流体作为一种新型的传热介质己引起国内外学者的广泛研究，然而对于其传热机理的研究至今仍是该领域的研究热点之一。结合目前纳米流体强化传热机理的研究进展，纳米流体中纳米粒子的运动被认为是引起纳米流体导热系数得到提高的一个重要因素。本文结合激光散斑测速技术 (LSV)，应用激光散斑过零法对定向流动的纳米流体中纳米粒子的运动状态进行了理论分析及实验研究。本论文从散斑统计特性出发，对动态散斑进行了理论分析，分析并讨论了利用动态散斑测量物体运动速度的各种方法。针对激光散斑过零法测量物体运动速度具有实验装置简单及可实现实时测量的优点，并根据该方法测量的基本原理，建立了过零法测量纳米流体运动速度的装置，并通过实验获得了散斑光强起伏信号，进而得到了散斑光强起伏信号的过零次数与物体运动速度间存在的正比关系。为了去除采集所得信号中的噪声及基线漂移对过零次数的影响，对信号进行了减去线性拟合值处理，得到信号的有效信息，并通过计算对此进行验证，得出该处理方法的可行性。基于对此信号的处理方法，对实验信号分析获得了纳米粒子运动速度与定向流动的纳米流体平均流速之间的关系，进而得到了纳米粒子具有良好跟随性的结论。9222
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关键词: 纳米流体 激光散斑 过零法散斑测速 信号去噪
毕业设计说明书（论文）外文摘要
Title Movement Monitoring of Nanoparticles in Flow field by Using the Method of Dynamic Laser Speckle
Abstract
Nanofluids, as the new next-generation coolants，have attracted great attention from researchers worldwide. However, the fundamental understanding of the mechanisms of enhanced heat transfer in nanofluids, which is one of the research focuses in heat transfer field，is still a mystery calling for new and comprehensive theories to explain. Basedon the existing studies of mechanism of nanoflulds so far,the movementof nanoparticles is one of the important factors controlling the therm-al conductivity of nanofluids. In this paper，combined with the idea of Laser Speckle Velocimetry(LSV)，experiments are carried out to meas-ure the velocities of nano-particles in directional nanofluids with Zera-Crossing Method.
Based on the statistical characteristics of laser speckle and the theoretical dynamic speckle analysis， methods using dynamic speckle are proposed to measure the velocities of nanoparticles in nanofluids.Since the Zero-Crossing method has two advantages that the optical sys-tem is very simple and that the measurements of the object velocity are carried out in real time, the principle of Zero-Crossing method isdescribed, and the relationship between the numbers of Zero-Crossing per second of speckle intensity fluctuation and the velocities of the object is obtained.
In order to remove the influences of noise in the signals and the baseline drift on the Zero- Crossing numbers，the signals are denoisedby wavelet transform and processed by subtracting the linear fitting values. The obtained signals are verified by calculating the velocity of moving nanofluids. Then，the relationship between velocities of nan-oparticles and average velocities of the directional nanofluids flow is obtained by statistical experimental results，which obtains the con-clusion that nanoparticles show the super following feature in nanofl-uids，which suggests its feasible and valuable method for measuring dir-cetional moving fluids. Moreover，in order to measure the direction of the nanofluids flow，the Zero-Crossing method used by TEM mode-likelaser is proposed and it is verified reliable by experimental results.
The results of this research may provide theoretical and experimen-tal references for researches on measuring the velocity and directionof moving fluid and understanding of the mechanisms of enhanced heat transfer in nanofluids.