激光散斑过零法测量纳米流体运动状态

Measurement of nanofluid motion with laser speckle zero-crossing method

为了测量纳米流体的运动状态，采用激光散斑测速技术和过零测试方法，分别对TEM00激光散斑过零法测量纳米流体中纳米粒子运动速率和类TEM10激光散斑过零法测量纳米流体运动方向进行了理论分析和实验验证，取得了含大量噪声和基线漂移的散斑光强起伏信号：．对该信号进行小波去噪和线性拟合，得到信号每秒过零次数与漫射物体运动速率间存在的正比关系。结果表明，纳米粒子具有良好的跟随性，且纳米粒子的速度可认为是纳米流体的实时运动速度；同时，通过实验验证了类TEM10激光散斑过零法测量流体运动方向的可行性。这一结果为纳米流体运动状态的测量和纳米流体传热机理的研究提供了理论和实验依据。

In order to measure movement state of nanofluid, based on the laser speckle velocimetry（LSV） and zero-crossing method, theoretical analysis and experiments were carried out to measure the velocities of nano-particles and direction of nanofluid with TEM00 mode and TEM10 mode-like laser speckle zero-crossing method respectively. The experimental data show a lot of noise and baseline drift in the fluctuant signals of dynamic speckle light intensity. In order to remove the influence of noise in the signals and the effect of the baseline drift on the zero-crossing numbers, the signals were de-noised by wavelet transform and processed by subtracting the linear fitting values. Then, it was found that the received zero-crossing numbers was direct proportional to the object movement speed. Experimental results show that nanoparticles have good following feature in nanofluid, and the speed of nanoparticles can be considered real-time fluid velocity. At the same time, it is a feasible and valuable method for measuring the direction of fluid flow verified by the zero-crossing TEM10 mode-like laser speckle veloeimetry. The results of this research provide theoretical and experimental basis for measuring fluid velocity, direction and the mechanism of heat transfer of nanofluid.