Measurement Method of Nanofluids Average Velocity Based on Laser Speckle Image

In this paper, based on the optical properties of speckle, the correlation between laser speckle image and nanoparticles is analyzed, and a method to measure the flow velocity of nanofluids using speckle image is proposed. The influence of nanofluids type, temperature and concentration on speckle image was investigated. On the basis of grating spatial filtering, based on PIV (Particle Image Velocimetry) cross-correlation algorithm and optical flow field algorithm, the principle of gray conservation and interpretation window are introduced to extract the spectral characteristic curve of speckle image signal. Considering the interference of the environment noise, the wavelet packet decomposition method is proposed to separate the low-frequency features and obtain the peak frequency of the signal. The static and dynamic speckle images are analyzed by establishing a circular tube flow measurement system with laser speckle circulation to verify the rationality and feasibility of the velocity measurement method. The experimental results show that the speckle image of CuO nanofluids in static experiment is better than that of Al 2 O 3 nanofluids, and increasing temperature has no obvious effect of improving image quality. The average relative error between the calculated results and the measured results is 4.9 and 4.5%, which proves that this method is reasonable and feasible.