Measurement of the velocities of nanoparticles in nanofluids with laser speckle velocimetry

Our recent work [1,2] revealed that speckles can be formed when illuminating nanofluids with a parallel monochromatic laser beam. Furthermore, we propose that laser speckle velocimetry (LSV) can be used to measure the velocities of nanoparticles in nanofluids and we establish an experimental setup after analysing the optical characteristics of nanoparticle. This paper focuses on the determination of the relationship between the velocities of nanoparticles in nanofluids and the velocities of speckles formed by the interference of the scattered light from the nanoparticles. Based on the experimental setup, a physical model is established after analysing the fluid flow in the pipe. On the basis of this physical model the statistical properties of the dynamic speckles are investigated, and the relationship between the velocities of nanoparticles and the velocities of speckles are finally obtained.