Detection of Nanoparticle Brownian Motions in a Nanofluid Using Laser Speckle Velocimetry

Nanofluids have much higher thermal conductivity than traditional heat transfer fluids owning to the existence within them of nanoparticles, even at a low particle concentration. Brownian motions of nanoparticles may contribute to the thermal conductivity enhancement. In this paper the motions of nanoparticles in a ferro-nanofluid flow were investigated with the laser speckle velocimetry (LSV) technique. Speckle patterns of the nanofluid were recorded by a CCD camera and processed with a cross-correlation algorithm to obtain nanofluid flow vectors. According to the findings, the overall motion trend of nanoparticles was along the pipe flow direction. To a small extent, however, nanoparticle motion vectors deviated from the axial direction. Further average processing over multiple vector diagrams yielded flow vectors obeyed typical laminar flow profile, which means that the derivations in flow direction were random in nature, and resulted from Brownian motions of the nanoparticles. The study indicates that LSV could be a useful tool for visualizing nanofluid flow.