• DNS
• Experimental techniques
• micro-PIV
• Particle trapping phenomenon

Micro/milli-fluidic devices are becoming an important reference for several disciplines and are quickly increasing their applications in scientific, as well as industrial, environment. As a consequence, the development of techniques able to analyse these kinds of systems is required to allow their progress.

In this thesis work is shown the implementation of the Ghost Particle Velocimetry (GPV) for the flow velocity field investigation in milli-fluidic channel. This innovative technique has been recently introduced, and has been already proven to be useful in describing phenomenon at a small scale. Herein the GPV has been developed to characterise an unexpected event lately discovered, the capture of light suspended material in a branching junction. This vortex breakdown induced phenomenon allows to test, for the first time, the brand new technique in the presence of complex fluid-dynamic structures, such as vortices and recirculation zones.

Several experiments have been performed, fully exploiting the GPV capability to carry out 3-D flow reconstructions in different geometries and fluid-dynamic states. The results obtained have been deeply validated and compared with the well-established $\mu$PIV, highlighting the differences in terms of qualitative and quantitative parameters. A performance comparison has been designed to underline the strengths and weaknesses of the two experimental techniques. Two fundamental parameters, the fast camera frame rate and tracers concentration, have been validated, identifying a new discovery about the seeded concentration influence. Ultimately the results have been compared with Direct Numerical Simulations (DNS) performed by \emph{Princeton University}; an hard “competition” for the experimental technique, which it has passed with flying colours.