Misure di Velocità in Mini- e Micro-canali mediante la Tecnica micro-PIV

In this work the recent significant progress made in the development and application of micronresolution Particle Image Velocimetry (μPIV) have been described. In these last years, the capability of μPIV has been demonstrated by applying this technique to flows in microchannels, micronozzles, BioMEMS, and flow around cells. The development of this specific optical technique for microfluidics has extended typical spatial resolutions of the conventional PIV from order 1-mm to order 1-μm. These advancements have been obtained as a result of novel improvements in instrument hardware and post processing software. In this paper the main hardware characteristics of a μPIV apparatus are discussed and commented. The main differences between the conventional PIV and μPIV are highlighted; in particular, theory describing the limits of in-plane and out-of-plane spatial resolution of the fluorescent particles is presented. Some experimental results have been presented in order to demonstrate that the concentration of the fluorescent seeding in the working fluid and the number of images analyzed in the correlation-averaging post-processing algorithm are important parameters to set the accuracy level of the velocity field measurement in a microchannel. It has been demonstrated that the random effects due to the Brownian motion of the seeding cannot be neglected in μPIV when nano-particles having diameters less than 500 nm and microflows having a characteristic velocity less than 1 mm/s are investigated.