Micro-PIV simulation and measurement in complex microchannel geometries

Using low numerical aperture lenses to achieve a large field of view when carrying out micron resolution particle image velocimetry (micro-PIV) experiments may result in the out-of-plane resolution being a significant fraction of the overall channel depth. A method to estimate the effect of out-of-plane resolution on micro-PIV velocity measurements is applied to two microchannel flows: a two-dimensional developed flow in a straight channel and a three-dimensional periodic flow in a ribbed channel. The method combines numerical simulation based on computational fluid dynamics (CFD) with an approximation for the contribution to the correlation function arising from partially defocused particles. The flows are then investigated experimentally with measurements obtained on a number of evenly spaced planes. The dominating factor in the comparison between the micro-PIV results and CFD simulations is not the spatial resolution of the experimental data, but instead the precision with which the geometrical parameters can be determined. A methodology is also presented for using micro-PIV results to measure the depth of microfluidic devices. Parabolic fitting of flow profiles allows the top and bottom surfaces of the channel to be located to within 0.2 µm.