Experimental Determination of the 2D Velocity Laminar Profile in Glass Microchannels using μPIV

In this work an experimental campaign for the determination of the 2D velocity profile in laminar regime of water flowing through glass microchannels is described. Two channels are considered: a microchannel with a side of 300 μm (test #1) having an aspect ratio (height/width) equal to 1 and a microchannel having a width of 300 μm and a height of 100 μm (test #2). Firstly, the real cross section of the glass microchannels has been determined by means of a Scanned Electron Microscope (SEM). The SEM images of the cross sections highlight how the real cross section of these channels differs from the cross section declared by the manufacturer. In particular, both the tested glass microchannels have evidenced a trapezoidal cross section and not a rectangular one as specified in the manufacturer data sheet. For both the channels, the experimental velocity data acquired by using the μPIV system have been compared with the theoretical values obtained by solving the Navier-Stokes equation for a incompressible fluid under steady state conditions. The results have evidenced that μPIV is able to determine the velocity profile within the glass microchannel with an average relative difference with respect the theoretical values of the order of 1-4% depending on the aspect ratio of the channel in the central part of the channels. On the contrary, moving towards the walls, the relative difference between the theoretical and experimental velocity grows up by reaching the maximum values close to the walls. The results presented in this paper are used in order to discuss how the accuracy of the velocity measurements obtained byμPIV can be optimized.