Flow Measurements in Microchannels Using a MicroPIV system

High quality PIV experiments in micro-channel flow geometries to get detailed and accurate flow measurements can be difficult and involves paying attention to a variety of aspects. In the experiments, the reasons could be ranging from uncontrolled transients in the fluidic flows systems to fouling of the micro-channels by impurities, bubbles, the seed particles themselves. Another factor which could have a significant effect is the distortion of the boundary of the channel caused by the difference in the refractive indices. Experimental measurements were taken on two channels in a PDMS (polydimethylsiloxane) micro-channel test facility shown in Figure 1. The two micro-channels under study were (a) the expansion channel with fully developed flow in a 150 µm wide rectangular section to a 750 µm wide channel, and (b) a ‘T ’ junction with two 100 µm wide outflow channels branch at two 90 degree elbow turns from a 100 µm inflow channel. Both micro-channels are 100 µm deep across the entire channel length. The measurements were performed for Reynolds number of 1, based on the centerline velocity of the channels. The experiments were performed using a PIV system equipped with an inverted microscope. Fluorescent particles of about 1 µm in size were employed as seed particles. Typical particle number concentration was around 2 to 3 particles per interrogation volume. Hence, the ensemble average of the correlation function was used to obtain the velocity vectors. Channel geometry imperfections, fouling and bubble formation affect the flow development and the nature of the flow, especially near the wall