2.6.1. High-Speed Imaging

A high-speed camera High-SpeedStar 6 (La Vision) and a set of attachments from Navitar (0.67 adapter tube, extension tubes 10, 20 and 40 mm, 0.5X Precise Eye lens) were employed to visualize the two-phase flow inside the microchannels. As a result of the high flowrates employed, a shutter speed (exposure time) of 1 µs and a frequency of 5000 images per second (some experiments performed at 40,000 images/s) were set as the acquisition conditions for image capturing. To sufficiently illuminate the visualization area at the extremely short exposure time selected, a halogen lamp OSRAM 12 V 50 W 24° 870 lm 3000 K was used as the backlight. Image acquisition and recovery were performed using the software Photron FASTCAM Viewer. Then, the images were processed and analyzed (feature extraction) using the open-source software ImageJ.