Buoyancy effect on the ultrafiltration of PEG 10,000. Visualization by digital holographic interferometry

Digital holographic interferometry has been used to visualize the buoyancy effects on dead-end ultrafiltration of PEG 10,000. Sets of experiments have been carried out with the membrane in different orientations (90°, 180°), using a feed concentration of PEG 10,000 ranging 5–12.5 kg/m3. These results were compared with those obtained in previous research with the cell placed in its natural position (0°). The interferometric fringe patterns obtained in this research were very different from those obtained previously. Whereas at the 0° position, an increasing number of interferometric fringes appeared parallel to the membrane surface at 90 and 180° positions, the number of interference fringes was much lesser and, with the 180° orientation, slightly curved protuberances appeared after a short period of time that, like big drops, fell downward from the membrane surface. The consequence is a decrease of the polarization layer and an enhancement of the membrane performance. © 2012 American Institute of Chemical Engineers AIChE J, 2012