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