Lodz University of Technology, Faculty of Process and Environmental Engineering Wolczanska 213, 90-924 Lodz, Poland
In studies of self-aspirating impellers found that gas bubbles are not broken down by the impeller blades. Break-up of bubbles is caused by the eddies generated by the blades. Therefore, to describe how the liquid flow near the blades is an important research issue for this type of impellers. Using the PIV method average velocity fields in the axial-radial plane between baffles in the stirred tank were defined for seven different positions of blades of a self-aspirating disk impeller in relation to that plane. It was found that in the small space in blade vicinity, big changes in fluid circulation were observed depending on the position of the blade relative to the baffle. In front of blade the liquid from bottom and from over impeller is directed radially towards the wall of tank and the average axial velocity is zero. Behind the blade the cavern (cavity) is formed, understood as a space of reduced pressure. Underpressure causes suction effect which directs the liquid inside the cavern. In just a few millimeters from the blade tip average axial and radial velocities are equal to zero. In this region the tangential component of velocity is dominant.