Turbulent velocity in flocculation by means of grids

Eleven types of single circular biplane grids with different diameter (d) a nd mesh (M) were vertically and constantly oscillated inside a 2 L, square jar. The velocity components were measured using a 2D laser doppler anemome ter. The average root-mean-square turbulent velocity q' values were found t o be relatively constant at both vertical and horizontal points of measurem ent-a condition that could not be achieved in the case of impeller mixing. Since the mixing intensity was uniform within the jar, the average volume v elocity gradient (G) over bar could be applied as the surrogate mixing inte nsity parameter. It was also found that q' was linearly related to the vert ical grid speed and grid physical characteristics, indicating that the mixi ng was easily controlled, The macro length scale (L) was calculated and was found to be constant and proportional to d or M, as it should be in the ca se of turbulent mixing. This study shows the potential of grids as the mixi ng devices that can be expected to produce an optimum mixing environment fo r the flocculation process.