Turbulent Velocity in Flocculation by Means of Grids

Eleven types of single circular biplane grids with different diameter (d) and mesh (M) were vertically and constantly oscillated inside a 2 L square jar. The velocity components were measured using a 2D laser doppler anemometer. The average root-mean-square turbulent velocity q′ values were found to be relatively constant at both vertical and horizontal points of measurement—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 velocity gradient ? could be applied as the surrogate mixing intensity parameter. It was also found that q′ was linearly related to the vertical grid speed and grid physical characteristics, indicating that the mixing 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 case of turbulent mixing. This study shows the potential of grids as the mixing devices that can be expected to produce an optimum mixing environment for the flocculation process.