An improved flocculator design for use in particle aggregation experiments

Abstract

Experimental studies of aggregate formation usually require knowledge of the rate of fluid shear. A type of Couette device which consists of a fixed inner and a rotating outer cylinder provides an easily quantifiable two-dimensional laminar flow in the annular space between the cylinders. Early designs of such devices had several drawbacks, however, including the sedimentation of particles in vertically oriented devices and difficulties in the ease and repeatability of sampling in horizontal units. The new horizontal design presented here addresses these problems through the use of a movable endcap and sampling port. This device has been shown experimentally to minimize the effects of sedimentation and also to allow multiple samples to be taken without the inconveniences associated with previous horizontal units. Use of the device is illustrated by repeated measurements, over a period of 34 d, of the coagulation efficiency (a) of the diatom Skeletonema costatum.