Experimental study of small aggregate settling.

The drag coefficient and hydrodynamic radius of particles are important parameters needed in crystallization science. Small aggregates of micrometric primary particles are mainly produced in stirred crystallizers. We present experimental results on the drag coefficient of macroscopic aggregates consisting of glass beads in the number range [2,100]. The drag coefficient is calculated from settling measurements in glycerol in order to preserve the Stokesian nature of typical flow around particles in a crystallizer. We show that the hydrodynamic radius of these aggregates is almost the radius based on the average projected area over all orientations. This result is extended to larger and more porous aggregates.