Atomization Characteristics of a Spinning Disc in Direct Droplet Mode

The direct droplet mode of atomization from a spinning disc is of fundamental interest. It is utilized for rapid mixing of liquids with low back-mixing in a new spinning disc-spinning bowl contactor. High-resolution images of the entire disc are used to study drop formation. The images can capture a 50 mu m drop moving at 8 m/s without blur. The individual detachment events show wide variations under all conditions. A primary drop leads a detachment event and produces one or more secondary drops through breakup of the connecting liquid thread. The two sets of drops have their distinct, nonoverlapping monomodal size distributions at low disc speeds. The secondary drops have nearly three times larger coefficient of variation (COV, 27-47%) than the primary drops (8-13%). The distributions merge into one broad monomodal distribution at high flow rate and disc speed. The first secondary drop is often not the largest secondary drop in a detachment event. The ratio of the size of secondary to primary drops increases with an increase in the rotational speed, and so does the fraction of the throughput carried by the secondary drops (6-25%). An increase in flow rates has only a marginal effect on the mean size of primary and secondary drops; they manifest different dependence of Weber number. The inlet flow rate sensitively impacts the number of active droplet generation sites. The drop release rate per active site per second is estimated to be in the range 100-1000. A few other new observations are also made.