Coagulation in a rotating cylinder

The need for laboratory systems to study coagulation processes in the ocean has led to the use of rotating cylinders as a means to simulate particle dynamics in marine systems. While their hydrodynamics are well understood, the nature of coagulation in them has not been analyzed. This article derives corrections to the standard coagulation equations that describe particle dynamics in the system and simulates the development of a growing algal culture. The results are compared to simulations of algal coagulation in an oceanic mixed layer. Coagulation rates are initially slower in the rotating system because of the lack of shear, but rates increase as coagulation creates larger particles that become concentrated within smaller regions of the rotating vessel. Once there is active coagulation, the reactors form a disproportionate number of the largest aggregates because large particles must remain within the vessel, whereas they can fall out of the surface mixed layer in the ocean. In addition, coagulation for larger particles within the rotating tanks is faster than in nature. These simulation results suggest that rotating coagulators simulate ocean conditions best in early stages of coagulation, before large particles form and are concentrated within smaller regions of the tanks. Having a quantitative description of the dynamics within the rotating tanks provides a means of testing hypotheses about ocean particle dynamics.