Cohesive particles display unique behaviors and involve numerous, diverse physical mechanisms encompassing phenomena such as elastic deformation and the liquid-glass transition. Our research is focused specifically on the collisions between solid particles coated with a liquid layer. Wetted particles can be found naturally such as in avalanches and pollen capture. Research has also been focused on wetted particles because of its industrial applications including granulation, water filtration, and pneumatic transport.

In our lab, we use both experiments and theory to study wetted collisions. To ensure a low experimental Reynolds number, the ratio of inertia to viscous forces, collisions are performed at low velocities using a variety of methods. Particle-wall collisions can be achieved by dropping a particle onto a wall. However, for particle-particle collisions, we have employed a pendulum apparatus, inspired by the Newton's cradle desktop toy, called the Stokes' cradle. Low-gravity collisions preformed in the KC-139 airplane, (aka Vomit Comet), validated these experimental methods.  

Below are example videos that exhibit all four possible outcomes of three-particles collisions; namely, fully agglomerated, Newton's cradle - where the striker and first target agglomerate and the opposite particle is separate, Reverse Newton's cradle - where the striker is separate from the targets, and fully separated.  

Fully Agglomerated

Newton's Cradle

Reverse Newton's Cradle

Fully Separated

During a wetted collision, the fluid between the solid particles can be described by Stokes flow. However, as the surfaces approach each other, the pressure rises dramatically resulting in (1) the elastic deformation of the solid surfaces (elastohyrdodynamics) and (2) a rise in the viscosity of the oil.  During rebound, the pressure then drops below the vapor pressure; and while cavitation may occur, outbound liquid resistance still exists.  

Previous Students

Carly Donahue, Mike Weber

Relevant Papers

Donahue, C. M. C. M. Hrenya, and R. H. Davis, "Stokes's cradle:  Newton's cradle with liquid coating," Physical Review Letters, 105, art. no. 034501 (2010).

Donahue, C. M., C. M. Hrenya, R. H. Davis, K. J. Nakagawa, A. P. Zelinskaya, and G. G. Joseph, “Stokes’ cradle: normal three-body collisions between wetted particles,” Journal of Fluid Mechanics650, 479-504 (2010).

Henthorn, K. H. and C. M. Hrenya, “Particle cohesion,” Encyclopedia of Chemical Processing, 1, 1-8 (2009).

Kantak, A. A., C. M. Hrenya, and R. H. Davis, “Initial rates of aggregation for dilute, granular flows of wet (cohesive) particles,” Physics of Fluids21, art. no. 023301 (2009).

Weber, M. W. and C. M. Hrenya, “Computational study of pressure-drop hysteresis in fluidized beds,” Powder Technology, 177, 170-184 (2007).

Weber, M. W. and C. M. Hrenya, “Square-well Model for Cohesion in Fluidized Beds,” Chemical Engineering Science61, 4511-4527 (2006).

Weber, M. W., D. K. Hoffman, and C. M. Hrenya, “Discrete-particle simulations of cohesive granular flow using a square-well potential,” Granular Matter, 6, 239-254 (2004).