Mechanics of immersed particle collisions

The present work investigates the mechanics of particle collisions submerge d in a liquid using a simple pendulum experiment. Particle trajectories for different particles in water are measured using a high-speed digital camer a and the magnitude of the collision is recorded using a high-frequency-res ponse pressure transducer at the colliding surface. The particle decelerati on occurs at distances less than half a particle diameter from the wall. Th e measured collision impulse increases with impact velocity and particle ma ss. Comparisons are drawn between the measured pressures and the prediction s of basic impact mechanics assuming a perfectly elastic collision. A contr ol-volume model is proposed that accounts for the fluid inertia and viscosi ty. When a particle approaches a planar surface or another particle, the fl uid is squeezed prior to contact reducing the initial kinetic energy and de celerating the particle. The pressure profile is integrated over the surfac e of the particle to obtain a force that is a function of the initial parti cle Reynolds number, Re-0, and the ratio of the the densities of the partic le and fluid phases, rho(p)/rho(f). The model predicts a critical Stokes nu mber at which the particle reaches the wall with zero velocity. Comparisons between the proposed model and the experimental measurements show qualitat ive agreement.