On the prediction of coalescence and rebound of fluid particles: A film drainage study

Abstract The collision of two fluid particles with similar sizes approaching each other with time dependent velocities is studied in this work via a film drainage model that can render both coalescence and rebound. The model equations are simplified following the lubrication theory and the interfaces are treated as deformable ones. The particle velocities are governed by a force balance that includes the added mass, the drag, the buoyancy and the film forces. The film force stems from the pressure build up within the film due to interfacial deformations, and its presence in the model enables the particles to bounce, provided that the film becomes resistant enough for the surface energy stored during the approach of the particles to convert back to kinetic energy. The simulations result in rebound when the collision energy is high, in coalescence when the energy is in an intermediate range, and in particles reaching a steady-state for even lower energies. The critical velocity value, at which the rebound regime starts, is found to be similar to the experimental ones in the literature, and presented as a function of key model parameters.