EFFECT OF SURFACE MOBILITY ON COLLISION OF SPHERICAL DROPS

The collision of two spherical liquid drops is considered which allows the effect of coalescence on the formation and stability of dispersio ns to be studied. An analytical solution is derived for the variation in the hydrodynamic force with the approach velocity and the separatio n thickness during the impact in terms of the drop diameter, allowing for the effect of induced flow inside the drops. Setting this force eq ual to the rate of change of momentum of the drops enables the variati on with time in the separation between the drops to be obtained in ter ms of the initial approach velocity, drop diameter, and viscosity rati o. The analysis also yields the time variation in the force and approa ch velocity. For a given impact velocity, the separation thickness dec reases with time until a minimum value is reached, which decreases as the impact velocity and the viscosity ratio of the continuous and disp ersed phases increase. Previous authors have only obtained the variati on in the approach velocity with the unknown variable force and separa tion thickness during the impact and therefore could not obtain the va riation in the separation thickness with time. Knowing this variation enables the possibility of coalescence during impact to be investigate d. Coalescence is influenced by the minimum separation thickness attai ned at low impact velocities and by drop deformation and inertial drai nage at high velocities. (C) 1998 Academic Press.