Coalescence limited by hydrodynamics

We consider an assembly of liquid drops imbedded in another immiscible liquid of similar viscosity. It is shown that a coalescence between two drops induces another coalescence when the average distance between the drops is less than a threshold value, resulting in a ''chain reaction'' of coalescences. The threshold value is calculated using a ''shell'' model that is based on the boundary integral approach. Another ''many-drop'' model is developed to test the shell approximation. We show that, although the shell model is adequate, its results can be improved by lowering the shell surface tension. (C) 1997 American Institute of Physics.