Fluid mechanics calculations in physics of droplets – III: Off-center numerical collisions of equal-size drops for the system water-heptane

In this study, numerical calculations of the collision process between water drops immersed in a continuous phase composed of a hydrocarbon (n-heptane) is reported. For the resolution of the hydrodynamic equations, i.e., the continuity and momentum equations, the finite volume method was used. A range of values for the velocity of collision between the drops was chosen. These values for the velocity of collision give two different outcomes. For these off-center collisions, it is shown that the system of drops rotates around its mass center acquiring certain angular momentum. When the velocity of collision is 0.2 m/s, the system of drops coalesces without the deformation of the surface of the drops and the prevailing surface tension forces. These surface tension forces with the evolution of the dynamics transform the bigger mass of water as a very well-defined circular drop. For a velocity of collision of 3.5 m/s, the system shows coalescence with a rotation of a bigger mass of water with certain angular momentum. In this case, there is a stretch of the surface of the drops, but due to the value of the velocity of collision, the prevailing inertial forces and the bigger mass of water are deformed spinning around its mass center.