Unsteady Motion of a Single Droplet in Surfactant Solutions

A numerical investigation of the unsteady motion of a deformed drop released freely in another quiescentliquid contaminated by surfactant is presented in this paper. The finite difference method was used to solvenumerically the coupled time-dependent Navier-Stokes and convective-diffosion equations in a body-fitted orthogonalcoordinate system. Numerical simulation was conducted on the experimental cases, in which MIBK drops with thesize ranging from 1.24 mm to 1.97 mm rose and accelerated free1y in pure water and in dilute sodium dodecyl sulphate(SDS)aqueous solution. The applicability of the numerical scheme was validated by the agreement between thesimulation results and the experimental data. Both the numerical and experimental results showed that the velocity-time profile exhibited a maximum rising velocity for drops in SDS solutions, which was close to the terminal velocityin pure water, before it dropped down to a steady-state value. The effect of the sorption kinetics of surfactant onthe accelera