Computational Simulation of Surfactant-Induced Interfacial Modification of Droplet Impact and Heat Transfer

Numerical investigation of heat transfer during drop impact, spreading, recoil, and rebound/break up has been carried out for water droplets with and without surfactant additives. The numerical model is based on a finite volume formulation on a structured grid. A volume-of-fluid (VOF) technique is used to track the deforming liquid-air interface. Comparisons between the numerical results and experimental data are presented, which show a remarkable agreement between the simulated impact-spreading-recoil behavior on a hydrophobic surface and highspeed visualization of the process. The simulations reveal that the water droplets spread and then recoil sharply so as to form a vertical column, which breaks up and ejects secondary droplets. The decrease in surface tension at the liquid-air interface and change in the wetting characteristics of the liquid-solid interface facilitates larger initial spreading and weaker recoil of surfactant solution droplets compared to water drops. As a result the transient heat transfer rate is significantly higher for aqueous surfactant solution droplets. The solution of lower molecular weight (higher mobility) surfactant (SDS) shows a higher maximum and final spread with weaker recoil compared to the higher molecular weight (lower mobility) Triton X-100 solution. * Corresponding author