낙하하는 액적의 계면활성제 흡수 거동에 관한 수치 해석 연구

Abstract

Surfactant, which has hydrophilic heads and hydrophobic tails, tends to accumulate at the phase interface. In general, surfactant decreases the surface tension coefficient locally, and thereby affects the dynamics of interface motion as well as flow characteristics. Although recent advances in numerical simulation for multiphase flow systems have made it possible to understand complicated interfacial phenomena interacting with surfactant, most of the existing numerical studies have mainly focused on the surfactant adsorption behaviors of rising bubbles so far. In this study, we attempt to analyze the effect from surfactant in the concentration field of external gas with a freely falling droplet. A Numerical model for tracking the movement of interface is proposed by using Level Contour Reconstruction Method (LCRM), and the governing equations for the surfactant transport are also formulated. Two benchmarking tests, i.e. Marangoni migration of a droplet, and a bubble rise interacting with surfactant, are performed to check the validity of proposed numerical formulation. Interaction behavior of surfactant with a freely falling droplet is compared with the case of rising bubble. In addition, the adsorption characteristics of surfactant during the free fall of a droplet are analyzed with various non-dimensional flow conditions. The absorption coefficient and the maximum surfactant concentration have been found to be the effective variables to increase the total absorption amount.