Simulating surfactant effects in phase-transforming fluids

TL;DR

This paper introduces a physics-based computational model to simulate the effects of surfactants on liquid-vapor phase transformations, addressing complex phenomena like Marangoni stresses and non-equilibrium thermodynamics.

Contribution

The work develops a first-principles model based on Navier-Stokes-Korteweg equations to accurately simulate surfactant effects in phase-changing fluids, a novel approach in this field.

Findings

Successfully reproduces surfactant-mediated surface tension reduction

Demonstrates impact of surfactants on bubble coalescence and condensation

Provides a new framework for future studies of surfactant-influenced phase transformations

Abstract

Surfactants are critical in natural processes and engineering, but measuring their concentrations in non-equilibrium conditions and in the presence of flow is difficult. Therefore, computational methods are a key tool for improving our understanding. Predicting the effect of surfactants on liquid-vapor transformations is particularly challenging due to (1) simultaneous mass transfer, non-equilibrium thermodynamics and Marangoni stresses, and (2) the phenomenological assumptions underlying many liquid-vapor phase-change models. Starting from the Navier-Stokes-Korteweg equations, a first-principles approach to liquid-vapor phase transformations, we developed a model of liquid-vapor flows with surfactants. We performed simulations of bubbles under equilibrium and liquid-vapor interface oscillations to demonstrate that the model successfully reproduces surfactant-mediated reductions in surface tension. We also investigated the mechanisms whereby surfactant affects bubble coalescence and condensation. Overall, this work provides a new framework for studying the effect of surfactants on liquid-vapor transformations and suggests multiple areas for future research, including the impact of complex surface chemistries on flow around bubbles and the acoustic response of bubbles with surfactants.