Mixing and solvent exchange in turbulent jet flows

Abstract

Solvent exchange is a physicochemical hydrodynamical process in a ternary liquid system, which consists of a good solvent, a solute, and a poor solvent. A poor solvent lowers the solubility of the solute in the mixture, triggering oversaturation and nucleation of the solute droplets. In this thesis, we have investigated several aspects of mixing and the subsequent nucleation in different types of turbulent jet flows, aiming to advance our understanding of solvent exchange toward the turbulent regime. The ternary liquid system of our choice consists of ethanol, anise oil, and water, namely the good solvent, the solute, and the poor solvent. We inject an ethanol/oil mixture into quiescent water to produce turbulent flow and facilitate mixing. Because of the opaque nature of the fluid, we use a light attenuation technique to estimate the concentration of the nucleated oil. Using an axisymmetric discretization and an optimization algorithm, we measure the time-averaged concentration field of a 3D turbulent buoyant jet in Chapter 1. In Chapter 2, we confine the turbulent jet with a quasi-2D, 2mm thin cell to identify the TNTI and study the temporal fluctuations of concentration. We measure the concentration near the TNTI of quasi-2D turbulent jets in steady state In Chapter 3, we shift our attention to the unsteady quasi-2D jet flows, including starting jets and finite-volume puffs. We adapted the analytical framework for a quasi-2D turbulent jet in the literature, estimating spatial-temporal variation of the concentration for the nucleated oil. In Chapter 4, we reverse the direction of injection, forming a quasi-2D turbulent fountain. We show that the degree of mixing increases with density difference. That is, a stronger negative buoyancy force leads to stronger mixing and dilution. The thin-cell confinement induces the shielding effect and inhibits entrainment and mixing into the fountain.