SUBJECT: Ph.D. Dissertation Defense
BY: Michael Ahmad
TIME: Monday, October 18, 2021, 10:00 a.m.
PLACE: Virtual, NA
TITLE: Turbulent Mixing Between Liquids of Disparate Viscosity and their Effect on Reaction
COMMITTEE: Dr. Devesh Ranjan, Chair (ME)
Dr. Cyrus Aidun (ME)
Dr. Timothy Lieuwen (ME/AE)
Dr. Peter Loutzenhiser (ME)
Dr. Joseph Oefelein (AE)
Dr. Irfan Khan (Dow)


The process of mass and momentum diffusion in a high Schmidt number disparate viscosity jet was observed through high fidelity particle Image velocimetry (PIV) and planar laser induced fluorescence(PLIF). The experimental campaign was carried out in a pressure driven facility specifically built to produce continuous flows with the viscosity disparities observed in chemical industry. Tests for the jet in coflow configuration were performed at constant inlet momentum and geometry with varying viscosity ratio. Test cases at viscosity ratios of 1, 10, 20, and 40 were achieved by increasing the viscosity of the outer jet. Further, these hydrodynamic experiments are coupled with reactive experiments with the same hydrodynamic inlet conditions that observe the product distribution of a mixing limited test reaction. These experiments were performed with a novel inline spectroscopy approach that enabled product distribution measurements throughout the reactor and not just at the reactor outlet. Collectively, these data sets provide the means to establish effective computational models for predictive modeling of variable viscosity flows with reaction. This will help in understanding a wide range of physical phenomena, specifically those necessary to optimize production within the materials industry. The viscosity disparity was found to retard the diffusion of both the momentum and passive scalar. This decrease in diffusion was accompanied by skewed mixing behavior leading the turbulent kinetic energy and scalar mixing to occur preferably in the low viscosity the inner jet. These findings inspired a study of conditional statistics based on the distance from the interface between the low and high viscosity fluids. This analysis demonstrated that the local shear rate at this interface decreases with increasing viscosity ratio, decreasing the role that Kelvin Helmholtz vortices can have in the mixing process. The concentration variance and Reynolds stresses showed a growing deficit in the adjustment layer that increases with viscosity ratio. This causes more of the mixing to occur in the inner stream which has implications for reactive mixing applications. Finally, this thesis demonstrated the efficacy of the dynamic spectroscopic method to observe and an LES model to simulate the complex test chemistry. For the first time, the technique was demonstrated effectively on the viscosity matched case, with product distributions matching within 3% of computational studies. These techniques were extended to the variable viscosity case with viscosity ratio ranging from 1 to 170 with similar experimental and computational agreement. This demonstrates both the effectiveness of the computational method for modeling complex reactions, but also the efficacy of the inline spectroscopic method for measuring the yield.