Portland State University. Department of Chemistry
Albert S. Benight
Term of Graduation
Date of Publication
Doctor of Philosophy (Ph.D.) in Chemistry
1 online resource (xvi, 59 pages)
Chemo-hydrodynamics generated from reaction-diffusion-convection processes of autocatalytic chemical systems are extensively studied for their applications in modeling complex systems. Compared to the more extensively studied autocatalytic systems, chlorite-tetrathionate and chlorite-trithionate, the chlorite-thiourea systems is relatively unexplored. Compared to the two previous systems, chlorite-thiourea has more straightforward chemical kinetics. To narrow the gap between chlorite-thiourea and the other systems a combination of experimental study and numerical simulation were employed to quantify this system.
Compared to established literature, experiments were performed at five orders of magnitude lower concentration of indicator, minimizing confounding effects of indicator on hydrodynamic motion. To accurately image the system, self-written MATLAB code was employed to enhance the color spectrum of experimental videos and images. A combination of two pH indicators was used to effectively isolate the wave front of the reaction system allowing for velocity measurements.
Utilizing experimental data, a simplified kinetics model was generated and a theoretical reaction rate constant was determined for the simplified model using a one-dimensional reaction diffusion solver written in MATLAB. The resulting rate constant of 3.6 x 105 M-2.5s-1 was then used to construct a two-dimensional numerical simulation in COMSOL 5.3a. This model was used to test validity of using the Boussinesq Approximation to treat these autocatalytic systems as incompressible rather than as compressible fluids.
Numerical simulations generated in COMSOL were able to accurately recreate chemo-hydrodynamic behaviors and wave velocities as measured experimentally. No detectable difference in results were determined between solving the system as incompressible with the Boussinesq Approximation compared to solving the full Navier-Stokes equations. However, there was a 20% time savings in solving the full Navier-Stokes equation compared to the simplified version. This result showed that when modeling these systems, computational efficiency was not saved by using the Boussinesq approximation. While these results were not different, larger or more complex systems may benefit from a full treatment of the Navier-Stokes equations rather than an approximation.
© 2021 Matthew Walter Eskew
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Eskew, Matthew Walter, "Complex Fluid Dynamics: Chemo-Hydrodynamics Driven by Autocatalytic Reaction Fronts" (2021). Dissertations and Theses. Paper 5668.
Available for download on Wednesday, March 09, 2022