Title

The stability of the iodate -arsenous acid reaction front while advected by Poiseuille flow

Semester

Fall

Date of Graduation

2005

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Physics and Astronomy

Committee Chair

Boyd F. Edwards.

Abstract

The competition between stabilizing and destabilizing effects is a motif that occurs in every aspect of the human experience. The coupling between the dynamics of chemical reactions and fluids offers a fruitful context in which to examine the patterns that arise in the presence of this competition.;The upward-propagating iodate-arsenous acid front is an example of a system in constant struggle. As it moves upward, it leaves a reacted solution of lesser density behind (and below) it. The system is thus subjected to a Raleigh-Taylor-like instability. On the other hand, the well understood (experimentally and theoretically) relationship between the front speed and the curvature of the front is such that the higher a section of front peaks, the slower it goes. The lower a valley of the front, the faster it goes. Thus, the front has a stabilizing tendency. So a natural question is, will the front remain stable, or will it suffer the fate of a convective instability?.;The answer is a resounding "it depends." Previous research has shown that the onset of instability occurs when a driving parameter exceeds some critical value Sc. This driving parameter involves the fractional difference in density between the chemical species, the acceleration due to gravity, the wall separation, the viscosity, and the chemical diffusivity. The only variable that the earthbound experimenter is free to alter is the wall separation, and experiments have agreed very well with the predicted value of Sc.;These successful experimental and theoretical developments were for the case of a stationary fluid. The next step is to extend the understanding of this dynamic to the case of a moving fluid. In a fluid moving between two no-slip boundaries, the fluid velocity assumes a parabolic (or Poiseuille) profile. An interesting question to ask is how is the stability of the chemical reaction front affected by the imposed fluid motion? The answer is contained in this text.

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