DOE Final Technical Report for Grant Number DE-FG03-90ER14148

Abstract

858 534 6880; csurko@ucsd.edu OverviewThis project focused on understanding the dynamics of a well-controlled fluid system driven far from equilibrium. The goal of the work was to gain a quantitative understanding of the role that traveling waves play in determining patterns and dynamics in such systems. Convection was studied in a horizontal layer of a binary fluid mixture of ethanol and water confined in a variety of interesting geometries, including a narrow annulus, to study one dimensional phenomena, and a large aspect ratio container to study two-dimensional phenomena. In these mixtures, the Soret effect couples the temperature and concentration fields leading to a wide range of dynamical behavior not present in convection in pure fluids. In particular, over a wide range of parameters, when the fluid is heated from below, convection takes the form of traveling waves composed of locally parallel rolls that move perpendicular to the roll axes. The system thus provides an insightful model for studying traveling-wave phenomena in systems driven far from equilibrium. Over the course of the project, a number of important questions were addressed. To a lesser extent, variants of this situation were also studied, including the patterns and dynamics when the fluid is heated from above. At the end of the grant, work focused on so-called non-Boussinesq effects, where there the fluid parameters vary with height in the convection cell, beyond that which can be taken into account by a thermal expansion coefficient. Technical approachBeyond the conventional techniques to study convection in a thin horizontal fluid layer with good temperature control of the upper and lower boundaries, techniques were developed to study very large convection cells. As a result, patterns of large lateral extent, D, could be investigated (i.e., D ≥ 40d, where d is the height of the fluid layer, and the pattern wavelength, λ = 2d). Experimental capabilities were developed to achieve good temperature uniformity over annular, circular, rectangular and oval convection cells as large as 21 cm in lateral extent. The entire pattern could be visualized from above using the shadowgraph technique. A shadowgraph was developed that is capable of imaging the entire pattern with excellent sensitivity and uniformity, free from distortions, over the entire the entire pattern.