Chaotic liquid shaker : design, implementation and application

Abstract

Data or flow mixing usually refers to the operation by which a system trajectory evolves from one state of simplicity (initial segregation) to another state of simplicity (complete uniformity). Between these two extremes, typically complex patterns emerge and then die out. Mixing operations on liquids, the main concern of this thesis, widely exist in the food, pharmaceutical, paper, plastics, ceramics, rubber industries and the like. The costs of mixing processes account for a considerable portion in the annual output of these industries. For quite a long time, therefore, researchers are looking for methods to achieve efficient and thorough mixing of liquids by all means. In most fluid flows, the dynamic regimes may be characterized as laminar or turbulent. Mixing in laminar flows, the viscosity of which is much greater than the turbulent ones, induces immense interests of researchers from mathematics, physics, engineering, biology and medicine. In 2-D laminar flows, it has been demonstrated that very mild perturbations in the velocity field can lead to widespread chaotic motions and consequently substantial enhancement of mixing performances. It has been argued that chaotic vibration provides the best possibility of achieving efficient and thorough mixing of fluids, by evoking complex and abundant perturbations into the original steady flows. Chaotic signals enjoy the advantages of having wide breadths of spectra in the frequency domain, fractal trajectories in the phase space, and complex random-like dynamics, etc. When chaos-control-based perturbations are applied to a flow, the blending flow can be considered as working spatially in a complex changing pattern, thereby achieving enhancements in mixing performances. In the last two decades, the advances in the understanding of chaos theory and nonlinear circuits technologies have brought up the bright prospects to take advantage of the favorable features of chaos in various technical fields, especially in liquid mixing applications. The technologies of implementing various chaotic systems in both analog circuits and digital hardware have enabled the possibilities of generating complex chaotic signals that can be applied to yield chaotic vibrations in mixing flows. In this thesis, a liquid mixing apparatus (an electromechanical shaker) based on the commonly used stirred thank model is introduced. The design and implementation of this liquid shaker, which is capable of working under the control of different kinds of signals, are reported with detailed descriptions. Constant voltage signals, periodic signals and chaotic signals are applied to the impeller/tank velocity control mechanisms, exploring the efficacy of different perturbation schemes for liquid mixing. Comparable experiments using different control signals are carried out to investigate the time consumption in sucrose dissolving processes and the homogeneity in visualized mixing flows. Experiments on the sucrose dissolution processes and the mixing-flow visualization are conducted in the laboratory. The results of these experiments reveal that chaotic perturbations help enhance the liquid mixing efficiency and homogeneity quite significantly, yielding faster and more uniform results than all the non-chaotic counterparts. The validated stirred-tank-based shaker is expected to be extended and applied to some industrial mixers so as to improve the mixing performances in the near future.