Oscillatory baffled reactors (OBRs) are a form of plug flow reactor, in which tubes fitted with orifice plate baffles have an oscillatory motion superimposed upon the net flow of the process fluid. The interaction of the baffles with the oscillatory motion of the fluid generates uniform mixing and enhanced transport rates, whilst maintaining conditions approximating plug flow. Unlike conventional tubular reactors, where a minimum Reynolds number must be maintained, the tube-side mixing is independent of any net flow, potentially allowing long residence times to be achieved in a reactor of greatly reduced length-to-diameter ratio leading to much more compact designs. This suggests a niche application in converting long reactions from batch to continuous processing. Fermentations show characteristically long residence times. Therefore, they could be intensified in an OBR. Since one major advantage of the OBR is its highly uniform, controllable mixing, which can be used to enhance gas-to-liquid mass transfer, it should be suitable for biological reactions. Fed-batch or continuous fermentation is a second advantage, as it should minimise substrate and product inhibition. Lower, more uniform shear rates than in a stirred tank reactor would be an additional advantage for processing shear-sensitive cells. Previous research has shown that the OBR can provide higher biomass concentrations and greater gas-liquid mass transfer than conventional fermenters. In this work two different fermentation systems were studied. Firstly, as a benchmark experiment, the fermentation stage of the beer production process was investigated in order to determine any relative advantages of using the OBR. Secondly, the production of biopolymers, namely polyhydroxyalkanoates (PHA), by Pseudomonas putida KT2442 was studied. Biopolymers are biodegradable polymers made from renewable resources. They can be made from plants or by microorganisms. P. putida is one such microorganism. Under nutrient limitation and carbon excess it produces polyhydroxyalkanoates (PHA), which are linear polyesters, to store carbon as energy resource. PHAs are biodegradable and are used in the production of bioplastics. The production of biopolymers from microorganisms is currently not cost-effective, because of expensive substrates, low yields and complex downstream processing. Therefore, intensification of PHA production to achieve higher yields in smaller, more efficient equipment at lower capital costs would be an advantage. The parameters investigated in the two systems were agitation rate and temperature. The main result of the beer fermentation was that beer could be successfully produced in the OBR with a significant reduction in time-to-completion to a fifth of that of a conventional beer fermentation. This was achieved at 37 ± 1 °C and an oscillatory Reynolds number (Reo) of 300. For the biopolymer production it was demonstrated that PHA can be produced in the OBR. The fermentation temperature and agitation rate resulting in the highest optical density (OD) and PHA yield in this parameter space were determined as 30 ± I °C and an oscillatory Reynolds number of 300 respectively. It was also demonstrated that using an OBR can lead to higher OD (10.8 vs 7.32) and dry cell weight (3.75 g/L vs 2.4 g/L) than in a comparable conventional stirred tank reactor.

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In this thesis we study four problems with potential biological and industrial applications which rely on fluid mixing and transport. The problem of simultaneous ultrafiltration, diffusion and osmosis across a membrane separating two fluids is studied, numerically and asymptotically, as a model for an artificial kidney dialyser. Couplings between the different transport mechanisms prove significant in determining overall transport rates. Our model appears to be the first to treat the three transport mechanisms in a spatially structured framework, and shows that previous, spatially averaged models can overestimate transport rates. Our results can be used to optimise dialyser geometry and to profile dialysis sessions. The remainder of this thesis concerns some fundamentals of fluid mixing and mixer design. Techniques for assessing the quality of fluid mixing are reviewed, and applied to a two-dimensional laminar chaotic flow. We find no outright optimum mixing method across the range of measures, suggesting that `sieving' a collection of mixing methods according to increasingly complicated mixing measures may fail to identify a global optimum. `Topological chaos' appears to allow good mixing stretch rate to be built-in to batch mixer design, avoiding the need to tune the mixer parameters, provided a correct flow topology is created. We show that the theoretical stretch rate predictions are achieved quite tightly, in practice in a significant fraction of the flow domain; we investigate the practicalities of topologically chaotic mixers. Finally, we discuss whether topological chaos may also apply to three-dimensional static mixer design, in a braided pipe mixer, in which pipe flow is mixed around carefully designed twisted inner pipes. We expect such a device to mix well if the inner pipes have appropriate topology. However, we demonstrate how three-dimensional flow features can undermine mixing performance.

No description available.

Bibliography: leaves 315-326 / xxv, 370 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Faculty of Engineering, 1993

This work presents significant development into chaotic mixing induced through periodic boundaries and twisting flows. Three-dimensional closed and throughput domains are shown to exhibit chaotic motion under both time periodic and time independent boundary motions, A property is developed originating from a signature of chaos, sensitive dependence to initial conditions, which successfully quantifies the degree of disorder withjn the mixing systems presented and enables comparisons of the disorder throughout ranges of operating parameters, This work omits physical experimental results but presents significant computational investigation into chaotic systems using commercial computational fluid dynamics techniques. Physical experiments with chaotic mixing systems are, by their very nature, difficult to extract information beyond the recognition that disorder does, does not of partially occurs. The initial aim of this work is to observe whether it is possible to accurately simulate previously published physical experimental results through using commercial CFD techniques. This is shown to be possible for simple two-dimensional systems with time periodic wall movements. From this, and subsequent macro and microscopic observations of flow regimes, a simple explanation is developed for how boundary operating parameters affect the system disorder. Consider the classic two-dimensional rectangular cavity with time periodic velocity of the upper and lower walls, causing two opposing streamline motions. The degree of disorder within the system is related to the magnitude of displacement of individual particles within these opposing streamlines. The rationale is then employed in this work to develop and investigate more complex three-dimensional mixing systems that exhibit throughputs and time independence and are therefore more realistic and a significant advance towards designing chaotic mixers for process industries. Domains inducing chaotic motion through twisting flows are also briefly considered. This work concludes by offering possible advancements to the property developed to quantify disorder and suggestions of domains and associated boundary conditions that are expected to produce chaotic mixing.

Bibliography: leaves 290-303 / xxi, 303 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Chemical Engineering, 1993?

Bibliography: 208-218. / 339 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Chemical Engineering, 1989