Chemical and Biomolecular Engineering - Theses
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ItemSwirling flow of viscoelastic fluids( 1998-10)The ability to understand and predict the flow behaviour of non-Newtonian fluids in swirling flow is industrially important for the efficient design and performance of processes which utilise fluids with complex rheological properties. In particular, fluids with elastic properties are not well described by non-Newtonian constitutive models, such that predictions using such models must be carefully validated. A benchmark problem is proposed here which provides a well defined geometry to study the swirling flow of non-Newtonian fluids as a test case for the validation of constitutive models. The confined swirling flow utilised is a torsionally driven cavity where the test fluid is confined in a cylinder with a rotating bottom lid, and stationary side walls and top lid. The flow field is three-dimensional and consists of both a primary motion, which is directed azimuthally, and a secondary motion, which is located in the radial and axial plane of the cylinder and driven by inertial and/or elastic forces.
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ItemThe melting point and viscosity of nickel smelter slags( 1995-02)Western Mining Corporation produces nickel matte at the Kalgoorlie Nickel Smelter(KNS)from nickel sulphide concentrates within an integrated flash smelter.
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ItemModelling of fluid flow and heat transfer of decaying swirl in a heated annulus( 1992-07)The fluid flow and heat transfer characteristics of the turbulent swirling flow of air through a heated annulus have been quantified. The motivation for this study was to improve the understanding of flow within a SIROSMELT top submerged industrial smelting lance. Within the lance, helical vane swirler flights are used to impart swirl to a coolant, so that heat transfer from the lance wall to the coolant is enhanced. A review of the literature revealed no information on the mean and turbulent flow structure for swirling flows in a heated annulus. (For complete abstract open document)
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ItemCharacterisation of suspensions in settling and compression( 1997-06)The concentration of fine particle suspensions is a crucial step in many industrial processes, two major processes that depend on this are the disposal of mine tailings as highly concentrated slurries, and the wet casting of ceramic components from highly concentrated suspensions. The thickening and filtration operations in these processes are still not completely understood. The successful design and operation consolidation equipment must be based on the properties of the target suspension. The quantitative characterisation of suspensions in settling and compression was the prime objective of this thesis. In a general consolidation model, the behaviour of suspensions in settling and con1pression is fully defined by two parameters; the compressive yield stress function and the hindered settling function. The compressive yield stress quantifies the strength of the suspension network in compression and determines the maximum concentration achievable for any given applied force. The hindered settling function quantifies the hydrodynamic drag forces experienced by consolidating particles in the suspension and determines the settling velocity and the time scale for the consolidation process. These suspension consolidation parameters were determined using a variety of techniques. For measurement of the compressive yield stress, two centrifuge based techniques and a pressure filtration technique were evaluated both independently and with each other - with good results. It was thus verified that the compressive yield stress is a material property of suspensions in compression. For measurement of the hindered settling function, two pressure filtration techniques were developed using a custom built apparatus. Measurements were successfully made using these techniques for the first time. The materials used in the study were three aqueous metal oxide suspensions systems; Zr02, Ti02 and A120 3. The shear and compression rheology of these systems is fully controlled by manipulation of the particle surface chemistry which changes the suspension micro-structure. The validity of the general consolidation model was systematically studied using suspensions prepared under various conditions. Factors studied were the effects of flocculation state, initial concentration, steric stabilisation, suspension preparation methods and prior shear and compression history. These factors affected the compression rheology to varying degrees and were quantified. The conditions for maximum consolidation were determined. A correlation between shear and compression rheology also generated a useful empirical relationship that can be used in design and operation of consolidation equipment. Finally, the measurement of the compressive yield stress and hindered settling function of a suspension was applied to the prediction of the concentration profile and sediment height in an operating continuous thickener. With some refinement, the model and techniques used in this study are a viable means for design and optimisation of continuous thickeners based on the material properties of the suspension.
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ItemSplashing due to gas injection( 1993)The splash event produced by a falling drop impinging on a bath of liquid was studied to enable a more fundamental understanding of the mechanisms of splash formation. An experimental method involving the use of a high speed photographic technique was developed to enable discrete splash events to be recorded at different time intervals. The effect of varying impact velocity, liquid viscosity and surface tension on the splash event was studied. The aspects of the splash mechanism that pertained to the projection of liquid above the liquid surface were monitored as a function of the experimental variables. Such aspects included the cavity depth, the Rayleigh jet behaviour and the extruded crown behaviour. Depending on the impact velocity of the falling drop, different shaped Rayleigh jets formed which varied in their manner of break up. Such changes in the Rayleigh jet behaviour could be related to the curvature of the interfacial cavity produced by the impact of the falling drop. As the impact velocity increased, the maximum height of the extruded crown increased. If the impact velocity exceeded a critical value, break up of the crown occurred. Increasing liquid viscosity had the effect of dissipating the energy of the system and hence producing less splash. Such viscous dissipating effects were quantified by the use of an energy balance. For liquids of a lower surface tension, there was evidence to suggest that a greater proportion of the incoming energy to the splash event was transferred to the extruded crown rather than to the cavity. Consequently, the splash produced from the break up and extrusion of the crown became more significant. A knowledge of the size of the bubbles reaching the liquid surface would assist in predicting the splashing behaviour of an industrial process which utilised gas injection.
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ItemAmmonia removal from Sirofloc treated sewage using natural zeolite from Australia( 1996)A high-rate process for the removal of ammonia from sewage was investigated. Of the existing high-rate processes, ion-exchange with an ammonium-selective zeolite has shown considerable advantages. The recent commercial mining of a natural Australian zeolite, clinoptilolite, encouraged the investigation of its application to wastewater treatment for ammonia removal. The applicability of the mineral, for continuous ammonia removal from sewage, depends on its chemical and physical properties. For Australian zeolite, these factors, and thus the potential usefulness of this mineral for wastewater treatment, were largely unknown prior to this study. The study endeavoured to determine the most viable way in which to use Australian natural zeolite in this process, with the most critical part being the economical regeneration of the zeolite. (From Abstract)
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ItemYielding of waxy crude oil and numerical simulation of gelled oil pipeline start-up( 1998)As a main resource of energy, crude oil has been produced for many decades around the world. Pipeline system has been considered as the only feasible and most economical means for transporting large quantities of crude oil due to its big and reliable transportation capacity. The oil flow in pipelines may be shut down regularly for operational reasons and occasionally for emergency reasons, although it is desirable to maintain a steady and continuous flow rate without any interruption for an efficient operation of a pipeline system. After the flow is shut down, the warm crude oil in pipelines may be statically cooled to a considerably low temperature) depending on the ambient temperature and the duration of the shutdown. The declining production of conventional oil and increasing market demand for petroleum have resulted in more and more waxy crudes being produced. Waxy crude oils have relatively large proportions of high-molecular-weight paraffins and therefore high pour points. Statically cooling a waxy crude oil below its pour point may lead to a strong interlocking network of waxy crystals forming in the oil, which imparts various complex non-Newtonian and nonlinear characteristics to the flow properties of the oil including its particular yielding behaviour. To restart a pipeline fiI1ed with the structured oil, a pressure higher than that required for the normal operation must be applied to make the oil yield. The yielding properties of the waxy crude oil, which will be studied in this work, are directly related to the start-up and restart operations of pipeline transportation systems, and are a key for the successful design and operation of a pipeline system. (From Summary)
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ItemThe break up and atomisation of dilute polymer solutions( 1996)The formation of drops from solutions is a common industrial and agricultural process. A fundamental understanding of how fluid rheology affects the formation of drops will permit a scientific approach to the design of nozzles and solution formulation. To that end, a systematic study of jet break up for dilute flexible molecule solutions was examined to determine the effect of the extensional fluid properties on the jet break up phenomena. The apparent extensional viscosity was measured with an opposed jet apparatus. The shear viscosity and surface tension of the test solutions was kept constant to isolate the effects of elastic properties. It was found that the break up of the capillary jet could be enhanced or retarded relative to Newtonian fluids by the presence of the polymer. This behaviour was a function of the polymer molecular weight and concentration and extended into a region where extensional viscosity measurements were unable to determine a difference between the test solutions. The polymers used were poly(ethylene oxide), and poly(vinyl alcohol). In addition a brief study was made on the atomisation of dilute polymer solutions in industrial spray systems to determine whether a correlation could be established between atomisation in a nozzle and laminar jet breakup. It was found that the trends in the volume mean diameter of the droplets approximately followed the same trend observed in the break up length of the capillary jet. Finally, a brief investigation on the effect of rigid, semi-rigid and flexible macromolecules in solution was conducted in the atomisation apparatus. The flexible macromolecule used was poly(acrylamide), the rigid macromolecule was Xanthan gum, and the semi-rigid macromolecule was carboxy(methyl cellulose). The main finding of the laminar capillary experiments was that the viscoelastic and extensional properties of polymer solutions cause competing effects in the break up of the jets; the viscoelastic properties promoting the break up, and the extensional properties retarding it. The implication of this finding is that the extensional and viscoelastic properties of flexible polymer solutions are not directly related as suggested by the current fluid models, and that the origin of the nature of the two phenomena is not as clear cut as was previously believed. The spray atomisation experiments yielded further information supporting the separation of the two fluid properties. The drop size distribution of the low molecular weight solutions demonstrated a narrowing of the size distribution with the addition of the polymer, resulting in a decrease in the percentage of fine droplets formed, with only a marginal increase in the mean drop size. The presence of high molecular weight polymers caused a degradation of the spray quality, due to a reduction of the cone angle. The drop size from these solutions was uniformly increased, resulting in few or no fine drops being formed, with a large increase in the mean drop size.
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ItemFundamentals of foaming in molten slag systems( 1998)Liquid drainage between intersecting bubble films is an important step in the coalescence and rupture process of slag foams. Information such as the rate and extent of film drainage, as well as the critical thickness of slag films prior to rupture (their stability), was thus investigated. This study consisted of withdrawing single, and sets of "free" films of Na20-B203melts (up to 1273 K) and CaO-Si02-Al203 slags (up to 1723 K), using thin platinum wire frames. A gravimetric technique was developed to measure the "average" film thickness and the film draining rate prior to rupture. The results showed that the average film thicknesses of a model Na20-B203 system varied from several hundred microns initially, down to tens of microns before rupture. However, these values represented the 'net' mass of the liquid contained within the films and also the Plateau borders, i.e., they are likely to be an overestimation of the thickness of slag films. Non-uniform thicknesses within the CaO-SiO2-Al203 free films were observed using a color video camera. Using laser interferometry, localized and non-uniform thinning regions (known to occur in "mobile" films) were observed within a (CaO/SiO2) = 0.60, 15 wt% Al203 slag film at 1623 K. A thickness change of - 8.6 µm was obtained over a lifetime of around 25 seconds, resulting in a thinning rate of Δδ/Δt ~0.3 - 0.4 µm/s. A laser absorption/transmission technique was developed to measure the thickness of the slag films, and this showed that they do drain to thicknesses below 1 µm. Profiling of the thinning films near the edge and centre revealed that at the well-drained stages, the films become very thin and plane-parallel prior to rupture; the bursting velocity being in the submillisecond range (estimated by high speed cinegraphic studies). Critical thicknesses of the films were measured and ranged from 0.1 - 0.4 µm, approaching those generally encountered with typical aqueous ("soap") films. The addition of P2O2 in (CaO/SiO2) = 0.60, 15 wt% Al203, 9.6 wt% Fe203 slags at 1573 K, decreased the critical thickness and extended the lifetime of the bubble films before rupture. For instance, a free film containing 0.8 wt% P205 ruptured at a critical thickness of around 0.3 µm after a lifetime of about 39 seconds, while a slag film containing 1.3 wt% P205 ruptured at a critical thickness of 0.1 - 0.15 µm, after a lifetime of 47 seconds. (From Summary)