No description available.

No description available.

No description available.

The research described in this dissertation is a computational study aimed at investigating blade row stability and stall inception in a high-speed compressor. Three-dimensional, steady and unsteady Navier-Stokes flow solvers were used to identify and understand the differences in the off-design low mass flow performance and stalling inception mechanism of a high-speed rotor blade row when it operates in isolation and as part of a single-stage (rotor-stator) build. The main conclusion from steady flow analysis is that when the rotor operates in the presence of a downstream stator, it is able to maintain stable axisymmetric performance down to a lower mass flow compared to when it operates in isolation. The rotor’s stability is extended when operating in the stage environment primarily because the stator acts to redistribution the radial pressure variation imposed at the rotor exit, thereby unloading the sensitive tip region. Unsteady flow analysis of the isolated rotor reveals that stall inception is associated with reversed flow at the tip region of a single rotor blade spilling forward of the leading edge. This results in the development of a spike-type disturbance that grows rapidly into a single finite stall cell. The reversed flow at the rotor tip and the resulting increase in tip-clearance related blockage that are both associated with the initial development of the spike disturbance are attributable to modal perturbations promoting localised flow separation at the rotor tip and to spanwise migration of fluid within the suction surface boundary layer. When the rotor operates as part of a stage, a qualitatively different type of stall inception mechanism is observed. Unsteady flow analysis reveals a one-dimensional breakdown of the rotor tip-clearance flow, with the flow observed to ‘surge’ upstream in an axisymmetric stalling pattern. Unlike the development of traditional rotating stall, no evidence of modal or spike-type disturbances are detected prior to the onset of stall and no stall cell structure is formed.

No description available.

The increasing use of granular materials in the chemical, petrochemical, food and pharmaceutical industries, both as intermediate and as end products, gives rise to the need for a better understanding of granule dissolution and disintegration (GDD). However, little is understood about the physical principles controlling the release of active ingredients from granules, a crucial knowledge for the design of product structure in order to optimise product performance. The aim of this work is to bring a scientific approach to the study of GDD in a systematic way. which has not been addressed hitherto. The work here is to highlight the testing of these hypotheses and provide insight into GDD mechanisms. The scientific concern in this thesis is to attempt to reveal the unique behaviour of GDD that is different from homogeneous material dissolution. Unlike homogeneous material dissolution, which depends mainly on the chemical properties of the solute and solvent, GDD is more complicated because the heterogeneous system involves mixed insoluble particles and soluble binder. Further complexity lies in the fact that various physical properties such as granule size, primary particle size, binder-solid ratio and internal pore structure play in influencing GDD behaviour. This thesis reports experiments and theoretical analysis of such GDD behaviour. Four hypotheses - reaction-limited consumption of binder, transport limit for binder removal, transport limit for particle removal and additional Hmit for particle and binder removal - were proposed to cover all of the possible GDD mechanisms. Theories were developed and experiments were set up to test the theory and give explanation of various limiting cases of GDD. A bimodal population balance model was developed. Furthermore, a dynamic shrinking-shell and core model was proposed to clarify GDD mechanisms. The analysis, which has its origin in comparing binder and particle transport coefficients, enables prediction of whether particle or binder transport will hmit GDD process. This evolved into a Sherwood number analysis, which provides a direct physical account of the controlling step. Based on a non-synchronous binder and particle transport analysis, a shrinking shell and core model was proposed to highlight that binder transport may be limited by internal particle shell build-up in the granule. A dynamic model was then developed to provide quantitative analysis of the binder Sherwood number, which was tested by experiment. A rigorous deduction of the model provided a clear physical meaning of the parameters in the equations. To demonstrate the theory and test hypotheses, an ionic binder, zeolite-NaLAS was used in high shear granulation, low shear granulation, fluidised bed granulation and spray drying granulation to provide a range of granule structures and to allow investigation of GDD by both PSD and electrical conductivity. Granules were characterised using mercury porosimetry, sieving, bulk density, particle size analyser and SEM to provide information concerning their various properties, such as binder content, internal pore structure and volume fraction, granule size and primary particle size distribution, as well as surface morphology and granule internal structure. Two main methodologies were adopted to investigate GDD behaviour including a): monitoring electrical conductivity and granule diameter simultaneously for a single granule; b) monitoring the evolution of the PSD by laser light scattering. Those results were analysed to support the theory. In general, the phenomena in GDD are quite different from the general cases of dissolution.

No description available.

Mixing miscible liquids with a large difference in viscosity is a complex process found in many industrial operations such as detergents manufacturing and the food industries. This operation is commonly carried out under turbulent conditions in stirred tanks, and with increasing liquid viscosity, it becomes difficult to maintain a turbulent flow throughout the tank, resulting in long mixing times. An alternative to stirred tanks are in-line mixers which consist of mixing elements inserted into a pipe section. In these devices mixing can be carried out under laminar conditions and the flow is usually a combination of distributive, shear and extensional flows. Although some studies have been presented for mixing liquids with a large viscosity difference under turbulent flow, a lack of quantitative data exists for processes in which the mixing operation is carried out under laminar conditions. This thesis presents a theoretical and experimental study of laminar mixing of miscible liquids with a large viscosity difference in constricted flows where extensional flow is prevalent. The principal objectives of this research are: (i) to develop experimental techniques that will allow quantitative measurements to be carried out when mixing liquids with a large difference in viscosity; (ii) to apply those techniques to improve the understanding of the mixing process; and (iii) to model the flow of a simple mixing device into which two streams with a difference in viscosity are fed. The concepts of interfacial line stretch and interfacial area increase as a measure of mixing were applied to slow viscous flow through an orifice and it was found that the largest line stretch (and area increase) occurred when extensional effects are strongest.

No description available.

No description available.