No description available.

No description available.

Thesis (M. Phil.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 141-148). Also available in print.

A technique for measuring fluid velocities by means of neutrally-buoyant, phophorescent particles was investigated in a small-scale water jet facility. A nitrogen laser briefly illuminated the flow, exciting only those particles resident within the pulsed beam. The particles luminesce for a short while following excitation, during which time they also move with the flow. This creates a visible particle streak, the intensity of which decays along the direction of motion. A strobe illuminates the particles again a known time following the laser pulse. The magnitude and direction of a particle's velocity in the plane of view are deduced from an image of it streak captured by a video camera and recorded by a digital image processing system.

published_or_final_version / Mechanical Engineering / Master / Master of Science in Engineering

No description available.

No description available.

The aim of this study was to further understand the fouling and cleaning mechanisms of synthetic membranes used to filter an industrially relevant feed. The main focus of this study was to understand the fouling layer properties during pressure driven filtration. A relatively new technique known as Fluid Dynamic Gauging (FDG) was applied to examine the fouling layer thickness. This work comprised of four main themes with overlapping objectives: (i) the optimisation of Spent Sulphite Liquor fouling and cleaning conditions, (ii) the optimisation of molasses fouling and cleaning conditions, (iii) the investigation of the effect of a simple pre-treatment upon the membrane separation performance, and (iv) the application of the FDG in the study of polymeric membranes. An understanding of the mechanisms involved in fouling and cleaning of microfiltration and ultrafiltration membranes used to filter molasses and SSL has been attained. The variables affecting permeate flux and quality were optimised and mechanistic information concerning the synergistic effects between fouling and cleaning was gathered. The application of a simple NaOH pre-treatment was found to affect both the type of foulant species attaching to the membrane surface, and resulted in an altered separation and cleaning performance. Zeta potential measurements, FTIR and AFM demonstrated that both in-pore and surface fouling was present. The data collected indicated that for both membranes evaluated, different fouling species were found to have attached, depending upon the pre-treatment protocol used. These findings are significant, as they offer support to the recommendations made by some polymeric membrane manufacturers that conditioning protocols should include a NaOH step. However, in the SSL system examined, the effect of NaOH pre-treatment resulted in an improvement in the subsequent performance only over the first two or three complete filtration cycles. It is therefore necessary to study membrane systems over multiple fouling and cleaning cycles before a recommendation can be made. An improved understanding of the interaction between the surface chemistry and surface physics during membrane filtration of complex food based material will benefit both membrane manufactures and food industry based users. The technique of Fluid Dynamic Gauging was incorporated into an existing system and validated to monitor the development of cake layers over time. The FDG was also used to optimise conditions and track the thickness of the cake layer during multiple fouling cycles and its removal rate during cleaning, as an aid to understanding removal mechanisms. It has been shown that operating conditions have to be carefully chosen to minimise the effect of membrane fouling. The results show that FDG is a versatile and powerful technique for characterising the dynamics and mechanical behaviour of fouling layers on membrane surfaces. A particular advantage of the FDG technique is its ability to determine the thickness of fouling layers where other techniques would find difficulty. For example, the layers formed in this study were opaque, and consequently the determination of the development of deposit thickness with time would have been very challenging using conventional optical microscopy techniques.

Thesis--M. Sc., University of Hong Kong, 1982.

A scroll vortex intake is a hydraulic structure that transfers water stably from one elevation to a lower one by generating a swirling vortex flow down a vertical drop- shaft. Scroll vortex intakes are applied widely in water supply, stormwater drainage and sewerage systems. For a good engineering design, a sufficiently large and stable air core needs to be maintained within the dropshaft. Although a number of the- oretical and experimental investigations have been conducted, the understanding and predictions of the vortex flow is still far from complete due to a lack of de- tailed velocity field and air core measurements. This study aims to achieve a better understanding of the scroll vortex intake flow. The hydraulic theory of scroll vortex intake is revisited and detailed measurements of air core and velocity field of the vortex flow is conducted. A 1:15 physical model of a scroll vortex intake has been designed according to dynamic Froude similitude and constructed. Experiments have been conducted to measure the head-discharge relation. Piezometric head and air core size are measured at the throat of the vortex flow. Velocity fields are measured using Laser Doppler Anemometry (LDA). The measurements show that the vortex flow in the chamber resembles a free vortex and the circulation is approximately equal to that at the inlet to chamber. The chamber flow is not affected by the bottom boundary effect at bottom above a depth of the order of the dropshaft diameter. The throat section of the vor- tex flow is located slightly below the chamber bottom and within the bellmouth at the entrance to dropshaft. For the vortex flow in and downstream of the bell- mouth, the tangential velocity distribution can be described by a Rankine vortex (combination of forced and free vortex); the transition from forced to free vortex occurs at around the middle of the vortex flow layer. The pressure is positive for all locations and all discharges. Due to viscous effect, the maximum circulation is found to be lower than the inlet circulation. Consistent with the free vortex theory, the vertical velocity in the dropshaft is approximately constant. By accounting for the loss of circulation between chamber inlet and the dropshaft, a new 1D theory is proposed. Unlike previous models, the new theory gives good predictions of head-discharge relation and minimum air core size without the need of physically unrealistic assumptions. This study has revealed the structure of a scroll vortex intake flow for the first time. Characteristic flow features of the scroll vortex intake have been elucidated. The findings have helped to explain and resolve the long-standing discrepancies between the theoretical predictions of three representative 1D hydraulic theories. The vortex flow measurements also provide a basis for the development of a new theory and the validation of 3D numerical models. / published_or_final_version / Civil Engineering / Master / Master of Philosophy