Thesis (doctoral)--Rijksuniversiteit te Utrecht.

Choke valves are important components in oil and gas production systems that are used to control the pressure and flowrate of fluids issuing from oil and gas reservoirs. The presence of sand in the production fluids can cause considerable damage to such components, and as sand is increasingly becoming an issue in oil and gas production, valve manufacturers need to find ways of reducing their product's susceptibility to solid particle erosion. A CFD-based erosion modelling tool is achieved by first solving the fluid flow through the component of interest; tracking particles through the fluid and extracting impact data on all solid surfaces; and finally relating the particle impact data to erosive wear through a semi-empirical equation. The present study has focussed on the development and validation of a CFD-based erosion modelling method for simple and complex geometries. Erosion testing has been carried out on a range of choke valve materials to provide the fundamental data required in constructing equations that relate erosion rate to particle impact velocity and angle. These equations have in turn been implemented in a commercial CFD code to provide the complete erosion modelling solution. Validation of the method has been effected by comparing predicted results to experimental test data for both simple and complex geometries. Both single phase and abrasive flows have been considered in comparisons. For the simple geometries, reasonable agreement was obtained between predicted and measured pressure drop for the simplest cases, but predicted mass loss was considerably less than the measured amount. With the complex geometries (Multi-Orifice Sleeve choke valves), good agreement for pressure drop was obtained for some valve positions, but not so good for others. Significant differences were observed in mass loss predictions for the complex geometries, which raise questions as to the usefulness of CFD-based methods for predicting component lifetime.

M.Med. (Paediatrics), Faculty of Health Sciences, University of the Witwatersrand, 2008 / Background: Posterior urethral valves (PUV) result in a spectrum of obstruction, and up to thirty percent of patients progress to renal failure. Objective: Descriptive study of patients with PUV, and to compare growth and renal function in the primary valve ablation versus vesicostomy group. Methods: Retrospective record review of patients with PUV at Chris Hani Baragwanath Hospital from January 1985 to December 2005. Results: A total of 128 boys were identified. The mean (range) age was 12.9 months (0 to 139.4). The mean duration of follow-up was 42 months, with 65% lost to follow- up. UTI and voiding problems were the most common modes of presentation. Young age at presentation and renal dysfunction after surgery were poor prognostic features. Hydronephrosis was present in 89.5%. Renal failure was present in 37% of patients at last visit. Primary valve ablation was performed in 44.2% and vesicostomy in 55.8%. No statistical difference in renal outcome or somatic growth was observed between the surgical groups. Conclusion: PUV is a common condition with significant morbidity. The renal outcome in black South African boys is similar to reports from developed countries. The type of initial surgical management did not impact on renal outcome or somatic growth.

A novel design, material, and fabrication method are presented to fabricate a passive micro-ball valve. Microvalves are critical components in microflow control devices used to control the fluid flows in microchannels. These microflow control devices can be integrated with microsensors to form micro analysis systems. Glass/silicon-based fabrication is complicated and expensive. Therefore, other materials and fabrication methods have been proposed. In this research, Melinex 453, a polyester film, and pressure sensitive adhesives were used to fabricate a micro-ball valve by a microlamination method. The valve was designed to have a 450 μm diameter glass ball floating inside a chamber size of 800 μm. The ball will permit flow in the forward direction and impede flow in the reverse direction. The fabrication method consists of three steps: patterning, registration and bonding. The patterning step was accomplished using laser micromachining. Registration and bonding were performed with the use of a pin-alignment fixture. Pressure sensitive adhesive was used in the bonding step using double-sided acrylic adhesive tape. The micro-ball valve has advantages over other microvalves in terms of little dead volume, simple design, disposability, low operating pressure in forward direction, and low leakage in reverse direction. The micro-bal1 valve was characterized by pressure drop testing at different flow rates from 1 to 7.5 ml/min. The experimental results tend to agree with a simple theoretical model of the pressure drop through an orifice. Moreover, an average pressure drop diodicity of at least 2980 has been achieved. / Graduation date: 2002

Thesis (M.S. in M.E.)--School of Mechanical Engineering, Georgia Institute of Technology, 2004. Directed by S.M. Jeter. / Bibliography: leaf 107.

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