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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Cineradiography of cardiac valves in man

Chaillet, Jean Louis. January 1965 (has links)
Thesis (doctoral)--Rijksuniversiteit te Utrecht.
22

CFD-based erosion modelling of simple and complex geometries

Wallace, Malcolm Scott January 2001 (has links)
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.
23

The outcome of posterior urethral valves: a twenty one year experience

Petersen, Karen Lavinia 11 November 2009 (has links)
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.
24

Development of a passive micro-ball valve

Wangwatcharakul, Worawut 19 October 2001 (has links)
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
25

Simulation and validation of liquid oxygen and liquid hydrogen pressurization systems

Rivera-Rivera, Ramiro Luis, January 2003 (has links) (PDF)
Thesis (M.S. in M.E.)--School of Mechanical Engineering, Georgia Institute of Technology, 2004. Directed by S.M. Jeter. / Bibliography: leaf 107.
26

Nonlinear giant magnetoresistance in dual spin valves

Banerjee, Niladri January 2012 (has links)
No description available.
27

Two-phase pressure losses in valves and fittings

Sharp, Robert McKinlock 05 1900 (has links)
No description available.
28

Quantification of valvular regurgitation with magnetic resonance phase velocity mapping

Chatzimavroudis, George P. 12 1900 (has links)
No description available.
29

Performance characteristics of various refrigeration expansion valves

Lauderdale, Woodrow Wilson 08 1900 (has links)
No description available.
30

Finite element modelling of eddy currents in nonlinear and moving media

Allen, Nancy January 1997 (has links)
No description available.

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