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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.
51

Hot gas ingress through turbine rim seals : heat transfer and fluid dynamics

Cho, GeonHwan January 2015 (has links)
This thesis experimentally investigates the phenomenon of ingress through gas turbine rim seals. The work focuses on developing experimental and numerical techniques for measuring the required sealing flow levels to purge the wheel-space against ingress and the effect of externally-induced ingress on the surface temperature as well as heat transfer to the rotor. Ingress is driven by a pressure difference between the mainstream annulus and wheel-space cavity resulting from the asymmetric external pressure profile in the annulus and/or the rotation of fluid in the rotor-stator wheel-space cavity. It can be prevented by pressurising the wheel-space through the supply of sealant flow. The University of Bath had measured and shown, for the first time, the thermal effects of ingress on the rotor in the wheel-space for a datum seal (axial-clearance seal) using thermo-chromic liquid crystal. However, as the previously used experimental technique with thermo-chromic liquid crystal was prone to large uncertainties, a non-intrusive temperature measurement technique using an infrared (IR) temperature sensor was developed. The new technique was successfully applied to the Bath one-stage gas turbine test facility and provided a full temperature history of the rotor surface in a transient heat transfer experiment. Moreover, a data analysis method appropriate for transient experiments using the IR temperature measurement technique was developed. The method was used to accurately calculate the heat transfer coefficient and the adiabatic surface temperature based on the full temperature history. A series of numerical experiments was carried out to develop the analysis method and the results from the numerical experiments were used to design new heat transfer experiments for both the 1 and 1.5-stage ingestion rigs of the University of Bath. Gas concentration measurements were made on the stator of the Bath one-stage gas turbine test rig to determine the variation of sealing effectiveness with sealant flow rate for four different seal geometries at design operational conditions. The IR temperature measurement technique was used to determine the effect of ingress on the heat transfer coefficient and the adiabatic wall temperature on the rotor of the ingestion test facility. Concurrent gas concentration measurements were made on the stator to compare the effects of ingress on the two discs (stator and rotor). Comparison between the adiabatic effectiveness on the rotor and the concentration effectiveness on the stator showed that the rotor was protected against the effects of ingress relative to the stator. The sealing air, which was drawn into the rotor boundary layer from the source region, thermally buffered the rotor against the ingested fluid in the core. Subsequently, a thermal buffer ratio hypothesis was developed and shown to be in good agreement with the experimental data. A previously published orifice model was modified so that the sealing effectiveness determined from the concentration measurements in a rig could be used to determine the effectiveness based on pressure measurements in an engine. There was good agreement between the effectiveness acquired from pressure measurement determined using the theoretical model and the sealing effectiveness determined from concentration measurements. It was also shown how parameters obtained from measurements of pressure and concentration in a rig could be used to calculate the sealing effectiveness in an engine.
52

Avaliação comparativa \"in vitro\" da capacidade seladora do cimento MBPc, CPM, MTA Angelus® branco e pasta Lysanda® à infiltração bacteriana em obturações retrógradas / In vitro comparative evaluation of MBPc, CPM, White Ângelus MTA cements and Lysanda paste®s sealing ability to bacterial infiltration in retrograde fillings

Medeiros, Paulo Leal 01 October 2009 (has links)
O objetivo deste estudo foi avaliar in vitro a capacidade seladora de alguns materiais odontológicos em retrobturações e para tanto, utilizou-se o MTA Ângelus® Branco, MBPc, CPM® e Pasta Lysanda®, através da análise da infiltração do Enterococcus faecalis. Noventa dentes humanos unirradiculares extraídos e instrumentados, tiveram seu ápice radicular cortado num plano perpendicular ao longo eixo onde foram preparadas cavidades retrógradas com 3mm de profundidade, para selamento com os materiais em teste já relacionados. Culturas específicas de Enterococcus faecalis foram preparadas e inoculadas nos condutos radiculares dos dentes previamente fixados em aparatos especiais que tinham do lado oposto um meio de cultura estéril e específico para a bactéria em questão, separados apenas pelas retrobturações dos grupos de materiais em teste. Diariamente, o meio estéril era checado para constatar sua possível turvação; caso ocorresse demonstrava a passagem bacteriana pela retrobturação. Os quatro grupos experimentais apresentaram ao menos um espécime com infiltração bacteriana logo nas primeiras 24 horas do teste, entretanto, o número de espécimes que apresentavam turvação foi diminuindo numericamente no decorrer do período experimental, que foi de 120 dias. Os cimentos MTA Ângelus® Branco, MBPc e CPM® mostraram capacidade seladora eficaz e também comportamento semelhante entre si, pois a turvação das poucas amostras ocorreu logo nos três primeiros dias. A pasta Lysanda® apresentou o maior número de amostras infiltradas (18), em maior período de tempo. / The objective of this study was to in vitro evaluate the sealing ability of some dental retrofilling material and for that, we used the White MTA Angelus®, MBPc, CPM® cements and Lysande® paste, by examining Enterococcus faecalis infiltration. Ninety human extracted single-rooted teeth were instrumented, had their apex cut perpendicular to the long axis where the retrograde cavities were prepared with 3 mm deep, sealed with the retrofilling materials used on the study. Specific cultures of Enterococcus faecalis were prepared and inoculated into the teeths root canals previously fixed in special apparatuses that had in their opposite side a sterile type of culture specific for the bacteria in question, separated only by the retrofilling materials under test. Daily, the sterile culture was checked to verify their possible turbidity; and when there was, it demonstrated the bacterials passage by the retrofilling material. All experimental groups showed at least one specimen with bacterial infiltration in the very first 24 hour testing, however, the number of specimens that showed turbidity had decreased numerically during the trial period of 120 days. White Angelus MTA®, CPM® and MBPC cements showed effective sealing capacity and also similar behavior among themselves, because the turbidity of the few samples occurred just in the first three days. Lysanda® paste presented the greatest number of samples infiltrated (18), in a greater period of time.
53

Methodology to quantify leaks in aerosol sampling system components

Vijayaraghavan, Vishnu Karthik 15 November 2004 (has links)
Filter holders and continuous air monitors (CAMs) are used extensively in the nuclear industry. It is important to minimize leakage in these devices and in recognition of this consideration, a limit on leakage for sampling systems is specified in ANSI/HPS N13.1-1999; however the protocol given in the standard is really germane to measurement of significant leakage, e.g., several percent of the sampling flow rate. In the present study, a technique for quantifying leakage was developed and that approach was used to measure the sealing integrity of a CAM and two kinds of filter holders. The methodology involves use of sulfur hexafluoride as a tracer gas with the device being tested operated under dynamic flow conditions. The leak rates in these devices were determined in the pressure range from 2.49 kPa (10 In. H2O) vacuum to 2.49 kPa (10 In. H2O) pressure at a typical flow rate of 56.6 L/min (2 cfm). For the two filter holders, the leak rates were less than 0.007% of the nominal flow rate. The leak rate in the CAM was less than 0.2% of the nominal flow rate. These values are well within the limit prescribed in the ANSI standard, which is 5% of the nominal flow rate. Therefore the limit listed in the ANSI standard should be reconsidered as lower values can be achieved, and the methodology presented herein can be used to quantify lower leakage values in sample collectors and analyzers. A theoretical analysis was also done to determine the nature of flow through the leaks and the amount of flow contribution by the different possible mechanisms of flow through leaks.
54

Methodology to quantify leaks in aerosol sampling system components

Vijayaraghavan, Vishnu Karthik 15 November 2004 (has links)
Filter holders and continuous air monitors (CAMs) are used extensively in the nuclear industry. It is important to minimize leakage in these devices and in recognition of this consideration, a limit on leakage for sampling systems is specified in ANSI/HPS N13.1-1999; however the protocol given in the standard is really germane to measurement of significant leakage, e.g., several percent of the sampling flow rate. In the present study, a technique for quantifying leakage was developed and that approach was used to measure the sealing integrity of a CAM and two kinds of filter holders. The methodology involves use of sulfur hexafluoride as a tracer gas with the device being tested operated under dynamic flow conditions. The leak rates in these devices were determined in the pressure range from 2.49 kPa (10 In. H2O) vacuum to 2.49 kPa (10 In. H2O) pressure at a typical flow rate of 56.6 L/min (2 cfm). For the two filter holders, the leak rates were less than 0.007% of the nominal flow rate. The leak rate in the CAM was less than 0.2% of the nominal flow rate. These values are well within the limit prescribed in the ANSI standard, which is 5% of the nominal flow rate. Therefore the limit listed in the ANSI standard should be reconsidered as lower values can be achieved, and the methodology presented herein can be used to quantify lower leakage values in sample collectors and analyzers. A theoretical analysis was also done to determine the nature of flow through the leaks and the amount of flow contribution by the different possible mechanisms of flow through leaks.
55

Elastohydrodynamic model of reciprocating hydraulic rod seals

Yang, Bo 23 April 2010 (has links)
Reciprocating rod seals are widely used in hydraulic systems to prevent the hydraulic fluid from leaking into and polluting the environment. In this research an elastohydrodynamic model of a generalized reciprocating hydraulic rod seal, including mixed lubrication and surface roughness, has been successfully developed. This model consists of coupled fluid mechanics, contact mechanics, thermal analysis and deformation analyses. Such model is capable of predicting the key seal performance characteristics, especially net leakage and friction force. This allows evaluation of potential seal designs and serves as design tools. Also as this model has been developed, the basic physics of seal operation has been clarified, which stimulates the development of innovative seal concepts, such as seals with engineered sealing surfaces. The results of this study indicate that in general, hydraulic rod seals operate in the mixed lubrication regime, although under certain conditions full film lubrication may occur over a portion of the sealing zone. The roughness of the seal surface and the rod speeds play important roles in determining whether or not a seal will leak. Cavitation during the outstroke and partial full film lubrication during the instroke tend to prevent net leakage. The behavior of a reciprocating hydraulic rod seal with a double lip or two seals in tandem arrangement can be very different from that of a similar seal with a single lip. For the double lip seal, the secondary lip can strongly affect the behavior of the primary lip by producing an elevated pressure in the interlip region. The same seal characteristics that promote effective sealing in a single lip seal and, in addition structural decoupling of multiple lips, are found to promote effective sealing in a multiple lip seal. The model is validated through comparisons of model predictions with experimental measurements and observations by industry partners. The results have shown the predicted leakage and friction force for various seal and operation conditions are consistent with the measurements. A seal with micro-pattern on the sealing surface also has been investigated. The results indicate that an elaborately designed pattern can improve the sealing characteristics of the seal, without significantly affecting the friction force. In the end, the selection of the rod seal for a specific application using this analytical model is demonstrated. The best design can be picked up before a prototype being built.
56

Pattern recognition for automated die bonding /

Tsang, Chiu-ming. January 1982 (has links)
Thesis--M. Phil., University of Hong Kong, 1983.
57

cAMP and oxidative mechanisms of plasmalemmal sealing and the effects on rapid and long lasting repair of severed axons in vivo by polyethylene Glycol

Spaeth, Christopher Scott 22 June 2011 (has links)
Traumatic neuronal injury inevitably causes plasmalemmal damage, and sometimes leads to axonal severance. For any eukaryotic cell to survive following traumatic injury, the plasmalemma must be repaired (sealed). Plasmalemmal sealing occurs via a Ca²⁺-dependent accumulation of vesicles or other membranous structures that form a plug at the damage site. Using uniquely identified and damaged rat hippocampal B104 cells that extend neurites with axonal properties, or rat sciatic nerves, plasmalemmal sealing is assessed by exclusion of an extracellular dye from each damaged B104 cell, or sciatic nerves ex vivo. B104 cells with neurites transected nearer (<50 [micrometres]) to the soma seal at a lower frequency and slower rate compared to cells with neurites transected farther (>50 [micrometres]) from the soma. Sealing in B104 cells is enhanced by 1) increased [cAMP], 2) increased PKA activity, 3) increased Epac activity, 4) H₂O₂ and 5) Poly-ethylene glycol (PEG). Sealing is decreased by 1) PKA inhibition, 2), Botulinum toxins A, B, E, 3) Tetanus toxin 4), NEM, 5) Brefeldin A, 6) nPKC inhibition, 7) DTT, 8) Melatonin and 9) Methylene Blue. Substances (NEM, Bref A, PKI, db-cAMP, PEG) that affect plasmalemmal sealing in B104 cells in vitro have similar effects on plasmalemmal sealing in rat sciatic nerves ex vivo. Based on data from co-application of enhancers and inhibitors of sealing, I propose a plasmalemmal sealing model having four partly redundant, parallel pathways mediated by 1) PKA, 2) Epac, 3) cytosolic oxidation and 4) nPKCs. The identification and confirmation of these pathways may provide novel clinical targets for repairing and/or recovery from traumatic injury. The fusogenic compound PEG rapidly repairs axonal continuity of severed axons, potentially by rejoining severed proximal and distal axons. PEG-fusion is influenced by plasmalemmal sealing, since unsealed axons are easier to PEG fuse. I demonstrate that PEG restores morphological continuity, and improves behavioral recovery following crush-severance to sciatic nerves in rats in vivo. Co-application of Mel or MB prior to PEG application further improves PEG fusion (as measured by electrophysiology) and behavioral recovery following crush-severance in vivo. These PEG data may provide novel clinical techniques for rapidly repairing axonal severance. / text
58

Pattern recognition for automated die bonding

曾昭明, Tsang, Chiu-ming. January 1982 (has links)
published_or_final_version / Electrical Engineering / Master / Master of Philosophy
59

Design and development of a test apparatus for a downhole tool metal face mechanical seal

Alajbegovic, Vahidin 08 1900 (has links)
No description available.
60

Labyrinth Seal Leakage Analysis

Inam, Orcun 2011 August 1900 (has links)
Annular seals are devices used in turbomachinery to avoid flow losses which reduce efficiency. The dynamic stability of the machine is also improved by the seal. Thus, it is an important subject to understand the flow behavior through the seal. Straight through triangular labyrinth seals are one of the most commonly used types of non-contacting annular seals. The energy dissipation through these seals is achieved by a series of teeth and cavities. As the flow passes above each tooth, a portion of its pressure energy is converted into kinetic energy. A portion of this kinetic energy is dissipated through turbulence-viscosity interaction in the cavity that follows. Moreover, some portion of the pressure energy is also lost through viscosity of the fluid. This research aims to understand the effects of flow parameters and seal geometry on these losses. This will make it possible to estimate the mass flow leakage through the seal. ANSYS Fluent is used to simulate the flow through the seal. The effect of seal geometry is studied by varying clearance, pitch, tooth height, tooth width and upstream side angle. It was found that, amongst other geometrical parameters, tooth clearance and pitch has a strong influence on carryover coefficient. Smaller values of c/s have better kinetic energy dissipation in the cavity. Carryover coefficient is also found to be a function of the Reynolds number and shaft speed. Discharge coefficient of the seal presents the overall efficiency while carryover coefficient only shows the cavity performance. Discharge coefficient is also found to be a strong function of tooth clearance, pitch, Reynolds number and shaft speed. Remaining parameters have smaller effects. It was observed that the discharge coefficient of first tooth is always lower than those of intermediate teeth. The compressibility effects are presented by using an expansion factor which is the ratio of compressible flow discharge coefficient to incompressible flow discharge coefficient. It was found that the expansion factor is fairly independent of geometrical parameters but a strong function of flow parameters. Considering the effects of seal geometry and flow parameters on carryover coefficient, discharge coefficient and expansion factor, the seal geometry is optimized to increase the kinetic energy dissipation and pressure head loss which in turn will reduce the mass flow leakage.

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