abstract: Efficient performance of gas turbines depends, among several parameters, on the mainstream gas entry temperature. At the same time, transport of this high temperature gas into the rotor-stator cavities of turbine stages affects the durability of rotor disks. This transport is usually countered by installing seals on the rotor and stator disk rims and by pressurizing the cavities by injecting air (purge gas) bled from the compressor discharge. The configuration of the rim seals influences the magnitude of main gas ingestion as well as the interaction of the purge gas with the main gas. The latter has aerodynamic and hub endwall heat transfer implications in the main gas path. In the present work, experiments were performed on model single-stage and 1.5-stage axial-flow turbines. The turbines featured vanes, blades, and rim seals on both the rotor and stator disks. Three different rim seal geometries, viz., axially overlapping radial clearance rim seals for the single-stage turbine cavity and the 1.5-stage turbine aft cavity, and a rim seal with angular clearance for the single-stage turbine cavity were studied. In the single-stage turbine, an inner seal radially inboard in the cavity was also provided; this effectively divided the disk cavity into a rim cavity and an inner cavity. For the aft rotor-stator cavity of the 1.5-stage turbine, a labyrinth seal was provided radially inboard, again creating a rim cavity and an inner cavity. Measurement results of time-average main gas ingestion into the cavities using tracer gas (CO2), and ensemble-averaged trajectories of the purge gas flowing out through the rim seal gap into the main gas path using particle image velocimetry are presented. For both turbines, significant ingestion occurred only in the rim cavity. The inner cavity was almost completely sealed by the inner seal, at all purge gas flow rates for the single-stage turbine and at the higher purge gas flow rates for 1.5-stage turbine. Purge gas egress trajectory was found to depend on main gas and purge gas flow rates, the rim seal configuration, and the azimuthal location of the trajectory mapping plane with respect to the vanes. / Dissertation/Thesis / M.S. Mechanical Engineering 2010

Doctorat en philosophie et lettres / info:eu-repo/semantics/nonPublished

Please read the abstract in the section 00front of this document / Dissertation (MSc (Zoology))--University of Pretoria, 2005. / Zoology and Entomology / unrestricted

The southern elephant seal (SES), Mirounga leonina, was intensively harvested during the 18th and 19th centuries, though never reduced to the levels seen for the northern species (Mirounga angustirostris). Although a number of putative populations occurring within the species’ circumpolar distribution in the Southern Ocean have been genetically assessed, no data was previously available for the Marion Island population. This study integrates Marion Island into the broader database by genetically profiling individuals with 9 microsatellite DNA loci (n = 73) and a single mitochondrial DNA (mtDNA, n = 68) locus corresponding to hypervariable region I (HVRI) of the non-coding displacement loop (D-loop). These data were then combined with existing haplotype datasets from five island populations, namely Heard Island, Peninsula Valdés, Macquarie Island, South Georgia, Elephant Island, and Sea Lion Island breeding colonies, and with comparable microsatellite typing data from four populations, namely Peninsula Valdés, South Georgia, Elephant Island and Sea Lion island, respectively, permitting inter-population level comparisons. Genetic variation of the Marion Island population was high for both microsatellite and mtDNA and consistent with levels previously reported for the other populations, with the exception of Peninsula Valdés (Argentina) where diversity levels are low. Forty polymorphic sites defined 44 mtDNA haplotypes from 68 Marion Island individuals. Of the 44 sequence haplotypes, three were shared with Sea Lion Island, one with Elephant Island, two with Heard Island and one with Macquarie Island. From the microsatellite data, it was found that Marion Island, like most other SES populations, had no private alleles. The one exceptional population is that at Sea Lion Island which has several private alleles at two loci. Marion Island was significantly differentiated from each of the other breeding colonies included in the study based on FST analyses for both microsatellite and mtDNA data. The magnitude of genetic differentiation between Marion Island and the South Georgia, Sea Lion and Elephant Islands was somewhat higher than that previously reported when the latter three islands were compared, but considerably less than the differentiation found between Marion Island and either Peninsula Valdés or Macquarie Island. Though the two markers showed similar trends with respect to population structuring, the pairwise differentiation at microsatellite loci was an order of magnitude lower than that of mtDNA, suggesting more frequent male-mediated gene flow between putative populations than female-mediated gene flow. Higher male dispersal was also confirmed by migration rate estimates from the microsatellite data compared to estimates from the mtDNA locus. These data are consistent with the earlier interpretation that most putative island populations show moderate levels of differentiation not directly related to geographic distance, while the mainland population in Argentina and the population at Macquarie Island stand out as being highly differentiated from the rest. / Dissertation (MSc)--University of Pretoria, 2008. / Zoology and Entomology / unrestricted

While studies of dispersal note significant fidelity to natal site and to the site of first reproduction, few consider fidelity to other sites, and none have done so systematically. This study examined fidelity to all terrestrial sites within the study area during the course of its life, by a migratory marine predator, the southern elephant seal, Mirounga leonina. It also attempted to assess the role played by the winter haulout in terms of site fidelity. Finally it examined the influence of possible deterioration in spatial memory over time on site fidelity. The data used in this study were generated by a long-term mark-recapture programme conducted at subantarctic Marion Island. Although immature elephant seals of both sexes return to the vicinity of their natal sites, they appear to avoid popular breeding beaches, returning closest to the site previously used. At the first reproductive haulout, however, females return closer to their natal site than any other site, while males, although hauling out in the vicinity of their natal site, haul out closest to sites used in the year prior to the first breeding haulout. Subsequently, adults of both sexes breed closest to the breeding haulout of the previous year and moult closest to the moult haulout of the previous year. While males show greater site fidelity during the breeding season, there is no difference in site fidelity during the moult. Primiparous females show greater levels of site fidelity if recorded in the study site as an immature animal during either the winter or the moult haulouts. Also in female elephant seals, lower site fidelity is associated with an increase in the duration of period of absence from a site, and a lower number of visits to a site. Various factors related to site familiarity, social factors and anthropogenic disturbance may be responsible for the lack of strict site fidelity that is evident. Dispersal patterns may differ between the sexes due to differences in their life history. While purpose of the winter haulout by immature seals may be to increase familiarity with haulout sites, and thus site fidelity, the moult haulout also plays a role. / Thesis (PhD)--University of Pretoria, 2013. / Zoology and Entomology / Unrestricted

No description available.

The analysis of oil seals is of great concern for the proper design of high pressure centrifugal compressors, because they can have significant influence on the dynamic stability of the compressor rotor. The lack of adequate analytical tools highlight the need for this type of study. An analytical tool to evaluate the oil seal characteristics, perform linear stability analysis of the compressor rotor and nonlinear transient analysis of the compressor rotor and the seal ring has been developed. An iterative finite element method is used to solve the non-linear and coupled hydrodynamic and thermal equations for the pressure and temperature distributions in oil seals. The perturbation technique is employed to determine the static and dynamic characteristics of oil seals. The hydrodynamic forces are calculated by integrating the pressure distribution along and around the oil seal. Eigenvalue analysis is performed to do the linear stability analysis of the compressor rotor. A numerical integration technique is used to solve the non-linear equations of motion of the seal ring and compressor rotor. This analysis has the ability to handle tapered seals, circumferentially grooved seals and seals with shaft misalignment. Results obtained from linear stability analysis and non-linear transient analysis for different seal geometries, including shaft misalignment, are presented. For centered seals, results obtained are in good agreement with a previous finite difference analysis. At an operating eccentricity of 0.098, the maximum percentage differences in the cross-coupled stiffness and direct damping coefficients obtained from this analysis and the finite difference analysis are 5.1 % and 1.5 % respectively. For eccentric seals, use of the true temperature distribution gives significantly different results. At an operating eccentricity of 0.497, the maximum percentage differences in the cross-coupled stiffness and direct damping coefficients obtained from this analysis and the finite difference analysis are 17.7 % and 22.9 % respectively. This analysis shows that the sharp edge grooves decrease the axial flow rate. In addition, groove depth typically applied to industrial seals is shown to be effective in breaking up the hydrodynamic pressures. Tapered and circumstantially grooved seals are shown to enhance both the locking mechanism in the seal ring and the dynamic stability of the compressor rotor. The resulting computer program gives the designer of compressors with liquid seals a much needed capability that is not available from any other known source. / Ph. D.

Since the MINER Act of 2006, the minimum static load of in-situ underground mine seals has been increased from 20-psi to either 50-psi if monitoring is conducted or 120-psi if left unmonitored. These minimum strength requirements in seals must be designed, built, and maintained throughout the lifetime of the seal. Due to this, it has become necessary to assess the effectiveness of non-destructive testing (NDT) technologies to determine seal integrity, which in this case, are explored using sonic waves and tracer gases. Through both small and large scale testing, two NDT methods were evaluated on their abilities to determine integrity of the seal. A sonic wave technique to observe a change in wave velocity to identify faults within the seal material. As a NDT method, tracer gases may be used as a potential indicator of a connection between both sides of the seal material through a series of faults and cracks within the material itself. This paper reviews the history of underground mine seals and discusses the overall assessment of sonic waves and tracer gases to serve as NDT methods for estimating the integrity of these seals. / Master of Science

Fuel cells represent a promising energy alternative to the traditional combustion of fossil fuels. In particular, solid oxide fuel cells (SOFCs) have been of interest due to their high energy densities and potential for stationary power applications. One of the key obstacles precluding the maturation and commercialization of planar SOFCs has been the absence of a robust sealant. A leakage computational model has been developed and refined in conjunction with leakage experiments and material characterization tests at Oak Ridge National Laboratory to predict leakage in a single interface metal-metal compressive seal assembly as well as multi-interface mica compressive seal assemblies. The composite model is applied as a predictive tool for assessing how certain parameters (i.e., temperature, applied compressive stress, surface finish, and elastic thermo physical properties) affect seal leakage rates.

Teilw. zugl.: New York, University, Diss., 1986.