Vacuum Arc Remelting (VAR) is a secondary process used for homogenization of high-melting-point and oxygen-sensitive materials such as superalloys and titanium alloys. The VAR process is carried out with the aim of melting a large consumable electrode in such a way that the resulting ingot has improved homogeneity. The Specialty Metals Processing Consortium (SMPC) has spent the past 20 years developing technology to improve control over the final ingot remelting and solidification processes to alleviate conditions that lead to the formation of inclusions and segregation. Channel segregates are concentration defects arising during the solidification of large-diameter solute-rich alloys. As manufacturers for turbine engines and generators call for larger ingots, it becomes more difficult to produce them without these defects. If, however, liquid pool depth can be controlled precisely to stabilize the solidification zone in the ingot, we could, in principle, produce larger ingots that are defect free. A problem arises because measurements obtained from the VAR furnace do not give enough information to accurately estimate the liquid pool shape in dynamic melting situations. Also, the solidification process in VAR is extremely complex due to the multiple physical domains present and a high-fidelity model is required to give an accurate description of the dynamic process. The Basic Axisymmetric Remelting (BAR) code was initially developed by Lee Bertram at Sandia National Laboratories as a high-fidelity multi-energy model to describe ingot casting in this system. In this work we present a new strategy to improve the accuracy of the estimates used in the control system. This strategy consists of implementing BAR as a new set of measurements to be used by the estimator. This new strategy was used in tests jointly sponsored by SMPC and Los Alamos National Laboratory (LANL) in February 2011 using a laboratory-scale furnace and alloy 718 electrodes. / text

Outokumpu Stainless tillverkar rostfri styckeplåt. ABB Industriunderhåll AB har sedan 11 år tillbaks i tiden ansvarat för underhållet på anläggningen i Degerfors åt avdelningen Hot Rolled Plate. Hjälpmedel för att transportera och förflytta plåtar är vakuumlyftok och en undersökning har gjorts om det finns möjlighet att modifiera vakuumlyftoken så att bättre underhållsmässighet uppnås. Två stycken äldre vakuumlyftok har modifierats med förslag på nya komponenter valda för att få en standard både för nya och äldre vakuumlyftok. Vakuumlyftok 173 (fr.1978): Ny vakuumvakt (PN7009), vakuummeter (AM80-N) och filter (PIAB G3/8”). Total kostnad för modifiering: 122 695 kr Underhållskostnad (år 2007): 538 127 kr Nytt vakuumlyftok (inköpspris): 700 000 – 1 200 000 kr Nytt vakuumlyftok med antisvajsystem rekommenderas för att få ner underhållskostnader som till stor del består av trasiga sugkoppar. Vakummlyftok 332 (fr.1992): Ny vakuumvakt (PN7009). Total kostnad för modifiering: 38 505 kr Underhållskostnad (år 2007): 69 230 kr Vakuumvakten är utgående och behöver ersättas med en ny. Plåtar som anses vara problem att lyfta med vakuumlyftok är de med en tjocklek på 20 mm då det händer att dessa tappas. FEM-analyser på tre valda vakummlyftok har gjorts i PRO/E Mechanica och Ansys som resulterat i följande: Vakuumlyftok 173: Maximal plåtlängd ca 12 170 mm och maximalt utstick ca 2000 mm Vakuumlyftok 332: Maximal plåtlängd +14 000 mm och maximalt utstick +1900 mm Vakuumlyftok 457: Maximal plåtlängd ca 11 300 mm och maximalt utstick ca 1900 mm / Outokumpu Stainless manufactures stainless steel plates. ABB Industriunderhåll AB has since 11 years been responsible for the maintenance of Hot Rolled Plate at Outokumpu, Degerfors. Transportation of plates is made with the help of vacuum lifting beams. Investigation has been made whether it is possible or not to modify vacuum lifting beams to achieve better maintainability. Two elderly vacuum lifting beams have been modified with proposals for new components selected to achieve a standard for both new and older vacuum lifting beams Vacuum lifting beam 173 (fr.1978): New underpressure switch (PN7009), vacuum gauge (AM80-N) and vacuum filters (PIAB G3/8") . Total cost of the modification: 122 695 SEK Cost of maintenance (year 2007): 538 127 SEK New vacuum lifting beam (purchase): 700 000 - 1 200 000 SEK A new vacuum lifting beam with a swing compensating system recommends to reduce maintenance costs of broken suction plates. Vacuum lifting beam 332 (fr.1992): New underpressure switch (PN7009). Total cost for modification: 38 505 SEK Cost of maintenance (year 2007): 69 230 SEK The underpressure switch is outgoing and needs to be replaced with a new one. Plates that considered causing problems for vacuum lifting beams are the long plates with a thickness of 20mm. Sometimes steel plates come loose which violates the safety. Three selected vacuum lifting beams have been FEM-analyzed in Pro/E Mechanica and Ansys, which resulted in the following. Vacuum lifting beam 173: Max. plate length 12 170 mm and a maximum projecting 2000 mm Vacuum lifting beam 332: Max. plate length +14 000 mm and a maximum projecting +1900 mm Vacuum lifting beam 457: Max. plate length 11 300 mm and a maximum projecting 1900 mm

Quantum gravity is one of the interesting fields in contemporary physics which is still in progress. The purpose of quantum gravity is to present a quantum description for spacetime at 10 33cm or find the `quanta' of gravitational interaction.. At present, the most viable theory to describe gravitational interaction is general relativity which is a classical theory. Semi-classical quantum gravity or quantum field theory in curved spacetime is an approximation to a full quantum theory of gravity. This approximation considers gravity as a classical field and matter fields are quantized. One interesting phenomena in semi-classical quantum gravity is Hawking radiation. Hawking radiation was derived by Stephen Hawking as a thermal emission of particles from the black hole horizon. In this thesis we obtain the spectrum of Hawking radiation using a new method. Vacuum is defined as the possible lowest energy state which is filled with pairs of virtual particle-antiparticle. Vacuum polarization is a consequence of pair creation in the presence of an external field such as an electromagnetic or gravitational field. Vacuum polarization in the vicinity of a black hole horizon can be interpreted as the cause of the emission from black holes known as Hawking radiation. In this thesis we try to obtain the Hawking spectrum using this approach. We re-examine vacuum polarization of a scalar field in a quasi-local volume that includes the horizon. We study the interaction of a scalar field with the background gravitational field of the black hole in the desired quasi-local region. The quasi-local volume is a hollow cylinder enclosed by two membranes, one inside the horizon and one outside the horizon. The net rate of particle emission can be obtained as the difference of the vacuum polarization from the outer boundary and inner boundary of the cylinder. Thus we found a new method to derive Hawking emission which is unitary and well defined in quantum field theory. / ix, 109 leaves : ill. ; 29 cm

Tensional Vacuum Vessels (TVV) are vessels constructed such that the walls are placed in tension rather than in compression as is the case with conventional vacuum vessels. TVVs have the advantage of being cost-effective, light weight in construction, and potentially portable. Tensional vessels have already been designed with regard to submarine applications. However, the use of this principle with regard to vacuum applications is believed to be novel. TVVs have two interlinked thin walled shells instead of the traditional single thick wall of conventional design. These shells are placed in tension by pressurising the intermediate space. This thesis outlines the theory of tensional vessels and describes the performance of a number of experimental chambers developed during this investigation. The fundamental theory of the TVV is outlined and developed in more detail with regard to cylindrical vessels. These include vessels constructed from longitudinal and circumferential tubes. The basic theory for any TVV can be derived from the equilibrium condition. This states that the force due to the gauge pressure on the outer shell must be greater than or equal to the force due to the absolute pressure on the inner shell. If the inward force predominates implosion will occur. Materials science considerations are also taken into account. If the tension in the walls exceeds that required for yield, the vessel will deform. The use of novel tensile materials is also explored. TVVs are potentially inflatable and theory is developed with regard to the possibility of buoyant vessels. The first experiments were based on earlier work performed at this institution with cylindrical TVVs constructed from longitudinal tubes. The tubes employed were soft drink cans which were sealed together with putty. The work described in this thesis outlines the development of larger versions and the instabilities which developed are noted. High vacuum experiments performed through the inclusion of a guard vessel are then described. This is followed by a further description of experiments performed with this basic tensional wall design in an attempt to gain a better understanding of its properties. These vessels were smaller and were gas pressurised in order to allow for increased flexibility with regard to pressure and volume variation. It is found that the compressional elements of such vessels cannot be ignored. A series of cylindrical TVVs with the walls constructed from circumferential tubes is then described, including high vacuum experiments, also performed through the inclusion of a guard vessel. The initial experiments were small in scale and made use of small bicycle tyres as the TVV walls. Larger vessels were then built, the walls being constructed from car tyres. These vessels are also inflatable and more stable than those constructed from longitudinal tubes. Also, the compressional elements do not play as great a role in these vessels. A fully tensional cylindrical vessel is then described which includes tensional end plates. Experiments performed with large bowls as the end plates are outlined. The theory of the deformation of a circular plate is also given including finite element analysis. Finally, a further novel vacuum vessel design is proposed. This is the spinning vacuum vessel. Proof of principle experiments are performed on a small scale vessel (a soft drink can with its interior reinforced with putty) which yields promising results. / Thesis (M.Sc.)-University of Natal, 1999.

No description available.

A need was identified to test multi–layer vacuum super insulation (MLVSI) used in cryogenic applications for hydrogen storage. The study focuses on the application of commercially available MLVSI to a locally patented liquid hydrogen cryogenic storage system. This led to an investigation of different types of multi–layer vacuum insulation configurations, as well as further research on tank inlet coupling configurations. It includes the manufacturing of a liquid nitrogen testing cryostat to be able to test and evaluate the system performance. The first set of tests was based on the development of an inlet coupling configuration to limit heat transfer through the inner tank inlet, of a double cryogenic tank system in order to reduce gas boil–off. The couplings were manufactured in the form of a bellow to handle cryogenic vacuum levels, while ensuring low heat transfer rates between inner and outer tanks. It was found that various coupling designs can be considered to limit gas boil–off. The second set of tests was conducted on a specific MLVSI configuration to determine its effectiveness to insulate the spherical header surface of a typical hydrogen storage vessel. The installation procedure, to limit heat transfer and boil–off due to edge effects in this configuration was investigated. It was found that insulation–overlap–edge effects will always have an impact on insulation performance when a spherical header of a storage vessel is insulated, due to its specific geometry. A time efficient way to install MLVSI on such a spherical header is presented and evaluated. Further investigations were carried out by combining findings into one single system to determine the performance of an optimised insulated cryogenic system. It was found that copper plate discs installed between the vanes of a bellowed inlet/outlet nozzle is the most promising to limit heat transfer to the cryogenic fluid. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2012.

A need was identified to test multi–layer vacuum super insulation (MLVSI) used in cryogenic applications for hydrogen storage. The study focuses on the application of commercially available MLVSI to a locally patented liquid hydrogen cryogenic storage system. This led to an investigation of different types of multi–layer vacuum insulation configurations, as well as further research on tank inlet coupling configurations. It includes the manufacturing of a liquid nitrogen testing cryostat to be able to test and evaluate the system performance. The first set of tests was based on the development of an inlet coupling configuration to limit heat transfer through the inner tank inlet, of a double cryogenic tank system in order to reduce gas boil–off. The couplings were manufactured in the form of a bellow to handle cryogenic vacuum levels, while ensuring low heat transfer rates between inner and outer tanks. It was found that various coupling designs can be considered to limit gas boil–off. The second set of tests was conducted on a specific MLVSI configuration to determine its effectiveness to insulate the spherical header surface of a typical hydrogen storage vessel. The installation procedure, to limit heat transfer and boil–off due to edge effects in this configuration was investigated. It was found that insulation–overlap–edge effects will always have an impact on insulation performance when a spherical header of a storage vessel is insulated, due to its specific geometry. A time efficient way to install MLVSI on such a spherical header is presented and evaluated. Further investigations were carried out by combining findings into one single system to determine the performance of an optimised insulated cryogenic system. It was found that copper plate discs installed between the vanes of a bellowed inlet/outlet nozzle is the most promising to limit heat transfer to the cryogenic fluid. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2012.

Mushrooms are one of the protein rich foods, however they have a short pro-harvest life (2 to 3 days) compared to most vegetables. The aim of this study was to evaluate whether applying an anti-browning solution using vacuum impregnation and then electron beam irradiation can be used to extend the shelf life of fresh-cut mushrooms (Agaricus bisporus). Solutions made with (a) 2% ascorbic acid + 1% calcium lactate, (b) 2% citric acid + 1% calcium lactate, (c) 1% chitosan + 1% calcium lactate, and (d) 1% calcium lactate were used to impregnate mushroom slices at different vacuum pressures, vacuum pressure times, and atmospheric restoration times. Mushrooms were also irradiated at a dose of 1 kGy using a 1.35 MeV e-beam accelerator and their quality was evaluated in terms of color, texture, and microbial growth during 15 days storage at 4 degrees C. The best vacuum impregnation treatment was the 2% ascorbic acid and 1% calcium lactate solution using a vacuum pressure of 50 mmHg for 5 minutes and an atmospheric restoration time of 5 minutes. The control (not treated) and impregnated samples lost their structure (softening) during storage. The irradiated samples lost their firmness by day 4 of storage. The addition of calcium lactate to the samples during the treatment helped to keep the product’s texture during the 15 days storage time. Color of the mushrooms changed during storage for all the control and impregnated samples and only the irradiated samples showed an acceptable color by the end of day 15. Aerobics and psychrotrophics counts were significantly reduced by irradiation; while yeast and molds population increased by day 9 and were not completely inactivated with a dose of 1 kGy. Sensory panelists preferred the treated samples over the controls. The best treatment was the combination of vacuum impregnation with irradiation according to the consumer studies.

Solar hydrogen has the potential to replace fossil fuels with a sustainable energy carrier that can be produced from sunlight and water via &quotewater splitting&quote. This study investigates the use of hematite (Fe&sub2O&sub3) as a photoelectrode for photoelectrochemical water splitting. Fe&sub2O&sub3 has a narrow indirect band-gap, which allows the utilization of a substantial fraction of the solar spectrum. However, the water splitting efficiencies for Fe&sub2O&sub3 are still low due to poor absorption characteristics, and large losses due to recombination in the bulk and at the surface. The thesis investigates the use of nanostructured composite electrodes, where thin films of Fe&sub2O&sub3 are deposited onto a nanostructured metal oxide substrate, in order to overcome some of the factors that limit the water splitting efficiency of Fe&sub2O&sub3. Doped (Si, Ti) and undoped Fe&sub2O&sub3 thin films were prepared using vacuum deposition techniques, and their photoelectrochemical, electrical, optical and structural properties were characterised. The doped Fe&sub2O&sub3 exhibited much higher photoelectrochemical activity than the undoped material, due to an improvement of the surface transfer coefficient and some grain boundary passivation. Schottky barrier modeling of Fe&sub2O&sub3 thin films showed that either the width of the depletion region or the diffusion length is the dominant parameter with a value around 30 nm, and confirmed that the surface charge transfer coefficient is small. An extensive review of the conduction mechanisms of Fe&sub2O&sub3 is presented. ZnO and SnO&sub2 nanostructures were investigated as substrates for the Fe&sub2O&sub3 thin films. Arrays of well-aligned high aspect ratio ZnO nanowires were optimised via the use of nucleation seeds and by restricting the lateral growth of the nanostructures. The geometry of the nanostructured composite electrodes was designed to maximise absorption and charge transfer processes. Composite nanostructured electrodes showed lower quantum efficiencies than equivalent thin films of Fe&sub2O&sub3, though a relative enhancement ofcollection of long wavelength charge carriers was observed, indicating that the nanostructured composite electrode concept is worthy of further investigation. The rate-limiting step for water splitting with Fe&sub2O&sub3 is not yet well understood and further investigations of the surface and bulk charge transfer properties are required in order to design electrodes to overcome specific shortcomings.

Bibliography: leaves [250]-268 / 268, ca. 130 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics, 1983