The purpose of this project is to verify if the so called capacitance method is a sensitive enough method to measure micrometer distance changes in an electrode system. This is done by heating up an electrode system to 60°C and make capacitance measurements during the procedure. With the inverse relationship between the capacitance and the distance between the surfaces the distance is attained. The incitement to find a sensitive measurement method is that in a particle accelerator the temperature is down to 4K and the components of an electrode system will contract which can lead to a breakdown of the system. The change in temperature gives a theoretical change in "gap distance" that is close to the measured change in gap distance, therefore the method is a reliable enough method to measure micrometer distance changes. A possible reason for the small deviation is that the measured temperature is the temperature of the surface of the electrode system. It would be preferable to measure the total temperature of the electrodes, not just the surfaces because it is the whole electrode that expands and contracts with the temperature. This could be done with an IR-camera.

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<p> Experiments were performed to investigate the effect that a gap between a heated fin and a porous plate has on the heat transfer performance of a simulated capillary evaporator. The heat transfer performance was examined for two porous plates with average pore radii of 50 and 200 μm respectively. Tests were performed for gap distances between 0 and 900 μm and heat fluxes ranging from 17 to 260 kW/m^2. The heat transfer performance of the simulated capillary evaporator initially increased as the gap distance was increased. However, a further increase in the gap distance caused a decrease in performance. The maximum heat transfer performance occurred at a smaller gap distance for the plate with the smaller pore radius. For small gap distances, persistent high temperature regions were observed on the surface of the heated foil that grew and became more frequent at higher heat fluxes. For larger gap distances, saturated regions that appeared on the foil at moderate heat fluxes suggest that microlayer evaporation may be taking place within the gap. At high heat fluxes, these saturated regions are no longer present, but the temperature of the heated foil remained stable.</p> <p> The heat transfer process in the porous media was examined using thermocouples embedded within the porous plates. These temperature measurements indicate that a two phase region forms within the porous plate for a pore radius of 200 μm. Little evidence of vapour was observed within the plate with a pore radius of 50 μm. In that case, there was more evidence of vapour present at the surface of the porous plate. There was less evidence of vapour at the surface of the porous plate for the larger gap distances, suggesting that the vapour escapes more easily through the gap at larger gap distances.</p> / Thesis / Master of Applied Science (MASc)

The modern trend of gas turbines design is towards lighter, highly efficient,and more compact engines. Such situation imposes on engineers to continuouslysearch for improved and optimum designs. The thesis presented aims at researching possible performance improvements regarding axial gapdistance in transonic compressors. Decreasing the axial gap would result inlighter engines and achieve design goals. The influence of decreasing the axialgap on performance and structure integrity should be throughly analyzed. This thesis work includes numerical investigations on the axial gap distance effect on performance efficiency and related unsteady aerodynamics phenomena. The first one and a half compressor stages of a Siemens Gas Turbine are modeled in ANSYS CFX. Different axial gap models are simulated for differentconfigurations. The steady state solution is obtained to be initialized for transient time marching calculations. Furthermore, the computational cost of transient calculations is reduced through a geometry scaling technique. The unsteady behavior is further analyzed by a Harmonic Balance solver implemented in STAR-CCM+ software, and compared to a reference case transient calculations. The results obtained supports the presence of an optimalaxial gap distance for maximum efficiency in transonic compressors. Further, the harmonic balance method shows good possibilities for cost and time reductions in transonic compressors performance calculations.

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The continuous increase of the voltage levels in power transmission systems has lead to the occurrence of higher switching transients during their operation. The design of equipment and grid components able to sustain such a stressful operation, requires an intensive study of the electric field stress generated by these transients, and their distribution to the vicinity of each configuration. Sphere-plane gaps are the most theoretically and practically interesting electrode configurations. So far, the majority of the conducted work is referred to the study of the discharge characteristics of this structure. However, a study of the electrostatic electric field is required. An accurate calculation of the electric field can contribute significantly to an even better understanding of the discharge characteristics and the principles behind them. In this project, is presented a simulation approach for the calculation of the electro-static field of a sphere-plane configuration, varying the dimensions of the sphere and the gap distance. For this purpose, a Finite Element Method (FEM) solver was used, in which the configuration was designed and the numerical solution of the problem was implemented. After that, an attempt was performed to specify the breakdown voltage based on the electric field calculation and distribution. Useful results were recorded from both the simulation of the electrostatic model and the calculation of the breakdown voltage. One of the most important findings, was the specification of an approximate relation between the diameters of the sphere and the tube where this is mounted. As a consequence, the study of the electric field distribution became easier, while at the same time an accurate calculation of the breakdown voltage was achieved. A series of validations were performed, through the comparison with the already ex-isting, published and unpublished, experimental tests and a number of conclusions were listed. One of the most significant, was the specification of the correlation between the electrostatic model and test measurements and how these different approaches can be linked to each other in a practically efficient way. At the end, there is a proposal for further work on the subject, and possible improvements of the already conducted work. / Ökningen av spänningsnivåerna i kraftöverföringssystem har lett till högre kop-plingstransienter under drift. Konstruktionen av utrustning och nätverkskomponen-ter som kan motstå en sådan påkänning, kräver en noggrann förstudie av de elektriska fältet som genereras av dessa transienter. Ett gap av sfär-platta är den mest teoretiskt och praktiskt intressanta elektrodkon-figurationen att studera. Hittills har majoritetet av genomfört arbete avsett att studera urladdningsegenskaper för denna struktur. Dock krävs studie av elektrostatiska elek-triska fältet. En noggrann beräkning av elektriska fältet kan bidra till en ännu bättre förståelse för urladdningsegenskaper och principerna bakom dem. I detta projekt presenteras en simuleringsmetod för beräkning av elektrostatiska fäl-tet av en sfär-plan konfiguration, med varierande dimensioner av sfären och gapavstån-det. För detta ändamål har använts en Finite Element Method (FEM) lösning, där kon-figurationen utformades och problemets numeriska lösningen genomfördes. Därefter har gjorts ett försök för att ange genombrottsspänningen baserad på beräkning och distribution av elektriskta fältet. Resultat registrerades från både simulering av elektrostatiska modellen och beräkn-ing av genomslagsspänningen. Ett av de viktigaste resultaten var specifikationen av ett ungefärligt förhållande mellan diametrarna av sfären och röret där sfären är monterad. Som en konsekvens blev studiet av elektriska fältfördelningen lättare, medan en exakt beräkning av genomslagsspänningen uppnåddes. En valideringsserie har genomförts genom jämförelse med de redan existerande, publicerade och opublicerade, experimentella tester och ett antal slutsatser har noterats. En av de mest meningsfulla, var specifikation av sambandet mellan den elektrostatiska modellen och provmätningarna samt hur dessa olika tillvägagångssätt kan kopplas till varandra på ett praktiskt och effektivt sätt. Slutligen finns det ett förslag för fortsatta arbete samt eventuella förbättringar av redan genomfört arbete.