This paper presents an analysis of the potential of Micro Gas Turbines (MGT) with regards to performance, economic and durability considerations. The performance potential was assessed by calculating the cycle efficiency based on the Brayton cycle and the mechanical efficiency of the expansion turbine. The economic potential was evaluated by calculating the specific fuel consumption and estimating the cost and manufacturability of the turbine components. The durability and reliability of the components were assessed by considering the effects of transient thermal stresses and unstable ignition. The results indicated that ceramic materials can achieve a 63% increase in efficiency over nickel-based alloys and a 39% reduction in specific fuel consumption. It was also found that the grinding process on the metal-ceramic shaft connection is the most expensive as it relies on diamond grinding, while ceramic turbines can have an initial procurement cost advantage whenproduced in higher volumes. Finally, it was found that ceramic materials are less reliable due to their higher hardness and sensitivity to pressure spikes, and therefore require careful consideration when designing the components. / I detta dokument presenteras en analys av potentialen hos mikrogasturbiner (MGT) med avseende på prestanda, ekonomi och hållbarhet. Prestandapotentialen bedömdes genom att beräkna cykelns effektivitet baserad på Braytoncykeln och expansionsturbinens mekaniska effektivitet. Den ekonomiska potentialen utvärderades genom att beräkna den specifika bränsleförbrukningen och uppskatta kostnaden och tillverkningsbarheten för turbinkomponenterna. Komponenternas hållbarhet och tillförlitlighet bedömdes genom att man beaktade effekterna av tillfälliga termiska påfrestningar och instabil tändning. Resultaten visade att keramiska material kan öka effektiviteten med 63% jämfört med nickelbaserade legeringar och minskaden specifika bränsleförbrukningen med 39%. Det konstaterades också att slipningen av axelförbindelsen mellan metall och keramik är den dyraste eftersom den bygger på diamantslipning, medan keramiska turbiner kan ha en kostnadsfördel vid den första anskaffningen när de tillverkas i större volymer. Slutligen konstaterades det att keramiska material är mindre tillförlitliga på grund av deras högre hårdhet och känslighet för tryckspikar, och att det därför krävs noggranna överväganden vid utformningen av komponenterna.

The finite element method is applied to an isolated and twisted wind turbine blade which is rotating in a vertical plane to determine its structural dynamic characteristics. The equations of motion are formulated for a rotating beam with flap and lead-lag degrees of freedom subjected to nonsymmetric bending. Using a variational approach, a blade finite clement is developed from these equations of motion. Additionally, expressions are formulated for the elastic strain energy and kinetic energy of a rotating wind turbine blade. Lagrange's equation is applied to these energy expressions and an isoparametric finite element based on three dimensional elasticity and quadratic interpolation functions is developed. Both sets of finite element equations are implemented in a general purpose computer program to solve the structural dynamics eigenvalue problem and results compare favorably with published data for the cases of a nontwisted cantilevered beam both at rest and while rotating. A blade finite element model of a 10KW horizontal axis wind turbine blade is presented and its lowest modes of vibration are calculated for the cases of the blade at rest and in operation at rotor speeds up to 250 RPM. / M.S.

This thesis presents the numerical and analytical study of the aerodynamic and heat transfer in laminar subsonic cascades along with the development of design guidelines and procedures to improve the design of microfabricated multistage radial turbines operating at low Reynolds number. Numerical analysis was performed on 24 cascade geometries using 2D computational fluid dynamics (CFD) for over 100 flow conditions for each cascade. Two dimensional correlations were extracted from CFD for profile and mixing losses, deviation and heat transfer. These correlations include Reynolds number and compressibility effects, and take into account incidence and various geometrical parameters (solidity, stagger, blade angles, thickness and mean-line distribution). Adaptation of losses to account for three dimensional effects and correlation for blockage were derived from analytical relationships. A turbomachinery simulation software based on mean-line analysis and conservation of rothalpy incorporating the developed correlations was programmed. The software can be adapted as for the physic it uses and the turbine configuration it analyses (axial, radial inward or outward, single or multi stage). The pressure profiles obtained from simulation were found to be in good agreement with experimental data for cold turbine tests. Design guidelines and charts are provided as well as cycle analysis considering microfabrication limitations. A considerable increase in stage isentropic efficiency compared to previous devices can result from the use of slender blades, lower solidity cascades and aspect ratios of 0.5, suggesting efficiencies as high as 85% for Re > 700. The study shows that higher power density and multistage matching can be achieved through the radial outward configuration. Two designs are presented, a single stage turbine for the next generation of microturbopump prototype and a turbine configuration with four rotors and 10 stages for closed Rankine cycle providing 50.7 W of net mechanical power.

This thesis describes four novel superconducting machine concepts, in the pursuit of finding a suitable design for large offshore wind turbines. The designs should be reliable, modular and light-weight. The main novelty of the topologies reside in using a single loop shaped stationary superconducting field winding, which eliminates the rotating transfer couplers and electric brushes or brushless exciters. Furthermore, the electromagnetic forces in the superconducting wire are also eliminated, which simplifies the design and manufacturing of the cryostat and the support structure. Among the four topologies presented, the claw pole type machine is the most promising one. The rotor of the machine composes of claw-poles made from laminated electrical sheets, the superconducting field winding and the armature winding are stationary. The machine is analysed using 3D FEA simulations and a small linear machine prototype is manufactured to verify the simulations. For large scale applications, a double-sided claw pole machine is proposed, which has balanced magnetic attraction forces in the rotor. The machine has a modular cryostat structure, which increases the availability of the machine. Thus, even if a fault occurs in the cryocoolers or in the armature coils, the rest of the machine can operate at partial load until the maintenance is performed. Moreover, it is much easier to replace the faulty parts, as full disassemble of the machine is not required, and a small on-site crane can be used. As a result, it offers operational advantages over the existing superconducting topologies. A 10 MW, 10 rpm generator design is presented, which has a diameter of 6.6 m and an axial length of 1.4 m. The total active mass of the generator is 58 tonnes, and the structural mass is 126 tonnes, which gives a total mass of 184 tonnes. There are four independent cryostats and two independent armature windings in the machine to improve modularity. The biggest advantage of the design is the significantly less superconducting wire usage compared to any other designs; 10 MW machine just needs 15 km of MgB2 wire at 30 K. Thus, it is believed that the proposed topology is a very cost effective and suitable candidate for a successful entry to the wind turbine market.

No description available.

No description available.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: This study is an introductory investigation into vaporizer technology as implemented in micro gas turbines. Experimental investigations are aimed at the development of expectations concerning the internal flow structure though vaporizers by generating application specific flow maps. Consolidation of these maps with other experimental data suggests that annular flow leads to increased evaporation rates. In addition, it was discovered that flow structure is affected by the injection angle and air and fuel flow rates. An investigation into the numerical modelling of vaporizers is based on two phase flow theory using a flow structure approach. The numerical behaviour is observed for parametric variations to establish the impact of assumptions. A final numerical model is formulated with empirically determined coefficients with fair correlation to experimental data. The results of this study yield recommendations towards the implementation and analysis of vaporizers with applied use in micro gas turbines. / AFRIKAANSE OPSOMMING: Hierdie studie is 'n inleidende ondersoek na verdamper tegnologie soos toegepas in mikro gasturbines. Eksperimentele ondersoeke is gerig op die ontwikkeling van kennis rakende die interne vloeistrukture deur verdampers met die bou van toepassingspesifieke vloeikaarte. Konsolidering van hierdie kaarte met verdere eksperimentele data dui daarop dat annulêre vloei lei tot verhoogde verdampingstempo’s. Daar is ook bevestig dat die vloei struktuur deur die inspuitingshoek en vloeitempo’s affekteer word. 'n Ondersoek na die numeriese modellering van verdampers is gebasseer op twee-fase vloei met 'n vloeistruktuur benadering. Die numeriese gedrag is waargeneem vir parametriese variasies om sodoende die impak van aannames te bevestig. Die numeriese model is voltooi met empiriese bepaalde koëffisiënte en lei tot goeie korrelasie met eksperimentele data. Resultate van hierdie studie lei tot aanbevelings rakende die implementering en ontleding van verdampers met spesifieke toepassing op mikro gas turbines.

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

No description available.

No description available.