In the recent years significant progresses in thedevelopment of high-temperature superconductors have been made.It is realistic to believe that power applications, based onthese conductors, in a few years will become available. To beable to utilise the conductors in an optimum way, theunderstanding of their behaviour under application-likecondition is essential. One important parameter that has to beoptimised is the power loss, which means that mathematicalmodels of these losses have to be developed. In a typicalapplication the superconductor is utilised in a coilconfiguration where the actual magnetic field is considerablehigher than for a straight structure. For power frequencies thelosses are dominated by hysteresis losses and flux flowlosses. In this thesis, mathematical models of the hysteresis andthe flux flow losses as a function of a transport current, anexternal magnetic field, the temperature and the frequency havebeen developed. The transport current and the magnetic field,which are assumed to be proportional to each other, includeboth an ac and a dc component. The models of the hysteresislosses are based on the critical state theory, and for twoidealised geometries, an infinite slab and a thin strip, newexact closed form equations have been derived. The equationsfor the two idealised geometries are then superimposed tofacilitate the description of a more realistic geometry, i.e. asuperconducting tape with a finite width and thickness. Themodel of the flux flow losses is valid for a tape shapedconductor and is based on both measurements and reasonablephysical assumptions. For the development and the validation ofthe models, a calorimetric measurement set-up has been used.From a limited number of relatively simple measurements, thedeveloped models can be adjusted to a certain superconductor,and the power losses for the actual superconductor can bepredicted in considerable more complicated cases. <b>Keywords:</b>high-temperature superconductor, hysteresislosses, flux flow losses, critical state model, calorimetricmeasurements

<p>In the recent years significant progresses in thedevelopment of high-temperature superconductors have been made.It is realistic to believe that power applications, based onthese conductors, in a few years will become available. To beable to utilise the conductors in an optimum way, theunderstanding of their behaviour under application-likecondition is essential. One important parameter that has to beoptimised is the power loss, which means that mathematicalmodels of these losses have to be developed. In a typicalapplication the superconductor is utilised in a coilconfiguration where the actual magnetic field is considerablehigher than for a straight structure. For power frequencies thelosses are dominated by hysteresis losses and flux flowlosses.</p><p>In this thesis, mathematical models of the hysteresis andthe flux flow losses as a function of a transport current, anexternal magnetic field, the temperature and the frequency havebeen developed. The transport current and the magnetic field,which are assumed to be proportional to each other, includeboth an ac and a dc component. The models of the hysteresislosses are based on the critical state theory, and for twoidealised geometries, an infinite slab and a thin strip, newexact closed form equations have been derived. The equationsfor the two idealised geometries are then superimposed tofacilitate the description of a more realistic geometry, i.e. asuperconducting tape with a finite width and thickness. Themodel of the flux flow losses is valid for a tape shapedconductor and is based on both measurements and reasonablephysical assumptions. For the development and the validation ofthe models, a calorimetric measurement set-up has been used.From a limited number of relatively simple measurements, thedeveloped models can be adjusted to a certain superconductor,and the power losses for the actual superconductor can bepredicted in considerable more complicated cases.</p><p><b>Keywords:</b>high-temperature superconductor, hysteresislosses, flux flow losses, critical state model, calorimetricmeasurements</p>

In the last decades, the focus of internal combustion engine development has moved towards more efficient and less pollutant engines. In a Diesel engine, approximately 30-40% of the energy provided by combustion is lost through the exhaust gases. The exhaust gases are hot and therefore rich of energy. Some of this energy can be recovered by recycling the exhaust gases into turbocharger. However, the energy losses in the exhaust port are highly undesired and the mechanisms driving the total pressure losses in the exhaust manifold not fully understood. Moreover, the efficiency of the turbine is highly dependent on the upstream flow conditions. Thus, a numerical study of the flow in the exhaust port geometry of a Scania heavy-duty Diesel engine is carried out mainly by using the Large Eddy Simulation (LES) approach. The purpose is to characterize the flow in the exhaust port, analyze and identify the sources of the total pressure losses. Unsteady Reynolds Averaged Navier-Stokes (URANS) simulation results are included for comparison purposes. The calculations are performed with fixed valve and stationary boundary conditions for which experimental data are available. The simulations include a verification study of the solver using different grid resolutions and different valve lift states. The calculated numerical data are compared to existent measured pressure loss data. The results show that even global parameters like total pressure losses are predicted better by LES than by URANS. The complex three-dimensional flow structures generated in the flow field are qualitatively assessed through visualization and analyzed by statistical means. The near valve region is a major source of losses. Due to the presence of the valve, an annular, jet-like flow structure is formed where the high-velocity flow follows the valve stem into the port. Flow separation occurs immediately downstream of the valve seat on the walls of the port and also on the surface of the valve body. Strong longitudinal, non-stationary secondary flow structures (i.e. in the plane normal to the main flow direction) are observed in the exhaust manifold. Such structures can degrade the efficiency of a possible turbine of a turbocharger located downstream on the exhaust manifold. The effect of the valve and piston motion has also been studied by the Large Eddy Simulation (LES) approach. Within the exhaust process, the valves open while the piston continues moving in the combustion chamber. This process is often analyzed modeling the piston and valves at fixed locations, but conserving the total mass flow. Using advanced methods, this process can be simulated numerically in a more accurate manner. Based on LES data, the discharge coefficients are calculated following the strict definition. The results show that the discharge coefficient can be overestimated (about 20 %) when using simplified experiments, e. g. flow bench. Simple cases using fixed positions for valve and piston are contrasted with cases which consider the motion of piston and/or valves. The overall flow characteristics are compared within the cases. The comparison shows it is impossible to rebuild the dynamic flow field with the simplification with fixed valves. It is better to employ LES to simulate the dynamic flow and associated losses with valve and piston motion. / <p>QC 20131204</p>

ith one controlled extraction and one uncontrolled extraction, calculation of the flow channel at all stage, design and calculation of the regulation valve and create connection diagram of steam turbine and air cooled condenser. At the beginning of this work is an overview of manufacturers of steam turbines and their unified products. Master thesis was developer with G-Team, a.s. as using calculations and the instructions given in the recommended literature with supporting CFD simulations to determine the loss coefficients and FEA simulations to determine the eigenfrequencies blades.