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- ItemComparative Studies on the Radiative Heat Transfer in Arc Plasma and Its Impact in a Model of a Free-Burning Arc(MDPI, 2024-08-05) Baeva, Margarita; Cressault, Yann; Kloc, PetrThe radiative heat transfer in arc plasma models is considered from the point of view of its description in terms of a net emission coefficient, the method of spherical harmonics in its lowest order, and the discrete ordinate method. Net emission coefficients are computed, applying approximate analytical and numerical approaches and a multi-band representation of the spectral absorption coefficient with three kinds of its averaging and two datasets. Self-consistent access to the radiative heat transfer is applied to a two-dimensional axisymmetric model of a free-burning arc in argon at atmospheric pressure. The results obtained from the models employing the net emission coefficient, the method of spherical harmonics, and the discrete ordinate method are compared.
- ItemA comprehensive overview of high-speed solid-rotor induction machines: Applications, classification, and multi-physics modeling(Elsevier, 2025-02-19) Bílek, Vladimír; Bárta, Jan; Toman, Marek; Lošák, Petr; Bramerdorfer, GerdSolid-rotor induction machines have gained significant attention in various industrial applications due to their robustness, reliability, and cost-effectiveness. This paper presents a comprehensive overview of these machines, covering their classification and various applications. The paper starts with discussing the widespread usage of solid-rotor induction machines in numerous industry sectors, including manufacturing, transportation, and renewable energy generation. The ability to operate under harsh environmental conditions and in safety-critical settings has made these machines indispensable in many fields of engineering. Their detailed classification based on different rotor topologies is provided, highlighting the unique design features and performance characteristics of each category. Simple and hybrid configurations and their distinct advantages and limitations in specific applications are included. This paper further explores the essential aspects of multi-physics modeling of solid-rotor induction machines, incorporating electromagnetic, mechanical, and thermal considerations to gain deep insights into the complex interactions between components and to guide the optimization process for enhanced performance and efficiency. This work is intended as a valuable reference for researchers and engineers seeking a comprehensive understanding of solid-rotor induction machines, from their diverse applications to the intricacies of their electromagnetic, thermal, and mechanical modeling. By shedding light on these aspects, this work contributes to the advancement and utilization uptake of these machines in modern industrial settings.
- ItemTopology Optimization of Rotor Bars Geometry and Arrangement for a Line-Start Permanent Magnet Synchronous Machine(IEEE, 2021-08-13) Bárta, Jan; Knebl, Ladislav; Bramerdorfer, Gerd; Lolová, Iveta; Silber, Siegfried; Vítek, OndřejAn optimally designed line-start permanent magnet synchronous machine may require a different squirrel-cage design than traditional induction machines. The objective of this paper is to apply topology optimization based on the normalized Gaussian network in order to find the optimal shape of the rotor bars for a line-start permanent magnet synchronous machine. This approach facilitates optimizing the shape of the bar, without the limitation of a predefined bar geometry and arrangement, as is usually considered for classic induction machine design. For this study, a previously designed four-pole line-start permanent magnet synchronous machine with a rated power of 1.5kW is used as an initial design. To verify the accuracy of performance evaluation by utilizing finite-element methods, a prototype of this machine was built and tested. Then, verified model of line-start permanent magnet machine is used for topology optimization of its rotor cage area. The outcome of the optimization is the Pareto front, from which three optimized designs are selected. Finally, these designs are analyzed and proved to have better steady-state performance than the initial machine. The results provide new insights for the design of squirrel-cage bars for line-start permanent magnet synchronous machines.
- ItemRadiative Heat Transfer in Models of DC Arc Plasma(Czech Technical University in Prague, 2023-08-08) Baeva, Margarita; Kloc, Petr; Cressault, YannThe radiative heat transfer in arc plasma models of a free-burning arc and a plasma torch in atmospheric pressure argon is taken into account in a self-consistent way. This is realized by the P1 method for solving the equation of radiative transfer and the multi-band approximation that considers the division of the emitted spectrum into a number of spectral bands. Net emission coefficients are evaluated by solving the equation of radiative transfer in three dimensions in an isothermal cylindrical plasma. The arc plasma parameters of the free-burning arc and the plasma torch obtained accounting for radiative transport have been compared with those from the temperature-dependent net emission coefficient for a radius of 1 mm. The results show that in general, the models applying the net emission coefficient provide results in the arc core close to that using the P1 method. The discrepancy is stronger in the arc periphery and near walls, where the P1 method predicts absorption of radiation.
- ItemA Review of Thermal Conductivity of Epoxy Composites Filled with AIN or BN(IEEE, 2017-08-31) Samek, Josef; Ondrůšek, Čestmír; Kurfűrst, Jiřínew possibility to improve thermal properties and lifetime of electrical machines is adding some micro- or nano- particles to the epoxy resin and improve the heat dissipation of the machine. This will reduce the temperature in a stator winding. The paper reviews actual work in the field of epoxy materials enriched with aluminum nitride (AlN) or boron nitride (BN). Properties of the particles are described, same as preparation process and influence of usage of coupling agents that creates a bond between particles and epoxy. Brief introduction to the thermal aging of insulation is presented same as influence of the temperature reduction on lifetime of the winding insulation. Further suggestions for improvements and trends are established in discussion.