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We present numerical simulations using Finite Elements Method (FEM) that test the validity of a quasi 1D analytical model for a winding in an oil-filled distribution transformer with partial cooling ducts. We do this by employing a 2D FEM model of the transformer winding. The winding in the analytical and simulation model is represented with homogeneously distributed heat source and anisotropic thermal conductivity. We show that the numerical results confirm the assumptions of the analytical model for typical values of the parameters of the winding, but for certain marginal situations the anisotropic conductivity and 2D FEM model may also lead to unphysical predictions. [ABSTRACT FROM AUTHOR]

We propose and test a simple analytical model of radial temperature profile for the VVER-440 fuel assembly sub-channel. The model includes 18 physical parameters, which affect the heat transport. Considering small changes in the input parameters of the model we evaluate their impact on temperature profile. The outcomes of this work include temperature profile in the representative thermo-hydraulic sub-channel and analysis of its sensitivity to changes in the input parameters. The analytical approach improves our understanding of thermo-physical and material-related phenomena inside the fuel rod under operational conditions. [ABSTRACT FROM AUTHOR]

We study the polyfluorene crystal using computational modelling based on the density functional theory. We assume a geometry with two monomers per unit cell and periodicity along the polymer's backbone structure. The stable structure determined at these conditions is characterized by significant torsion angles between individual units. We calculate its optical spectra using the TDDFT method and find a gap of 2.73 eV which is in a very good agreement with the experimental value of 2.83 eV reported in our recent paper for a thermally annealed PFO film. [ABSTRACT FROM AUTHOR]

We present a description of the heat transfer mechanism in an oil-filled transformer that incorporates two main bottlenecks for the heat flow. The first one, the transfer from its windings into the oil, is simulated using a realistic 3D model and a finite element method. The second, the transfer from the transformer’s wall into the environment is described with a robust analytical model. The combination of the two gives an accurate prediction of critical temperatures better than 2ºC. The study was done in collaboration with BEZ Transformatory, a.s. [ABSTRACT FROM AUTHOR]

The effect of heat source position on the heat transfer in an aluminium tube was investigated experimentally and analytically. The experimental data were obtained by measuring the temperature distribution along the tube wall for two different heat source locations. A theoretical model of the tube was developed and validated with the experimental data. A finite element method simulation was performed to analyze the temperature profile and to endorse assumptions for theoretical model. The results showed that the heat transfer rate depend on the heat source position. [ABSTRACT FROM AUTHOR]

This article introduces a simplified model for analyzing heat transfer in oil-filled transformers enhanced with magnetic nanofluids. The model integrates natural convection with thermomagnetic effects to predict the cooling performance of transformer oil channels and fins. The study employs a combination of theoretical formulations and Finite Element Method (FEM) simulations to evaluate the impact of magnetic field on heat transfer characteristics. The results indicate a notable contribution of thermomagnetic convection to the overall cooling efficiency, providing insights into the design and optimization of transformer cooling systems. [ABSTRACT FROM AUTHOR]

Defects in organic semiconductors can significantly affect the functionality of organic photonic devices. However, unlike inorganic materials, they are still little researched. This article investigates structural defect states in the bandgap of n-type small molecular semiconductor 2,2'-{[5,5'-(Naphthalene-2,6-diyl)bis(thiophene-5,2-diyl)]bis(2,2,2-trifluoroethan-1-yl-1-ylidene)}dimalononitrile (TNT-FEC). Using the energy-resolved electrochemical impedance spectroscopy (ER-EIS), we mapped the presence of defect states in this material, and by comparing measurements in the solution and the film, we identified the structural ones. Furthermore, we investigated the influence of the substrate on defect formation. Finally, using DFT and DFTB calculations, we analyzed the possibility of the conformers' presence, which can influence the structural properties of thin films. The combination of experimental and theoretical approaches in the analysis of defect states has been shown as suitable for studying structural defects' presence in the thin films of organic semiconductors. [ABSTRACT FROM AUTHOR]