Superconductors are essential components of future fusion power plants. The magnet coils responsible for producing the field required for confining the fusion plasma are exposed to considerable neutron radiation. This makes irradiation studies necessary for understanding the radiation response of the superconductor. High temperature superconductors are promising candidates as magnet coil materials. YBCO and GdBCO tapes of several manufacturers were irradiated to fast neutron fluences of up to 3.9×10 22 m −2 in the research reactor at the Atominstitut. Low energy neutrons contribute to the fission reactor spectrum but not to the expected spectrum at the fusion magnets. Low energy neutrons have to be shielded in irradiation experiments to avoid their substantial effect on the superconducting properties of tapes containing gadolinium. The critical current (I c ) of the tapes in this study was examined at fields of up to 15 T and down to a temperature of 30 K. I c first increases upon irradiation and reaches a maximum at a certain fluence, which depends highly on temperature, being highest at low temperature. I c declines at high fluences and eventually degrades with respect to its initial value. Tapes with artificial pinning centers (APCs) degrade at lower fluences than tapes without them. The n-values decrease in all types of tapes after irradiation even when the critical currents are increased. The field dependence of the volume pinning force differs in pristine tapes with and without APCs but shows the same behavior after irradiation.
Technical-grade and mixed solid/liquid phase change materials (PCM) typically melt and solidify over a temperature range, sometimes exhibiting thermal hysteresis. Three phenomenological phase transition models are presented which are directly parametrized using data from complete melting and solidification experiments. They predict hysteresis phenomena and are used to calculate effective PCM properties. Two models have already been implemented in commercial building simulation and/or multiphysics software, but not the third novel model. Applications are presented for two commercial PCM: a paraffin, and a salt water mixture with additives. Numerical implementation aspects are discussed, and significant differences in the predicted absorbed and released heat are highlighted when simulating consecutive incomplete phase transitions. The models are linked with energy balance equations to predict recorded PCM temperatures of a thermal energy storage. The cross-validation with data from 26 partial load conditions clearly indicate a superior predictive performance of the novel hysteresis model.
Current transport in polycrystalline magnesium diboride is highly non-uniform (percolative) due to the presence of secondary phases and also due to the intrinsic anisotropy of the material.The influence of secondary phases on the transport properties of MgB 2 was investigated. Bulk samples were prepared from a mixture of MgB 2 and MgO powders by the ex-situ technique in order to vary the MgO content systematically. The samples were characterized by resistive and magnetization measurements. The reduced MgB 2 fraction is modeled by a reduced effective cross section (connectivity), which was assessed directly by the experiments. The presence of MgO also increases the percolation threshold, which reduces the zero resistivity (or irreversibility) field.
Monitoring of the state of charge of the thermal energy storage component in solar thermal systems for space heating and/or cooling in residential buildings is a key element from the overall system control strategy point of view. According to the literature, there is not a unique method for determining the state of charge of a thermal energy storage system that could generally be applied in any system. This contribution firstly provides a classification of the state-of-the-art of available techniques for the determination of the state of charge, and secondly, it presents an experimental analysis of different methods based on established sensor technologies, namely temperature, mass flow rates, and pressure measurements, tested using a lab-scale heat exchanger filled with a commercial phase change material for cooling applications. The results indicate that, depending on the expected accuracy and available instrumentation, each of the methods studied here can be used in the present application, the deviations between the methods generally being below 20%. This study concludes that a proper combination of two or more of these methods would be the ideal strategy to obtain a more reliable and accurate estimation of the state of charge of the latent heat thermal energy storage.
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