38 research outputs found
3D Modeling of the Magnetization of Superconducting Rectangular-Based Bulks and Tape Stacks
In recent years, numerical models have become popular and powerful tools to
investigate the electromagnetic behavior of superconductors. One domain where
this advances are most necessary is the 3D modeling of the electromagnetic
behavior of superconductors. For this purpose, a benchmark problem consisting
of superconducting cube subjected to an AC magnetic field perpendicular to one
of its faces has been recently defined and successfully solved. In this work, a
situation more relevant for applications is investigated: a superconducting
parallelepiped bulk with the magnetic field parallel to two of its faces and
making an angle with the other one without and with a further constraint on the
possible directions of the current. The latter constraint can be used to model
the magnetization of a stack of high-temperature superconductor tapes, which
are electrically insulated in one direction. For the present study three
different numerical approaches are used: the Minimum Electro-Magnetic Entropy
Production (MEMEP) method, the -formulation of Maxwell's equations and the
Volume Integral Method (VIM) for 3D eddy currents computation. The results in
terms of current density profiles and energy dissipation are compared, and the
differences in the two situations of unconstrained and constrained current flow
are pointed out. In addition, various technical issues related to the 3D
modeling of superconductors are discussed and information about the
computational effort required by each model is provided. This works constitutes
a concrete result of the collaborative effort taking place within the HTS
numerical modeling community and will hopefully serve as a stepping stone for
future joint investigations
Qualitative and quantitative characterization of a coal power plant waste by TG/DSC/MS, XRF and XRD
SO2 removal from coal-fired power plant flue gases can be done by dry, semi-dry or wet desulphurization processes, using limestone or lime-containing products as sorbents. In a Brazilian coal power plant, there is a dry desulphurization unit to capture SO2 with hydrated lime from the combustion gases. A part of the flying ashes produced is mixed with the bottom coal ashes and the spent sulphated product generated after SO2 capture. This residual solid blend is then buried in a non-productive area, from which coal was already extracted and is studied in this work. According to the authors’ experience in the development and characterization of adsorbents for low temperature dry desulphurization processes and in thermogravimetric analysis, this paper shows and discusses a method which was developed to characterize qualitatively and quantitatively the chemical and mineral composition of this waste by using thermogravimetry coupled with mass spectrometry, X-ray fluorescence and X-ray diffraction, to preview new potential industrial applications for this waste.We are thankful to the University of Cantabria for the financial support under the Project: 51.VP61.64005, to the Brazilian Research Council, under the project CNPq no. 407005/2013-7, and to the Brazilian Education Council CAPES
Estimation of hysteretic losses for MgB2 tapes under the operating conditions of a generator
Hysteretic losses in the MgB2 wound superconducting coils of a 550 kW synchronous hybrid
scaled generator were estimated as part of the European project SUPRAPOWER led by the
Spanish FundaciĂłn Tecnalia Research & Innovation. Particular interest was given to the losses
caused by the magnetic flux ripples in the rotor coils originating from the conventional stator
during nominal operation. To compute these losses, a 2D finite element analysis was conducted
and Maxwell’s equations written in the H-formulation were solved considering the nonlinear
material properties of the conductor materials. The modeled tapes are made of multiple MgB2
filaments embedded in a Ni matrix and soldered to a high purity copper strip and insulated with
Dacron braid. Three geometrical models of single tape cross sections of decreasing complexity
were studied: (1) the first model reproduced closely the actual cross section obtained from tape
micrographs. (2) The second model was obtained from the computed elasto-plastic deformation
of a round Ni wire. (3) The third model was based on a simplified cross section with the
superconducting filaments bundled in a single elliptical bulky structure. The last geometry
allowed the validation of the modeling technique by comparing numerical losses with results
from well-established analytical expressions. Additionally, the following cases of filament
transpositions of the multi-filamentary tape were studied: no transposition, partial and full
transposition; thereby improving understanding of the relevance of the tape fabrication process
on the magnitude of the determination of ac losses. Finally, choosing the right level of
geometrical detail, the following operational regimes of the machine and its impact on individual
superconducting tape losses in the rotor were studied: bias-dc current, ramping current under
ramping background field and magnetic flux ripples under dc background current and field.European Commission's FP