International audienceIn numerous applications developed at the Commissariat a` lEnergie Atomique, Direction de lEnergie Nucle´ aire (CEA-DEN, French Atomic Agency, Atomic Energy Department), particularly those encountered in the processing of nuclear wastes, metallic components are subjected to extreme environments in service, in terms, for example, of ageing at moderated temperature (several months at about 300 C) coupled to thermal shocks (numerous cycles up to 850 C for a few seconds and a few ones up to 1500 C) under a reactive environment made of a complex mixture of acid vapors in the presence of an electric field of a few hundred volts and a radioactive activity. Alumina plasma-sprayed coatings manufactured with feedstock of different particle size distributions, graded alumina-titania coatings, and phosphate-sealed alumina coatings were investigated to improve the properties of metallic substrates operating in such extreme environments. The effects of particle size distribution, phosphate sealant, and graded titania additions on the dielectric strength of the as-sprayed, thermally cycled and thermally aged coatings were investigated. Thermal ageing test was realized in furnace at 350 C for 400 h and thermal shocks tests resulted from cycling the coating between 850 and 150 C using oxyacetylene flame and compressed air-cooling. Alumina coating structures and phase content were characterized in parallel by scanning electron microscopy (SEM) coupled to image analysis and stereological protocols and X-ray diffractometry (XRD). The dielectric strength was assessed by measuring the breakdown voltage at 50 Hz during and after the thermal tests
A mechanically stirred molten-glass bath heated by direct induction in a cold crucible was numerically modeled. The aim of the study was to develop numerical tools to understand thermal, hydrodynamic and electromagnetic phenomena that occur in the bath. Models and coupling between these phenomena are described. This coupling and the high content of elements in the 3D mesh result in a long calculation time. The study demonstrates how to couple programs to yield the highest degree of accuracy in the shortest calculation time possible. Numerical studies are also used to characterize the fluid dynamic behavior and heat transfer in an industrial-size tank. Classical correlations commonly used to characterize stirrer efficiency and heat transfer for fluids with constant physical properties were adapted for molten glass. The power number N p and the Nusselt number Nu are used as macroscopic indicators. The results of these global studies will be useful for the operation and optimization of the vitrification facilities. ᭧
Purpose -To produce a controlled stirring in a low conducting liquid thanks to a new kind of multiphase inductor. Design/methodology/approach -An experimental pilot consisting of a cylindrical salt water pool surrounded by an innovative multiphase inductor configuration, based on the single phase asynchronous motor principle, is setup. The maximum bulk stirring velocities are measured and compared with the estimate by numerical modelling. Findings -Shows the possibility of controlling the stirring of a low conducting liquid thanks to a multiphase inductive system. The corresponding measurement results give a significant bulk velocity of a few centimetres per second. Practical implications -This new kind of multiphase inductor, working with a single phase induction generator, seems a promising way to produce a controlled stirring in low conducting media which cover a large range of induction applications. Originality/value -Such an innovative inductor configuration has already been tested successfully for metal alloys stirring in the middle frequency area. In this paper, an extension of this kind of multiphase inductive system for electromagnetic stirring of low conducting liquids like electrolytes in the high frequency area is presented.
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