Defect and Diffusion Forum Vols. 283-286

Abstract: We intend in this work to model an industrial burner replica of the ceramic tunnel furnace of the Ceramics Modern Society (SOMOCER, TUNISIA). This study aims to evaluate the ability of turbulence and radiation models to predict the dynamics and heat transfer fields. The study is conducted by means of numerical simulations in presence of a reactive flow using the commercial code FLUENT. The 3D Navier-Stokes equations and four species transport equations are solved with the eddy-dissipation (ED) combustion model. We use three turbulence models (k- standard, k- RNG, and RSM) and two radiation models (DTRM and DO). The obtained results demonstrate that the k- standard turbulence model is unable to predict the flow characteristics whereas; the k- RNG and RSM models give a satisfying agreement with the experiments. Suitable results are provided by the DTRM radiation model; whereas, those given by the DO model can be improved.

Abstract: Not many studies have been found in the literature on the effect of Ag ions on the structure and phase stability of hydroxylapatite which may be recognized as important information in the scaffold fabrication. The objective of the current study is to develop a better understanding on the structure and behavior of the antibacterial Ag incorporated hydroxylapatite. In order to do this, Ag doped hydroxylapatite was made by a precipitation method, and sintered in air at 1300oC. The materials were characterized by X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), density measurements and scanning electron microscopy (SEM).

Abstract: Numerical predictions are carried out in order to investigate the fractured horizontal well behaviour. A control volume based approach is used to solve the transient 3D diffusivity equation adopting an irregular hybrid grid. Effect of several parameters such as reservoir characteristics, fracture properties and physical and geometrical parameters of the reservoir and the well that may affect the well productivity and production are discussed. Simulation results allow to predict the optimum number of induced fractures.

Abstract: Fission of fissile uranium or plutonium nucleus in nuclear fuel results in fission products. A small fraction of them are volatile and can migrate under the effect of concentration gradients to the grain boundaries of the fuel pellet. Eventually, some fission gases are released to the rod void volumes by a thermally activated process. Local transients of power generation could distort even further the already non-uniform axial power and fission gas concentration profiles in fuel rods. Most of the current fuel rod performance codes neglects these gradients and the resulting axial fission gas transport (i.e., gas mixing is considered instantaneous). Experimental evidences, however, highlight axial gas mixing as a real time-dependent process. The thermal feedback between fission gas release, gap composition and fuel temperature, make the “prompt mixing assumption” in fuel performance codes a key point to investigate due to its potential safety implications. This paper discusses the possible scenarios where axial transport can become significant. Once the scenarios are well characterized, the available database is explored and the reported models are reviewed to highlight their major advantages and shortcomings. The convection-diffusion approach is adopted to simulate the axial transport by decoupling both motion mechanisms (i.e., convection transport assumed to be instantaneous) and a stand-alone code has been developed. By using this code together with FRAPCON-3, a prospective calculation of the potential impact of axial mixing is conducted. The results show that under specific but feasible conditions, the assumption of “prompt axial mixing” could result in temperature underestimates for long periods of time. Given the coupling between fuel rod thermal state and fission gas release to the gap, fuel performance codes predictions could deviate non-conservatively. This work is framed within the CSN-CIEMAT agreement on “Thermo-Mechanical Behaviour of the Nuclear Fuel at High Burnup”.

Abstract: In the present study, a method based on sulfuric acid dehydration of sugar was developed to synthesize a precursor material, which can yield B4C/SiC composites at much lower temperatures compared to traditional carbothermal methods. The precursor material for pure B4C was heat treated at the temperatures between 400 and 1600oC under inert atmosphere. The precursor material for B4C /SiC composites was heat treated only at 1600oC under an inert atmosphere. Then the samples were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The results showed that B-C bonds formed as low as 400oC. On the other hand, crystallized B4C and B4C / SiC composites can be obtained at the heat treatment temperatures between 1400 and 1600oC.

Abstract: The structure and phase composition of high-speed steels of different grades after casting, annealing, and subsequent final heat treatment (quenching and tempering) have been studied focusing on diffusion processes. In order to investigate kinetics of both the structure and phase transformations in eutectic carbides upon heat treatments, different techniques of optical microscopy, electron microscopy (both scanning and transmission ones), X-ray diffraction, and energy dispersive X-ray analysis have been used.

Abstract: The structure and phase composition of high-speed steels of different grades additionally alloyed with boron after casting, annealing, and subsequent final heat treatment (quenching and tempering) have been studied focusing on diffusion processes. In order to investigate kinetics of both the structure and phase transformations in eutectic carbides upon heat treatments, different techniques of optical microscopy, electron microscopy (both scanning and transmission ones), X-ray diffraction, and energy dispersive X-ray analysis have been used.

Abstract: The present work concerns development of porous materials for medicine applications. The implant alloys should be paramagnetic because of the danger of reaction with blood cells. However, the strain-induced martensitic transformation may take place due to high strain during implants use. The porous samples made of the 316 stainless steel by the powder metallurgy method were investigated. The results of magnetic studies as well as X-Ray diffraction analysis of sintered specimens after compression tests are presented. The changes in magnetic properties of sintered steel were observed as result of mechanical testing, particularly in case of compression with high strain. Whereas, the X-Ray diffraction did not confirm the phase transformation of austenitic steel.

Abstract: The paper concerns the problem of exploitative composite materials with solid lubrication additions. The goal of the present investigation was to research the composite materials based on 316L stainless steel powders with the addition of calcium pyrophosphate (Ca2P2O7). The diffusion processes of main elements during sintering were analyzed. The influence of volume fraction of additions on structure of composites and their tribological properties were examined. Tribological tests were performed by a special tribometer, which allowed to realize research during the periodically variable motion with low velocity and variable values of pressure. The structure of materials was observed with scanning electron microscope (SEM). The intensive diffusion of main alloying elements brought the segregation of components and appearance of new phases. Changes in the microstructure, particularly the solution of phosphorus in austenite and attendance of phosphides and oxides insertions, had an effect on mechanical properties of materials. The microhardness, yield strength values as well as wear resistance increased considerably with the rise of modifier addition.

Abstract: The contribution of this work is to characterize the travelling wave’s appearance and to generalize the behavior of Poiseuille-Rayleigh-Benard (PRB) systems for a broad range of dimensionless parameters, which control the double diffusive mixed convection. The numerical results consist to analyzing the flow regimes of the steady longitudinal thermoconvectives rolls for the case of purely thermal mixed convection and for both thermal and mass diffusion. The passage from an opposed volume forces to cooperating one at fixed Rayleigh (Ra), Reynolds (Re) and Lewis (Le) numbers, affects considerably the birth and the development of the longitudinal rolls R//. The distribution of the heat and mass transfer, presented by the average Nusselt and Sherwood numbers, is also examined.