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Thermo-kinetic modelling of the acidic leaching of anorthosite: Key learnings toward the conception of a sustainable industrial process
Get PDFThe world is facing critical technological and environmental challenges in the production of basic materials in high demand, such as aluminium and silica, whose processes were developed long ago. New production routes, involving using alternative resources and innovative technological solutions, are needed to secure access to these base materials at a lower cost to the environment, in terms of waste and carbon footprint. The European project AlSiCal is currently investigatingan environmentally friendly multi-step process for producing alumina and silica from anorthosite, an abundant feldspar mineral. The present paper focuses on the modelling strategy of the dissolution of anorthosite in concentrated hydrochloric acid, which is the first step of the AlSiCal process. The objectives of this study are (i) to give a reliable first-level prediction of the product speciation in the aqueous and solid phases, (ii) to provide the sensitivity of the process to key operating variables, and finally, (iii) to evaluate the performance of both batch and continuous leaching processes. The proposed methodology is based on the coupling of geochemical equilibrium simulations and particle reaction models, using different computational tools and relevant literature data. This makes it possible to select the favourable operation window and process configuration for the quantitative extraction of aluminium in solution and the production of amorphous silica with an acceptable purity for large-market applications
Percolating and nonpercolating liquid phase continuum model of drying in capillary porous media with application to solute transport in the very low Péclet number limit
Get PDFA three equation continuum model of drying is presented. The model explicitly considers the liquid phase as formed by a percolating liquid phase and a nonpercolating liquid phase. The model is tested against pore network simulations. A quite good agreement is obtained between the predictions of the continuum model and data obtained by volume averaging the pore network simulation results. Then, the model is extended to the case where a solute is present in the liquid phase. This leads to the consideration of a five equation continuum model as opposed to the classically considered two equation model. The model is tested when diffusion is the solute dominant transport mechanism. In agreement with the pore network simulations, the five equation continuum model predicts that the solute concentration in the percolating liquid phase is greater than in the nonpercolating liquid phase in the considered situation. The work illustrates the key role of the liquid fragmentation process occurring during drying on the solute dynamics. Counterintuitively, although diffusion is dominant, it is shown that the solution concentration varies over the liquid phase as the result of the liquid phase fragmentation process
Loss assessment of the NASA SDT configuration using LES with phase-lagged assumption
Get PDFThis paper presents the numerical study of the Source Diagnostic Test fan rig of the NASA Glenn (NASA SDT). Large-Eddy Simulations (LES) based on a finite volume approach are performed for the three different Outlet Guide Vane (OGV) geometries (baseline, low-count and low-noise) and three rotational speeds corresponding to approach, cutback and sideline operating conditions respectively. The full stage and nacelle geometries are considered in the numerical simulations, and results are compared to available measurements. The NASA SDT configuration is equipped respectively with 22 fan blades and either 26 of 54 vanes depending on the OGV geometry. The simulation domain could only be reduced to half of the full annulus and would still be a significant cost for the LES.
In order to reduce computational cost, an LES with phase-lagged assumption approach is used. This method allows to perform unsteady simulations of multistage turbomachinery configurations including multiple frequency flows with a reduced computational domain composed of one single blade passage for each row. The large data storage required by the phase-lagged approach is handled by a compression method based on a Proper Orthogonal Decomposition replacing the traditional Fourier series decomposition. This compression method improves the signal spectral content especially at high frequency. Based on the numerical simulations, the flow field is described and used to assess the losses generated in the turbofan configuration based on an entropy approach. The results show different flow topologies for the fan depending on the rotational speed with a leading edge shock at high rotational speed. The fan boundary layer contributes strongly to losses with the majority of the losses being generated close to the leading edge for the dissipation due to mean strains and close to the recirculation zone occurring on the suction side for the turbulent kinetic energy production
On some applications of Generalized Geometric Projection to optimal 3D printing
Get PDFIn recent years, Topology Optimization (TO) gained interest in the scientific community. It assists in finding the best arrangement of material in a design volume. The classical approach named ”Solid Isotropic Material with Penalization” (SIMP) associates a fictitious density to each finite element in the domain. While SIMP is described as an implicit approach which can lead to problems with dimensionality of variables, explicit methods adopt a geometric projection of simple elements (eg.: bars) to reduce the number of design variables. This simplifies the geometric interpretation of the optimal architecture. The major explicit methods were recently unified into a general framework, Generalized Geometric Projection (GGP).
Currently it is quite challenging to take into account manufacturing constraints in the topology optimization design phase. Therefore this paper presents an application of the GGP Method to the design of products made by Additive Layer Manufacturing (ALM). Every printed layer constitutes a geometric element, involving design variables relative to position and width. Specific constraints of ALM, including bridge length and overhang angle, can be easily monitored by exploiting the geometric features of the combined elements.
Examples in two dimensions will be reported, analyzing two academic benchmark problems. A comparison to other proven techniques is also detailed. An mean difference of 7.7% is observed for solutions with only overhang angle constraint, while a mean difference of 11% is observed for solutions with overhang angle and bridge length constraint. The presented work integrates design and manufacturing, directly identifying the path of the printed layers
Characterisation of bursts in a turbulent boundary layer over circular cavities
Get PDFBoundary layer surveys are performed to characterise
the turbulent boundary layer grazing over a a surface
with flush-mounted circular cavities disposed in a staggered
arrangement (staggered angle of 45 deg). The momentum
thickness based Reynolds number varies from
Reθ = 1830 to 3380 and the cavity diameter and spacing
in wall units from d+ = 130 to 250 and L+ = 587 to
1075 respectively. A decrease in the local skin friction
drag with respect to a smooth baseline is evidenced as
well as a thickening of the viscous sublayer. The bursts
frequency profile for the perforated case is shifted away
from the wall while the intensity of the bursts is reduced.
The production term of the turbulent kinetic energy budget
is obtained from Particle Image Velocimetry data. An
upward shift and a decrease in magnitude of the peak associated with the streaks suggests that the cavities modify the near wall turbulent cycle
Fluid dynamic simulation of CrO2(OH)2 volatilization and gas phase evolution during the oxidation of a chromia forming alloy
Get PDFThe influence of the chromia volatilization on the oxidation kinetics of Inconel 625 was investigated at 900 ◦C under flowing wet air (74%N2-18.5%O2-7.5%H2O) through an interdisciplinary approach, coupling experiments and gas phase simulation. Oxidation tests showed a strong decrease in the volatilization rate of lined-up samples from the inlet to the outlet of a horizontal tubular furnace. Gas phase simulation allowed to relate it to an increase in the CrO2(OH)2 partial pressure along the tube. Considering gas composition changes appears as essential to provide correct interpretation of oxidation test results in humid and oxidizing environments
High Temperature Oxidation of Additively Manufactured Structural Alloys
Get PDFMetal alloys produced by additive manufacturing have specific microstructures and compositions. Their microstructure is generally out of equilibrium, textured, and inhomogeneities can be observed. They can have pores and nano-inclusions. The contents of volatile elements may deviate from the nominal composition. These alloys often experience significant internal stresses and present fairly rough surfaces depending on the process used. Hipping these alloys modifies their microstructure and defects. This literature review shows that open porosity can lead to much higher oxidation kinetics than dense materials, with very deep internal oxide penetrations. Nevertheless, when fabricated with optimized parameters, LBM- or EBM-alloys, such as TA6V, 718, or 316L, can behave as well as, or even better than, wrought alloys. The roughness of the surface is not necessarily problematic, but it can lead to local breakaway phenomena and premature spalling on some alloys. It has been verified that the nature of the grain boundaries strongly affects the intergranular oxidation. The effect of chemical segregations on the protective nature of the outer oxide layer has also been reported. Today, too few studies have been devoted to the effect of raw and pre-oxidized surface states after HIP on cyclic oxidation and on hot corrosion of these alloys
In-situ reactive synthesis of dense nanostructured β-FeSi2 by Spark Plasma Sintering
Get PDFβ-FeSi2 is a promising material for thermoelectric application, especially if it can be nanostructured to decrease the lattice contribution to the thermal conductivity. It can be even more interesting if the entire chain of processes implemented to obtain it is not too time and energy consuming. In this paper we report a simple route to synthesize nano-β-FeSi2 by combining mechanical milling and reactive spark plasma sintering of Fe-Si alloys. A map of the pressure-temperature conditions using a spark plasma sintering setup was performed and shows that it is possible to obtain nano-β-FeSi2 pellets with a density above 90% using dwell times as short as 5 min. The impact, of both, the density and nanostructuring on the hardness of the β-FeSi2 pellets obtained by this process are presented as well as the impact of the thermoelectric properties of the materials
Aeraulic transfer mechanisms through openings on enclosures in maintenance and dismantling sites : evaluation of aerosol aerodynamic behavior contribution to backflow phenomenon
Get PDFThe context of my thesis concerns the safety of ventilated enclosures implemented on maintenance and dismantling sites of nuclear sites. It aims to characterize the efficiency of dynamic containment of ventilated airlocks by studying the backflow of gaseous and particulate pollutants. Backflow phenomenon can occur through nominal or accidental openings on ventilated enclosures under the effect of an internal or external aeraulic disturbance. Our works are the continuation of S. Kaissoun1 works who studied the phenomenon of local backflow of a gaseous pollutant at a rectangular opening on a reduced-scale enclosure. As part of my thesis, we added an external envelope around the experimental enclosure in order to characterize the overall quantity of pollutants coming from the backflow. The main objectives of my thesis are as follow. On one hand, we aim to characterize the backflow phenomenon experimentally using laser visualization techniques (Schlieren, PIV) and to measure the local and global quantities of gaseous and 5 μm particulate pollutants emitted through an opening using dedicated tracing techniques. On the other hand, we aim to validate the capacity of hybrid CFD turbulence models (SST-DES) to qualitatively and quantitatively transcribe the unsteady backflow phenomena of gaseous and particulate pollutants. The experimental and numerical results obtained allow us to draw the following two conclusions. First, the aeraulic behavior of gas and 5 μm aerosol is similar near the opening for our aeraulic conditions. Secondly, the capacity of SST-DES hybrid model to reproduce the backflow phenomenon is qualitatively and quantitatively validated. Experimental and numerical studies of the backflow phenomenon were finally carried out on a full-scale airlock with flexible vinyl walls. Preliminary works show that quantitative results obtained experimentally matches those obtained from numerical simulations
Al matrix composites reinforced by in situ synthesized graphene–Cu hybrid layers: interface control by spark plasma sintering conditions
Get PDFTremendous impacts are usually made by the synthesis method and consolidation technique on microstructure and interface of graphene/Al composites. In the present work, an in situ gel-precursor decomposition route is proposed for the one-step synthesis of graphene nanosheet (GNS) decorated with Cu nanoparticles in the form of hybrid layers encapsulating Al grains (designated as GNS–Cu/Al). Consolidation is performed by spark plasma sintering (SPS) using markedly different sets of maximum temperature and maximum uniaxial pressure (400 °C/400 MPa or 500 °C/100 MPa). The powder and dense samples are investigated by several techniques including thermal analysis, X-ray diffraction and electron microscopy. The microhardness and elastic modulus of selected GNS–Cu/Al composites are investigated and related to the microstructure and preparation conditions. Results demonstrate that the interface structure is primarily determined by the roles of GNS–Cu hybrid layers and finely controlled by SPS conditions. This work paves a novel way to elucidate the evolutions of metal-decorated graphene hybrids in Al matrix composites