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Thermal investigations of supercritical CO 2 jet impingement and its cooling applicability in a machining context
No full textInternational audienceIn recent years, the use of supercritical carbon dioxide (sCO2) as cutting fluid during machining operations has gained attention of the manufacturing community. The present paper intends to address thermal characteristics of sCO2 free jet impingement on a hot plate. An experimental approach has been hereby chosen in order to assess the heat transfer coefficient (HTC) in various experimental conditions. Infrared thermography along with high speed imaging are set up in order to access the cooling of a titanium plate. HTC is then calculated from an analytical solution of the heat transfer equation adapted to the specific conditions of the proposed setup.Investigations are focused on the influence of nozzle-to-plate distance (from 4 to 106 times jet diameter), angle of incidence (from 90° to 50°) and flow initial temperature (40 ◦C to 80 ◦C) and pressure (100 bar to 285 bar).Results provide with metric and dimensionless values of the HTC. Preliminary conclusions are drawn from the presence of solid carbon dioxide at the plate’s surface and leads are proposed to investigate in further detail the effect of the jet nature and structure on its cooling ability
Achieving tunable and interconnected porosity of biomimetic apatite scaffolds through Pickering emulsion templates
No full textInternational audienceSynthetic apatitic calcium phosphates are widely used to develop biomaterial devices due to their excellent biological properties. The aim of this study was to develop nanocrystalline apatitic calcium phosphates (NCA) bioceramics with tunable porosity (size of pores, total porosity percent) to preserve surface reactivity and improve bioactivity based on an original manufacturing process. For this purpose, a low-temperature method of elaboration via Pickering emulsions was used and the influence of several process parameters (emulsion-to-gel weight ratio and formulation of the emulsion) on the properties of the bioceramics was studied. This process allows the formation of NCA crystals–based materials as shown by X-ray diffraction and FTIR spectroscopy. The initial conditions of the emulsion control the final porous structure evidenced by X-ray micro-computed tomography: if the diameter of the droplets of the starting emulsions controls the pores size, it does not influence the total porosity percent and interconnection which depend only on the emulsion-to-gel ratio. The viability of the scaffolds was assessed using the osteoblast cell line in two steps: cell adhesion assays and photobiomodulation. None of the scaffolds showed cytotoxic effects. With the proposed process, scaffolds were obtained with controlled pore size and interconnected pores, composed of reactive biomimetic apatites with mechanical properties suitable for applications in filling bone defects and good osteoblastic adhesion and proliferation properties
A prospective vision of the evolution of immersive technologies: Towards a definition of metaverse
No full textInternational audienceThis article focuses on identifying and describing the current status of immersive technologies, to project them, from this initial point, towards the near future, by considering the evolutionary trajectory of these technologies based on mechanisms of progress and innovation. The ambition of this study is then on the one hand to describe a next point of arrival for these technologies, but above all to confront it with the current vision of the concept of the metaverse, and even to extract a more completed and structured vision. The conclusions of the article underline the compatibility between the potential evolution of present immersive technologies and the current vision of the concept of metaverse. Moreover, a metaverse framework is presented to consolidate and structure this concept. Finally, the framework is broken down into the properties inherent to the nature of a metaverse and evaluated through two real cases relating to crisis management training and immersive teaching
Optimisation of the control curves of load-changing nuclear power units taking into account thermal stress
No full textInternational audienceBesides the increasing share of uncontrollable renewables in the energy mix, the consumption/production balance of the grid must be permanently assured. Additionally, the successive stopping of traditional, fossil-fuelled power plants necessitates the controllability also of nuclear power plants. The major drawback of the load-following operation of such units is the side effect of load changes. They are, namely, carried out via non-stationary transitions, during which the temperature changes result in thermal stresses. The most critical, practically unchangeable part of the plant is the reactor pressure vessel, which is a thick-walled component of complex geometry. Hence, determining the optimal curves of the unit’s available control inputs is a crucial issue. For this, several tools are needed, such as a dynamical model of the entire power unit, a dynamical description of the thermal stress in the most critical points, a practical system of criteria of the optimisation condition, and numerical method for seeking the optimal pathway. The results demonstrate that optimised actuator trajectories can reduce thermally induced stress in the nozzle corner of the reactor pressure vessel during load-following operation
A Hybrid Machine Learning Model for Predicting Surgical Procedure Duration: Integrating Random Forest and K-Means Clustering
No full textInternational audienceEfficient operating room (OR) management depends on the accurate prediction of surgical procedure durations to improve scheduling, enhance patient outcomes, and reduce operational costs. This study presents a hybrid machine learning model that combines Random Forest and K-Means clustering to predict the duration of cholecystectomy procedures. The model is trained using real-world data from the digestive surgery department at Mahmoud El Matri Hospital in Tunis, Tunisia, incorporating patient demographics, surgeon experience, and other contextual factors. Synthetic data generation was also applied to reinforce model reliability. The proposed approach achieved strong performance, with a root mean square error (RMSE) of 0.45 minutes, a mean absolute error (MAE) of 0.36 minutes, and a coefficient of determination (R2) of 0.99. Comparative analysis with individual models such as Random Forest, K-Means, decision trees, and linear regression confirms the hybrid model’s superior predictive capability. These results demonstrate the potential of the proposed hybrid model as a practical tool for optimizing OR scheduling and improving healthcare resource management
In-plane and out-of-plane compressive properties of regular and graded cellular cores of sandwich panels fabricated by additive manufacturing
No full textInternational audienceCellular materials with a gradient of properties become appealing as cores of the sandwich panels due to the possibility of improving strength and absorbed energy in lightweight components. 2D cellular structures designated by honeycombs have an anisotropic behaviour when loaded under in- and out-plane. Thus, when proposing new designs, it is essential to analyse how the in-plane arrangement with a gradient in cell wall thickness affects in-plane and out-of-plane mechanical properties. This work aims to study graded cellular structures in comparison with regular hexagonal honeycombs. Structures were manufactured by laser powder bed fusion using an aluminium alloy. Regular arrangements were formed with cells with the same thickness, while graded structures possessed a radial gradient of cell thickness. Three types of innovative gradients, where cell length varies radially along concentric layers, were analysed. The compressive properties of regular and graded structures were evaluated when loaded both under in-plane and out-of-plane conditions. Compression behaviour was assessed, both experimentally and by numerical modelling. Even though there is a mismatch between numerical and experimental results, they exhibit the same trends. All graded samples showed an increased mechanical performance when loaded under out-of-plane conditions in comparison with the results from tests under in-plane loading with values, for example, of stiffness four hundred times larger, absorbed energy around thirty times higher and with yield stress four times larger. The results showed that the graded samples attain higher values of strength, stiffness and absorbed energy in comparison with regular hexagonal honeycombs, for the same relative density
Biocarbon Emissions and Risks Assessment in Pyrolysis and Combustion
No full textInternational audienceDecarbonization of society requires industry to urgently reduce carbon-based and toxic gas emissions, such as polycyclic aromatic hydrocarbons (PAH), to mitigate their environmental impact and associated health risks. Biocarbon (Biochar), due to its properties closer to those of coal and the biogenic nature of its emissions, is a renewable alternative to replace fossil fuels in industrial processes. In this context, the objective of this work is to determine gaseous emissions fate and toxicity in pyrolysis and combustion for biocarbon from solid refuse fuels (SRF, named BC1) and 2 biocarbons from wood with different H/C ratios and volatile matter (VM) content (WBC1, WBC2). The obtained results were correlated to resource characteristics and compared with standard values reported for fossil fuels. Emission factors (EF, ggas/gfuel) were calculated for the main permanent gases (CO, CO2, H2, CH4), as well as for PAH. Biocarbons EF were directly related to their physicochemical characteristics, namely their VM content and, to a lesser extent, their inorganic composition, catalyzing or inhibiting thermochemical conversion reactions. High VM content biocarbon (WBC1, 18.5 wt%) was associated with higher EF values (i.e., 3696 gCO2/kgfuel). However, EF(CH4+H2) values at pilot scale met EN ISO 562 standard (<4 wt%) both in pyrolysis (2.8 wt% yield for WBC1) and combustion (0.07 and 0.3 wt% for WBC2 and BC1, respectively). Although PAH released by high VM content biocarbon (WBC1) were less toxic due to their lower number of aromatic rings (<3), they presented a higher EF (46.3 mgPAH/kgfuel) than that reported for fossil fuels (0.002–64.0 mgPAH/kgfuel). As a result, the toxicity equivalent factor (TEQ), associated with the carcinogenic potential of a PAH and its yield, was higher for biocarbon (WBC1, 0.132) compared with fossil fuels (0.005–0.03). Most importantly, reduce condensable species production, and, consequently, lower EF values for permanent gases were measured (2000–2980 gCO2/kgfuel) in combustion, and no PAH was detected, resulting in a lower TEQ
High-pressure acid leaching of laterite ores: Effect of acid and solid content on Ni and Co yield under non-isothermal and isothermal conditions
No full textInternational audienceThe increasing demand for nickel (Ni) in electric vehicle batteries necessitates efficient extraction methods fromlaterite ores. High-Pressure Acid Leaching (HPAL) is a prominent hydrometallurgical technique known for itsrapid kinetics and high (>90 %) metal dissolution. This study examines the influence of acid-to-ore (A/O) ratios(0.25, 0.35, and 0.45) and slurry solid contents (22, 26, and 30 wt.%) on Ni yield and selectivity under both non-isothermal (100 ◦C, 1.2 bar; 150 ◦C, 4.7 bar; 200 ◦C, 18.9 bar; 265 ◦C, 50.5 bar) and isothermal (265 ◦ C)conditions.Under non-isothermal conditions, Ni leaching efficiency improved with temperature, achieving a maximumyield of 94.67 ± 0.02 wt.% at 265 ◦C, compared to 50.86 ± 0.02 wt.% at 200 ◦C, using an A/O ratio of 0.45 and26 wt.% solids over 60 min. Isothermal experiments at 265 ◦C revealed that higher A/O ratios enhanced Ni yield,reaching 94.45 ± 0.01 wt.% at 60 min with 26 wt.% solids and an A/O of 0.45. However, this increased yieldwas accompanied by higher dissolution of Fe (1.07 ± 0.12 wt.%) and Al (38.84 ± 0.07 wt.%), reducing selec-tivity to 0.73 ± 0.01. Conversely, an A/O ratio of 0.25 at 26 wt.% solids achieved a higher selectivity of 3.83 ±0.05 but with a lower Ni yield of 79.14 ± 0.03 wt.%. Lower slurry solid content further improved Ni leaching; at22 wt.% solids and an A/O of 0.45, Ni yield reached 95.87 ± 0.01 wt.% with a selectivity of 0.89 ± 0.02 at 60min.Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) analyses of leached residues indicated thathigh temperatures facilitate the transformation of primary minerals like goethite and gibbsite into hematite andhydronium alunite. This transformation is more pronounced at higher A/O ratios, affecting the mineralogicalcomposition of the post-leach solid residue
Packing of spheres by clusters of regular tetrahedra configurations
No full textInternational audienceWe study the packing of monodisperse spheres generated by setting spheres into contact of three spheres in mutual contact. The network obtained by connecting the centres of the spheres is a cluster of regular tetrahedra glued face to face. In a previous study, we investigated the case of a unique cluster built by aleatory placing a new sphere to fill as much as possible a spherical container [de Ryck, Granular Matter (2023) 25:42]. We extend here the investigation to the case of a cluster limited by periodic boundary layers. The mean packing fraction and the close contact interdistance distribution are found to reach a plateau if the smallest boundary layer length is higher than a threshold value around five times the spheres diameter, independently on the relative values of the boundary layer lengths
Configuration of heterogeneous robot fleets for mission planning: A constraint programming-based approach
No full textInternational audienceWith the increasing autonomy of robots and the variety of tasks they are now able to perform, they are increasingly used in complex and critical missions. This paper focuses on the problem of configuring robot fleets for mission planning. In our work, planning a mission, before its execution phase, is based on solving three intrinsically linked configuration problems: the agent configuration problem, denoted ACP, the agent fleet configuration problem, denoted FCP and the mission plan configuration problem, denoted PCP. In this paper, we consider mission planning as a single problem, composed of three interdependent subproblems. A constraint programming (CP) model is proposed for the global problem. Our model is evaluated on the IBM ILOG CP Optimizer solver and on sixty-four artificially generated Search & Rescue instances