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The Influence of In-Cavity Pressure on Heat Transfer and Porosity Formation During High-Pressure Die Casting of A380 Alloy
No full textAccès à la correction de cette publication : https://doi.org/10.1007/s11837-020-04341-yNature de la correction : "This article was updated to correct the spelling of A. Hamasaiid’s name."International audienceThis paper is concerned with the measurement of thermal properties and in-cavity pressures in cold chamber high-pressure die casting. The influence of in-cavity pressure on the casting porosity, heat flux, and heat transfer coefficient has been investigated during die casting of an A380 alloy. The die was instrumented with heat transfer and pressure sensors to measure these values directly. Direct measurement of the in-cavity pressure was found to be more reliable than the metal pressure calculated from pressure measurements in the hydraulic system. Variations on the intensification pressure directly affect the in-cavity pressure. Changing the intensification pressure between 17 MPa and 90 MPa had little effect on the heat flux and heat transfer which likely reach saturation at a lower pressure during the rapid filling stages. Increases in intensification pressure reduced the level of porosity within the castings, being most effective up to a value of 67.4 MPa
Improving the logistic process of orders dispatching through a multi-criteria decision-making perspective
No full textInternational audienceFar from being a mere production-oriented mission, competition among companies has to be considered as a much wider concept, largely based on effective supply chain management. Implementing suitable supply chain strategies is indeed crucial for enterprises seeking to strengthen their own position in the market against their competitors. With this recognition, one of the main issue in the logistic field is the suppliers and orders management, that is a complex decision-making problem depending on a wide set of aspects mutually correlated and often conflicting each other. This is the reason why assuming a Multi-Criteria Decision-Making (MCDM) perspective is useful to deal with the topic of interest. In particular, the present paper is aimed at sorting out a real world case study about distributing and dispatching orders, through a MCDM approach based on the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). On the one hand, this method is proposed to prioritise the vehicles used to transfer orders, by taking into account criteria such as pallet capacity, tailgate presence, energy type and so on. On the other hand, a final ranking of orders to be delivered will be achieved under the evaluation of aspects such as loading/unloading time, kind of vehicle and driver, among others. Final results will be helpful to establish a degree of priority in assigning orders to vehicles and their robustness will be checked by performing a sensitivity analysis on criteria weights
Effect of spraying parameters on surface roughness, deposition efficiency, and microstructure of electric arc sprayed brass coating
No full textInternational audienceThermal, chemical, and metallurgical surface treatment techniques are being applied to give materials the desirable properties for numerous applications in service. Nowadays, electric arc spraying of copper alloys has gained importance in surface engineering owing to their excellent mechanical properties. However, electric arc sprayed metallic coating usually has high coating roughness and low deposition efficiency upon adherence to the substrate. In this article, the brass coating was deposited onto a mild steel substrate using a twin wire arc spraying technique. The spraying parameters current, voltage, and spray off distance were varied during the deposition process. To gain an understanding, the effect of these spraying parameters on the characteristics of the coating was investigated in terms of its surface roughness, deposition efficiency, and microstructure. The primary purpose of this research is to optimize the process in terms of coating roughness and deposition efficiency. Based on the results obtained, it was observed that an increase in voltage and spray off distance resulted in an increase in coating roughness, whilst an increase in current resulted in a decrease in coating roughness. Deposition efficiency was also greatly affected by the process parameters and decreased significantly with the longer spray off distance. Furthermore, the deposition efficiency increased with the decrease in surface roughness and vice versa. The best results in terms of low coating roughness, high deposition efficiency, and optimized microstructure were found at 24V, 240A, and 100 mm. The use of small diameter feedstock, supersonic nozzle incorporated in equipment, better surface preparation, and optimized process parameters gave better results as compared to the previous study in the field of electric arc spray coating
Experimental and numerical analysis of a packed-bed thermal energy storage system designed to recover high temperature waste heat: an industrial scale up
No full textInternational audienceAn industrial-scale air-ceramic horizontal packed-bed thermal energy storage (Eco-Stock®) has been designed and built by Eco-Tech Ceram and tested during an experimental campaign of 500h. The goal is to provide experimental data and analysis of a horizontal and containerized packed bed TES at high temperature, with performance indicators specific to waste heat recovery. A single charge-discharge at 525°C and 3 cycles at 500°C were carried out (300 kWTh for charge, 350 kWTh for discharge). The unit was able to store up to 1.9 MWhTh in a TES system (1.7 × 1.7 × 3.08 m3) composed by 16-ton of bauxite ceramic media. The packed bed was able to valorize up to 90% of the heat source, which demonstrates the system ability to recover waste heat up to 525°C at industrial scale. No channeling effect and moderate radial thermal gradient were detected, even though the tank had a horizontal geometry. The plug and play TES presents a non-negligible part of its energy stored in the insulant, which can be recovered during discharge. To take into account such phenomenon, a one-dimension 3 temperature model is proposed. The model fitted well with experimental results, with a root mean standard deviation of the model below 20°C for the temperature profiles
Microwave-assisted dry reforming of methane for syngas production: a review
No full textInternational audienceAbatement of emissions of greenhouse gases such as methane and carbon dioxide is crucial to reduce global warming. For that, dry reforming of methane allows to convert methane and carbon dioxide into useful synthesis gas, named 'syngas', a gas mixture rich in hydrogen and carbon monoxide. However, this process requires high temperatures of about 900 degrees C to activate methane and carbon dioxide because dry reforming of methane reaction is highly endothermic. Therefore, a solid catalyst with appropriate thermal properties is needed for the reaction. As a consequence, efficient heating of the reactor is required to control heat transfer and optimize energy consumption. Microwave-assisted dry reforming of methane thus appears as a promising alternative to conventional heating. Here we review the recent research on microwave-assisted dry reforming of methane. We present thermodynamical aspects of the dry reforming of methane, and basics of microwave heating and apparatus. We analyse reformers that use microwave heating. Catalysts used in a microwave-assisted reformer are presented and compared with reactors using conventional heating. Finally, the energy balance is discussed
Mechanically Robust Antibacterial Nanopapers Through Mixed Dimensional Assembly for Anionic Dye Removal
No full textInternational audienceThere is a piqued interest in development of biobased sorbents for water treatment. Here in we reported, the fabrication of mechanically strong nanopapers by mixed dimensional assembly of 1D Cellulose nanofibers and 2D amino functionalized graphene oxide for water treatment. The fabricated amino functionalized GO/ cellulose nanofiber (AMGO-CNF) nanopaper showed superior antibacterial resistance towards Escherichia coli MTCC 1610 and Klebsiella due to the enhanced surface roughness which was confirmed from SEM and AFM studies. The amino group present in the AMGO enhanced the adsorption efficiency of the nanopaper towards methyl orange dye. The fabricated nanopaper showed an adsorption of 11.05 mg/gm 30 mg/L concentration at pH 2. Maximum adsorption was observed at pH 2 which was due to protonation of amine group. Moreover, the fabricated membrane showed excellent hydrolytic stability which can be corroborated to the surface roughness and reduced hydrophilicity. The investigation into the surface chemistries of cellulose nanofibers beyond the adoption of toxic solvents can enhance the economic usefulness of the process and yield a new eco-friendly adsorbent material that is agreeable to adsorbing various toxic pollutants
A robust method for mechanical characterization of heterogeneous materials by nanoindentation grid analysis
No full textInternational audienceThe study presents the analysis of the contour plots obtained from nanoindentation grids conducted on CuZn40Pb2 brass and W-Cu, which are heterogeneous materials having different microstructure and mechanical properties. The aim is to increase the detection capacity of the mechanical properties of the phases respect to the statistical analysis, but also to propose a formulation for the inverse analysis of nanoindentation data allowing the full elastoplastic characterization. Analysis of contour plots provides curves where the mean value of the phases and the bulk value can be read directly. In complex microstructures, this gives access to the predominant mechanical properties facilitating the interpretation of the results. The estimation of the phase fractions by this proposed method is better than the estimation performed with statistical analysis. The estimation of the standard deviation is equivalent to the statistical analysis in most cases; however the difference is large on skewed distributions. The formulation of the objective function for inverse analysis is able to manage large number of indentations, producing elastoplastic parameters with excellent accuracy compared to parameters identified by tensile test
High temperature oxidation of NiCrAlY coated Alloy 625 manufactured by selective laser melting
No full textInternational audienceThe high temperature oxidation of fully SLM-processed NiCrAlY coated Alloy 625 parts was investigated between 800 °C and 1000 °C. For comparison, bulk NiCrAlY and bulk Alloy 625 were also fabricated using SLM. Two thin layers of NiCrAlY powder were lasered at the surface of Alloy 625 to form the bi-materials. Bulk NiCrAlY and bi-materials showed an improved oxidation behavior compared to Alloy 625. The oxidation of the NiCrAlY coating results in regions with a dense and continuous external Al2O3 layer and regions composed of a mixture of external Cr2O3 and internal Al2O3. Large EDS maps at the surface and cross-sections of the bi-material highlighted a heterogeneous distribution of constitutive elements of the NiCrAlY coating, resulting in some regions with an Al activity lower than the one required for the formation of a continuous and dense Al2O3 layer (≤10 atomic percent). Low Al activity and high Al activity regions were related to the topography of the SLMed surface and correspond to hill and valley regions, respectively. In addition, cracks, mainly occurring in high Al activity regions, were observed across NiCrAlY specimens. The fabrication of coated but small components with a brittle coating by SLM is not trivial and needs further investigations
An experimental and simulation study of heteroaggregation in a binary mixture of alumina and silica colloids
No full textInternational audienceHeteroaggregation corresponds to an attraction between two different types of particles. It can either lead to stable or instable systems, depending on the conditions. In this paper heteroaggregation in binary mixtures of alumina and silica colloids (size ratio = 8.5) is studied, by coupling an experimental approach and Brownian dynamics simulations. Two main objectives are targeted. The first one is to bridge the gap between coagulation and dispersion, by examining the effect of the relative concentrations of silica and alumina. The second one is to study the effect of the volume fraction of solid, which impacts strongly the aggregation mechanism. The coagulation or the dispersion are evidenced by sedimentation tests, granulometry, and rheological measurements, supported by zeta potential measurements. Heteroaggregates could be observed by transmission electron microscopy. Brownian dynamics simulations give more insight into the very first moments of the process, to predict the adsorption kinetic and the heteroaggregates structure. A very good agreement is obtained between experiments and simulations, which both show adsorption of silica leads to the bridging of alumina particles and thus coagulation at low concentration. This adsorption is rapidly limited by electrostatic interactions, then hindering alumina agglomeration by repulsive interactions. For the higher solid fractions, alumina aggregation is more likely, as two alumina particles can easier encounter before their surface is enough covered by the silica to avoid their aggregation
Integrating alum sludge with waste-activated sludge in co-conditioning and dewatering: a case study of a city in south France
No full textInternational audienceThe unique geographical location of waterworks and wastewater treatment plant (WWTP) in Graulhet (France) profited the environmental resource integration and “Circular Economy.” Alum sludge from a local waterworks was introduced to co- conditioning and dewatering with waste-activated sludge from a nearby WWTP to examine the role of the alum sludge in improving the dewaterability of the mixed sludge. Experiments demonstrated that the optimal mixing ratio was 1:1 (waste- activated sludge/alum sludge, v/v). Alum sludge has been shown to beneficially enhance mixed sludge dewaterability, by decreasing both the specific resistance to filtration (SRF) and the capillary suction time (CST). Moreover, the optimal polymer (Sueprfloc-492HMW) dose for the mixed sludge (mix ratio 1:1) was 200 mg/L, highlighting a huge savings (14 times) in polymer addition without alum sludge involvement. In addition, cost-effective analysis of its potential full-scale application has demonstrated that the initial investment could be returned in 11 years. The co-conditioning and dewatering strategy can be viewed as a “win-win” strategy for the Graulhet, France, water and wastewater industry