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Modeling and optimal control of fast filling process of hydrogen to fuel cell vehicle
No full textInternational audienceDue to the rapid compression of hydrogen and the Joule-Thompson effect specific to hydrogen during the fast filling process, the internal temperature of the cylinder rises sharply which may lead to hidden safety hazards. In this study, a high-pressure hydrogen filling process is considered, and a simple mathematical model of a cascade storage system of a hydrogen refilling station is developed to analyze the temperature rise in hydrogen cylinders under different working conditions. The results show the pressure switching coefficient has a great impact on the filling time, and the pre-cooling of hydrogen has a significant impact on the temperature rise and the states of charge (SOC) within cylinder. Herein, a multi-objective iterative optimization algorithm is proposed to calculate the above two controllable variables (pressure switching coefficient, pre-cooling temperature of hydrogen) with the objectives of faster refueling, lower energy consumption and higher SOC within cylinders in cascade hydrogen refueling. Besides, this method could significantly decrease energy consumption, improve SOC and allow acceptable refueling time
Predicting the flowability of powder mixtures from their single components properties through the multi-component population-dependent granular bond number; extension to ground powder mixtures
No full textInternational audienceThe granular Bond number, defined as the ratio between interparticle attractive forces and particle's weight, can be computed to predict the flow behavior of powders. Previous studies used this dimensionless number to predict the flowability of various pharmaceutical or ceramic powders, exhibiting polydispersed particle size distributions. In this paper, we employ a multi-component population-dependent granular Bond number in order to apply this model to powder mixtures. Some binary and ternary mixtures are prepared using two different techniques: a Turbula® mixer and a ball mill. The flowability predictions appear to be in very good agreement with the empirical measurements, carried out with a powder shear tester. However, the model parameters seem to be slightly different between milled and raw powders. The model discussed in this paper allows a prediction of the flowability of powder mixtures according to their composition and serve as a guide for product formulation and equipment design
A comparative study of the crystallinity of Polyetheretherketone by using density, DSC, XRD, and Raman spectroscopy techniques
No full textInternational audienceA comparative study of the crystallinity of Polyetheretherketone by using density, DSC, XRD, and Raman spectroscopy techniques.In this work, the microstructure of Polyetheretherketone is first analyzed with usual techniques such as density, Differential Scanning Calorimetry, X-ray Diffraction, and secondly, compared with Raman Spectroscopy. Assessing the degree of crystallinity of PEEK is challenging because of the different interpretation of the crystallinity according to each technique. The density measurement gives the highest most trusted absolute uncertainty for the degree of crystallinity, around 4%, compared to the other techniques. The Differential Scanning Calorimetry, usually used by the polymer community, overestimates up to 18% the degree of crystallinity due to a competitive phenomenon between crystallization and melting of PEEK over the same temperature range, and a fast crystallization. When Analyzing the X-ray Diffraction data, the degree of crystallinity is underestimated up to 11% as a consequence of the broad amorphous halo. Lastly, our investigation proves that Raman microspectroscopy is appropriate to determine the local crystallinity on the sample surface and compares 18 indicators in the same study. The 1651band shift has the highest correlation coefficient of 0.92 with the degree of crystallinity determined by density. This work attempts to correlate the results of degree of crystallinity of PEEK obtained by these four techniques in order to establish the best evaluation of this fundamental property for numerous applications
Binary and ternary alkali polyphosphates (MPO3, M = Li, Na, K) for thermal energy storage
No full textInternational audienceUp-to-date, solar salt (a mixture of 60 mass% NaNO3 and 40 mass% KNO3) is practically the only media for thermal energy storage (TES) in concentrated solar power (CSP). This commercial product’s utilization is limited below 550 °C to avoid an irreversible thermal decomposition. The development of new performing TES materials is decisive for the deployment of CSP technology. Our recent work reported promising results obtained with mono-alkali polyphosphate (M-PO3) as TES materials. These materials can work up to around 900 °C, but their melting point is still high, which is at least 628 °C. In order to lower their melting point, binary and ternary mixtures of alkali polyphosphates are investigated in this work. Dif- ferent mixtures made of two or three alkali polyphosphates were prepared and studied using thermal analysis methods. The most promising mixture found in this work was the ternary Li-Na-K-PO3, which contained 33.3% (mol%) of each alkali metal. This mixture can be used as a liquid TES material in the temperature range of 398 to 900 °C. The results open new prospects for the development of the thermal energy storage field
Role of Non-metallic Inclusions and Twins on the Variability in Fatigue Life in Alloy 718 Nickel Base Superalloy
No full textInternational audienceNon-metallic inclusions (NMIs) and slip bands parallel to and slightly offset from twin boundaries are observed to be preferential sites for fatigue crack nucleation in wrought superalloys. Potential interactions between NMI cracking and slip activity within neighboring grains or at twin boundaries were investigated under monotonic tensile loading (up to 1.3% total strain) at room temperature. High resolution- and Heaviside-digital image correlation measurements were performed during interrupted tensile loading to identify strain localization, associated slip systems, and damage initiation. Different mechanisms and scenarios were identified: (1) Microplasticity generally starts at twin boundaries even at stresses as low as 70% of the macroscopic yield strength, (2) transgranular slip activity intensively develops above the macroscopic yield stress, (3) intense slip activity develops near and parallel to 21% of the twin boundaries intercepting NMIs, (4) 7% of the twin boundaries intercepting NMIs lead to slip-assisted NMI cracking, (5) no transgranular slip activity participates in NMI cracking, (6) the fraction of cracked NMIs progressively increases with the load, and (7) within the NMIs that initiated cracks, 67% cracked below 90% of the macroscopic yield strength without the presence of slip activity in the neighboring grains. While slip-assisted NMI cracking was evidenced in the present study, most NMI cracking is due to strain incompatibility between NMIs and neighboring grains at the high end of the elastic regime without slip interaction
Enhancement of nifedipine solubility in supercritical carbon dioxide: role of co-solvents
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Modeling the reactive PA6 flow for LCM processes
No full textInternational audienceFiber reinforced thermoplastic composites have shown to be attractive for industry as they can be reused, reshaped, welded and repaired, while keeping mechanical properties on par with thermoset composites. Since thermoplastics usually have high melt viscosities unsuitable for liquid composite molding processes, in-situ synthesis of PA6 from ε-caprolactam is considered. Its reactive mix has low viscosity which allows impregnation. However, the coupled crystallization and polymerization affects the resin viscosity and its flow is altered by the dual-scale permeability of the fiber preform. Thus, to predict the local differences in the thermoplastics properties, a coupled polymerization crystallization model needs to be integrated in the LCM processing simulation at representative scales. This study aims to propose a reliable simulation of the resin flow through a fibrous preform. Hence, viscosity measurements on the reactive mix are achieved using a rheometer with parallel-plate geometry, aiming to associate a viscosity model with the Hillier coupled polymerization-crystallization model previously determined by Vicard. The full chemorheological model will then be integrated into a simulation of LCM process in OpenFOAM®, an open source CFD software in order to follow the extent of the synthesis in the resin flow during the process. As a future work, simulations including microscale tow information extracted from a real textile specimen will permit to investigate the effect of permeability and double scale porosity in fibrous preforms on the final polymerization rate and crystallinity
Physics of Decision: Application to Polling Place Risk Management
No full textInternational audienceManaging a system involves defining, assessing and trying to reach objectives. Objectives are often measured using Key Performance Indicators (KPIs). In the context of instability (crisis, global pandemic or just everyday uncertainty), managers have to adapt to multi-dimensional complex situations. This article introduces an innovative approach of risk and opportunity management to help managers in their decision-making processes. This approach enables managers to deal with the considered system's performance trajectory by viewing and assessing the impact of potentialities (risks and opportunities). Potentiality impacts are designed by forces, modifying the system's performance trajectory and its position within its multi-dimensional KPI framework. This approach is illustrated by an application to polling place risk management. This paper presents the results of simulations of a such place confronting pre-identified risks within a KPI framework
A User Interface for Consistent AHP Pairwise Comparisons
No full textInternational audienceDecision Makers generally reason on several criteria, aiming to obtain a total consistency or partial order of several alternatives. MultiCriteria analysis is based on the assumption that such ordering exists. Decision Makers are supported by several kinds of approaches or tools. One approach consists in comparing the criteria two by two, i.e. pairwise comparison, to find the relative importance of each criterion. This relative importance, called weight of criteria, is used to find the final order of alternatives. One methodology, developed by Saaty, called Analytical Hierarchical Process (AHP), is based on this principle of pairwise comparison. Having the weights of criteria, the decision makers have then to compare the alternatives two by two for each criterion. Pairwise comparisons are simple to use; however, as the number of items to compare increases, so do the effort of conducting all comparisons and the probability of introducing inconsistencies. In this article we present an innovative approach to conduct pairwise comparisons based on a UI widget that resembles an interactive data plot. It uses the transitivity property of a consistent comparison matrix to infer comparisons. Our hypothesis is that this new approach is more efficient (as it reduces the number of actions the user must conduct to compare all items), more effective (as it limits the sources of inconsistencies), and yields better user satisfaction. We conducted a controlled experiment involving 50 participants. We observed that the proposed widget reduces the effort of making pairwise comparisons, improves the consistency of the comparisons, and leads to a better user experience
Atomic Supply Chain Modelling for Risk Management based on SCOR
No full textPart 16: Sentient Immersive Response NetworkInternational audienceAt the time of instability becomes the norm (climate changes, natural disasters, epidemic, etc.) the management of collaborative networks, such as supply chains, is becoming more and more complex and critical. This instability only adds to the complexity of an already very complex system. Thus, supply chain managers have to adapt to multi-dimensional complex situations. Dealing with instability is a key expectation for these managers. One tool to help managers make decisions in this unstable environment is simulation. This article introduces some first results on an “atomic” reconfigurable supply chain simulation model based on Supply Chain Operations Reference (SCOR) model. This simulation tool will be used to apply an innovative physics-based approach of risk and opportunity management, that designs disturbances by forces moving the considered supply chain within its performance framework. This approach enables managers to monitor supply chain’s performance trajectory by viewing and merging the impact of risks and opportunities