Portail des publications scientifiques IMT Mines Alès
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Flame spread experiments on a horizontal preheated black PMMA plate
No full textInternational audienceThe current work addresses flame spread experiments on a horizontal 1.2 m long black poly(methyl methacrylate) (PMMA) plate to collect data that aim at supporting the calibration or validation of pyrolysis models. A second main purpose of the thirteen tests that were carried out in this work, is to study the impact of the plate preheating on the pyrolysis (mass loss rate, MLR) and the flame spread velocity (Vf). The preheated plate temperature, Tpp, is considered in the 20-180 °C range. Temperature measurements performed in and above the black PMMA plate allowed to assess Tpp and Vf, respectively. All tests show that Vf reaches a steady value over a plate length that reduces when Tpp increases. An opposed flow flame spread is revealed for tests conducted at Tpp < 150 °C while the flame spread regime changes for tests performed at Tpp ≥ 150 °C. A temperature dependence of the steady Vf according to a power law is also highlighted. Measurements of the total heat flux and the length of flame heating were also performed and contributed to show the consistency of the empirical spread law with the Quintiere's flame spread model
Specification of Affordances in the Global Array (Chapter 9)
No full textInternational audienceThe theory of the global array claims (1) that lawful, 1:1 specification exists, making it possible for perception to be direct and (2) that such specification exists solely in the global array, that is, in patterns that emerge from relations between different forms of ambient energy. In this chapter, we focus on lawful, 1:1 specification of affordances. We claim that such specification exists, but that it exists solely in the global array. We argue that all affordances are specified solely in patterns in the global array, including higher-order affordances relating to culture, customs, conventions, language, and other aspects of so-called higher cognition. Thus, we claim that sensitivity to patterns in the global array is necessary and sufficient for direct perception of all affordances
Hydrological regime shifts in Sahelian watersheds: an investigation with a simple dynamical model driven by annual precipitation
No full textInternational audienceAbstract. The Sahel, the semi-arid fringe south of the Sahara, experienced severe meteorological droughts in the 1970s–1980s. During and after these droughts, watersheds in the Central Sahel have experienced an increase in the annual runoff coefficient (annual runoff normalized by annual precipitation). We hypothesize that these increases correspond to regime shifts. To investigate the timing of these regime shifts, we introduce a lumped model that represents feedbacks between soil, water and vegetation at the watershed scale and the annual time step. This model relies on runoff coefficient as a constraint for the state variable and precipitation as unique external forcing. Four watersheds (Gorouol, Dargol, Nakanbé and Sirba), with pluri-decennial observations (1950s–2010s), are modeled. For each watershed, one million parameterizations of this model are sampled and run, and an ensemble of one thousand best parameterizations is selected based on observed runoff coefficients. Our results show that this model can reproduce the trend of runoff coefficients. For all watersheds, almost all selected parameterizations from the ensemble are bistable. We define two alternative runoff coefficient regimes (a low and a high regime) by splitting with a threshold the bifurcation diagram of bistable parameterizations. Most selected parameterizations undergo regime shifts: simulated runoff coefficients belong to the low regime in 1965 and to the high regime in 2014. Finally, we find that the year of the regime shift, defined as the year when the number of regime shifts is maximized, was 1971, 1972, 1973, 1983 for the Gorouol, Nakanbé, Dargol and Sirba watershed, respectively. These results were obtained with a parsimonious model which deliberately neglects fine-scale processes of Sahelian hydrology. It would therefore be wise to supplement this analysis with other models – with varying levels of complexity – that also allow regime shifting. Overall, this article proposes simple ideas toward improving the modelling and characterization of hydrological regime shifts
Equilibrium partition coefficients of semi-volatile organic compounds (SVOCs) between indoor surfaces and air assessed using two experimental methods
No full textInternational audienceIndoor exposure to semi-volatile organic compounds (SVOCs) is affected by their sorption onto indoor surfaces such as clothes, toys, building materials and furniture. They are transferred from these contaminated surfaces to the body via various routes such as skin contact, inhalation or hand-to-mouth transfer. Knowledge of their sink surface/air partition coefficients KSurf are needed to apply indoor fate models and assess occupants’ exposure to SVOCs.Partition coefficients of triphenyl phosphate (TPP), 2-ethylhexyl diphenyl phosphate (EHDPP) and 1,2-cyclohexane-dicarboxylic acid, dinonyl ester (DINCH) on cotton, glass and stainless steel (SS) surfaces were experimentally determined using two different methods. In the Micro-Chamber/Thermal Extractor (M-CTE), Kcotton values were close to 104 m. For this method, improvements were proposed to investigate the sorption on surfaces having lower sorption capacities such as glass or SS. In the sandwich-like emission cell, Kglass and KSS values ranged from 20 to 465 m, and from 99 to 1570 m, respectively. In coherence with the literature, sorption on cotton was higher than on SS and glass. Moreover, based on literature data, the SVOC vapor pressure (VP) could be a good predictor of KSurf for non-porous surfaces such as SS and glass. For porous surfaces (cotton), additional parameters related to the surface (porosity or composition) should be used with VP. Strong sorption capacity of cotton reinforces the health risk posed by contaminated clothes. This study highlights the need for further research to understand the key parameters of SVOC sorption on textiles
Experimental and numerical investigation of the hygrothermal behaviour of various building limestones
No full textInternational audienceThis study investigates the hygrothermal behaviour of six French limestones commonly used in construction. An extensive experimental program was carried out to characterize their mineralogical, microstructural, thermal, and hydric properties. The results reveal clear relationships between pore structure and hygrothermal performance. The capillary absorption coefficient increases with the volume fraction of pores larger than 2 μm, confirming the key role of pore size in liquid transport. Water vapour permeability decreases exponentially with tortuosity, highlighting the combined effect of pore connectivity and pore size distribution. Thermal conductivity decreases with increasing total porosity following a geometric-mean relationship, as described by the Woodside and Messmer model, while volumetric heat capacity shows a linear correlation with dry apparent density. Despite compositional similarities, significant variability in performance is observed among the stones. Under transient climatic conditions, coupled heat and moisture simulations – based on the Künzel model – closely match experimental temperature measurements and reasonably capture humidity variations. Minor discrepancies are attributed to sorption hysteresis, not accounted for in the modelling. The quantified links between hygrothermal properties and pore structure provide valuable insights for the selection and simulation of natural stone in energy-efficient envelope design
Multi-period replenishment planning with supplier assignment under a dynamic demand and stochastic lead-times
No full textInternational audienceWe consider a multi-period replenishment planning problem with dynamic demand and multiple suppliers. Each supplier has its own selling price and random lead time. The objective is to decide how the demands for different periods are distributed among the pre-selected suppliers while minimising the expected total cost, which comprises holding and backlogging costs, as well as the selling price. This statement highlights the trade-off between supplier prices and uncertain lead times in replenishment planning. Two scenario-based stochastic programmes, one linear and one non-linear, are provided to simultaneously consider dispatching orders between suppliers, order crossover, and order release flexibility. The non-linear model, which relies on power sets to reduce the number of aggregated scenarios, is coupled with two approximate solution methods. The numerical experiments prove the computational effectiveness of the non-linear model. These results can be helpful for decision-makers when negotiating prices with suppliers. For instance, we can determine the purchasing cost at which we order almost 100% from a given supplier. If we now turn to the uncertainty of lead times, this study can also help negotiate with suppliers whose firms cannot decrease their selling prices and advise them, thereby reducing the variance of their lead times
Functionalized cellulose for enhanced uranium(VI) and thorium(IV) sorption: Mechanisms and performance
No full textInternational audienceHerein, an efficient functionalized cellulose-based sorbent (F-Cel) was synthesized via chlorination followed by 1-amino-2-naphthol-4-sulfonic acid grafting. Comprehensive characterization (via CHN analysis, XRD, XPS, pHPZC, SEM-EDX) validated successful functionalization and revealed critical structure-property relationships. The sorption efficiency exhibited strong pH-dependence, peaking at pH 3.5 for Th(IV) and 4.5 for U(VI). Kinetic equilibria occurred at 90 min (Th(IV)) and 120 min (U(VI)), adhering to pseudo-first-order (Cel) and pseudo-second-order (F-Cel) kinetics, reflecting their distinct surface functionalities. The F-Cel achieved superior sorption capacities (0.716 mmol/g for Th(IV) and 0.655 mmol/g for U(VI) at 298 K) compared to Cel (0.341 mmol/g for U(VI) and 0.309 mmol/g for Th(IV) at 298 K). This represents a ∼2.1-fold and ∼2.3-fold increase in capacity for Th(IV) and U(VI), respectively. This leap stems from synergistic –SO₃H (ion-exchange) and–OH/–NH₂ (chelation) groups, contrasting Cel’s physisorption, as conclusively validated through multispectral mechanistic analysis. Thermodynamically, F-Cel exhibits spontaneous endothermic sorption for both metals, contrasting Cel's exothermic behavior. U(VI) shows > 86 % desorption efficiency in NaHCO3/HCl with stable recyclability over 7 cycles (<14 % capacity loss), demonstrating robust regeneration potential. Moreover, functionalization boosts Th(IV) affinity, evidenced by a higher distribution coefficient (DTh = 3.064 L/g vs. DU = 0.293 L/g), and an exceptional selectivity separation coefficient (SCTh/U= 10.7), representing about 5.4 × fold improvement over Cel
Evaluation and modeling of barrier layer efficiency for flame retardant PE-EVA systems containing low-melting phosphate glasses using a double layer setup
No full textInternational audienceThe improvement of the flame-retardant properties of the outer sheath in optical cables is driven by the increasing packing density of cable architectures, the reduction in polymeric sheath thickness, and the demand for higher fire safety in densely installed environments. In this work, a dedicated methodology was established to evaluate the efficiency of barrier layers in flame-retardant cable sheath compounds. First, cone calorimetry and pyrolysis-combustion flow calorimetry (PCFC) data were combined to characterize the behavior of monolayer systems. These characterizations were then complemented by a bilayer configuration, where two key descriptors were defined: the slowdown factor (Sf) and the time-shift (δ), quantifying the ability of a barrier to attenuate and delay heat and mass transfer. Application of this methodology to polyethylene–ethylene vinyl acetate (PE–EVA) systems incorporating aluminum trihydrate (ATH) and low-melting phosphate glasses (LMGs) highlighted the superior performance of a potassium phosphate glass with a low glass transition temperature (∼165 °C) with Sf2 = 3.8 and δ = 565 s due to the strong expansion of the residue. Depth temperature analyses confirmed that the expanded mineral residue effectively limited heat penetration from the outer to the inner layer. The approach was further extended to ternary formulations, where 10 wt.% vermiculite reinforced the barrier, achieving Sf2 = 5 and δ = 572 s, while other synergists produced less efficient protection. These results demonstrate that the proposed methodology provides a reliable framework to quantify and compare barrier-layer efficiency, offering new insights into the condensed-phase mechanisms governing flame retardancy of cable sheath materials
Proof of concept for manufacturing of composite tapes with household PolyEthylene Terephthalate (PET) as matrix
No full textInternational audienceNew recycling method for PET is investigated by manufacturing thermoplastic tapes using recycled PolyEthylene Terephthalate (PET) as matrix. PET, which is widely used in the packaging industry, especially for bottles, remains a challenge due to the degradation of its properties during mechanical recycling. Faced with these challenges, a new recycling method for PET is investigated by manufacturing recycled and recyclable thermoplastic tapes using recycled PET as matrix. The process is based on a dissolution-precipitation method inspired by the phase inversion membrane technique. A solubility theory have been used to identify the best solvent/non-solvent combinations.Experimental results show the efficiency of three solvents: Trifluoroacetic Acid (TFA) , Hexafluoroisopropanol (HFIP) and Gamma-Valerolacone (GVL) combined with water and ethanol as non-solvent and evaporation to dissolve and precipitate PET in the fibrous reinforcement to create the thermoplastic tape. Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) analyses show that the chemical structure of PET has been preserved. SEM images reveal the influence of the choice of solvent/non-solvent combination on porosity and pore distribution in the material.Proof-of-concept studies carried out with TFA and HFIP suggest that the HFIP/ethanol combination is the most suitable for minimizing degradation and maximizing the matrix content in the fibrous reinforcement. This work therefore lays the foundations for the development of this new recycling method as part of a move towards a circular economy and a reduction in the impact of composite materials, which are difficult to recycle