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Thermal energy storage systems based on phase change materials are interesting candidates to handle the difficulties raised by intermittent renewable sources or by batch processes. Among these systems, many rely on the use of steam, as for instance in concentrating solar power plants or district heating, or in the pharmaceutical or food industries. Today, there is no systematic method to design such systems quickly and easily since complex heat transfer is observed due to the influence of the geometry and to the dual characteristics associated with solid/liquid and liquid/gas transitions. The aim of the present work is thus to propose a multi-scale modelling methodology of a latent heat storage system for the storage of steam. It mainly involves two different simulation models with different scales for the heat transfer fluid and the phase change material. Furthermore, it relies on the use of a heat transfer correlation based on specific non-dimensional numbers, which is deduced from previous simulations of the phase change material’s behavior, obtained with fine 3D computational fluid dynamics calculations. Consequently, a reduced model is built to simulate the whole system. This model does not need to be tuned against experiments. This model is then directly used to compare the numerical results with measurements coming from a prototype scale latent heat storage available at CEA Grenoble. The results are very promising and show that an a priori approach that is more physically consistent and not based on any model tuning can lead to acceptable results. Moreover, the computational time can be divided by 10–40, thus allowing future design and real performance evaluations of latent heat storage modules.

International audience; The last few years have seen the proliferation of anaerobic digestion plants to produce biomethane. Oxygen (O2) traces added to biogas during the desulfurization process are co-injected in the gas network and can be stored in Underground Gas Storage (UGS). However, there are no data available for the undesirable effects of O2 on these anoxic environments, especially on deep aquifers. In addition to mineral alteration, O2 can have an impact on the anaerobic autochthonous microbial life. In our study, the storage conditions of an UGS aquifer were reproduced in a high-pressure reactor and bio-geo-chemical interactions between the aqueous, gas and solid phases were studied. Sulfate was depleted from the liquid phase for three consecutive times during the first 130 days of incubation reproducing the storage conditions (36 °C, 60 bar, methane with 1% CO2). Sulfate-reducers, such as Desulfovibrionaceae, were identified from the high-pressure system. Simulations with PHREEQC were used to determine the thermodynamic equilibrium to confirm any gas consumption. CO2 quantities decreased in the gas phase, suggesting its use as carbon source by microbial life. Benzene and toluene, hydrocarbons found in traces and known to be biodegradable in storages, were monitored and a decrease of toluene was revealed and associated to the Peptococcaceae family. Afterwards, O2 was added as 1% of the gas phase, corresponding to the maximum quantity found in biomethane after desulfurization process. Re-oxidation of sulfide to sulfate was observed along with the end of sulfate reducing activity and toluene biodegradation and the disappearance of most of the community. H2 surprisingly appeared and accumulated as soon as hydrogenotrophic sulfate-reducers decreased. H2 would be produced via the necromass fermentation accomplished by microorganisms able to resist the oxic conditions of 4.42·10-4 mol.Kgw-1 of O2. The solid phase composed essentially of quartz, presented no remarkable changes.

This thesis deals with the thermal comfort of precast concrete panels incorporating phase change materials (PCM). Beyond providing an answer to one of the important issues in the fight against climate change, namely the energy consumption of buildings, the proposed solution is bio-sourced and therefore fits into an approach beyond these objectives.Concretely, it is a question of developing a thermal energy storage concrete (TESC) by adding to an ordinary concrete composite lightweight aggregates (cLWA), made up of LWA impregnated with a low cost biosourced PCM. Three types of mineral LWA were used (bentonite, sepiolite and silica gel), as well as two impregnation methods, namely direct impregnation and vacuum impregnation. The selected PCM is a vegetable oil, whose phase change is located around 23-26 °C. The microstructure and morphology of the cLWAs were analyzed by SEM, while the chemical compatibility was determined with FTIR. TESCs were prepared either by simple addition or by replacing a base component (sand or gravel) with cLWA. The thermo-physical properties of PCM and cLWA were obtained using DSC, while the thermal characteristics of TESC were evaluated with the so-called hot guarded plate experimental setup. The best impregnation rates were obtained with silica gel, but mechanical tests showed that sepiolite should be preferred. Despite a loss of mechanical strength, it is shown that TESCs with a compressive strength greater than 7-10 MPa are feasible. It is also shown that an improvement of 24.4% and greater than 13.5% is achievable for energy storage capacity and thermal conductivity, respectively. Next, the evaluation of the thermal performance of a test cell called TESC- S25-b-Cell designed with lightweight concrete wall panels in which the sand, which represents 25% of the total volume, is replaced by the same volume of cLWA-S. This cell was subjected to the vagaries of climatic variations over a few days at the same time as another cell, of the same dimensions, with ordinary concrete walls called C-R-Cell, for comparison purposes. The measurements concerned the air temperature inside and outside the cells, the temperature of the walls as well as the heat fluxes exchanged at the level of the walls and the quantity of heat absorbed by these walls. Our experiments, carried out mainly in summer, showed an increase in the thermal capacity of the envelope by the addition of PCM, leading to a decrease in the interior temperature of the cells. This effect, which is positive for the thermal comfort of the cells, is accompanied by a reduction in the thickness and therefore the weight of the wall panels compared to ordinary concrete wall panels.; Cette thèse porte sur le confort thermique de panneaux en béton préfabriqué intégrant des matériaux à changement de phase (MCP). Au-delà d’apporter une réponse à l’un des enjeux importants dans la lutte contre le dérèglement climatique, à savoir la consommation énergétique des bâtiments, la solution proposée est bio-sourcée et donc s’inscrit dans une démarche dépassant ces objectifs.Concrètement, il s’agit de développer un béton de stockage d'énergie thermique (TESC) en ajoutant à un béton ordinaire des agrégats légers composites (cLWA), constitués de LWA imprégnés d'un MCP biosourcé à faible coût. Trois types de LWA minéraux ont été utilisés (bentonite, sépiolite et gel de silice), ainsi que deux méthodes d'imprégnation, à savoir l'imprégnation directe et l'imprégnation sous vide. Le MCP retenu est une huile végétale, dont le changement de phase est situé autour de 23-26 °C. La microstructure et la morphologie des cLWA ont été analysées par MEB, tandis que la compatibilité chimique a été déterminée avec une FTIR. Les TESC ont été préparés soit par simple ajout, soit en remplaçant un composant de base (sable ou gravier) par le cLWA. Les propriétés thermo-physiques du MCP et du cLWA ont été obtenues au moyen d’une DSC, tandis que les caractéristiques thermiques du TESC ont été évaluées avec un montage expérimental dit des plaques chaudes gardées. Les meilleurs taux d'imprégnation ont été obtenus avec du gel de silice, mais les tests mécaniques ont montré que la sépiolite devait être préférée. Malgré une perte de résistance mécanique, il est démontré que des TESC avec une résistance à la compression supérieure à 7-10 MPa sont réalisables. On montre également qu'une amélioration de 24,4% et supérieure à 13,5% est réalisable pour la capacité de stockage d'énergie et la conductivité thermique, respectivement. Ensuite, ont été évaluées les performances thermiques d'une cellule d'essai appelée TESC-S25-b-Cell conçue avec des panneaux muraux en béton léger dans lequel le sable, qui représente 25% du volume total, est remplacé par le même volume de cLWA-S. Cette cellule est soumise aux aléas des variations climatiques sur quelques jours en même temps qu'une autre cellule, de mêmes dimensions, avec des murs en béton ordinaire appelés C-R-Cell, à des fins de comparaison. Les mesures ont porté sur la température de l'air à l'intérieur et à l'extérieur des cellules, la température des parois ainsi que les flux thermiques échangés au niveau des parois et la quantité de chaleur absorbée par ces parois. Nos expériences, réalisées principalement en période estivale, ont montré une augmentation de la capacité thermique de l'enveloppe par l'ajout de MCP, conduisant à une diminution de la température intérieure des cellules. Cet effet, positif pour le confort thermique des cellules, s'accompagne d'une réduction de l'épaisseur et donc du poids des panneaux muraux par rapport aux panneaux muraux en béton ordinaire.

International audience; Experimental CO2 solubility data in brine at high temperatures and pressures are important for CO2 capture and storage (CCS) applications. Many data have been acquired in single-salt aqueous solutions such as NaCl, CaCl2, and Na2SO4. CO2 solubility data in aqueous solutions containing MgCl2 are extremely scarce. In this work, new experimental data of CO2 solubility in MgCl2 solutions were acquired. Thirty-three experimental points of CO2 solubility have been reported in an original range of pressure (1.5 to 20 MPa), temperature (323.15, 373.15, and 423.15 K), and salinity (1, 3, and 5 mol/kg). Measurements were made using the potentiometric titration method. Results show that the CO2 solubility increases with the evolution of pressure and decreases with the evolution of MgCl2 concentrations. A discussion about the salting-out effect on MgCl2 solutions is made, and a comparison is proposed on the same effect in aqueous systems containing calcium chloride.

International audience; This article contributes to the development of a thermodynamic model for simulating CO2 solubility in pure water and aqueous brines under different conditions of temperature, pressure and ionic strength. The modeling activity-fugacity (γ-φ) approach allows calculating CO2 solubility, based on the Pitzer electrolyte theory for activity coefficient and Peng-Robinson's equation of state for fugacity. The present work proposes a new set of Pitzer interaction parameters through the set of CO2 solubility data in saline systems such as CO2-H2O-NaCl and CO2-H2O-Na2SO4. The determined model is capable of covering a wide T − P − I range (273.15–473.15 K, 0.1–40 MPa and 0–6 mol/kg). Average absolute deviation of CO2 solubility is about 5% compared to a large number of experimental data available (more than 700 data analyzed). New experimental solubility data for the CO2-H2O-NaCl-Na2SO4 system were also acquired in this study (303.15–423.15 K, 1.5–20 MPa and 0–6 mol/kg) to test the model's capacity: it is able to describe the CO2 solubility in aqueous salt mixtures without any further optimizations of interaction parameters.

Regarding the global warming caused by human activity and the urgent need to reduce greenhouse gas emissions, solutions to overcome the ongoing fossil fuels phase-out have to be found. District heating networks have already proved their relevance to mutualise and then enhance renewable resources that are inaccessible or difficult to access in urban areas, especially solar thermal energy. However they are still underdeveloped in the world today, especially in France. The use of such systems, which require important investments, is still low. One of the impediments to this development is the lack of tools and knowledge to optimize the integration of solar energy in multi-source district heating networks. The objective of this thesis, financed by ADEME and Region Nouvelle-Aquitaine in partnership with a consortium of companies, is to optimize the integration of solar thermal energy via an "open-access" tool that can be used to size and operate the heat production of such networks.The different production elements of a solar district heating network were modelled: a solar thermal field, two boilers (gas and wood) and a thermal storage. A dynamic multi-period approach was chosen in order to transform, by discretization, an algebro-differential model into an algebraic one. Likewise, a method for creating characteristic days was implemented in order to represent a year with a minimum number of days. The algebraic equations of the resulting model are non linear. All the variables are continuous. The chosen objective function is economic: the project partners provided the input data for an accurate economic model using non linear equations. Finally the formulated problem is a NLP (Non Linear Programming) problem. As non-linear optimization guarantees neither systematic convergence nor a global optimum, a solution strategy was developed to guarantee a confidence optimum.A first application case optimizing the sizing and operation of a new network using inter-seasonal storage was studied. The first results showed a certain robustness of the resolution strategy and converged towards a sizing that valorises the solar energy up to 50% of the total energy supplied over the lifetime of the installation, which was set at 20 years. Different storage connections were studied to conclude on the relevance of connecting the storage at the output of the solar field. Sensitivity analyses on the minimum renewable rate and the lifetime of the installation were carried out, highlighting that it is possible to greatly increase the renewable rate with moderate additional investments.In some cases (very dense urban area for example) the implementation of inter-seasonal storage and a large solar field may be impossible. Then, a second application case, an optimization of a new network using daily storage, was studied. This optimization led to a result where solar energy covers 12 % of the total energy supplied with a smaller solar field. These applications show that solar thermal can cover a large part of demand (>50%) when the use of inter-seasonal storage and a large solar field is possible, but that it also presents an interest in covering a smaller but nonetheless not insignificant part of the demand with daily storage.; L’objectif de ces travaux est de développer une méthodologie pour l'optimisation dynamique d'un système intégré incluant la production, le stockage et la distribution de chaleur. Un tel système est soumis à de nombreuses perturbations à différentes échelles de temps. L'objectif est donc de développer un outil d'aide à la conception d'un système dynamique complexe. Cette thèse vise dans un premier temps à développer un modèle dynamique du système global. Ensuite, le problème d'optimisation dynamique avec variables mixtes sera formulé puis résolu.

International audience; Deep aquifers (up to 2km deep) contain massive volumes of water harboring large and diverse microbial communities at high pressure. Aquifers are home to microbial ecosystems that participate in physicochemical balances. These microorganisms can positively or negatively interfere with subsurface (i) energy storage (CH 4 and H 2 ), (ii) CO 2 sequestration; and (iii) resource (water, rare metals) exploitation. The aquifer studied here (720m deep, 37°C, 88bar) is naturally oligotrophic, with a total organic carbon content of

International audience; The Inuit of the Canadian North live in isolated territories where there are no land routes. As a result, for the past few decades, they have been facing major adaptation challenges, particularly in terms of food and access to energy. Since June 2016, our research focuses on the potential of greenhouse farming in circumpolar territories with the case study of the cooperative greenhouse of Kuujjuaq (largest village in Nunavik in terms of population - 2375 inhabitants in 2011, latitude 58° north and longitude 68° west). Measurements in this greenhouse revealed a major problem: a temperature difference between day and night that was too large, hindering the development of crops. To address this, a thermal storage system was installed in October 2018. It is based on a rock bed of known porosity, positioned under the crop land, in which a heat transfer fluid that circulates, will allow the daily heat surplus to be stored during period with temperature peak, in order to reheat the greenhouse when the temperature in low, especially in the nighttime. The poster will focus on the performance of the system after two years of operation.; Les Inuits du Nord canadien vivent sur des territoires isolés où aucune route terrestre ne permet de se rendre. De ce fait, depuis les dernières décennies ils affrontent de grands défis d’adaptation, notamment sur le plan de l’alimentation et de l'accès à l'énergie. Notre recherche s’intéresse depuis juin 2016 aux potentiels de la serriculture dans les territoires circumpolaires, avec comme cas d’étude la serre coopérative de Kuujjuaq (plus grand village du Nunavik en termes de population – 2375 habitants en 2011, latitude 58° nord et longitude 68° ouest). L’instrumentation de cette serre a permis de mettre en évidence une problématique majeure : un écart de température entre le jour et la nuit trop important, gênant le développement des cultures. Pour y répondre, un système de stockage de chaleur a été mis en place en octobre 2018. Il est basé sur un lit de roche de porosité connue, positionné sous la terre de culture, parcouru par un flux d’air servant de fluide caloporteur. Ce dispositif permet de stocker le surplus de chaleur journalier afin de combler le déficit nocturne. Le poster se focalisera sur les performances du système après deux années de fonctionnement.

International audience; Around the world, several dozen deep sedimentary aquifers are being used for storage of natural gas. Ad hoc studies of the microbial ecology of some of them have suggested that sulfate reducing and methanogenic microorganisms play a key role in how these aquifers' communities function. Here, we investigate the influence of gas storage on these two metabolic groups by using high-throughput sequencing and show the importance of sulfate-reducing Desulfotomaculum and a new monophyletic methanogenic group. Aquifer microbial diversity was significantly related to the geological level. The distance to the stored natural gas affects the ratio of sulfate-reducing Firmicutes to deltaproteobacteria. In only one aquifer, the methanogenic archaea dominate the sulfate-reducers. This aquifer was used to store town gas (containing at least 50% H2 ) around 50 years ago. The observed decrease of sulfates in this aquifer could be related to stimulation of subsurface sulfate-reducers. These results suggest that the composition of the microbial communities is impacted by decades old transient gas storage activity. The tremendous stability of these gas-impacted deep subsurface microbial ecosystems suggests that in situ biotic methanation projects in geological reservoirs may be sustainable over time.

Due to the difficult access to their territories, Northern Canada’s Inuit have faced major adaptation challenges in recent decades, notably in terms of food and energy. Traditional food from hunting, fishing and gathering activities is increasingly difficult to obtain, while European and Canadian foods brought by air or by sea are increasingly expensive. Culture in greenhouses appears as a solution allowing to improve access to fresh vegetables by reducing the ecological and financial costs linked to the transportation of these.The scientific literature on the physical study of northern greenhouses and energetic data (temperature, electricity consumpion, etc.) is scarce. The first part of this thesis has to do with the pinpointing of northern greenhouses existing in North America and shows that this subject is relatively recent. On the other hand, this literature review revealed that the majority of counted greenhouses are not adapted to a cold climate, hence short growing seasons.The second part of this work focuses on the experimental aspect. Data coming from an instrumentation campaign in a northern greenhouse were analysed to demonstrate the relevance of the establishment of a daily thermal energy storage (TES) system. The dimensioning and construction of this system using air as a coolant fluid and local rocks as storage material are also presented. The instrumentation of the rockbed which stores heat has allowed to study energetical data during charge and discharge phases of the stock. This analysis demonstrated the positive impact of the set up of the TES system on the thermal behavior of the greenhouse.The last part of this work concerns the modeling of the thermal behavior of the greenhouse and the TES system. As a matter of fact, the numerical simulation of the climate in a greenhouse is basic in order to understand the improvement mechanisms of existing greenhouses and/or to optimize the conceiving of enclosures for vegetable production in a northern environment. Indeed, a nodal model of the greenhouse and an independent model of the TES system are detailed and validated. A process of calibration about the numerical values of the models’ parameters is also developed to improve the performances of these models.; Vivant sur des territoires isolés où aucune route terrestre ne permet de se rendre, les Inuits du nord canadien (Nunavik) font face, depuis les dernières décennies, à de grands défis d’adaptation, notamment sur le plan de l’alimentation et de l'accès à l'énergie. La nourriture traditionnelle issue des activités de chasse, de pêche et de cueillette est de plus en plus difficile à obtenir, tandis que les aliments euro-canadiens apportés par avion ou par bateau coûtent de plus en plus cher. La serriculture apparaît alors comme une solution permettant d'améliorer l'accès aux légumes frais en réduisant les coûts écologique et financier liés au transport de ces légumes.La littérature scientifique portant sur l'étude physique des serres nordiques et les données énergétiques (température, consommation d’électricité, etc.) sur le sujet sont rares. Dans un premier temps, nous avons recensé les serres nordiques existantes d'Amérique du Nord, et nous avons montré que le sujet est relativement récent. Par ailleurs, cette revue de littérature a révélé que la majorité des serres dénombrées ne sont pas adaptées au climat froid, conduisant à des saisons de cultures courtes. Ensuite, nous avons abordé l'aspect expérimental. Les données issues d'une campagne d’instrumentation de la serre nordique de Kuujjuaq ont été analysées afin de démontrer la pertinence de l'installation d'un système de stockage thermique journalier. Le dimensionnement et la construction de ce dernier, utilisant l'air comme fluide caloporteur et des roches locales en tant que matériau de stockage, sont également présentés. L'instrumentation du lit de roches stockant la chaleur a permis l'étude des données énergétiques durant les phases de charge et de décharge du stock. Cette analyse a démontré l'impact positif de l'installation du système de stockage sur le comportement thermique de la serre. Enfin, nous avons modélisé le comportement thermique de la serre et du système de stockage. En effet, la simulation numérique du climat sous serre est essentielle afin de comprendre les mécanismes d'amélioration des serres existantes et/ou d'optimiser la conception des enceintes de production végétale en milieu nordique. Ainsi, un modèle nodal de la serre et un modèle du système de stockage sont détaillés et validés. Un processus de calibration portant sur les valeurs numériques des paramètres des modèles est également développé afin d'en améliorer les performances.

International audience; The sustainability of the anaerobic digestion industry is closely related to proper digestate disposal. In this study, an innovative cascading biorefinery concept coupling anaerobic digestion and subsequent pyrolysis of the digestate was investigated with the aim of enhancing the energy recovery and improving the fertilizers from organic wastes. Continuous anaerobic co-digestion of quinoa residues with wastewater sludge (45/55% VS) exhibited good stability and a methane production of 219 NL CH4/kg VS. Subsequent pyrolysis of the solid digestate was carried out (at 500 °C, 1 h, and 10 °C/min), resulting in a products distribution of 40 wt% biochar, 36 wt% bio-oil, and 24 wt% syngas. The organic phase (OP) of bio-oil and syngas exhibited higher and lower heating values of 34 MJ/kg and 11.8 MJ/Nm3, respectively. The potential synergy of coupling biochar with liquid digestate (LD) for agronomic purposes was investigated. Interestingly, coupling LD (at 170 kg N/ha) with biochar (at 25 tons/ha) improved the growth of tomato plants up to 25% compared to LD application alone. In parallel, co-application of biochar with LD significantly increased the ammonia volatilization (by 64%) compared to LD application alone, although their simultaneous use did not impact the C and N mineralization rates.

International audience; The industrial sector is increasingly obliged to reduce its energy consumption and greenhouse gases emissions to contribute to the world organizations’ targets in energy transition. An energy efficiency solution lies in the development of thermal energy storage systems, which are notably lacking in the low-temperature range (50–85 °C), for applications such as district heating or low-temperature waste heat recovery. This work aims to bring a latent heat storage solution from material selection to prototype evaluation. The first part of this paper is dedicated to the characterization and aging of a phase change material selected from a screening of the literature (fatty acid mixture mainly composed by stearic and palmitic acid). Then, this material is encapsulated and tested in a prototype whose performances are evaluated under various operating conditions. Finally, a numerical model validated by the experimental results is used to explore the influence of a wider range of operating conditions, dimensioning choices, and material conductivity improvements.

International audience; Laminarization of a turbulent flow due to wall heating has been known for more than 50 years, to the point that it is sometimes used as means of reducing friction. However this phenomenon has been mainly studied for cylindrical pipes and with imposed heat flux but not for channel flows and with imposed temperature boundary conditions, especially with asymmetric ones (that is to say in presence of a transverse thermal gradient). Based on the recent success of some Reynolds-averaged Navier-Stokes (RANS) models to correctly describe the influence of a strong transverse temperature gradient on turbulent Poiseuille flows, when compared to similar direct numerical simulations (DNS) or large eddy simulations (LES) results, these approaches are used here to investigate reverse transition. Since the choice of turbulence model has a non-negligible influence on the results, however, it is necessary to use different models to get an indication of the uncertainty associated with them. The proposed methodology is based on the use of RANS closures that do not involve any wall functions due to the strong gradient in the wall layer that has to be modeled. Thus, two first-moment closures and a second-moment closure are considered: the k − ω − SST and the k − ε − v 2 /k, and the EB-RSM. The latter two rely on an elliptic blending. The turbulent heat flux is modeled with a simple gradient diffusion hypothesis (SGDH) and a generalized gradient diffusion hypothesis (GGDH) for the first-moment and second-moment closures respectively. In summary, more than 800 calculations are performed for the above three models in order to analyze the reverse transition, and to open room for debate on the possibility for such approaches to correctly reproduce the experimentally observed behavior.

This work presents a contribution to the latent heat thermal energy storage LHTES technology by working on both phase change materials PCMs and storage systems that are technically and economically viable for their integration in buildings. Regarding the PCM material, the urea and sodium nitrate eutectic mixture has been previously identified as a good candidate for the Domestic Heating Water (DHW) and heating applications. One of the main objectives of the PhD thesis was the characterization of these aspects to evaluate the urea and sodium nitrate eutectic mixture long term feasibility to be used as a PCM in application. The study of the material includes the development of methodologies that are more practical and representative of the operation in the final application than the traditionally used in PCM characterization. The characterization of the hygroscopicity or water uptake of the urea and sodium nitrate eutectic mixture under different conditions was performed. A sample preparation method and handling conditions are proposed for avoiding the mixture water uptake.The thermal degradation of the urea and sodium nitrate eutectic mixture was evaluated by measuring the thermo-physical behavior after exposure time at different defined temperatures. DSC measurements were carried out to determine the variation of parameters that are directly related to the thermal energy storage of the PCM and its long-term stability. In addition, the degradation products and their influence on the variation of the system properties were assessed.The eutectic mixture showed unforeseen segregation at temperatures above the melting point upon melting and solidification cycles. Several tests were done including thermal cycling, XRD of the segregates, DSC after the redissolution of the segregates in the liquid material, and microscopy (PLM and SEM) of samples cooled down under different conditions. The experiments permitted to stablish a relationship between the operation conditions, more specifically the cooling rates, with the resulting crystal structures which explains the phase segregation in the eutectic mixture, and how to reduce it and how to reverse the process.The study of the supercooling comprised the use of the urea and sodium nitrate eutectic mixture and PEG10000. The experiments were performed in different conditions: sample containers (with different geometries and volumes), cooling rates and heat transfer fluids (HTF) were implemented. Finally, the results served to evaluate the relationship of the supercooling degree with parameters associated with the sample volume, cooling media and PCM parameters. Afterwards, linear regression models were gathered for each material and one for both materials. The specific aim of the chapter is to get a step further into the supercooling understanding and prediction, in order to efficiently design LHTES systems to be used with materials that show supercooling.Finally, regarding the storage system a shell and tubes heat exchanger is studied in order to evaluate the use of devices already commercially available the use as latent heat energy storage LHTES devices. The first objective was to get a deeper understanding of the thermal behavior of the device. The characterization was performed using RT60 paraffin as PCM inside the shell, a well known commercial material, to assure the reproducibility of the results, and water as heat transfer fluid in the tubes. Several flow rates and temperature ranges were used to obtain a greater scope of the operation of the device as LHTES. The work included the determination of the thermal losses, and the study of charging and discharging cycles, initial and final temperatures and flow rates.; La technologie de stockage de l'énergie thermique par chaleur latente (LHTES) est abordée en travaillant à la fois sur les matériaux à changement de phase MCP utilisés et sur les systèmes de stockage techniquement et économiquement viables pour leur intégration dans les bâtiments. En ce qui concerne le matériau MCP, un mélange eutectique d'urée et de nitrate de sodium a été précédemment identifié comme un bon candidat pour les applications eau chaude sanitaire et chauffage. L'un des principaux objectifs de la thèse de doctorat était la caractérisation de ces aspects pour évaluer l’utilisation à long terme du mélange eutectique d'urée et de nitrate de sodium comme MCP. L'étude du matériau comprend le développement de méthodologies qui sont plus représentatives de son utilisation dans l'application finale que celles traditionnellement rencontrées pour la caractérisation des MCP. La caractérisation de l'hygroscopicité ou de l'absorption d'eau du mélange eutectique d'urée et de nitrate de sodium a été réalisée dans différentes conditions. Une méthode de préparation des échantillons et des conditions de manipulation sont proposées pour éviter l'absorption d'eau du mélange.La dégradation thermique du mélange eutectique d'urée et de nitrate de sodium a été évaluée en étudiant le comportement thermo-physique après un temps d'exposition à températures élevées. Des mesures DSC ont été effectuées pour déterminer la variation des propriétés directement liées au stockage de l'énergie thermique du MCP et à sa stabilité à long terme. En outre, les produits obtenus lors de la dégradation et leur influence sur la variation des propriétés du MCP ont été étudiés.Le mélange eutectique a montré une ségrégation imprévue à des températures supérieures au point de fusion lors des cycles de fusion et de solidification. Plusieurs tests ont été effectués, notamment le cyclage thermique, la diffraction par rayons X des phases due à la ségrégation, DSC après la redissolution de ces phases dans le matériau liquide et la microscopie (PLM et MEB) d'échantillons refroidis dans différentes conditions. Les expériences ont permis d'établir une relation entre les conditions de fonctionnement, et les structures cristallines résultantes qui expliquent la ségrégation de phase dans le mélange eutectique, et la manière de la réduire et d'inverser le processus.L'étude de la surfusion comprenait l'utilisation de deux MCPs : l’eutectique urée - nitrate de sodium et le PEG 10000. Les expériences ont été réalisées dans différentes conditions: des récipients de géométrie et de volume différents, diverses vitesses de refroidissement et divers fluides de transfert thermique. Les résultats ont servi à évaluer la relation entre le degré de surfusion et les paramètres associés. Après, des modèles de régression linéaire ont été définis pour chaque matériau puis pour les deux matériaux. L'objectif spécifique de ce chapitre est de faire un pas de plus dans la compréhension et la prédiction de la surfusion, afin de concevoir efficacement des systèmes LHTES utilisant des matériaux qui peuvent présenter une surfusion.Enfin, en ce qui concerne le système de stockage, un échangeur de chaleur à tubes-calandre est étudié afin d'évaluer l'utilisation de ce type de dispositifs déjà commercialisés comme dispositifs de stockage de l'énergie thermique latente (LHTES). Le premier objectif était de mieux comprendre le comportement thermique de l’échangeur. L’étude a été réalisée en utilisant, dans la calandre, de la paraffine RT60 comme MCP, un matériau commercial bien connu assurant ainsi la reproductibilité des résultats, et de l'eau comme fluide de transfert de chaleur dans les tubes. Plusieurs débits et plages de température ont été envisagés pour réaliser l’étude complète du fonctionnement de l’échangeur. Le travail a inclus la détermination des pertes thermiques et l'étude des cycles de charge et de décharge avec différentes températures initiales et finales et différents débits.

This paper presents the simultaneous optimization of the design and operation in nominal conditions of a geothermal plant where the geothermal fluid is split into two streams to feed an Organic Rankine Cycle (ORC) and a District Heating Network (DHN). The topology of the DHN is also investigated. A Mixed Integer Non-Linear Programming (MINLP) optimization problem is formulated and solved using the GAMS software in order to determine the ORC sizing and the DHN topology. In this study, only R-245fa is used as ORC working fluid, an optional Internal Heat Exchanger (IHE) is considered in the ORC and consumers in DHN can be definite or optional. A multi-objective optimization is performed by maximizing the annual net profit and minimizing the total exergy losses in the plant. The weighted sum of objective functions is used to solve the problem. By varying the weight factor, a Pareto front is obtained and the distance to the ideal, but infeasible, solution enabled to choose the best compromise. Four different DHN topologies are observed depending on the weight factor. Using a suitable criterion to make a decision, the selected configuration corresponds to the most expanded DHN with the smallest value of profit. A sensitive analysis shows that, in case of lower geothermal temperature, it is possible to obtain a unique DHN topology whatever the weight factor.

International audience; A novel prototype of a microcalorimetric cell with in-situ stirring has been developed to per-form DSC measurements under atmospheric or pressure conditions. After a brief technical description of the apparatus, preliminary tests are presented which analyzed the influ-ence of the stirrer rotation on the heat-flow signal. Experiments were then performed with complex fluids such as ice slurries and clathrate hydrates formed with cyclopentane and with carbon dioxide. They took place in stirred and non-stirred conditions and the results obtained were then compared. It was proven that the rotation of the microstirrer in the measuring cell does not disrupt the heat-flow signal during the analysis. As regards the prac-tical applications tested, the in-situ stirrer efficiently reduces crystallization metastability, increases the water-to-hydrate conversion, and reduces the amount of time needed for anal-ysis. The dissociation enthalpy of cyclopentane (CP) hydrates was measured at atmospheric pressure; it is effectively very difficult to analyze this system with non-stirred calorimetry techniques because the two liquid phases are immiscible. The experimental results, in good agreement with other data found in the literature, showed complete water-to-CP hydrate conversion within a short period of time using a simple protocol. Experiments were also performed under pressure to demonstrate that CO2 hydrate phase equilibrium data could be obtained rapidly and easily. It is therefore our opinion that the potential of this novel technology has been thoroughly demonstrated.

International audience; In this work, numerical simulations are carried out to characterize the impact of obstacles on flame propagation velocity to properly assess the consequences of Unconfined Vapor Cloud Explosions (UVCE).Within this scope, an UVCE within a congested environment is simulated using RANS modeling of the turbulence. Combustion phenomena are characterized through the progress variable transport equation. The simulation is done with the open source library OpenFoam. Numerical results are compared with data from the INERIS and GDF-SUEZ experimental campaign EXJET (hydrogen-air and methane-air explosions).

This research focuses on the potential of greenhouse cultivation in circumpolar territories. It begins with a survey that encompasses most of the northern greenhouses in North America. This review emphasizes the need for appropriate data and for the right energy system design. Next, the paper focuses on a case study located in Nunavik, which is the northern Inuit territory of the province of Quebec. The Kuujjuaq cooperative greenhouse has been instrumented since June 2016 to collect data on temperature and relative humidity throughout the growing season. These measures have highlighted a major problem: a temperature difference between day and night that is too large, hindering crop development. To counteract this thermal behavior, a heat storage system was designed, built and installed in October 2018. It is the first time that a rock and air-based sensible thermal energy storage system, taking into account local materials and resources, has been designed and built in a northern greenhouse. This paper presents its main characteristics as well as records of temperature changes throughout the growing season. Moreover, an energy balance is presented for three days at the beginning of June 2019.

International audience; After press separation of the liquid and solid digestate from an agricultural biogas plant, pyrolysis of solid anaerobic digestate was carried out (i.e., at 500 • C, 1h, and 10 • C/min) to produce biochar (37.6 wt%), bio-oil (33.7 wt%) and syngas (29.3 wt%). The organic phase of bio-oil and syngas exhibited high and low heating values of 28.4 MJ/kg and 12.9 MJ/Nm 3 , respectively. Then, the synergy of coupling biochar with liquid digestate for agronomic purposes was investigated by leaching experiment and growth plant tests on wheat. Leaching experiments using combination of liquid digestate (170 kg N/ha) and biochar demonstrated that biochar addition increases the cumulative leaching of all nutrients, except nitrate, that have a significant decrease of 82% and 91%, respectively at 50 and 100 t/ha, compared to soil treated only with liquid digestate. The co-application of biochar with liquid digestate on growth wheat plant tests demonstrated that biochar application at 50 t/ha did not exhibit a negative impact on the relative seed germination and improved aerial dry biomass production (up to 27.5%) compared to soil with only liquid digestate addition.

International audience; Les Observatoires Hommes-Milieux (OHM, dispositifs du LabEx DRIIHM créés à l’initiative duCNRS) étudient les interrelations société–environnement interrogées suite à un événementfondateur anthropique qui a produit une réorganisation de l’ensemble du socio-écosystème initial.Cet article s’intéresse à la mise en oeuvre, aux rôles et fonctionnement d’un de ces OHM, l’OHMiNUNAVIK, développé depuis 2014 en contexte autochtone dans l’Arctique canadien au Nord duQuébec. L’OHMi NUNAVIK tend à développer un cadre de recherche holistique et intégrateurfaisant tomber les barrières entre disciplines d’une part, et types de savoirs (scientifiques /autochtones) d’autre part. Il vise ainsi à créer une structure de recherche innovante en Arctiquepar le prisme (i) des représentations arctiques des Inuits et des Qallunaat, (ii) les collaborationsentre chercheurs, gestionnaires territoriaux et habitants. L’objectif de l’OHMi NUNAVIK portesur l’acquisition de connaissances et de nouvelles manières de les produire afin d’identifier lesimpacts cumulatifs des programmes de développements économiques du Nunavik et des PlansNord successifs du Québec depuis 2011, et des changements socio-environnementaux globauxsur cette aire d’étude. Au total, sept projets de recherche se déploient au sein de l’OHMiNUNAVIK ; quatre d’entre eux (Nuna, Kingaq, Niqiliriniq et Siqiniq) sont ici mobilisés pourillustrer le fonctionnement de l’OHMi NUNAVIK, les techniques d’observations utilisées, lescollaborations produites.

International audience; The geological storage of carbon dioxide CO2 in deep saline aquifers hasbeen gaining interest to reduce greenhouse gas emissions. Thus, the number of studiesfocusing on the solubility of CO2 in brines at high temperature and high pressure hasbeen increasing in the last decades, but information remains scarce particularly at highsalt molality. In this work, an analytical method was developed for experimentalmeasurement of CO2 solubility in sodium sulfate (Na2SO4) solutions (1 and 2 mol/kg)at high pressures (1.5−20 MPa) and temperatures (303.15, 323.15, 373.15, and 423.15K). Forty-eight experimental points of CO2 solubility are reported here. Solubility hasbeen shown to increase with pressure evolution and decrease with temperature andNa2SO4 concentrations evolution. A discussion is proposed about the salting-out effectin Na2SO4 solutions, and a comparison is made with the same effect in aqueous systemscontaining sodium chloride (NaCl) and calcium chloride (CaCl2).

The conditioning stage is a key parameter for enhancing the efficiency of sludge dewatering. However, the choice of the conditioning procedure (type of flocculant, dosage, mixing conditions) remains a current difficulty. A new index (called drainage index) was introduced to optimize conditioning parameters specifically for sludge thickening on draining table and by extension for sludge dewatering in belt filter press. This easy and quick to measure index was tested via lab-scale drainage experiments. Drainage performance was measured in terms of particles capture rate, final sludge dryness and drainage kinetics. The drainage index allowed to select optimal flocculation conditions prior to gravity drainage. Its relevance to select flocculation conditions insuring a good sludge compression was also demonstrated (except for the polymer selection) from tests carried out in lab-scale filtration–compression device.

International audience; A large part of Li production comes from the exploitation of saline lakes and salars. Industrial processes for Li recovery from such resources have to deal with highly saline waters. It is therefore necessary to develop the knowledge of Li chemistry adapted to these contexts. The present work aims to present a new set of Pitzer interaction parameters able to describe the chemical behavior of the H-Li-Na-K-Ca-Mg-Cl-H2O system up to salt solubility, at 25 °C. In a previous work, the model was limited to the H-Li-Na-K-Cl-H2O system. It is extended here by including Ca and Mg, taking into account recently revised parameters allowing the thermal properties of the binary CaCl2-H2O and MgCl2-H2O systems to be represented. The consistent extension of the thermodynamic database was made possible by the study of the binary CaCl2-H2O system up to the supersaturated metastable region and of nine ternary systems, namely X-Ca-Cl, X-Mg-Cl and Ca-Mg-Cl (where X = H, Li, Na, K). The model was finally tested on five quaternary systems.

ACL; International audience; This paper discusses the impact of nanofluids and vapor grooves position on the performance of capillary evaporators. The phase change that occurs within the wick structure is simulated using a 2D transient mathematical model. The model combines Darcy’s law, Langmuir’s law, and energy equations to describe the heat and mass transfers inside the wick and the metallic wall. A comparison with experimental visualizations and numerical simulations is proposed. The analysis was performed for water and aluminum oxide nanoparticles with three volume concentrations of nanoparticles. Also, the effect of the vapor grooves configuration on the capillary evaporator performance is studied. The numerical results show that substituting water with nanofluids had a significant effect in reducing the evaporator temperature and the pressure drop in the whole loop. The present work has also shown that the contact between the metallic wall and the wick is an important element that must be taken into account in the design of the evaporator.

International audience; The composition of the captured CO 2 mixture may considerably vary both qualitatively and quantitatively depending on the sources, the selected technologies for purification... Many other compounds could be co-captured at various concentration levels and their potential co-storage along with CO 2 could be considered. Since these compounds may change the behavior of the CO 2 rich mixture, operators of the whole CCTS chain therefore wait for Jerome Corvisier et al. / Energy Procedia 114 (2017) 3322-3334 3323 clear recommendations in terms of admissible concentration levels for the various co-injected impurities while regulators need tools allowing them to formulate these recommendations. The SIGARRR project aims at conducting precise geochemical simulations to model the long-term behavior of co-injected gases within CO 2 storage sites based on a combination of experimental and numerical approaches, to ensure the reliability of numerical simulations. Within this context and the recent improvements in both processes and geochemical codes, this paper presents the water solubility precise calculations for CO 2 and most of the potential impurities N 2 , O 2 , Ar, CO, H 2 S, SO 2 , CH 4 , H 2 and the brine solubility relatively accurate geochemical simulations for CO 2 , N 2 , O 2 and CH 4 as well.

Compared to conventional extractive techniques, bacterial assisted leaching, also called “biomining” is an eco-friendly technology that provides improved metal/solid separations. These separations are enhanced by the synergistic activities of astonishingly diverse groups of microorganisms, which lead to an extraction process with low energy consumption, low capital investment and low impact on the environment. Recently, biomining has received great attention in a variety of niche areas, especially in the mineral industries and solid industrial waste materials (e.g. galvanic sludge, sewage sludge, fly ash, electronic waste, spent petrochemical catalysts, medical waste, spent batteries, waste slag) where the metals values are low, or where the presence of certain elements would lead to smelter damage, or where environmental considerations favor biological treatments options. It allows the recovery of metal from low-grade sulfide ores and concentrates that cannot be processed economically by conventional techniques, as well as the production of concentrated metal salt solutions, which could be recycled. Bacterial assisted leaching processes are based on the ability of certain microorganisms to solubilize/or expose the metals contained in the ores and concentrates by direct oxidation, or through indirect chemical oxidation instigated by the corrosive metabolic by-products generated by an electrochemical option, or a combination of both of these. The valuable metals in solution can be recovered using conventional hydrometallurgical techniques. If the material of interest constitutes part of or is in the pre-treated residue then it can be further processed for metal recovery. The majority of microorganisms involved in bacterial assisted leaching processes are chemolithotrophs. Carbon dioxide (CO 2 ) and oxygen (O 2 ) are essential nutrients that are used by microorganisms for their growth, maintenance, metabolite production, and survival. This literature review aims to provide a fundamental understanding of the various mechanisms involved in microbial leaching of sulfide minerals and provide a brief look at the various factors affecting this process. Special attention is focused on the mass transfer rates in the gas phase and how they exert a pivotal role in microbially assisted leaching of sulfide minerals. Also reviewed are the major parameters that can affect gas phase mass transfer, with particular emphasis on how it is related to the efficiency of bacterial assisted leaching.

Phase change materials (PCM) used in thermal energy storage systems present high storage capacity and require low temperature variation to allow effective heat charge or discharge density. However, these materials involve too low thermal conductivities ( −1 K −1 ) which can limit the heat transfer power between the heat transfer fluid and the phase change zone. In the first part of this study, high power level composites made of PCM (organic and also inorganic) and graphite have been elaborated in the thermal range from 50 to 350 °C in order to increase the effective thermal conductivity. In a second part, the assessment of their use as solar absorbers has been realized. Results show that these composites present high absorptance with respect to the whole solar radiation spectra. This allows new potentiality of integration of such materials in solar thermal processes offering a direct management of heat variation at the very first step of the process.

Building and furniture materials are known to be major sources of volatile organic compounds (VOCs) indoors. During the construction process, an introduced material can have a more or less long-term impact on the indoor air quality according to the building characteristics. In this study, field measurements were carried out at six construction stages in three energy-efficient timber-frame houses. Data analysis focused on the ten most abundant compounds found among an initial list of fifteen target VOCs, namely formaldehyde, acetaldehyde, hexanal, toluene, m/p-xylenes, ethylbenzene, styrene, α-pinene, 3-carene and D-limonene. The chemical compositions and concentration variation patterns were recorded. The results showed a high pollution count, with m/p-xylenes and ethylbenzene concentrations ranging from 1900 to 5100 μg m−3 occurring at the time of the structural work (representing more than 88% of the sum of the target VOCs). Emission tests done on a large number of materials used in the construction revealed that this pollution is due to the emissions from the polyurethane adhesive mastic used as a sealing material. The emission kinetics of polyurethane adhesive mastic was assessed alone and also within a material assembly reconstituting a room wall. The results showed that the superposition of materials led to a slowing down of the VOC emission process from polyurethane adhesive mastic, which explains the concentration decays recorded in houses during the construction process. At the final construction stage, the concentration levels were low for all compounds (the sums of the target VOCs were between 18 and 32 μg m−3), with the aldehydes (formaldehyde, acetaldehyde and hexanal) now becoming the major fraction in the chemical composition in the last stages of construction (representing 50–70% of the sum of the target VOCs). This is in agreement with the fact that the sources of aldehydes are the most numerous among the materials and have rather slow emission kinetics.

The design sizing of heat exchangers in geothermal installations requires a good knowledge of geothermal fluids and gas/liquid equilibrium. The efficiency of heat exchangers is affected by the presence of gas. It is therefore essential to avoid degassing. Thermodynamic models are used to describe gas/liquid equilibrium. Nevertheless, model parameters are fitted from experimental data. Thus, the acquisition of gas solubility data in brine is fundamental. Moreover, geothermal fluids contains many corrosive species regarding materials. Material corrosion resistance has to be studied to ensure the better choice for heat exchangers.The first part of this PhD consisted in reproducing subsoil conditions of Upper Rhine Graben in a device used to characterize gas/liquid equilibrium at high pressure and high temperature. Carbon dioxide solubility has been measured in two synthetic brines containing sodium chloride NaCl, calcium chloride CaCl2 and potassium chloride KCl at 50, 100 and 150°C from 1 to 20 MPa.The second part of this work was focused on the corrosion study of material in CO2-brine environment at high temperature and high pressure. A new experimental pilot has been developed to conduct corrosion studies. Then, the surface of exposed material was characterized with different technics: X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM)… The obtained results allow a better understanding of the formation of corrosion products. The nature of the corrosion product is controlled by the temperature and the composition of the material.; Le dimensionnement des échangeurs de chaleur dans les installations géothermiques nécessite d’avoir une bonne connaissance des fluides géothermaux et des équilibres gaz/liquide. La présence de gaz dans les échangeurs diminue leur efficacité. Il est donc essentiel d’éviter le dégazage. La description des équilibres gaz/liquide est possible grâce à l’utilisation des modèles thermodynamiques dont les paramètres sont optimisés partir de données expérimentales. Ainsi, l’acquisition de données de solubilité de gaz dans les saumures est primordiale. De plus, les fluides géothermaux contiennent de nombreux sels et des gaz dissous constituant un environnement agressifs pour les matériaux utilisés dans les installations. La résistance à la corrosion doit être évaluée afin de sélectionner les matériaux adéquats pour les échangeurs de chaleur.La première partie de ce travail de thèse a consisté à reproduire les conditions rencontrées dans les sous-sols du Bassin Rhénan dans un pilote expérimental dédié à la caractérisation de équilibres gaz/liquide sous haute pression et haute température. La solubilité du dioxyde de carbone a été mesurée dans des saumures synthétiques contenant principalement du chlorure de sodium NaCl, du chlorure de calcium CaCl2 et du chlorure de potassium KCl à 50, 100 et 150°C entre 1 et 20 MPa.La seconde partie de ce travail s’est focalisée sur l’étude de la corrosion de matériaux dans les environnements CO2-saumures sous haute température et haute pression. Pour cela un nouveau pilote expérimental destiné à ce type d’étude a été développé au cours de cette thèse. La surface des matériaux exposés a ensuite été caractérisée par différentes méthodes expérimentales telles que la Spectroscopie Photoélectronique à Rayonnement X (XPS) et la Microscopie Electronique à Balayage (MEB). Différents mécanismes de formations de produits de corrosion de nature plus ou moins protectrice en fonction de la température et de la nature des matériaux ont notamment pu être mis en avant.

Livestock manure management constitutes a major challenge at this time. Traditionally, this waste has been used as fertilizer. Excessive application of this residual organic matter on agricultural soils can cause soil quality degradation due to heavy metals accumulation, migration of pathogens to water sources and food, and generation of greenhouse gases. As a promising alternative to land application, pyrolysis of livestock manure allows to obtain biochar, bio-oil and syngas. The goal of this work is to study slow pyrolysis of digested dairy cattle manure (DM) both through one-step and multi-step pyrolysis at increasing temperature in the range 250-600 °C. The non-condensable gases composition was continuously analyzed by gas chromatography. Char properties were characterized by ultimate analysis, heavy metals content, ash content, higher heating value (HHV), pH, electrical conductivity (EC), water holding capacity (WHC), cation exchange capacity (CEC), textural properties (specific surface area, pore volume and average pore width) and Fourier Transform Infrared (FTIR) spectroscopy. The experimental results showed that both the product distribution and the properties of char depended on pyrolysis temperature. Char obtained after the last step of multi-step pyrolysis had similar properties to that obtained in one-step pyrolysis. Thus, the cooling and re-heating of the solid between steps did not have a significant effect on the pyrolysis pathway. Pyrolysis at between 400-550 °C allowed to reach a compromise between char pH and electrical conductivity for its potential use as soil amendment.

One of the main issues concerning the inclusion of renewable energies as a way to produce electricity is the fluctuation of the production. This explains why there is a need for efficient solutions which will allow to store the energy when there is no need for it and release it when renewable energies are not able to sustain the production. This work concerns a Power-to-Power solution based on thermal energy storage at high temperature (around 900 °C). It relies on a simple heating loop to convert electrical energy into heat, and a thermodynamic cycle such as a gas cycle or a combined cycle to convert heat into electricity. One of the questions raised by this system is how it can be profitable from the economic point of view. Indeed a lot of studies have been conducted on energy storage, but very few propose solutions which can be relevant in terms of global costs and payback time. The aim of this study is to investigate if this system could be competitive in the European, and more specifically, French energy market. To look further into this topic, the system architecture and its components are defined. A thermodynamic model is also built to represent the behavior of the cycle. Finally, an economic discussion is performed using cost functions from the literature. The results show that the system does not accumulate enough running hours to justify high investment costs and should rely on simple technologies to insure its profitability. Furthermore, while the high capital expenditures of the whole system could be challenging, the thermal storage itself is not a big expense when compared to the cost of a natural gas fired power plant.

The sequestration of carbon dioxide fumes from oxy-fuel combustion units is used to reduce significantly the carbon dioxide emissions in the atmosphere. Impurities like nitrogen oxides, sulfur oxides, water and oxygen can cause technical difficulties during the capture, the treatment, the transport and the storage steps of the carbon dioxide fumes. To produce carbon dioxide at specifications required for storage, the flue gas has to be treated. During all the steps of the carbon dioxide purification process, the nitrogen oxides are in the presence of residual oxygen and water in the vapor state or in the aqueous state. Consequently, to design the process, it is important to know the evolution of the composition of the mixture and in particular, the formation of nitric acid and nitrous acid in the aqueous phase and the distribution of the nitrogen oxides in the vapor phase.Air Liquide and the LaTEP are working together on this problematic for several years. The works presented in this manuscript derive from this collaboration. The aim of the thesis is to study on one hand the thermochemical and liquid vapor equilibrium of nitric oxide in the presence of water, carbon dioxide and oxygen and on the other hand the formation of nitrous and nitric acids.In the first part, a bibliography of the studies on CO2-H2O and NOx-H2O systems is made, with a study of the nitric oxide oxidation to nitrogen dioxide. In a second part, the experimental set-up as well as the methods of analysis of the aqueous and the gas phase put in place have been described. Finally, the results obtained are presented and analyzed in the last part of the manuscript. The measurements obtained by the analysis of the aqueous phase and an appropriate reaction mechanism make it possible to estimate the concentration of all the nitrogen oxides present in the aqueous phase.; La séquestration des fumées de dioxyde de carbone provenant des usines de production d'énergie par oxy-combustion est utilisée pour réduire considérablement les émissions de dioxyde de carbone. Des impuretés telles que les oxydes d’azote, de soufre, l’eau et l’oxygène sont présentes dans les fumées. Pour produire du dioxyde de carbone selon les spécifications requises pour le stockage, les fumées de combustion doivent être traitées. Au cours de toutes les étapes du processus de purification du dioxyde de carbone, les oxydes d’azote sont en présence d’oxygène et d’eau à l’état vapeur ou à l’état aqueux. Par conséquent, pour dimensionner l’unité de traitement du dioxyde de carbone, il est important de connaître l'évolution de la composition du mélange, et en particulier la formation d'acide nitrique et d'acide nitreux dans la phase aqueuse.Air Liquide et le LaTEP travaillent ensemble sur cette problématique depuis plusieurs années. Les travaux présentés dans ce manuscrit découlent de cette collaboration. Le but de la thèse est d’étudier d’une part, l’équilibre thermochimique et liquide vapeur du monoxyde d’azote en présence d’eau, de dioxyde de carbone et d’oxygène et d’autre part, la formation des acides nitreux et nitrique.Dans une première partie, une synthèse bibliographie des études sur les systèmesCO2-H2O et NOx-H2O a été réalisée, avec également une étude de la réaction d’oxydation du monoxyde d’azote en dioxyde d’azote. Dans une deuxième partie, le dispositif expérimental ainsi que les méthodes d’analyse mises en place ont été décrits. Pour finir, les résultats obtenus sont présentés et analysés. Les mesures obtenues par l’analyse de la phase aqueuse et un mécanisme réactionnel approprié permettent, notamment, d'estimer la concentration de tous les oxydes d'azote présents dans la phase aqueuse.

The sequestration of carbon dioxide fumes from oxy-fuel combustion units is used to reduce significantly the carbon dioxide emissions in the atmosphere. Impurities like nitrogen oxides, sulfur oxides, water and oxygen can cause technical difficulties during the capture, the treatment, the transport and the storage steps of the carbon dioxide fumes. To produce carbon dioxide at specifications required for storage, the flue gas has to be treated. During all the steps of the carbon dioxide purification process, the nitrogen oxides are in the presence of residual oxygen and water in the vapor state or in the aqueous state. Consequently, to design the process, it is important to know the evolution of the composition of the mixture and in particular, the formation of nitric acid and nitrous acid in the aqueous phase and the distribution of the nitrogen oxides in the vapor phase.Air Liquide and the LaTEP are working together on this problematic for several years. The works presented in this manuscript derive from this collaboration. The aim of the thesis is to study on one hand the thermochemical and liquid vapor equilibrium of nitric oxide in the presence of water, carbon dioxide and oxygen and on the other hand the formation of nitrous and nitric acids.In the first part, a bibliography of the studies on CO2-H2O and NOx-H2O systems is made, with a study of the nitric oxide oxidation to nitrogen dioxide. In a second part, the experimental set-up as well as the methods of analysis of the aqueous and the gas phase put in place have been described. Finally, the results obtained are presented and analyzed in the last part of the manuscript. The measurements obtained by the analysis of the aqueous phase and an appropriate reaction mechanism make it possible to estimate the concentration of all the nitrogen oxides present in the aqueous phase.; La séquestration des fumées de dioxyde de carbone provenant des usines de production d'énergie par oxy-combustion est utilisée pour réduire considérablement les émissions de dioxyde de carbone. Des impuretés telles que les oxydes d’azote, de soufre, l’eau et l’oxygène sont présentes dans les fumées. Pour produire du dioxyde de carbone selon les spécifications requises pour le stockage, les fumées de combustion doivent être traitées. Au cours de toutes les étapes du processus de purification du dioxyde de carbone, les oxydes d’azote sont en présence d’oxygène et d’eau à l’état vapeur ou à l’état aqueux. Par conséquent, pour dimensionner l’unité de traitement du dioxyde de carbone, il est important de connaître l'évolution de la composition du mélange, et en particulier la formation d'acide nitrique et d'acide nitreux dans la phase aqueuse.Air Liquide et le LaTEP travaillent ensemble sur cette problématique depuis plusieurs années. Les travaux présentés dans ce manuscrit découlent de cette collaboration. Le but de la thèse est d’étudier d’une part, l’équilibre thermochimique et liquide vapeur du monoxyde d’azote en présence d’eau, de dioxyde de carbone et d’oxygène et d’autre part, la formation des acides nitreux et nitrique.Dans une première partie, une synthèse bibliographie des études sur les systèmesCO2-H2O et NOx-H2O a été réalisée, avec également une étude de la réaction d’oxydation du monoxyde d’azote en dioxyde d’azote. Dans une deuxième partie, le dispositif expérimental ainsi que les méthodes d’analyse mises en place ont été décrits. Pour finir, les résultats obtenus sont présentés et analysés. Les mesures obtenues par l’analyse de la phase aqueuse et un mécanisme réactionnel approprié permettent, notamment, d'estimer la concentration de tous les oxydes d'azote présents dans la phase aqueuse.

In an industrial process where steam is employed as a heat carrier, the integration of a steam storage solution allows to make the production of steam independent of its usage. Steam storage technologies can be used to decrease the energy consumption of the process, or to valorize waste heat from steam flows. Steam storage is also crucial for thermal solar power plants with direct steam generation. This work presents a model of a shell-and-tube steam storage system using Phase Change Material (PCM). These systems store the thermal energy of steam through the latent heat of the solid-liquid phase change transition of a material called PCM. The heat transfers in a storage module are often influenced by the natural convection flow of the liquid PCM during fusion and solidification. Predicting the thermal performances of a module can only be done by simulating this flow with a Computational Fluid Dynamics (CFD) numerical model with a fine mesh, whose computational times are too high for engineering needs. The goal of this work is to develop a model for the design and the performance prediction of a storage module, which takes into account the fine physical phenomena while having reasonable computational times. A multi-scale modelling approach is adopted: both a fine CFD model of the PCM and a system model of a storage module with a coarser mesh are employed.The CFD model is based on the enthalpy-porosity approach, which allows 3D simulation of solid-liquid phase change, and takes into account the movements of the liquid PCM. The sensitivity of the model to several parameters which characterize the phase change is studied, on two case studies where the natural convection flows has different amplitudes. The crossed influences of the parameters are identified. The comparison to experimental results allows to emit good practices for the use of the model. The values of the latent heat and of the temperature interval where the phase change takes place appear to be fundamental for both cases; this shows that the precision of the PCM characterization is very important for the numerical simulation of solid-liquid phase change. The mushy zone constant, which governs the damping of the liquid flow in the vicinity of the fusion or solidification front, has a different effect on the results and a different optimal value depending on the case study. Therefore, it is recommended to fit the value of this constant on experimental data, whenever such data are available.The system model represents the 1D liquid water / steam two-phase flow in the tubes of a module, and the heat transfers and the phase change in the PCM outside the tubes. The PCM is represented by a purely conductive model with an equivalent conductivity. A prototype storage module with segmented fins, installed at CEA Grenoble, is simulated with the CFD model; sodium nitrate is used as PCM (phase change temperature: 305°C). A 1D law for the heat transfer between the tube and the PCM is obtained from the CFD results; this law takes into account the convective heat transfer, and the heat transfer enhancement by the fins and the conductive inserts that are disposed in the PCM. An equivalent conductivity of the PCM in the system model is computed from the law. The modelling methodology is validated on charge tests from the prototype module (PCM fusion and steam condensation). The system model correctly reproduces the transient heat transfer rate to the PCM that the CFD predicts and the one measured experimentally, while allowing 10 to 90 times shorter computational times.; Dans un procédé industriel dans lequel de la vapeur intervient, l’intégration d’une solution de stockage de vapeur permet de découpler sa production de son utilisation ; cela permet de réaliser des économies d’énergie, ou bien de valoriser l’énergie thermique d’un effluent de vapeur autrement perdu. Le stockage de vapeur est par ailleurs crucial pour les centrales solaires thermiques à génération directe de vapeur. Ce travail porte sur la modélisation d’un système de stockage de vapeur par Matériau à Changement de Phase (MCP) de type tubes-calandre. Ces systèmes stockent l’énergie thermique de la vapeur via la chaleur latente de changement de phase solide-liquide d’un matériau dit MCP. Les transferts de chaleur dans un module de stockage sont souvent influencés par les mouvements de convection naturelle du MCP liquide pendant la fusion ou la solidification. La prédiction des performances thermiques d’un module requiert de simuler ces mouvements à l’aide d’un modèle de mécanique des fluides numériques (Computational Fluid Dynamics ou CFD) à maille fine, dont les temps de calculs sont incompatibles avec les besoins du dimensionnement. L’objectif de ce travail est de développer un modèle de dimensionnement et de prédiction des performances d’un module de stockage, qui tienne compte des phénomènes physiques d’échelle fine tout en permettant des temps de calcul raisonnables. L’approche de modélisation est multi-échelles : deux modèles de finesses différentes sont utilisés, à savoir un modèle CFD fin du MCP, et un modèle système d’un module.Le modèle CFD se fonde sur l’approche enthalpie-porosité de Voller, qui permet de simuler en 3D le changement de phase solide-liquide, en tenant compte des mouvements du MCP en phase liquide. La sensibilité du modèle à plusieurs de ses paramètres caractéristiques du changement de phase est étudiée, sur deux cas d’étude pour lesquels les mouvements de convection naturelle sont d’intensités différentes. Les effets d’influence croisée des paramètres sont mis en évidence. La comparaison à des résultats expérimentaux permet de dégager des préconisations pour l’utilisation du modèle. Les valeurs de la chaleur latente et de la plage de température du changement de phase du MCP s’avèrent fondamentales pour les deux cas étudiés, ce qui souligne l’importance de caractériser précisément le MCP pour la simulation numérique du changement de phase solide-liquide. La constante de zone pâteuse, qui détermine le taux de freinage de l’écoulement de liquide au niveau du front de fusion ou de solidification, a une influence différente selon le cas d’étude, aussi bien du point de vue de la tendance suivie par les résultats que de la valeur optimale à adopter. Il est ainsi préconisé de caler ce paramètre sur des résultats expérimentaux, lorsque cela est possible.Le modèle système représente l’écoulement 1D d’eau liquide / de vapeur dans les tubes d’un module, et les transferts de chaleur et le changement de phase dans le MCP à l’extérieur des tubes. Le MCP y est représenté par un modèle de conduction pure avec conductivité équivalente. Le modèle CFD est utilisé pour simuler un module de stockage prototype, installé au CEA Grenoble, avec tubes à ailettes segmentées ; le MCP est du nitrate de sodium (point de fusion : 305°C). Les résultats CFD permettent d’obtenir une loi d’échange thermique 1D entre le tube et le MCP, qui tient compte des échanges convectifs, et de l’intensification des transferts par les ailettes et les inserts conducteurs disposés dans le MCP. Cette loi est utilisée pour calculer une conductivité équivalente du MCP pour le modèle système. La méthodologie de modélisation est validée sur des essais de charge du module prototype (fusion du MCP et condensation de vapeur). Le modèle système reproduit correctement le taux de charge transitoire prédit par le modèle CFD, ainsi que celui mesuré expérimentalement, pour un temps de calcul 10 à 90 fois plus faible.

In an industrial process where steam is employed as a heat carrier, the integration of a steam storage solution allows to make the production of steam independent of its usage. Steam storage technologies can be used to decrease the energy consumption of the process, or to valorize waste heat from steam flows. Steam storage is also crucial for thermal solar power plants with direct steam generation. This work presents a model of a shell-and-tube steam storage system using Phase Change Material (PCM). These systems store the thermal energy of steam through the latent heat of the solid-liquid phase change transition of a material called PCM. The heat transfers in a storage module are often influenced by the natural convection flow of the liquid PCM during fusion and solidification. Predicting the thermal performances of a module can only be done by simulating this flow with a Computational Fluid Dynamics (CFD) numerical model with a fine mesh, whose computational times are too high for engineering needs. The goal of this work is to develop a model for the design and the performance prediction of a storage module, which takes into account the fine physical phenomena while having reasonable computational times. A multi-scale modelling approach is adopted: both a fine CFD model of the PCM and a system model of a storage module with a coarser mesh are employed.The CFD model is based on the enthalpy-porosity approach, which allows 3D simulation of solid-liquid phase change, and takes into account the movements of the liquid PCM. The sensitivity of the model to several parameters which characterize the phase change is studied, on two case studies where the natural convection flows has different amplitudes. The crossed influences of the parameters are identified. The comparison to experimental results allows to emit good practices for the use of the model. The values of the latent heat and of the temperature interval where the phase change takes place appear to be fundamental for both cases; this shows that the precision of the PCM characterization is very important for the numerical simulation of solid-liquid phase change. The mushy zone constant, which governs the damping of the liquid flow in the vicinity of the fusion or solidification front, has a different effect on the results and a different optimal value depending on the case study. Therefore, it is recommended to fit the value of this constant on experimental data, whenever such data are available.The system model represents the 1D liquid water / steam two-phase flow in the tubes of a module, and the heat transfers and the phase change in the PCM outside the tubes. The PCM is represented by a purely conductive model with an equivalent conductivity. A prototype storage module with segmented fins, installed at CEA Grenoble, is simulated with the CFD model; sodium nitrate is used as PCM (phase change temperature: 305°C). A 1D law for the heat transfer between the tube and the PCM is obtained from the CFD results; this law takes into account the convective heat transfer, and the heat transfer enhancement by the fins and the conductive inserts that are disposed in the PCM. An equivalent conductivity of the PCM in the system model is computed from the law. The modelling methodology is validated on charge tests from the prototype module (PCM fusion and steam condensation). The system model correctly reproduces the transient heat transfer rate to the PCM that the CFD predicts and the one measured experimentally, while allowing 10 to 90 times shorter computational times.; Dans un procédé industriel dans lequel de la vapeur intervient, l’intégration d’une solution de stockage de vapeur permet de découpler sa production de son utilisation ; cela permet de réaliser des économies d’énergie, ou bien de valoriser l’énergie thermique d’un effluent de vapeur autrement perdu. Le stockage de vapeur est par ailleurs crucial pour les centrales solaires thermiques à génération directe de vapeur. Ce travail porte sur la modélisation d’un système de stockage de vapeur par Matériau à Changement de Phase (MCP) de type tubes-calandre. Ces systèmes stockent l’énergie thermique de la vapeur via la chaleur latente de changement de phase solide-liquide d’un matériau dit MCP. Les transferts de chaleur dans un module de stockage sont souvent influencés par les mouvements de convection naturelle du MCP liquide pendant la fusion ou la solidification. La prédiction des performances thermiques d’un module requiert de simuler ces mouvements à l’aide d’un modèle de mécanique des fluides numériques (Computational Fluid Dynamics ou CFD) à maille fine, dont les temps de calculs sont incompatibles avec les besoins du dimensionnement. L’objectif de ce travail est de développer un modèle de dimensionnement et de prédiction des performances d’un module de stockage, qui tienne compte des phénomènes physiques d’échelle fine tout en permettant des temps de calcul raisonnables. L’approche de modélisation est multi-échelles : deux modèles de finesses différentes sont utilisés, à savoir un modèle CFD fin du MCP, et un modèle système d’un module.Le modèle CFD se fonde sur l’approche enthalpie-porosité de Voller, qui permet de simuler en 3D le changement de phase solide-liquide, en tenant compte des mouvements du MCP en phase liquide. La sensibilité du modèle à plusieurs de ses paramètres caractéristiques du changement de phase est étudiée, sur deux cas d’étude pour lesquels les mouvements de convection naturelle sont d’intensités différentes. Les effets d’influence croisée des paramètres sont mis en évidence. La comparaison à des résultats expérimentaux permet de dégager des préconisations pour l’utilisation du modèle. Les valeurs de la chaleur latente et de la plage de température du changement de phase du MCP s’avèrent fondamentales pour les deux cas étudiés, ce qui souligne l’importance de caractériser précisément le MCP pour la simulation numérique du changement de phase solide-liquide. La constante de zone pâteuse, qui détermine le taux de freinage de l’écoulement de liquide au niveau du front de fusion ou de solidification, a une influence différente selon le cas d’étude, aussi bien du point de vue de la tendance suivie par les résultats que de la valeur optimale à adopter. Il est ainsi préconisé de caler ce paramètre sur des résultats expérimentaux, lorsque cela est possible.Le modèle système représente l’écoulement 1D d’eau liquide / de vapeur dans les tubes d’un module, et les transferts de chaleur et le changement de phase dans le MCP à l’extérieur des tubes. Le MCP y est représenté par un modèle de conduction pure avec conductivité équivalente. Le modèle CFD est utilisé pour simuler un module de stockage prototype, installé au CEA Grenoble, avec tubes à ailettes segmentées ; le MCP est du nitrate de sodium (point de fusion : 305°C). Les résultats CFD permettent d’obtenir une loi d’échange thermique 1D entre le tube et le MCP, qui tient compte des échanges convectifs, et de l’intensification des transferts par les ailettes et les inserts conducteurs disposés dans le MCP. Cette loi est utilisée pour calculer une conductivité équivalente du MCP pour le modèle système. La méthodologie de modélisation est validée sur des essais de charge du module prototype (fusion du MCP et condensation de vapeur). Le modèle système reproduit correctement le taux de charge transitoire prédit par le modèle CFD, ainsi que celui mesuré expérimentalement, pour un temps de calcul 10 à 90 fois plus faible.

International audience

Due to the increasing demand for cooling worldwide and the need for reliable and energy-efficient alternatives to provide it, the analysis of district cooling (DC) networks has become a focus of interest in recent years. Currently, most of the developments in the field of numerical simulation and optimization of these systems have been done by implementing steady-state models. Considering this, in the present work we proposed a methodology based on mathematical programming for the dynamic simulation and optimization of the distribution system in district cooling networks.The dynamic model includes a partial differential equation to describe the variation of the temperature in the pipes, and heat and mass balances in the users and in the interconnecting nodes of the network. This arrangement is known as a partial differential algebraic equation (PDAE) problem. We detail the implementation of 2D- Orthogonal Collocation on Finite Elements (OCFE) for the discretization of the dynamic problem. Then the previously discretized model is added to the optimization constraint set, according to the simultaneous (equation-oriented) solution strategy. The optimization variables (decision variables) include the spatial and temporal profiles of the temperatures and temporal profiles of the mass flows of the system. Additional optimization variables (pipe diameters…) are progressively introduced. We apply this methodology for the analysis of an operational and a cost objective function in a medium size cooling system, serving 20 consumers grouped in five different categories with fluctuating cooling demands subject to variable external conditions. The first objective function considers that in DC networks, the temperature of the cooling utility returning to the production site must be close to the design temperature of the installed technology to ensure proper efficiency and avoid the technical issue known as low ΔT syndrome. Then, still ensuring this condition, the second objective function aims to minimize a cost function (production and pumping costs) including the diameter of the pipes as decision variables. The methodology allowed the computation of the optimal mass flow profiles to operate the system under the desired conditions and the estimation of the pipe diameters of the distribution network for two different costs of production. For the two objective functions, the dynamic simulation and optimization were performed using insulated and non-insulated piping. The proposed methodology exhibits low CPU cost that demonstrates its potential use for the development of applications for the operation and forecasting of distributed systems.; L’utilisation de froid (industriel et climatisation) dans le monde ne cesse d’augmenter et les prévisions annoncent un accroissement continu de la demande de froid dans les années à venir. De ce fait, la recherche d’un moyen fiable et performant permettant la fourniture de froid est plus que jamais d’actualité. Dans ce contexte, les réseaux de froid urbains sont de plus en plus étudiés. Actuellement, la plupart des études portant sur la simulation numérique ou l’optimisation de ces systèmes ont été mises en œuvre en régime stationnaire. Compte tenu de cela, le présent manuscrit propose une méthodologie de résolution mathématique pour la simulation et l’optimisation dynamiques d’un réseau de froid urbain.Le modèle dynamique inclut les équations différentielles permettant de représenter les variations de température dans les canalisations, ainsi que les bilans de masses et d’énergie aux nœuds du réseau et dans les échangeurs thermiques alimentant les consommateurs. Le modèle ainsi construit est un système d’équations aux dérivées partielles et algébriques. Nous détaillons la méthode de double collocation orthogonale sur éléments finis permettant de discrétiser ces équations afin d’obtenir un système comprenant uniquement des équations algébriques. Le modèle ainsi discrétisé est alors ajouté aux contraintes du problème d’optimisation à résoudre, conformément à la stratégie de résolution orientée équations. Les variables d’optimisation (de décision) sont les profils spatiaux et temporels de température et les profils temporels de débit dans tout le système. D’autres variables d’optimisation, tels que les diamètres des canalisations, sont ajoutées par la suite. Cette méthodologie d’optimisation dynamique est résolue pour deux fonction objectif différentes (exploitation et économique) appliquées à un cas test, inspiré de la littérature, comprenant 20 consommateurs représentant 5 catégories de bâtiments différents ayant des demandes temporelles de froid variables. Tout ceci est soumis aux variations de température extérieure pour différentes localisations.La première fonction objectif a pour but de maintenir la température de retour dans l’unité de production de froid proche de la température considérée pour le dimensionnement de cette unité afin d’assurer un fonctionnement efficace et d’éviter un problème bien connu dans les réseaux de froid appelé « low ΔT syndrome ». Ensuite, en garantissant toujours un tel fonctionnement, la seconde fonction objectif a pour but de minimiser une fonction coût incluant les coûts de production de froid et de pompage dans le réseau en considérant les diamètres comme variables d’optimisation. Une procédure particulière, enchainement de simulations stationnaires puis dynamiques, est proposée afin d’obtenir une initialisation permettant la convergence vers un optimum de confiance du problème d’optimisation dynamique. Cette méthodologie a permis d’obtenir les profils temporels optimaux des variables de contrôle du système dans les conditions d’utilisation désirées ainsi que les diamètres de l’ensemble du réseau pour deux coûts représentant différents types de technologie de production de froid. Les simulations et optimisations dynamiques (pour les deux fonctions objectif) ont été réalisées pour des tuyaux isolés et pour des tuyaux non isolés. La méthodologie mise en place présente un temps de résolution faible sur un ordinateur portable classique ce qui démontre son potentiel d’utilisation pour le développement d’application de contrôle et de prédiction de ce type de système.

Due to the increasing demand for cooling worldwide and the need for reliable and energy-efficient alternatives to provide it, the analysis of district cooling (DC) networks has become a focus of interest in recent years. Currently, most of the developments in the field of numerical simulation and optimization of these systems have been done by implementing steady-state models. Considering this, in the present work we proposed a methodology based on mathematical programming for the dynamic simulation and optimization of the distribution system in district cooling networks.The dynamic model includes a partial differential equation to describe the variation of the temperature in the pipes, and heat and mass balances in the users and in the interconnecting nodes of the network. This arrangement is known as a partial differential algebraic equation (PDAE) problem. We detail the implementation of 2D- Orthogonal Collocation on Finite Elements (OCFE) for the discretization of the dynamic problem. Then the previously discretized model is added to the optimization constraint set, according to the simultaneous (equation-oriented) solution strategy. The optimization variables (decision variables) include the spatial and temporal profiles of the temperatures and temporal profiles of the mass flows of the system. Additional optimization variables (pipe diameters…) are progressively introduced. We apply this methodology for the analysis of an operational and a cost objective function in a medium size cooling system, serving 20 consumers grouped in five different categories with fluctuating cooling demands subject to variable external conditions. The first objective function considers that in DC networks, the temperature of the cooling utility returning to the production site must be close to the design temperature of the installed technology to ensure proper efficiency and avoid the technical issue known as low ΔT syndrome. Then, still ensuring this condition, the second objective function aims to minimize a cost function (production and pumping costs) including the diameter of the pipes as decision variables. The methodology allowed the computation of the optimal mass flow profiles to operate the system under the desired conditions and the estimation of the pipe diameters of the distribution network for two different costs of production. For the two objective functions, the dynamic simulation and optimization were performed using insulated and non-insulated piping. The proposed methodology exhibits low CPU cost that demonstrates its potential use for the development of applications for the operation and forecasting of distributed systems.; L’utilisation de froid (industriel et climatisation) dans le monde ne cesse d’augmenter et les prévisions annoncent un accroissement continu de la demande de froid dans les années à venir. De ce fait, la recherche d’un moyen fiable et performant permettant la fourniture de froid est plus que jamais d’actualité. Dans ce contexte, les réseaux de froid urbains sont de plus en plus étudiés. Actuellement, la plupart des études portant sur la simulation numérique ou l’optimisation de ces systèmes ont été mises en œuvre en régime stationnaire. Compte tenu de cela, le présent manuscrit propose une méthodologie de résolution mathématique pour la simulation et l’optimisation dynamiques d’un réseau de froid urbain.Le modèle dynamique inclut les équations différentielles permettant de représenter les variations de température dans les canalisations, ainsi que les bilans de masses et d’énergie aux nœuds du réseau et dans les échangeurs thermiques alimentant les consommateurs. Le modèle ainsi construit est un système d’équations aux dérivées partielles et algébriques. Nous détaillons la méthode de double collocation orthogonale sur éléments finis permettant de discrétiser ces équations afin d’obtenir un système comprenant uniquement des équations algébriques. Le modèle ainsi discrétisé est alors ajouté aux contraintes du problème d’optimisation à résoudre, conformément à la stratégie de résolution orientée équations. Les variables d’optimisation (de décision) sont les profils spatiaux et temporels de température et les profils temporels de débit dans tout le système. D’autres variables d’optimisation, tels que les diamètres des canalisations, sont ajoutées par la suite. Cette méthodologie d’optimisation dynamique est résolue pour deux fonction objectif différentes (exploitation et économique) appliquées à un cas test, inspiré de la littérature, comprenant 20 consommateurs représentant 5 catégories de bâtiments différents ayant des demandes temporelles de froid variables. Tout ceci est soumis aux variations de température extérieure pour différentes localisations.La première fonction objectif a pour but de maintenir la température de retour dans l’unité de production de froid proche de la température considérée pour le dimensionnement de cette unité afin d’assurer un fonctionnement efficace et d’éviter un problème bien connu dans les réseaux de froid appelé « low ΔT syndrome ». Ensuite, en garantissant toujours un tel fonctionnement, la seconde fonction objectif a pour but de minimiser une fonction coût incluant les coûts de production de froid et de pompage dans le réseau en considérant les diamètres comme variables d’optimisation. Une procédure particulière, enchainement de simulations stationnaires puis dynamiques, est proposée afin d’obtenir une initialisation permettant la convergence vers un optimum de confiance du problème d’optimisation dynamique. Cette méthodologie a permis d’obtenir les profils temporels optimaux des variables de contrôle du système dans les conditions d’utilisation désirées ainsi que les diamètres de l’ensemble du réseau pour deux coûts représentant différents types de technologie de production de froid. Les simulations et optimisations dynamiques (pour les deux fonctions objectif) ont été réalisées pour des tuyaux isolés et pour des tuyaux non isolés. La méthodologie mise en place présente un temps de résolution faible sur un ordinateur portable classique ce qui démontre son potentiel d’utilisation pour le développement d’application de contrôle et de prédiction de ce type de système.

A measurement campaign was conducted in 24 student rooms where formaldehyde emissions from all the indoor surfaces were measured using a passive flux sampler (PFS) parallel to monitoring of indoor and outdoor concentrations as well as the assessment of air exchange rate. Two mass balance models were used to predict indoor concentrations basing on input data recorded during this measurement campaign. The first model only takes into account the total emission from the indoor sources and the incoming and outgoing flows of compound brought by the air exchange rate. The second model added to these terms a further component related to the overall rate of removal processes (or "indoor sinks") which was assessed in these same rooms during a previous field test campaign. A good agreement was found between the concentrations calculated by the model with the component relative to indoor removal processes and the measured concentrations. On the other hand, the predicted concentrations with a first model tend to highly overestimate the measured concentrations by a factor 1.9 on average. Apportionment of formaldehyde inputs and losses in the rooms was estimated and discussed. The results highlighted that indoor removal processes are a component to consider for formaldehyde budget indoors.

International audience

This works provides a new insight on the adsorption of CH4/CO2 and its components on carbonaceous materials. The equimolar mixture adsorption isothemrs were obtained for 5 well characterized activated carbons at a temperature of 303 K on the pressure range of 0–3 MPa. A higher BET surface area in addition to a narrow pore size distribution centered at a pore size of 0.8 nm resulted in higher CH4/CO2 total adsorption capacity. Furthermore, whilst the presence of basic functionalities on the surface of the adsorbents enhanced the adsorption of carbon dioxide, the adsorption selectivity was influenced by both textural and chemical properties of the samples. The selectivity was determined to be higher for carbon ROx 0.8 (selectivity factor of up to 4.7), a microporous steam activated carbon with a mild surface area (1323 m2 g−1), narrow pore size distribution with an average pore size of 0.84 nm. Higher BET surface areas and average pore sizes resulted in a detriment of the selectivity. In addition, the presence of sulfur surface groups increased resulted in a rise of the selectivity factor.

International audience

International audience; In this article, we focus on the condenser of a loop thermosiphon designed to cool power electronic component. The objective here is to condense Novec 649, our chosen working fluid for this loop. It is a fluid recently developed by 3M, which is known for having low environmental impact and non-flammable. We first present a theoretical analysis with the calculation and the hypotheses leading to the design of the multi-tubular condenser. Then we present a full size thermosiphon built for experimental validation. A discussion then addresses some of the design hypotheses. Three main parameters are studied : the tilting angle of the condenser (from horizontal to vertical orientations), the temperature of the coolant and finally the mass flow effect at different saturation temperatures. In our setup, we dissipate up to 2.4 kW at the evaporator level. The produced vapor is then condensed in the heat exchanger using cold water flowing at countercurrent. A number of measurements are made via thermocouples and pressure sensors located at both ends of the condenser to measure the average heat exchange coefficient.

International audience

With the increase in the share of intermittent renewable energies as part of the global energy mix comes the issue of energy storage. This work concerns a power-to-power electricity storage relying on sensible storage at high temperature (900 °C). A focus is put on finding the best compromise between the valorization of the stored energy and the optimal functioning of the power-to-power process. The charging loop is made of an electrical heater and fans, while the conversion of the stored heat to electricity can be done in a gas cycle or a combined cycle. To set up a relevant base design for the system, the reciprocal influence of the storage and the discharging cycle needs to be evaluated. A thermodynamic modeling was therefore carried on and first and second law (or exergy) analyses were performed. Results show that the choice of the discharging cycle has a high impact on the sizing of the storage, by inducing different levels of pressure or temperature. Adding combustion in the discharging phase allows to achieve a better power-to-power efficiency and to reduce the storage volume, but also involves a fuel consumption that is not negligible. Finally, the power-to-heat conversion leads to high exergy destructions in the charging loop but thanks to the high temperature of the storage, this exergy destruction is not excessive when compared to conventional heat input from combustion systems.

The determination of both the thermal and thermodynamical properties of a composite material containing phase change material is done thanks to an inverse method, which combines experimental measurements and numerical computations. Given first an in-house experiment, which allows us to test samples at a macroscopic scale (i.e., close to the real conditions) and to set various types of thermal stresses, and secondly the simulation of the corresponding thermal behavior, relying on an accurate thermodynamical modeling and taking into account the real operating parameters (e.g., thermal contact resistances and non-symmetric heat fluxes on each side), it is possible to characterize the solid and liquid thermal conductivities and heat capacities, as well as the temperature range associated with a non-isothermal phase transition and the associated latent heat. The specificity of the present approach is to allow, in a single step, a characterization of all the involved thermo-physical parameters that are usually required in simulation tools (e.g., EnergyPlus&hellip, ). Moreover, the hitherto studies dealing with repeatability and uncertainties of the enthalpy characterization are generally very scant and not encountered very often or only with qualitative assessments. This is a clear caveat, especially when considering any system design. Therefore, for the first time ever, the present paper pays a special attention to the repeatability of the identification method and studies the scedasticity of the results, that is to say the deviations of the determined enthalpy curves, not only from a qualitative point of view but also by proposing quantitative arguments. Finally, the results are very promising since the agreement between all trials is excellent, the maximum error for all parameters being lower than 4%. This is far below the current quality thresholds admitted when characterizing the enthalpy of a phase change material.

International audience; Formaldehyde is considered as a priority pollutant of indoor air due to its numerous indoor sources and health impact. Due to its physico-chemical properties, the interaction of gaseous formaldehyde with material surfaces is suspected to play an important role in the distribution and fate of this compound indoors. This paper proposes an experimental method providing several parameters characterizing the material/air exchanges for formaldehyde namely, the adsorption and desorption rate constants (kam and kdm) and the material/air equilibrium partition coefficient (Ke) and the initial gas-phase concentration in equilibrium with the material surface (Cieq0). These parameters are assessed in a closed system (glass cell) containing the material and by a static sampling using solid-phase microextraction (SPME) fibers for measuring gaseous concentrations at the material surface during the emission and adsorption phases. Compared to the available methods of determining these parameters described in the literature, this method has the following advantages: (1) Taking into account of sorption on the inner walls of cell in the calculation of the material sorption parameters; (2) An analytical solution assessing the adsorption and desorption rate constants simultaneously from data of the adsorption phase; (3) An assessment of these sorption parameters under experimental conditions close to those encountered in indoor environments; (4) a satisfying reproducibility of the measured sorption parameters. The main performance of SPME sampling was assessed. The applicability of this method was proven to compare the sorption behavior of formaldehyde towards floor coverings.

International audience; Experimental CO 2 solubility data in brine at high pressures and high temperatures are needed in different technologies such as carbon dioxide storage or geothermal process. A lot of data have been acquired in single-salt solutions, whereas data for mixed-salt solutions remain scarce. In this study, new carbon dioxide solubility data in salt solutions have been measured. Two synthetic brines have been studied at 323, 373, and 423 K from 1 to 20 MPa. The brine 1 is composed of a mixture of NaCl and CaCl 2 and the brine 2 is made from a mixture of NaCl, CaCl 2 , and KCl. Measurements have been carried out by conductimetric titration. In this study, 6 isotherms presenting 48 new solubility data have been reported. These results have been obtained in an original range of temperature, pressure, and salinity. In these conditions of temperature and pressure, we verified that an increase of the temperature or the salinity involves a decrease of the CO 2 solubility. On the other hand, an increase of the pressure implies an increase of the CO 2 solubility. Then, the obtained results were compared with the values calculated using PhreeSCALE and PSUCO2 models. The comparison between experimental and calculated values revealed a good agreement.

Among existing heat storage technologies, dual-media thermocline systems are considered an economical option, experimentally demonstrated at several scales. To obtain cost reduction for these storage systems, a part of the heat transfer fluid is replaced by a low-cost solid. The contact between these two media raises the question of their compatibility and behavior in time, as the storage performance directly depends on it. Ageing and compatibility tests have been performed at the laboratory scale with Jarytherm® DBT oil and various solid media. These tests, carried out at 340°C for 500 h, have shown the strong influence of the solid composition on its compatibility with oil. A strong incompatibility has been highlighted between Jarytherm® DBT oil and the selected natural rocks at 330°C, through chromatographic analysis and oil properties evaluation before and after ageing. To the contrary, glass, steel and alumina fared well, and are thus considered as promising storage media.

International audience; This paper presents the optimization of parallel distribution between electricity and heat production for a geothermal plant. The geothermal fluid is split into two streams, one used for an Organic Rankine Cycle (ORC) system, and the other for a District Heating Network (DHN). The superstructure to be used for the optimization problem includes the ORC components and the DHN topology constituted by a definite consumer and optional consumers. A Mixed Integer Non-Linear Programming (MINLP) optimization problem is formulated and solved using the GAMS software. This paper is focused on exergetic aspect. The main lines for formulation of the problem are reminded, yet the exergetic model is fully described. Exergy analysis is performed for two optimal solutions (economic and exergetic objective functions). Results for both optimizations are first compared. The analysis of exergetic efficiency of the ORC and the DHN may suggest that exergetic optimization privileges the system with the highest efficiency: the ORC. The DHN configuration is then the smallest as possible. Finally, a sensitive analysis is performed for the exergetic optimization. This analysis reveals our previous conclusion is not necessarily true. Taller configuration can exist even if ORC efficiency is higher than DHN efficiency. These results highlight the relevance of using an optimization approach for a Combined Heat and Power (CHP) plant.