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Effects of urban air pollution on health and environment have lead researchers to find economic air quality monitoring regulations. Since tin dioxide (SnO2) was demonstrated as a gas sensing device in 1962, tin oxide based thin film sensors have been widely studied due to their high sensitivity and fast response. The main advantages of using tin oxide sensors are their low cost, small size and low power consumption for mobile system applications. But, in order SnO2 based sensors to meet low concentration of gases they should be highly upgraded in sensitivity, selectivity and stability. This study was focused on the capacity of dopants in the SnO2 layer to increase the sensitivity of the sensor in detecting carbon monoxide. 1 wt. % Pd promoted and 0.1 wt. % Na-1 % Pd promoted SnO2 multilayer thin films were produced by sol-gel technique followed by spin coating route on soda-lime glass substrates. The EDX and SEM studies showed the surface composition and the surface structure is homogeneous throughout the films. The film thickness was determined app. 450 nm from the SEM image of the cross-section, after coating 8 layers. The experiments conducted at several temperatures namely 150, 175 and 200oC, in oxygen free and 1% oxygen containing atmospheres showed that the responses at higher temperatures in the presence of oxygen were much sharper with respect to others. Besides, Na promoted test sensors showed larger responses with shorter response time in oxygen free atmospheres at relatively lower temperatures. The results showed that the sensor signal is not directly correlated with the carbon dioxide production in oxygen free atmospheres.

Ces travaux ont donc visé le développement d’une plateforme complète de détection de gaz pour environnement sévère haute température. Cette plateforme intègre un dispositif à ondes acoustiques de surface sur substrat Langasite, une résistance chauffante, une couche sensible inorganique nanostructurée et est placée dans une enceinte hermétique. Des températures de l’ordre de 450°C ont été atteintes et des tests de cyclages ont démontré un fonctionnement en accord avec les modèles théoriques et une reproductibilité des mesures. Des tests de détection de composés organiques volatils (éthanol et toluène) ont mis en avant des seuils de détection de l'ordre de quelques ppm. / Measuring pollutants concentrations in gas and vapors emissions are important environmental issues. This work presents a stand-alone portable device for high temperature assessment. The system includes a Langasite (LGS) acoustic sensor, a ceramic heater and a platform with RF connections for remote in-situ measurements. The packaging consists in a hermetic stainless steel cell which enables safe gas detection. In situ temperature measurements have been achieved and the thermal behavior was successfully investigated in the temperature range 25-450°C. The designed cell highlights good agreement with theoretical models and reproducibility of the measures. Volatile organic compounds exposures have been investigated and promising ppm level detections have been obtained.

Thermal and chemical recovery processes are important EOR methods used often by the oil and gas industry to improve recovery of heavy oil and high viscous oil reservoirs. Knowledge of underlying mechanisms and their modeling in numerical simulation are crucial for a comprehensive study as well as for an evaluation of field treatment. EOS-compositional, thermal, and blackoil reservoir simulators can handle gas (or steam)/oil/water equilibrium for a compressible multiphase flow. Also, a few three-phase chemical flooding reservoir simulators that have been recently developed can model the oil/water/microemulsion equilibrium state. However, an accurate phase behavior and fluid flow formulations are absent in the literature for the thermal chemical processes to capture four-phase equilibrium. On the other hand, numerical simulation of such four-phase model with complex phase behavior in the equilibrium condition between coexisting phases (oil/water/microemulsion/gas or steam) is challenging. Inter-phase mass transfer between coexisting phases and adsorption of components on rock should properly be modeled at the different pressure and temperature to conserve volume balance (e.g. vaporization), mass balance (e.g. condensation), and energy balance (e.g. latent heat). Therefore, efforts to study and understand the performance of these EOR processes using numerical simulation treatments are quite necessary and of utmost importance in the petroleum industry. This research focuses on the development of a robust four-phase reservoir simulator with coupled phase behaviors and modeling of different mechanisms pertaining to thermal and chemical recovery methods. Development and implementation of a four-phase thermal-chemical reservoir simulator is quite important in the study as well as the evaluation of an individual or hybrid EOR methods. In this dissertation, a mathematical formulation of multi (pseudo) component, four-phase fluid flow in porous media is developed for mass conservation equation. Subsequently, a new volume balance equation is obtained for pressure of compressible real mixtures. Hence, the pressure equation is derived by extending a black oil model to a pseudo-compositional model for a wide range of components (water, oil, surfactant, polymer, anion, cation, alcohol, and gas). Mass balance equations are then solved for each component in order to compute volumetric concentrations. In this formulation, we consider interphase mass transfer between oil and gas (steam and water) as well as microemulsion and gas (microemulsion and steam). These formulations are derived at reservoir conditions. These new formulations are a set of coupled, nonlinear partial differential equations. The equations are approximated by finite difference methods implemented in a chemical flooding reservoir simulator (UTCHEM), which was a three-phase slightly compressible simulator, using an implicit pressure and an explicit concentration method. In our flow model, a comprehensive phase behavior is required for considering interphase mass transfer and phase tracking. Therefore, a four-phase behavior model is developed for gas (or steam)/ oil/water /microemulsion coexisting at equilibrium. This model represents coupling of the solution gas or steam table methods with Hand’s rule. Hand’s rule is used to capture the equilibrium between surfactant, oil, and water components as a function of salinity and concentrations for oil/water/microemulsion phases. Therefore, interphase mass transfer between gas/oil or steam/water in the presence of the microemulsion phase and the equilibrium between phases are calculated accurately. In this research, the conservation of energy equation is derived from the first law of thermodynamics based on a few assumptions and simplifications for a four-phase fluid flow model. This energy balance equation considers latent heat effect in solving for temperature due to phase change between water and steam. Accordingly, this equation is linearized and then a sequential implicit scheme is used for calculation of temperature. We also implemented the electrical Joule-heating process, where a heavy oil reservoir is heated in-situ by dissipation of electrical energy to reduce the viscosity of oil. In order to model the electrical Joule-heating in the presence of a four-phase fluid flow, Maxwell classical electromagnetism equations are used in this development. The equations are simplified and assumed for low frequency electric field to obtain the conservation of electrical current equation and the Ohm's law. The conservation of electrical current and the Ohm's law are implemented using a finite difference method in a four-phase chemical flooding reservoir simulator (UTCHEM). The Joule heating rate due to dissipation of electrical energy is calculated and added to the energy equation as a source term. Finally, we applied the developed model for solving different case studies. Our simulation results reveal that our models can accurately and successfully model the hybrid thermal chemical processes in comparison to existing models and simulators. / text

Depuis la révolution industrielle les niveaux des concentrations atmosphériques des gaz à effet de serre ne cessent d’augmenter provocant ainsi une accélération du réchauffement climatique. Les composés organiques volatils (COVs) contribuent non seulement à cet effet de serre mais aussi à la pollution environnementale qui a un impact négatif sur toutes les espèces vivantes de la planète. Par exemple, au cours de l’année 2012, la pollution de l'air a été à l’origine 7 millions de décès, selon l'Organisation mondiale de la santé (OMS) [1]. Très récemment, une étude médicale de la commission Lancet sur la pollution et la santé a révélé qu'en 2015 un décès sur six était lié à la pollution de l'air et de l'eau, 6,5 millions de décès dans le monde chaque année sont liés à la pollution de l'air intérieur et extérieur [2]. En effet, les COVs, très volatils et utilisés comme solvants par exemple, peuvent être indirectement à l’origine de toux, d’inconfort thoracique, de gêne douloureuse, d’essoufflement respiratoire, d’irritation nasale ou oculaire ou encore de la gorge. Ils peuvent aussi être directement toxiques ou explosifs ou encore perturbateurs de la réponse immunitaire. De plus certains d’entre eux sont classés CMR (cancérogène, mutagène et reprotoxique). Dans ces conditions une meilleure connaissance des effets liés à l’exposition aux COVs sur la santé et l’environnement est vraiment nécessaire. Cette connaissance passe également par la détection et la quantification des concentrations de COVs afin de proposer un meilleur aménagement des environnements et d'alerter les individus concernés en temps réel sur les dangers encourus. La plupart des plateformes déjà existantes ou commercialisées sont soient trop coûteuses, soient très consommatrices d'énergie, soient fonctionnelles à des températures élevées, soient instables pour la détection en temps réel ou à long terme ce qui limite la prolifération des sites de mesures. Ainsi, cette thèse s’inscrit dans le domaine des capteurs de gaz dédiés pour la détection de la pollution dans l’air. Elle porte sur le développement d’une plateforme de détection, de suivi et de quantification des composés organiques volatils (COVs) en temps réel, utilisant un capteur de gaz différentiel flexible et imprimé basé sur des transducteurs micro-ondes et des matériaux carbonés polymères composites comme couches sensibles. Le dispositif proposé vise à fournir des informations directement exploitables pour constituer à terme une plateforme de faible coût embarquée, dédiée à l’internet des objets pour faciliter la prolifération des sites de détection et de contrôle en réalisant des réseaux de capteurs communicants sans fil fonctionnant en environnements variés. / Since the Industrial Revolution, the levels of atmospheric concentrations of greenhouse gases have been increasing, causing an acceleration of global warming. Volatile organic compounds (VOCs) contribute not only to this greenhouse effect, but also to environmental pollution, which has a negative impact on all living species on the planet. For example, in the year 2012, air pollution caused 7 million deaths, according to the World Health Organization (WHO) [1]. In addition, a very recent medical study by the Lancet Commission on Pollution and Health found that one in six deaths in 2015 was related to air and water pollution [2]. Also, indoor and outdoor air pollution is linked to 6.5 million deaths worldwide each year. VOCs can indirectly cause cough, chest discomfort, painful discomfort, shortness of breath, as well as nasal, ocular or throat irritation. They can also be directly toxic or explosive or disruptive of the immune response. In addition, some of them are classified as CMR (carcinogenic, mutagenic and reprotoxic). They are very volatile and often used as solvents for example. In these conditions, a better understanding of the health and environmental effects of exposure to VOCs is necessary. Such knowledge also involves the detection and quantification of VOC concentrations in order to propose a better management of the environments and to alert people in real time of the dangers incurred. Most of the existing or commercially available platforms are either too expensive, energy intensive, high temperature functional, unstable for real-time or long-term detection, which limits the proliferation of measurement sites. This thesis is in the field of dedicated gas sensors for the detection of pollution in the air. It deals with the development of a platform for the detection, monitoring and quantification of volatile organic compounds (VOCs) in real time, using a flexible and printed differential gas sensor based on microwave transducers and composite polymeric carbon materials as sensitive layers. The proposed device aims at providing directly exploitable information such as a low-cost embedded platform dedicated to the Internet of things and which offers increasing possibilities for the proliferation of detection and control sites by realizing networks of wireless communicating sensors operating in various environments.