Les recherches dans le domaine des matériaux innovants possédant une meilleure efficacité énergétique présentent un enjeu environnemental majeur. L'un des moyens d'économiser l'énergie est le stockage. L'utilisation des matériaux à changement de phase est une solution permettant d'absorber, de stocker et de restituer de grandes quantités d'énergie. Ce travail porte sur l'étude expérimentale des propriétés thermophysiques et des changements de phase de matériaux composites à matrice polymère contenant un matériau à changement de phase microencapsulé et sur l'optimisation de ces propriétés. Des composites contenants différentes fractions massiques de microcapsules de paraffine ont d'abord été caractérisés. Afin d'améliorer le transfert thermique des microcapsules de paraffine métallisées avec de l'argent ont ensuite été utilisées. Une nouvelle série d'échantillons a été réalisée. Dans les composites la matrice polymère choisie est le polycaprolactone (PCL), ce polymère a une température de fusion particulièrement faible (53°C), qui permet de le mélanger aux microcapsules sans les détériorer. Les mélanges polymère/microcapsules ont été réalisés à l'aide d'un mélangeur interne, ils ont ensuite été pressés pour obtenir des plaques de composites. L'homogénéité des échantillons a été vérifiée en faisant des observations au microscope électronique à balayage et des mesures de densité. Le matériau à changement de phase utilisé est un mélange de paraffines qui a une température de changement de phase de 26°C, microencapsulé dans du PMMA hautement réticulé, et commercialisé par la société BASF® sous la dénomination commerciale de Micronal® DS 5001 X. Le PCL a une température de fusion inférieure à la température de ramollissement du PMMA. Un des objectifs de cette étude était d'obtenir un matériau qui reste solide même quand la paraffine fond. La microencapsulation a permis cela en évitant que la paraffine ne diffuse hors de l'échantillon lors de cycles successifs, elle permet également d'éviter les phénomènes de convection quand la paraffine est liquide. D'autre part, un autre objectif était de voir si la métallisation des particules permettait d'améliorer les propriétés thermiques en augmentant significativement la conductivité et la diffusivité thermique. La DSC a été utilisée pour connaître les températures et les enthalpies de changements de phase ainsi que les Cp des matériaux entre -20 et 40 °C. Une technique expérimentale développée au laboratoire (DICO) permet de mesurer simultanément la conductivité thermique (λ) et la diffusivité thermique (a) à température ambiante. Une évolution récente de ce dispositif permet maintenant de faire des mesures en rampe en température entre -15°C et 180°C. Les mesures de l'évolution de la conductivité et de la diffusivité thermique en fonction de la température ont donc été réalisées en chauffe et en refroidissement. Les changements de phase observés en DSC se retrouvent sur l'évolution de la conductivité et de la diffusivité thermiques tracées en fonction de la température. On voit également l'impact de l'état solide ou liquide de la paraffine contenue dans les microcapsules sur ces propriétés. Enfin l'évolution de la capacité calorifique volumique a pu être calculée à partir des résultats obtenus avec la DICO (Cp=λ/a) et comparée à l'évolution de la capacité calorifique massique mesurée en DSC. Globalement le transfert thermique a été amélioré pour les composites contenant des Micronal® argentés mais leur capacité de stockage est inférieure aux composites ne contenant que des Micronal® / Research in the field of innovative materials with improved energy efficiency have a major environmental issue. One way to save energy is storage. The use of phase change materials (PCM) is a solution for absorbing, storing and releasing large amounts of energy. This study focuses on the experimental study of the thermophysical properties and phase changes of polymer matrix composite materials containing microencapsulated PCM and the optimization of their thermophysical properties. Composite containing different mass fractions of paraffin microcapsules were first characterized. To improve heat transfer, paraffin microcapsules metallized with silver were then used. A new set of samples was elaborated. In the composite the selected polymer matrix is polycaprolactone (PCL), this polymer has a particularly low melting point (53°C), which allows to mix the microcapsules without damaging them. The polymer/microcapsules mixtures were prepared using a blender, they were then pressed to obtain plates of composites. The homogeneity of the samples was verified by scanning electron microscopy observations and density measurements. The phase change material used is a mixture of paraffins having a phase change temperature of 26°C, in microencapsulated highly crosslinked PMMA, and marketed by BASF under the trade name of Micronal®DS 5001 X. PCL has a melting temperature lower than the softening temperature of PMMA. One objective of this study was to obtain a material that remains solid even when the paraffin melts. Microencapsulation has avoided that the paraffin in the sample diffuses out during successive cycles, it also avoids convection when paraffin is liquid. On the other hand, another goal was to see if metallization of the particles allowed to improve the thermal properties by significantly increasing the thermal conductivity and diffusivity. DSC was used to determine the temperatures and enthalpies of the phase changes and the materials Cp between -20 and 40 ° C. An experimental technique, developed in the laboratory (DICO), can simultaneously measure the thermal conductivity (λ) and thermal diffusivity (a) at room temperature. A recent development of this system now allows to make measurements in ramp between -15°C and 180°C. The measures of the change in thermal conductivity and diffusivity as a function of temperature have been carried out by heating and cooling. Phase changes observed in DSC are found on the evolution of thermal conductivity and thermal diffusivity plotted as a function temperature. It also shows the impact on these properties of solid or liquid state of the paraffin contained in the microcapsules. Finally the evolution of the volumetric heat capacity was calculated from the results obtained with DICO (Cp=λ/a) and compared with the evolution of the specific heat capacity measured by DSC. Globally, heat transfer was improved for composites containing silver but their storage capacity is lower than for the composites containing only Micronal®

Refrigerant management is crucial in the attempts to slow climate change. Emissions from the refrigeration sector are primarily due to poor management and unsafe destruction of refrigerants currently in circulation. Safe refrigerant management and improving system operating efficiency can result in a reduction of emissions. Ice rinks are some of the most energy-intensive public buildings, providing both heating and cooling. The major share of energy in an ice rink is the refrigeration system, which consumes about 43%. There are more than 360 ice rinks in Sweden as of 2018 and the most common type of refrigeration system is an indirect system. With the push for natural fluids, aqua ammonia is becoming a more appealing option as a secondary fluid in ice rinks because of its minimal negative impact on the environment and favorable thermophysical properties. The main drawbacks of the fluid are its toxic characteristics and material compatibility. However, since the first use in 2007, there has been an increase to 34 of the total ice rinks in Sweden that have aqua ammonia as a secondary fluid.  Thermophysical properties are used to calculate refrigeration design parameters, including secondary fluid concentration and pumping power required. The properties of aqua ammonia have not been experimentally tested within this century to the extent presented in this thesis. Existing data is either derived from measured values taken several decades ago or has been calculated. The novelty of this thesis project stems from the unique and more accurate results measured through laboratory work and from the ability to determine the impact of the newly measured values in ice rink refrigeration design. A total of 11 varying concentrations of aqua ammonia were tested for density, dynamic viscosity, specific heat capacity, thermal conductivity, and corrosion of 7 metal specimens. The solutions tested ranged from 2 wt-% to 30 wt-%, correlating to freezing points from -2C to -84C. The measurements for density resulted in values similar to reference values, ranging in a difference of only 0.3% to 1.7%. Dynamic viscosity results followed nearly the same trend as references with changing temperature and solution concentration, with values varying from 0.8% to 17% different than references. Specific heat capacity measurements proved significantly different than reference values. The trend is opposite of the reference, leading to drastically different values, especially at lower temperatures and higher solution concentrations. The difference in values ranges from 0.1% to 28%. Thermal conductivity results show similar trends, but higher values than expected. The difference between measured values and reference values range from 0.1% to 13%. Corrosion results show that copper and brass have the highest corrosion rates of 16.2 mm/yr and 1.84 mm/yr, respectively. The most compatible specimen was stainless steel, followed by carbon steel, with maximum corrosion rates of 0.041 mm/yr and 0.11 mm/yr, respectively. Brass connections commonly used in industry were also tested and resulted in corrosion rates ranging from 69.6 g/yr to 112 g/yr, which accounts for about 1% and 1.5% of the connections’ total weight lost per year. Compiling the laboratory measurements taken during the completion of this thesis project results in a more complete and accurate list of thermophysical properties for aqua ammonia that has never existed before.  These updated thermophysical properties for aqua ammonia, along with measured properties for other secondary fluids, were used to calculate operational parameters in a hypothetical ice rink refrigeration system. The results show that aqua ammonia is favorable with high COP and low pumping power, and therefore low pressure drop. Ammonia is most comparable to CaCl2 and K-formate for most results. The changes in calculated COP between old reference data and new measured data were less than a 1% decrease when plotting versus the temperature of the ice surface and with a set pump control (T) for cooling capacities of 200kW and 300kW. The change in heat transfer coefficients was more significant, with a range of about a 9% to 27% decrease in either the U-pipe under the rink floor or in a plate of the heat exchanger. Even though these heat transfer coefficient values are lower than previously calculated, the required pumping power is also lower using updated properties: 40% lower at a secondary fluid temperature of -10C. Even though the change in heat transfer coefficients is larger with experimental values, the impact on COP is minimal.  The takeaway from this project is that aqua ammonia is a favorable secondary fluid compared to calcium chloride and ethylene glycol, the two most commonly used secondary fluids in ice rink refrigeration. A system using aqua ammonia would have a 45% and 47% lower pumping power requirement compared to calcium chloride and ethylene glycol, respectively. The system would also have a 4.7% and 11.6% higher COP when compared to systems with calcium chloride and ethylene glycol, respectively. The significantly lower pumping power will lower total energy demand of the ice rink, thus decreasing operation costs. / Köldmediehantering är avgörande i försöken att sakta ner klimatförändringen. Utsläppen från kylsektorn beror främst på dålig hantering och osäker destruktion av köldmedier som för närvarande är i omlopp. Säkrare hantering av köldmedium och förbättrad systemdriftseffektivitet kan leda till ett minskat utsläpp. Ishallar är några av de mest energiintensiva offentliga byggnaderna som ger både uppvärmning och kylning. Den största andelen energi i en ishall är kylsystemet som förbrukar cirka 43%. Det finns mer än 360 isbanor i Sverige från och med 2018 och den vanligaste typen av kylsystem är ett indirekt system. Med trycket på naturliga vätskor blir ammoniakvatten ett mer tilltalande alternativ som en köldbärare i ishallar på grund av dess minimala negativa påverkan på miljön och gynnsamma termofysikaliska egenskaper. Köldbärares främsta nackdelar är dess toxiska karaktär och materialkompatibilitet. Sedan den första användningen 2007 har det dock skett en ökning till 34 av de totala ishallar i Sverige som har ammoniakvatten som köldbärare.  Termofysikaliska egenskaper används för att beräkna parametrar för kyldesign, inklusive köldbärares koncentration och pumpeffekten som krävs. Ammoniakvattens egenskaper har inte testats experimentellt under detta sekel i den utsträckning som presenteras i detta exjobb. Befintliga data härleds antingen från uppmätta värden som tagits för flera decennier sedan eller har beräknats. Nyheten härrör i detta exjobbsprojekt från de unika och mer exakta resultat som mätts genom laboratoriearbetet och från förmågan att bestämma effekten av de nyligen uppmätta värdena i kylskåpsdesign. Totalt 11 olika koncentrationer av ammoniakvatten testades med avseende på densitet, dynamisk viskositet, specifik värmekapacitet, värmeledningsförmåga och korrosion av 7 metallprover. De testade lösningarna varierade från 2 vikt-% till 30 vikt-%, korrelerade med fryspunkter från -2 ° C till -84 ° C. Mätningarna för densitet resulterade i värden som liknar referensvärdena, med en skillnad på endast 0,3% till 1,7%. Dynamiska viskositetsresultat följde nästan samma trend som referenser med förändrad temperatur och lösningskoncentration, med värden som varierade från 0,8% till 17% annorlunda än referenser. Specifika värmekapacitetsmätningar visade sig vara väsentligt annorlunda än referensvärden. Trenden är motsatt referensen, vilket leder till drastiskt olika värden, särskilt vid lägre temperaturer och högre koncentrationer. Skillnaden i värden varierar från 0,1% till 28%. Värmeledningsförmåga visar liknande trender, men högre värden än förväntat. Skillnaden mellan uppmätta värden och referensvärden sträcker sig från 0,1% till 13%. Korrosionsresultat visar att koppar och mässing har de högsta korrosionshastigheterna på 16,2 mm / år respektive 1,84 mm / år. Det mest kompatibla exemplet var rostfritt stål, följt av kolstål, med maximala korrosionshastigheter på 0,041 mm / år respektive 0,11 mm / år. Mässinganslutningar som vanligen används i industrin testades också och resulterade i korrosionshastigheter från 69,6 g / år till 112 g / år, vilket motsvarar för cirka 1% och 1,5% av anslutningarnas totala viktförlust per år. Att sammanställa laboratoriemätningarna som gjorts under slutförandet av detta projekt resulterar i en mer fullständig och noggrann lista över termofysikaliska egenskaper för ammoniakvatten som aldrig funnits tidigare.  Dessa uppdaterade termofysikaliska egenskaper för ammoniakvatten, tillsammans med uppmätta egenskaper för andra köldbärare, användes för att beräkna driftsparametrar i ett hypotetiskt kylsystem. Resultaten visar att ammoniakvatten är gynnsam med hög COP och en låg pumpeffekt och därmed ett lågt tryckfall. Ammoniakvatten är mest jämförbart med CaCl2 och K-formiat för de flesta resultat. Förändringarna i beräknad COP mellan gamla referensdata och nya uppmätta data var mindre än 1% minskning vid planering jämfört med isytans temperatur och med en inställd pumpkontroll (T ) för kylkapacitet på 200 kW och 300 kW. Förändringen i värmeövergångstal var mer signifikant, med ett intervall på cirka 9% till 27% minskning i antingen U-röret under golvet eller i en platta på värmeväxlaren. Även om dessa värmeövergångstal är lägre än tidigare beräknat, är den erforderliga pumpeffekten också lägre med hjälp av uppdaterade egenskaper: 40% lägre vid en köldbärarestemperatur på -10 ° C. Även om förändringen i värmeövergångstal är större med experimentella värden, är påverkan på COP minimal.  Slutsatser från detta projekt är att ammoniakvatten är en lämplig köldbärare jämfört med kalciumklorid och etylenglykol, de två vanligaste köldbärare i ishallskylning. Ett system som använder ammoniakvatten skulle ha ett pumpeffektbehov på 45% respektive 47% jämfört med kalciumklorid respektive etylenglykol. Systemet skulle också ha en 4,7% och 11,6% högre COP jämfört med system med kalciumklorid respektive etylenglykol. Den betydligt lägre pumpeffekten kommer att sänka det totala energibehovet för ishallar, vilket minskar driftskostnaderna.

Les problèmes liés au réchauffement climatique, conséquences de la production d'énergie et de la pollution, rendent ce thème de recherche un des plus importants du moment. La course pour trouver de nouveaux matériaux pour mettre au point des applications innovantes est à son apogée, et de grands progrès voient le jour dans chaque domaine de recherche. Par exemple, les chercheurs en physique se concentrent sur la fabrication de matériaux ou de couples de matériaux avec des propriétés électriques/thermiques supérieures pour améliorer les systèmes électroniques aux échelles nano- et micro- métriques. Certains de ces éléments sont formés de couches simples, de multicouches ou de membranes. Ainsi, des techniques expérimentales appropriées sont essentielles pour mesurer les propriétés thermophysiques de ces nouveaux composants. Dans cette thèse, la caractérisation thermique de diverses sortes de matériaux est réalisée en utilisant une technique de radiométrie photothermique (PTR). PTR est une méthode sans contact dans laquelle la réponse thermique de matériaux induite par rayonnement est mesurée. Deux types de configurations ont été utilisées, la première avec une modulation dans le domaine fréquentiel jusqu'à 10 MHz et l’autre avec une modulation hybride fréquence/spatial jusqu'à 2 MHz avec ~ 30 µm de résolution. Avec ces méthodes, il est possible d'extraire indépendamment des paramètres thermophysiques comme la diffusivité thermique, l’effusivité thermique ou la résistance de Kapitza. Ces deux configurations sont utilisées pour caractériser thermiquement des combinaisons particulières de matériaux comme des nanocomposites, des couches minces organiques, des matériaux irradiés, des matériaux à changement de phase ou les résistances thermiques à l’interfaces métal/semiconducteur. Les résultats obtenus donnent de nouvelles pistes de recherche sur le transport thermique et la gestion de la chaleur à l’échelle nanométrique. / The recognition of problems connected to the global warming linked to energy production and pollution, makes it the most important research topic of the moment. The race of finding new materials for improved applications is at its peak, while big advancements in technologies within each field of research have seen the light. For example, researchers in physics are focusing on making superior materials or couple of materials with enhanced thermo-/electric- physical properties for nano- and micro- electronic devices. The constituents in question, embody simple or complicated multiscale layers or membranes. Thus, proper experimental techniques are essential to measure the thermophysical properties of these new components. In this thesis, thermal characterization of diverse kinds of materials is made using a photothermal radiometry (PTR) technique. PTR is a contactless method which measures the thermal response of materials induced by optical heating. Two types of PTR setups were utilized, one using frequency domain modulation up to 10 MHz and one based upon hybrid frequency/spatial domain modulation up to 2 MHz with ~30 µm resolution. With these methods, it is possible to extract independent thermophysical parameters like the thermal diffusivity, thermal effusivity or Kapitza resistance. These two setups are used jointly to thermally characterize peculiar combinations of materials like: nanocomposite, organic, irradiated, phase changing and silicide materials. The results grasp new insights on the thermal transport and heat management across these set of materials and encourages novel ways to apply them in diverse applications throughout many research fields.

Um fator importante para o desenvolvimento de projetos de microssistemas é o conhecimento de propriedades termomecânicas dos materiais e a compreensão dos mecanismos de falhas. Este trabalho estuda o comportamento mecânico de microvigas atuadas termicamente e propõem um método para ser utilizado na caracterização de propriedades termomecânicas de filmes finos. Fabricou-se vigas de Oxinitreto de Silício em que se aplicou a microscopia Nomarski para observar a deformação e a ocorrência do fenômeno de flambagem. / An important factor to develop microsystems is knowledge of materials properties and failure mechanisms. This research studies the thermal actuated microbeam mechanical behavior and propose a method in order to characterize thermomechanical properties of thin films. Silicon Oxynitride microbeams are fabricated and Nomarski microscopy was applied to observe strain and buckling phenomenon ocurrence.

L’objectif de cette thèse a été d’utiliser une approche numérique pour étudier l’impact des dommages d'irradiation sur la microstructure du combustible nucléaire composé d'un mélange d’oxyde de plutonium et d’uranium (MOX). Cette approche, réalisée à l'échelle atomique, repose sur l'utilisation de potentiels empiriques développés dans la littérature pour l'oxyde mixte $(U,Pu)O_2$ dans l’approximation des interactions d’ions rigides.Une première étape a été une analyse critique des propriétés structurales, thermodynamiques et mécaniques prédites par 5 potentiels de la littérature. Les calculs de dynamique moléculaire ont été réalisés à l'aide du code LAMMPS, sur l'ensemble de la gamme de composition de $UO_2$ à $PuO_2$ et à des températures comprises entre 300 K et le point de fusion. Nous montrons que les potentiels les plus satisfaisants sont ceux développés par Cooper et Potashnikov. Ces deux potentiels reproduisent correctement la stabilité thermodynamique des phases ainsi que l'évolution en température des paramètres de maille et de la chaleur spécifique. Cependant le comportement mécanique des oxydes est différent selon le potentiel choisi. Tout d'abord, on note que les constantes élastiques et le facteur d'anisotropie obtenus par le potentiel Cooper sont plus fidèles aux recommandations de la littérature. Ensuite, nous montons que la propagation d'une fracture induit une transformation de phase en pointe de fissure avec le potentiel de Cooper alors qu'une fissuration fragile est observée avec le potentiel Potashnikov.Une seconde étape a été l'étude des dommages d'irradiation dans les oxydes mixtes en se limitant à l'utilisation des deux potentiels de Cooper et de Potashnikov. Des calculs de dynamique moléculaire de cascades de déplacement ont été réalisés à différentes énergies, température et compositions en plutonium. Ensuite, afin d'évaluer les dommages d'irradiation sur des temps plus longs que ceux accessibles en dynamique moléculaire, la méthode d’accumulation de défauts a été utilisée. Pour les deux potentiels, l’évolution des dommages primaires avec l’augmentation de la dose suit globalement les mêmes étapes que celles trouvées précédemment dans $UO_2$. Tout d’abord, les défauts ponctuels sont créés. Par la suite, ils se regroupent et forment de petites boucles de Frank, qui après se transforment en dislocations parfaites. Cependant, la cinétique de la recombinaison de défauts ponctuels est significativement plus lente avec le potentiel de Cooper ce qui conduit à la création de petites régions désordonnées pour les cascades d'énergie élevée. L’effet de la teneur en plutonium est analysé. Nous montrons en particulier que la densité de dislocations crée diminue lorsque la teneur en plutonium augmente.Bien que la dynamique moléculaire a été décrite comme un microscope moléculaire en raison de sa capacité à décrire avec précision des systèmes atomiques, elle présente un inconvénient majeur, celui lié aux temps de l’ordre de la femto-seconde nécessaires pour résoudre les vibrations atomiques. Cela limite le temps total de simulation approximativement quelques nanosecondes. Afin de stimuler les processus, tels que la diffusion de cations, un autre outil de calcul est nécessaire. Les techniques de Monte Carlo (KMC) atomiques peuvent simuler de plus longtemps que la dynamique moléculaire . Cependant, pour que KMC fonctionne avec précision, il est nécessaire de connaître a priori tous les mécanismes de transition entre les états possibles. Pour cette raison, la method de Monte Carlo cinétique adaptative (aKMC) est choisie pour surmonter ces limitations. Cette méthode détermine les états de transition disponibles pendant la simulation. De cette manière, elle entraîne le système dans des états imprévus via des mécanismes complexes. La puissance de cet outil s'est révélée efficace pour découvrir la recombinaison de cations sur de plus longues périodes de temps que la DM. / The objective of this doctoral research is to use a numerical approach to study the impact of irradiation damage on the microstructure of the mixed uranium-plutonium oxide fuel (MOX). This numerical approach comprises mainly the use of Molecular Dynamics (MD) using empirical potential. Several empirical potentials for $(U,Pu)O_2$ can be found in the literature. The results of these potentials can exhibit significant differences. For this reason an extensive assessment of the main empirical potential found in the literature had to be performed.Five empirical interatomic potentials were assessed in the approximation of rigid ions and pair interactions for the $(U_{1-y},Pu_y)O_2$ solid solution. Simulations were carried out on the structural, thermodynamics and mechanical properties over the full range of plutonium composition, meaning from pure $UO_2$ to pure $PuO_2$ and for temperatures ranging from 300 K up to the melting point. The best results are obtained by potentials referred as Cooper and Potashnikov. The first one reproduces more accurately recommendations for the thermodynamics and mechanical properties exhibiting ductile-like behaviour during crack propagation, whereas the second one gives brittle behaviour at low temperature.From our results from the empirical potentials assessment, we can move to the radiation damage using only two potentials (Cooper and Potashnikov). In order to know the main source of defect during irradiation, MD displacement cascades were simulated. This revealed the damage created due to varying projectile energies. In addition, the Frenkel pair accumulation method was chosen to investigate the dose effect. This method circumvents the highly computing time demanding accumulation of displacement cascade by directly creating their final states, i.e. mainly point defects. Overall, results obtained with both potentials show the same trend. However, kinetics of point defect recombination are significantly slower with Cooper potential implying creation of small disordered region with high energy displacement cascades. The evolution of the primary damage with increasing dose follows the same steps as those found previously in pure $UO_2$. First, point defects are created. Subsequently, they cluster and form small Frank loops, which in turn transform and grow into unfaulted loops. We demonstrate also that increasing temperatures accelerate the production of dislocations shifting their creation to lower doses. The effect of the plutonium content is also evidenced, especially with Cooper potential. It shows that the dislocation density decreases when the plutonium content increases.Although, MD has been described as a molecular microscope due to its ability to discribe accuratily systems of atoms, it has a large drawback that is the short time steps of the order of femto-seconds needed to resolve the atomic vibrations. This limits the time typically few microsecond. In order to invetigate processess, such as, cation diffusion and rare-event annihilation of defects after cascaces, another computational tool is required. Atomistic or object kinetic Monte Carlo (KMC) techniques can run for longer timescales than MD. However, for KMC to work accurately, all of the possible inter-state transition mechanisms and their associated rates need to be known a priori. For this reason, the adaptive kinetic Monte Carlo (AKMC) is chosen to overcome these limitations. This method determines the available transition states during simulation. In this way, it takes the system into unforeseen states via complex mechanisms. The power and range of this tool proved to be efficient to discover cation Frenkel pair recombination over a longer periods of time than MD.

Secondary working fluids (secondary refrigerants, heat transfer fluids, antifreezes, brines) have long been used in various indirect re-frigeration and heat pump systems. Aqueous solutions (water solu-tions) have long been used as single phase (liquid only) secondary working fluids for cooling in supermarkets, ice rinks, heat recovery systems, heat pumps and other applications. However, aqueous solutions are increasingly used also for freezers in supermarkets and other applications in low temperature refrigeration. Of importance when comparing different secondary working fluids for indirect systems are the following basic thermophysical properties: freezing point, density, viscosity, specific heat, and thermal conductivity. Reliable data of these properties are needed to choose suitable fluid and to make technical calculations of an indirect refrigeration or heat pump system. The main intention of this work has been to select thermophysical property data with good or acceptable technical accuracy of a number of aqueous solutions that can be used by the refrigeration and heat pump industry, rather than focusing on a limited number of property values or scientifically very accurate measuring techniques. A thorough literature search was in view of this made to find the most reliable property values of aqueous solutions. Detailed literature references are given for thermo-physical properties of the following aqueous solutions, without other additives: Ethylene and propylene glycol, ethyl and methyl alcohol, glycerol, ammonia, potassium carbonate, calcium, lithium, magnesium and sodium chlorides as well as potassium acetate and potassium formate. Some laboratory measurements were made of most of the fluid types when literature values were incomplete or deemed unreliable. Methods used are briefly described and results are given. Much of the work was reported on in the Engineering Licentiate Thesis: Thermophysical properties of liquid secondary refrigerants, A Critical Review on Literature References and Laboratory Measure-ments (Melinder 1998a). That material forms the basis for the charts and tables used in the IIR-publication Thermophysical properties of liquid secondary refrigerants (Melinder, 1997). The present thesis reports on an update made since 1998, including re-view work done on two additional fluids not covered in Melinder (1998a). The thesis describes how the selection of property values results in tables and charts intended for the industry. Coefficients for poly-nomial equations are generated from these property values using a Matlab program and this material is intended as a useful tool for computer treatment. Aqueous solution of ethyl alcohol is used as example to see how this process is made. This choice of fluid can also be seen as a test of this method, as the basic thermophysical properties of aqueous solutions of ethyl alcohol present more chal-lenges than the other fluids examined. A comparison is made of a few types of aqueous solutions used as secondary working fluids for two types of applications. The first example is bedrock heat pumps and the second is cooling cabinets in a supermarket. An effort is made to see how the additive con-centration affects the thermal performance. Most aqueous solutions used as single-phase secondary fluids can also be used as ice slurry, a fluid consisting of liquid and ice where small ice crystals are produced, usually with some type of ice generator. The ice crystals are then transported to the cooling object from which heat is removed when ice crystals melt. This results in less temperature change in the cooling object and makes it also possible to reduce the volume flow rate and to use smaller pipe dimensions in the system. In order to choose a secondary fluid for ice slurry use and to make correct technical calculations of the ice slurry system there is a need to examine and evaluate thermo-physical properties and other aspects of ice and of the aqueous solution used. For dimensioning purposes it is of interest to estimate ice mass fraction and enthalpy values and enthalpy-phase diagrams can serve that purpose. This thesis presents enthalpy-phase diagrams made by author that besides isotherms contain lines with ice fraction and lines connecting enthalpies at freezing point and 1, 2, etc. to 10 K below the freezing point curve. / QC 20100609

Submitted by Deyse Queiroz (deysequeirozz@hotmail.com) on 2018-06-13T13:06:26Z No. of bitstreams: 1 JOÃO TAVARES NUNES - DISSERTAÇÃO PPGEA 2011..pdf: 11091920 bytes, checksum: d63185b45641e3f0c461d42c911f608b (MD5) / Made available in DSpace on 2018-06-13T13:06:26Z (GMT). No. of bitstreams: 1 JOÃO TAVARES NUNES - DISSERTAÇÃO PPGEA 2011..pdf: 11091920 bytes, checksum: d63185b45641e3f0c461d42c911f608b (MD5) Previous issue date: 2011-09 / Com o intuito de aproveitar o fruto do mandacaru produzido na região semiárida do Nordeste visando à produção de polpas e sucos, o presente trabalho teve como objetivo determinar as principais propriedades termofísicas, massa específica, condutividade térmica, difusividade térmica e calor específico, além do comportamento reológico das polpas integral e concentradas do fruto do mandacaru até os teores de 35 e 56 °Brix. A massa específica foi determinada pelo método picnométrico; para a difusividade térmica utilizou-se o método do cilindro infinito de Dickerson; o valor do calor específico foi obtido usando através do método das misturas e a condutividade térmica foi calculada por método indireto. Equações propostas em literatura também foram utilizadas para estimar as propriedades termofísicas. Os dados reológicos foram determinados utilizando-se um viscosímetro Brookfield e os modelos de Casson, Ostwald-de-Waelle e Herschel-Bulkley, ajustados aos dados experimentais, ressaltando-se que o último modelo foi o que proporcionou os melhores ajustes. As polpas com a concentração de 12 °Brix apresentaram comportamento não-newtoniano do tipo dilatante; no entanto, as polpas com concentrações de 35 e 56 °Brix apresentaram comportamento não newtoniano do tipo pseudoplástico. A viscosidade foi influenciada pela concentração e temperatura. A polpa integral do fruto do mandacaru foi considerada um alimento ácido, com baixo conteúdo mineral, alto teor de umidade e de atividade de água, com predominância da intensidade de amarelo. As propriedades termofísicas se mantiveram em faixa esperada para polpas de frutas. A massa específica aumentou com o aumento do teor de sólidos solúveis totais e o calor específico e a difusividade térmica diminuíram com o aumento da concentração. Das equações utilizadas para estimar a massa específica, calor específico, difusividade térmica e condutividade térmica, apenas as referentes a massa específica podem ser consideradas razoáveis para todas as amostras, com erros abaixo de 20%. / In order to make better use of mandacaru fruit grown in the semiarid Northeast of Brazil for pulp and fruit production, this study sought to determine the main thermophysical properties, density, thermal conductivity and specific heat capacity, in addition to rheological behavior of whole and concentrated mandacaru fruit pulp up to a content of 35 and 56 °Brix. Density was determined by the pycnometric method; the Dickerson infinite cylinder method was used for thermal diffusivity; the heat capacity value was obtained by the method of mixtures and thermal conductivity by the indirect method. Equations proposed in the literature were also applied to estimate thermophysical properties. Rheological data were determined using a Brookfield viscometer and Casson, Ostwald-de-Waelle and Herschel-Bulkley models, fit to experimental data, with the last model exhibiting best fit. Pulps with a concentration of 12 °Brix showed dilatant non- Newtonian behavior; however, those with concentrations of 35 and 56 °Brix displayed pseudoplastic non-Newtonian behavior. Viscosity was influenced by concentration and temperature. Mandacaru whole fruit pulp, predominantly yellow, was considered acidic, with low mineral content, high moisture content and water activity. Thermophysical properties were in the expected range for fruit pulp. Density increased with a rise in soluble solid content, while heat capacity and thermal diffusivity decreased with increased concentrations. Of the equations used to estimate density, heat capacity, thermal diffusivity and thermal conductivity, only those related to density are adequate for ali samples, with an error of less than 20%.

Différentes familles de liquides ioniques ont été sélectionnées pour leur capacité d’absorption de gaz et plus particulièrement de dioxyde de carbone. L’objectif de ces travaux est de définir les liquides ioniques les plus à même d’être utilisés en tant qu’absorbants dits alternatifs dans les procédés de captage de gaz, l’enjeu principal étant à terme de diminuer les coûts de production des procédés industriels. Les systèmes retenus sont des liquides ioniques purs issus de la combinaison de cations imidazolium, pyrrolidinium et phosphonium avec des anions de type carboxylate ou tris (pentafluoroethyl) trifluorophosphate ainsi que des mélanges binaires de liquides ioniques avec anion carboxylate + eau. L’absorption de différents gaz - dioxyde de carbone, azote, protoxyde d’azote et éthane - dans les liquides ioniques purs ainsi que dans les mélanges liquide ionique +eau a été mesurée dans une gamme de températures comprises entre 303.15 et 353.15 K et pour des pressions proches de l’atmosphérique. La sélectivité des liquides ioniques pour l’absorption de dioxyde de carbone par rapport aux autres gaz a pu être déterminée. La caractérisation de l’absorption de gaz est fonction des systèmes étudiés, les interactions entre les gaz et certains liquides ioniques (ou certains mélanges liquide ionique + eau) étant uniquement de type physique alors que dans d’autres systèmes, l’absorption est le résultat à la fois d’interactions physiques mais également de la présence de réaction chimique. / Different classes of ionic liquids have been selected for their ability to solubilize gases and more particularly carbon dioxide. The objective of this work is to define the ionic liquids which are most likely to be used as alternative absorbents in capture processes of gases, the main issue is to reduce the costs of production of the industrial processes. The systems used are the pure ionic liquids from the combination of imidazolium, phosphonium and pyrrolidinium cation with carboxylate or tris (pentafluoroethyl) trifluorophosphate anion and binary mixtures of ionic liquids with carboxylate anion + water. The absorption of different gases - carbon dioxide, nitrogen, nitrous oxide and ethane – in pure ionic liquids as well as in mixtures of ionic liquid + water was measured in a temperature range of between 303.15 and 353.15 K and pressures close to atmospheric. The selectivity of ionic liquids for the absorption of carbon dioxide from other gases could was determined. Characterization of gas absorption is a function of the studied system, since the interactions between gas and ionic liquid (or mixture ionic liquid + water) are of the physical type for some systems, while in other, the absorption is the result of both physical interaction and chemical reaction.

Um fator importante para o desenvolvimento de projetos de microssistemas é o conhecimento de propriedades termomecânicas dos materiais e a compreensão dos mecanismos de falhas. Este trabalho estuda o comportamento mecânico de microvigas atuadas termicamente e propõem um método para ser utilizado na caracterização de propriedades termomecânicas de filmes finos. Fabricou-se vigas de Oxinitreto de Silício em que se aplicou a microscopia Nomarski para observar a deformação e a ocorrência do fenômeno de flambagem. / An important factor to develop microsystems is knowledge of materials properties and failure mechanisms. This research studies the thermal actuated microbeam mechanical behavior and propose a method in order to characterize thermomechanical properties of thin films. Silicon Oxynitride microbeams are fabricated and Nomarski microscopy was applied to observe strain and buckling phenomenon ocurrence.

Ces travaux de thèse s’inscrivent dans le cadre du projet ANR HUMIBATex « Comment prédire les désordres causés par l’humidité ? Quelles solutions techniques pour rénover le bâti existant ? » (2012-2016). Elle traite de la modélisation numérique et expérimentale des transferts couplés hydro-thermo-aérauliques à différentes échelles : matériau, paroi et ambiance de bâtiment. Sur le plan théorique, un modèle phénoménologique des transferts couplés de chaleur, d’air et d’humidité à travers les enveloppes de bâtiments (HAM) a été élaboré. Après la phase de validation (confrontation avec des solutions analytiques et des résultats expérimentaux), ce modèle a été implémenté avec confiance dans un code de simulation thermique dynamique du bâtiment (BES). Ceci a permis, ainsi, de développer une plateforme de co-simulation HAM-BES. Grâce à l’outil mis en œuvre, les comportements hygrothermiques de la paroi et de l’ambiance habitable des bâtiments ont été prédits finement. Deux cas d’études ont été entrepris. Le premier avait pour but de mettre en évidence l’impact des transferts hygrothermiques sur la prédiction des consommations énergétiques. Le deuxième cas d’étude a été dédié à l’étude de l’efficacité de différentes stratégies de ventilation (extraction ou insufflation) sur le contrôle et la diminution des risques d’apparition de désordres liés à l’humidité au niveau des bâtiments résidentiels. Sur le plan expérimental, une campagne de caractérisation des propriétés physiques, hydriques et thermophysiques des matériaux de construction a été effectuée. Cette campagne expérimentale s’est focalisée sur l’analyse de l’impact de l’état thermique et hydrique du matériau sur les valeurs des propriétés hygrothermiques. Dans un autre travail expérimental, des dispositifs expérimentaux, à petite échelle mais également à l’échelle de la paroi, ont été conçus au laboratoire dans le but d’étudier la réponse hygrothermique des enveloppes de bâtiment ainsi que valider la plateforme de co-simulation dynamique HAM-BES. La confrontation des résultats a montré une bonne concordance entre la résolution numérique et les mesures expérimentales. Les résultats obtenus dans le cadre de ce travail de thèse ont mis en exergue l’influence d’une modélisation fine des transferts couplés de chaleur, d’air et d’humidité, à la fois sur la prédiction du comportement hygrothermique des ambiances habitables mais aussi sur le calcul des besoins énergétiques des bâtiments. / The present PhD thesis work is conducted in the framework of the National Program ANR HUMIBATex Project « How to predict the disorders caused by moisture? What technical solutions to renovate the existing buildings? ». It deals with the numerical and experimental modeling of a coupled heat, air and moisture transfers at different scales: material, envelope and building ambience. In the theoretical part, based on expression of heat and moisture (vapor, liquid and air) balances equations, a phenomenological model describing the coupled heat, air and moisture transfer (HAM) through the wall has been developed. After validation stage (comparison with experimental results and analytical solution), the model has been implemented with confidence in a building energy simulation code (BES). Using this HAM-BES dynamic co-simulation tool, the hygrothermal behavior of the wall and indoor air of buildings were predicted finely. Two cases studies have been undertaken. The aim of the first one was to highlight the impact of hydrothermal transfers on the prediction of building energy consumption. However, the second case study was devoted to study efficiency of different ventilation strategies (extracting or insufflation) on the control and reduction of disorders caused by moisture in residential buildings. In the experimental part, a characterization campaign of physical, hydric and thermophysical properties of construction materials has been carried out. This experimental campaign has been focused on analyzing of the impact of thermal and hydric state of the construction material on the hygrothermal properties values. In another work, several experimental devices, at small-scale and wall scale, were designed in the laboratory to study the hygrothermal response of different building envelopes configuration and validate the developed HAM-BES dynamic co-simulation platform. Results of confrontation have showed good agreement between the numerical solution and experimental measurements.The obtained results in the framework of this PhD thesis have highlighted the influence of a detailed modeling of coupled heat air and moisture transfer through the wall on the hygrothermal behavior prediction of the indoor air, on assessment of pathology indicators and on the evaluation of the buildings energy loads.