<p>The latent-heat-storage capacity in Phase-Change Materials can be used for storing or releasing energy within a small temperature interval. Upon the phase transition taking place in a narrow temperature span, the material takes up or releases more energy compared to sensible heat storage. For an ideal phase-change material, the transition temperature is a single value, but for the most common phase-change materials on the market, used in building applications, the transition temperature is distributed within a temperature range of several degrees.</p><p>Integration of phase-change materials in building applications can be effected in several ways, for example by impregnating phase-change materials into porous building materials like concrete, wallboards, bricks or complements of the building structure. Integrating storages filled with phase-change materials makes other implementations, for instance accumulating tanks or envelopes as presented in this thesis, in an air heat exchanger. An appropriate phasetransition temperature of the supposed application is critical to the functionality of the material. For example, in cooling applications, the transition temperature of the material should be a few degrees lower than the requested comfort temperature in the building, and the opposite for heating applications.</p><p>In order to assess the thermal properties and the durability of the material, a watercalorimetric equipment was developed and employed in an accelerated testing programme. The heat capacity of the material and in particular possible change in the heat capacity over time, after thermal cycling of the material, were measured. In the thermal cycling of the material from solid to liquid phase, the temperature rise and required energy supply were recorded. The testing programme was undertaken according to control procedures and documents. In order to be able to utilize the heat-storage capacity in the best way, it is necessary to gain knowledge about thermal properties of the material, especially the long-term behaviour of the material and the deterioration rates of the thermal properties.</p><p>A semi-full-scale air heat exchanger based on phase-change material was developed and tested under real temperature conditions during the summer of 2004. The test results were used to compare and verify computer simulations made on a similar plant. The air heat exchanger utilises the ambient diurnal temperature swing to charge and discharge the phasechange material. The material tested in the calorimeter and in the air heat exchanger has an estimated phase-change temperature of about 24 °C.</p>

Les mémoires à base de semi-conducteur sont indispensables pour les dispositifs électroniques actuels. La demande croissante pour des dispositifs mémoires fortement miniaturisées a entraîné le développement de mémoires non volatiles fiables qui sont utilisées dans des systèmes informatiques pour le stockage de données et qui sont capables d'atteindre des débits de données élevés, avec des niveaux de dissipation d'énergie équivalents voire moindres que ceux des technologies mémoires actuelles.Parmi les technologies de mémoires non-volatiles émergentes, les mémoires à changement de phase (PCM) sont le candidat le plus prometteur pour remplacer la technologie de mémoire Flash conventionnelle. Les PCM offrent une grande variété de fonctions, comme une lecture et une écriture rapide, un excellent potentiel de miniaturisation, une compatibilité CMOS et des performances élevées de rétention de données à haute température et d'endurance, et peuvent donc ouvrir la voie à des applications non seulement pour les dispositifs mémoires, mais également pour les systèmes informatiques à hautes performances. Cependant, certains problèmes de fiabilité doivent encore être résolus pour que les PCM se positionnent comme un remplacement concurrentiel de la mémoire Flash.Ce travail se concentre sur l'étude de mémoires à changement de phase intégrées afin d'optimiser leurs performances et de proposer des solutions pour surmonter les principaux points critiques de la technologie, ciblant des applications à hautes températures. Afin d'améliorer la fiabilité de la technologie, la stœchiométrie du matériau à changement de phase a été conçue de façon appropriée et des dopants ont été ajoutés, optimisant ainsi la stabilité thermique. Une diminution de la vitesse de programmation est également rapportée, ainsi qu'un drift résiduel de la résistance de l'état de faiblement résistif vers des valeurs de résistance plus élevées au cours du temps.Une nouvelle technique de programmation est introduite, permettant d'améliorer la vitesse de programmation des dispositifs et, dans le même temps, de réduire avec succès le phénomène de drift en résistance. Par ailleurs, un algorithme de programmation des PCM multi-bits est présenté. Un générateur d'impulsions fournissant des impulsions avec la tension souhaitée en sortie a été conçu et testé expérimentalement, répondant aux demandes de programmation d'une grande variété de matériaux innovants et en permettant la programmation précise et l’optimisation des performances des PCM. / Semiconductor memory has always been an indispensable component of modern electronic systems. The increasing demand for highly scaled memory devices has led to the development of reliable non-volatile memories that are used in computing systems for permanent data storage and are capable of achieving high data rates, with the same or lower power dissipation levels as those of current advanced memory solutions.Among the emerging non-volatile memory technologies, Phase Change Memory (PCM) is the most promising candidate to replace conventional Flash memory technology. PCM offers a wide variety of features, such as fast read and write access, excellent scalability potential, baseline CMOS compatibility and exceptional high-temperature data retention and endurance performances, and can therefore pave the way for applications not only in memory devices, but also in energy demanding, high-performance computer systems. However, some reliability issues still need to be addressed in order for PCM to establish itself as a competitive Flash memory replacement.This work focuses on the study of embedded Phase Change Memory in order to optimize device performance and propose solutions to overcome the key bottlenecks of the technology, targeting high-temperature applications. In order to enhance the reliability of the technology, the stoichiometry of the phase change material was appropriately engineered and dopants were added, resulting in an optimized thermal stability of the device. A decrease in the programming speed of the memory technology was also reported, along with a residual resistivity drift of the low resistance state towards higher resistance values over time.A novel programming technique was introduced, thanks to which the programming speed of the devices was improved and, at the same time, the resistance drift phenomenon could be successfully addressed. Moreover, an algorithm for programming PCM devices to multiple bits per cell using a single-pulse procedure was also presented. A pulse generator dedicated to provide the desired voltage pulses at its output was designed and experimentally tested, fitting the programming demands of a wide variety of materials under study and enabling accurate programming targeting the performance optimization of the technology.

O design de produto através de suas interfaces multidisciplinares possibilita o desenvolvimento de novas tecnologias destinadas a pessoas com deficiência física. A Tecnologia Assistiva (TA) engloba todo arsenal de recursos e serviços que contribuem para proporcionar ou ampliar habilidades funcionais de pessoas com deficiência e tem como principal exemplo a cadeira de rodas, onde o usuário fica longos períodos na posição sentada e o conforto térmico é necessário. Neste trabalho, desenvolveu-se microcápsulas de eicosano e impregnou-se espumas de poliuretano (PU) com as microcápsulas visando o conforto térmico nessas espumas. O eicosano é um material de mudança de fase (PCM) com temperatura de mudança de fase ao redor de 37°C, que é igual a temperatura de equilíbrio térmico do corpo humano. As microcápsulas inseridas em espumas de poliuretano possuem potencial uso na Tecnologia Assistiva, mais especificamente em assentos de cadeiras de rodas visando o conforto térmico. As microcápsulas foram obtidas através da polimerização in-situ, utilizando resina melamina-formaldeído como invólucro e eicosano como núcleo. As técnicas usadas para a caracterização das microcápsulas envolveram análises de microscopia óptica, microscopia eletrônica de varredura (MEV), granulometria, Espectroscopia do Infravermelho por Transformada de Fourier (FT-IR), Análise Termogravimétrica (TGA) e Calorimetria Exploratória Diferencial (DSC). As microcápsulas de eicosano foram então inseridas em espumas de poliuretano com diferentes densidades e foram analisadas por termografia. As microcápsulas de eicosano impregnadas nas espumas de PU possuem capacidade de absorver ou liberar calor do ambiente circundante e manter a temperatura ao seu redor constante por um determinado período de tempo, sendo assim possuem aplicação potencial na Tecnologia Assistiva, como em assentos de cadeiras de roda por exemplo, devido a sua capacidade de isolamento térmico e absorção ou liberação de calor enquanto ocorre a mudança de fase do eicosano. / The product design through its multidisciplinary interfaces allows de development of new technologies for people with some physical disability. The Assistive Technology (TA) includes all the resources and services that contribute to give and enlarge the functional abilities of people with some disability. The most significant sample of TA resource is the wheel chair, where the person stays long time in the seat position and the thermal comfort is necessary. In this work, microcapsules of eicosane were developed and then polyurethane foams were impregnated with the microcapsules aiming the thermal comfort on the polyurethane foams. The eicosane is a phase change material (PCM) with temperature of phase change of 37°C which is similar to the human body temperature in thermal equilibrium. The microcapsules added to the polyurethane foams have potential use on the Assistive Technology, more specifically on cushion seats aiming the thermal comfort. The microcapsules were obtained by in-situ polymerization using resin melamine-formaldehyde as wall and eicosane as the core. The analysis used to evaluate the properties of the microcapsules were: optical microscopy, scanning electron microscopy (SEM), particle size analysis, fourier transform infrared spectroscopy (FT-IR), thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). Then the microcapsules of eicosane were added in polyurethane foams with different densities and were analyzed by infrared thermography. The microcapsules of eicosane added to the polyurethane foams present the capacity of absorb or release heat to the environment and maintain the around temperature constant for a period of time. So they have potential application on the Assistive Techology, as wheel chair cushion seats for example, due to its capacity of thermal insulation and absorption or release of heat while occurs the eicosane phase change.

O design de produto através de suas interfaces multidisciplinares possibilita o desenvolvimento de novas tecnologias destinadas a pessoas com deficiência física. A Tecnologia Assistiva (TA) engloba todo arsenal de recursos e serviços que contribuem para proporcionar ou ampliar habilidades funcionais de pessoas com deficiência e tem como principal exemplo a cadeira de rodas, onde o usuário fica longos períodos na posição sentada e o conforto térmico é necessário. Neste trabalho, desenvolveu-se microcápsulas de eicosano e impregnou-se espumas de poliuretano (PU) com as microcápsulas visando o conforto térmico nessas espumas. O eicosano é um material de mudança de fase (PCM) com temperatura de mudança de fase ao redor de 37°C, que é igual a temperatura de equilíbrio térmico do corpo humano. As microcápsulas inseridas em espumas de poliuretano possuem potencial uso na Tecnologia Assistiva, mais especificamente em assentos de cadeiras de rodas visando o conforto térmico. As microcápsulas foram obtidas através da polimerização in-situ, utilizando resina melamina-formaldeído como invólucro e eicosano como núcleo. As técnicas usadas para a caracterização das microcápsulas envolveram análises de microscopia óptica, microscopia eletrônica de varredura (MEV), granulometria, Espectroscopia do Infravermelho por Transformada de Fourier (FT-IR), Análise Termogravimétrica (TGA) e Calorimetria Exploratória Diferencial (DSC). As microcápsulas de eicosano foram então inseridas em espumas de poliuretano com diferentes densidades e foram analisadas por termografia. As microcápsulas de eicosano impregnadas nas espumas de PU possuem capacidade de absorver ou liberar calor do ambiente circundante e manter a temperatura ao seu redor constante por um determinado período de tempo, sendo assim possuem aplicação potencial na Tecnologia Assistiva, como em assentos de cadeiras de roda por exemplo, devido a sua capacidade de isolamento térmico e absorção ou liberação de calor enquanto ocorre a mudança de fase do eicosano. / The product design through its multidisciplinary interfaces allows de development of new technologies for people with some physical disability. The Assistive Technology (TA) includes all the resources and services that contribute to give and enlarge the functional abilities of people with some disability. The most significant sample of TA resource is the wheel chair, where the person stays long time in the seat position and the thermal comfort is necessary. In this work, microcapsules of eicosane were developed and then polyurethane foams were impregnated with the microcapsules aiming the thermal comfort on the polyurethane foams. The eicosane is a phase change material (PCM) with temperature of phase change of 37°C which is similar to the human body temperature in thermal equilibrium. The microcapsules added to the polyurethane foams have potential use on the Assistive Technology, more specifically on cushion seats aiming the thermal comfort. The microcapsules were obtained by in-situ polymerization using resin melamine-formaldehyde as wall and eicosane as the core. The analysis used to evaluate the properties of the microcapsules were: optical microscopy, scanning electron microscopy (SEM), particle size analysis, fourier transform infrared spectroscopy (FT-IR), thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). Then the microcapsules of eicosane were added in polyurethane foams with different densities and were analyzed by infrared thermography. The microcapsules of eicosane added to the polyurethane foams present the capacity of absorb or release heat to the environment and maintain the around temperature constant for a period of time. So they have potential application on the Assistive Techology, as wheel chair cushion seats for example, due to its capacity of thermal insulation and absorption or release of heat while occurs the eicosane phase change.

O design de produto através de suas interfaces multidisciplinares possibilita o desenvolvimento de novas tecnologias destinadas a pessoas com deficiência física. A Tecnologia Assistiva (TA) engloba todo arsenal de recursos e serviços que contribuem para proporcionar ou ampliar habilidades funcionais de pessoas com deficiência e tem como principal exemplo a cadeira de rodas, onde o usuário fica longos períodos na posição sentada e o conforto térmico é necessário. Neste trabalho, desenvolveu-se microcápsulas de eicosano e impregnou-se espumas de poliuretano (PU) com as microcápsulas visando o conforto térmico nessas espumas. O eicosano é um material de mudança de fase (PCM) com temperatura de mudança de fase ao redor de 37°C, que é igual a temperatura de equilíbrio térmico do corpo humano. As microcápsulas inseridas em espumas de poliuretano possuem potencial uso na Tecnologia Assistiva, mais especificamente em assentos de cadeiras de rodas visando o conforto térmico. As microcápsulas foram obtidas através da polimerização in-situ, utilizando resina melamina-formaldeído como invólucro e eicosano como núcleo. As técnicas usadas para a caracterização das microcápsulas envolveram análises de microscopia óptica, microscopia eletrônica de varredura (MEV), granulometria, Espectroscopia do Infravermelho por Transformada de Fourier (FT-IR), Análise Termogravimétrica (TGA) e Calorimetria Exploratória Diferencial (DSC). As microcápsulas de eicosano foram então inseridas em espumas de poliuretano com diferentes densidades e foram analisadas por termografia. As microcápsulas de eicosano impregnadas nas espumas de PU possuem capacidade de absorver ou liberar calor do ambiente circundante e manter a temperatura ao seu redor constante por um determinado período de tempo, sendo assim possuem aplicação potencial na Tecnologia Assistiva, como em assentos de cadeiras de roda por exemplo, devido a sua capacidade de isolamento térmico e absorção ou liberação de calor enquanto ocorre a mudança de fase do eicosano. / The product design through its multidisciplinary interfaces allows de development of new technologies for people with some physical disability. The Assistive Technology (TA) includes all the resources and services that contribute to give and enlarge the functional abilities of people with some disability. The most significant sample of TA resource is the wheel chair, where the person stays long time in the seat position and the thermal comfort is necessary. In this work, microcapsules of eicosane were developed and then polyurethane foams were impregnated with the microcapsules aiming the thermal comfort on the polyurethane foams. The eicosane is a phase change material (PCM) with temperature of phase change of 37°C which is similar to the human body temperature in thermal equilibrium. The microcapsules added to the polyurethane foams have potential use on the Assistive Technology, more specifically on cushion seats aiming the thermal comfort. The microcapsules were obtained by in-situ polymerization using resin melamine-formaldehyde as wall and eicosane as the core. The analysis used to evaluate the properties of the microcapsules were: optical microscopy, scanning electron microscopy (SEM), particle size analysis, fourier transform infrared spectroscopy (FT-IR), thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). Then the microcapsules of eicosane were added in polyurethane foams with different densities and were analyzed by infrared thermography. The microcapsules of eicosane added to the polyurethane foams present the capacity of absorb or release heat to the environment and maintain the around temperature constant for a period of time. So they have potential application on the Assistive Techology, as wheel chair cushion seats for example, due to its capacity of thermal insulation and absorption or release of heat while occurs the eicosane phase change.

Orientadores: Luiz Fernando Milanez, Alcides Padilha / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-12T14:21:28Z (GMT). No. of bitstreams: 1 Oliveira_SantiagodelRio_D.pdf: 2035815 bytes, checksum: 7d72e5c223058fb0ce3675f4600214f5 (MD5) Previous issue date: 2008 / Resumo: O objetivo desse trabalho é fazer uma otimização exergética de um sistema térmico de energia solar. Esse sistema é composto por um coletor solar e por um tanque armazenador de água retangular que contém material de mudança de fase distribuído em um conjunto de barras. Esse estudo leva em consideração ambas transferências de calor por condução e convecção para a água no coletor solar, e também o processo de mudança de fase para o PCM no armazenador térmico. Assim, no coletor solar são determinadas a temperatura ótima de saída e vazão mássica ótima da água em função das condições de radiação solar. Além disso, para o tanque armazenador, são determinadas a temperatura ótima de fusão do PCM e o máximo trabalho que pode ser obtido levando em consideração o processo de mudança de fase. O processo de fusão do PCM é analisado por meio de uma solução analítica aproximada. Finalmente, foram feitas uma análise energética e exergética de cada componente do sistema bem como de todo o sistema e foram calculadas eficiências de primeira e segunda lei da termodinâmica. Resultados numéricos de um estudo de caso são apresentados e discutidos. / Abstract: This work deals with the exergetic optimization of a solar thermal energy system. This consists of a solar collector and a rectangular water storage tank that contains a phase change material distributed in an assembly of slabs. The study takes into account both conduction and convection heat transfer modes for water in the solar collector, and also the phase change process for the PCM in the storage tank. Thus, in the solar collector, optimal output temperature and optimal mass flow rate are determined as a function of solar radiation conditions. Moreover, for the storage tank, optimal melting temperature and the maximum power output taking into account the phase change process are determined. The melting process in a PCM is analyzed by means of an approximated analytical solution. Finally, energetic and exergetic analysis were done for each system component and for the overall system, and efficiencies of first and second law of thermodynamics were calculated. Results of a numerical case study are presented and discussed. / Doutorado / Termica e Fluidos / Doutor em Engenharia Mecânica

Interest in the use of heat pipe technology for heat recovery and energy saving in a vast range of engineering applications has been on the rise in recent years. Heat pipes are playing a more important role in many industrial applications, especially in increasing energy savings in commercial applications and improving the thermal performance of heat exchangers. Computational techniques play an important role in solving complex flow problems for a large number of engineering applications due to their universality, flexibility, accuracy and efficiency. However, up to now, computational studies on heat pipes are still at an early stage due to the complexity of multiphase flow characteristics and heat and mass transfer phase changes. Therefore, the main objective of this study is to develop a CFD modelling that includes the complex physical phenomena of both the heat transfer processes of evaporation and condensation and the mass transfer process of phase change during the pool boiling and film condensation. In this thesis, two novel numerical models were developed in ANSYS FLUENT. In the first, a two-dimensional CFD model was developed to visualise the two-phase flow and the evaporation, condensation and heat transfer phenomena during the operation of a wickless heat pipe, that otherwise could not be visualised by empirical or experimental work. An in-house code was developed using user-defined functions (UDFs) to enhance the ability of FLUENT to simulate the phase change occurring inside the heat pipe. Three different fluids, water, R134a and R404a, were selected as the working fluids of the investigated wickless heat pipe. The cooling system of the condenser section was simulated separately as a three-dimensional CFD model of a parallel-flow double pipe heat exchanger to model the heat transfer across the condenser section's heat exchanger and predict the heat transfer coefficients. The overall effective thermal resistance along with the temperature profile along the wickless heat pipe have been investigated. An experimental apparatus was built to carry out a thermal performance investigation on a typical wickless heat pipe for the purpose of validating the CFD simulation. A theoretical model based on empirical correlations was developed to predict the heat transfer thermal resistances in the evaporator and the condenser section. The second model was developed to combine the two-dimensional CFD simulation of the wickless heat pipe and the three-dimensional CFD simulation of the condenser section's heat exchanger to simulate the two-phase flow phenomena of boiling and condensation and the cooling system of the condenser section through a comprehensive three-dimensional CFD model of a wickless heat pipe. Two fluids, water and R134a, were selected as the working fluids of the investigated wickless heat pipe. This model was validated using a transparent glass wickless heat pipe to visualise the phenomena of pool boiling and comparing the results with the three-dimensional CFD flow visualisation. This study demonstrated that the proposed CFD models of a wickless heat pipe can successfully reproduce the complex physical phenomena of both the heat transfer process of evaporation and condensation and the mass transfer process of phase change during the pool boiling that takes place in the evaporator section and the filmwise condensation that takes place in the condenser section. The CFD simulation was successful in modelling and visualising the multiphase flow characteristics for water, R134a and R404a, emphasising the difference in pool boiling behaviour between these working fluids. The CFD simulation results were compared with experimental measurements, with good agreement obtained between predicted temperature profiles and experimental temperature data.

La récupération de chaleur fatale est un véritable challenge pour l’amélioration de l’efficacité énergétique. Le stockage par chaleur latente est une solution qui répond à cet enjeu. Nous nous intéressons aux procédés industriels avec un rapport puissance sur énergie élevé. L’un des procédés identifiés est la stérilisation de produits agroalimentaires. Cependant, les matériaux à changement de phase, peu conducteurs, ne permettent pas d’obtenir des puissances thermiques suffisantes pour ces applications. L’amélioration de la surface d’échange ou l’augmentation de la conductivité thermique du matériau sont alors nécessaires. Un premier dispositif expérimental de stockage thermique comparant différentes techniques d’intensification des transferts a été réalisé. Le concept à base de paraffine et de Graphite Naturel Expansé (GNE) s’est montré le plus performant par rapport à des solutions de type ailettes ou poudre de graphite. La caractérisation thermique du matériau composite GNE/paraffine sélectionné a été réalisée par plusieurs méthodes. Des valeurs de conductivité thermique effective de l’ordre 20 W.m-1.K-1 ont été obtenues. Dans un second temps, un démonstrateur de 100kW/6kW.h est dimensionné et réalisé. Ce dispositif testé sur un procédé de stérilisation existant permet une économie d’énergie de 15%, conforme aux prévisions. L’identification de la conductivité thermique plane du matériau et l’influence de la résistance thermique de contact sont réalisées à l’aide d’un dispositif expérimental, couplé à un modèle numérique. Enfin, le développement d’un dispositif de vieillissement permet l’étude de la stabilité thermique de ce matériau. / Waste heat recovery is a challenge for the improvement of energy efficiency. Latent heat storage is a solution that addresses this issue. We focus on industrial processes with high energy on power ratios. One of the identified processes is the sterilization of food products. However, phase change materials, which have low thermal conductivities, do not provide sufficient thermal powers for these applications. The improvement of the heat exchange surface or the increase in thermal conductivity of the material are then necessary. A first experimental thermal storage comparing various heat transfer intensification techniques was achieved. The concept based on paraffin and Expanded Natural Graphite (ENG) has proven to be the most efficient compared to solutions using fins or graphite powder. The thermal characterization of the selected composite material ENG/paraffin was performed by several methods. Effective thermal conductivities values of about 20 W.m-1.K-1 were obtained. In a second step, a 100kW/6kW.h demonstrator is designed and realized. This device tested on an existing sterilization process provides an energy saving of 15%, as expected. The identification of the planar thermal conductivity of the composite material and the influence of the thermal contact resistance are carried out using an experimental device, coupled to a numerical model. Finally, an aging device is used to study the thermal stability of this material

Climate change is no longer imminent but eminent. To combat climate change, effective, efficient and smart energy use is imperative. Thermal energy storage (TES) with phase change materials (PCMs) is one attractive choice to realize this. Besides suitable phase change temperatures and enthalpies, the PCMs should also be robust, non-toxic, environmental-friendly and cost-effective. Cost-effective PCMs can be realized in bulk blends. Blends however do not have robust phase change unless chosen articulately. This thesis links bulk blends and robust, cost-effective PCMs via the systematic design of blends as PCMs involving phase equilibrium evaluations. The key fundamental phase equilibrium knowledge vital to accurately select robust PCMs within blends is established here. A congruent melting composition is the most PCM-ideal among blends. Eutectics are nearly ideal if supercooling is absent. Any incongruent melting composition, including peritectics, are unsuitable as PCMs. A comprehensive state-of-the-art evaluation of the phase equilibrium-based PCM design exposed the underinvestigated categories: congruent melting compositions, metal alloys, polyols and fats. Here the methods and conditions essential for a comprehensive and transparent phase equilibrium assessment for designing PCMs in blends are specified. The phase diagrams of the systems erythritol-xylitol and dodecane-tridecane with PCM potential are comprehensively evaluated. The erythritol-xylitol system contains a eutectic in a partially isomorphous system unlike in a non-isomorphous system as previous literature proposed. The dodecane-tridecane system forms a probable congruent minimum-melting solid solution, but not a maximum-melting liquidus or a eutectic as was previously proposed. The sustainability aspects of a PCM-based TES system are also investigated. Erythritol becomes cost-effective if produced using glycerol from bio-diesel production. Olive oil is cost-effective and has potential PCM compositions for cold storage. A critical need exists in the standardization of methods and transparent results reporting of the phase equilibrium investigations in the PCM-context. This can be achieved e.g. through international TES collaboration platforms. / Energi är en integrerad del av samhället men energiprocesser leder till miljöbelastning, och klimatförändringar. Därför är effektiv energianvändning, ökad energieffektivitet och smart energihantering nödvändigt. Värmeenergilagring (TES) är ett attraktivt val för att bemöta detta behov, där ett lagringsalternativ med hög densitet är s.k. fasomvandlingsmaterial (PCM). Ett exempel på ett billigt, vanligt förekommande PCM är systemet vatten-is, vilket har använts av människor i tusentals år. För att tillgodose de många värme- och kylbehov som idag uppstår inom ett brett temperaturintervall, är det viktigt med innovativ design av PCM. Förutom lämplig fasförändringstemperaturer, entalpi och andra termofysikaliska egenskaper, bör PCM också ha robust fasändring, vara miljövänlig och kostnadseffektiv. För att förverkliga storskaliga TES system med PCM, är måste kostnadseffektivitet och robust funktion under många cykler bland de viktigaste utmaningarna. Kostnadseffektiva PCM kan bäst erhållas från naturliga eller industriella material i bulkskala, vilket i huvudsak leder till materialblandningar, snarare än rena ämnen. Blandningar uppvisar dock komplexa fasförändringsförlopp, underkylning och/eller inkongruent smältprocess som leder till fasseparation. Denna doktorsavhandling ger ny kunskap som möjliggör att bulkblandningar kan bli kostnadseffektiva och robusta PCM-material, med hjälp av den systematiskutvärdering av fasjämvikt och fasdiagram. Arbetet visar att detta kräver förståelse av relevanta grundläggande fasjämviktsteorier, omfattande termiska och fysikalisk-kemiska karakteriseringar, och allmänt tillämpliga teoretiska utvärderingar. Denna avhandling specificerar befintlig fasjämviktsteori för PCM-sammanhang, men sikte på att kunna välja robusta PCM blandningar med specifika egenskaper, beroende på tillämpning. Analysen visar att blandningar med en sammansättning som leder till kongruent smältande, där faser i jämvikt har samma sammansättning, är ideala bland PCM-blandningar. Kongruent smältande fasta faser som utgör föreningar eller fasta lösningar av ingående komponenter är därför ideala. Eutektiska blandningar är nästan lika bra som PCM, så länge underkylning inte förekommer. Därmed finns en stor potential för att finna och karakterisera PCM-ideala blandningar som bildar kongruent smältande föreningar eller fasta lösningar. Därigenom kan blandningar med en skarp, reversibel fasändring och utan fasseparation erhållas – egenskaper som liknar rena materialens fasändringsprocess. Vidare kan man, via fasdiagram, påvisa de blandningar som är inkongruent smältande, inklusive peritektiska blandningar, som är direkt olämpliga som PCM. Denna avhandling ger grundläggande kunskap som är en förutsättning för att designa PCM i blandningar. Genom en omfattande state-of-the-art utvärdering av fas-jämviktsbaserad PCM-design lyfter arbetet de PCM-idealiska blandningarna som hittills inte fått någon uppmärksamhet, såsom kongruenta smältande blandningar, och materialkategorierna metallegeringar, polyoler och fetter. Resultatet av arbetet visar dessutom att vissa PCM-material som ibland föreslås är direkt olämpliga då fasdiagram undersöks, bl a pga underkylning och även peritektiska system med fasseparation och degradering av kapaciteten (t ex Glauber-salt och natriumacetat-trihydrat). Denna avhandling specificerar och upprättar grundläggande teori samt tekniker, tillvägagångssätt och förhållanden som är nödvändiga för en omfattande och genomsynlig fasjämviktsbedömning, för utformning av PCM från blandningar för energilagering. Med detta som bas har följande fasdiagramtagits fram fullständigt: för erytritol-xylitol och för dodekan-tridekan, med PCM-potential för låg temperaturuppvärmning (60-120 °C) respektive frysning (-10 °C till -20 °C) utvärderas fullständigt. Erytritol-xylitol systemet har funnits vara eutektiskt i ett delvis isomorft system, snarare än ett icke-isomorft system vilket har föreslagits tidigare litteratur. Dodekan-tridekan systemet bildar ett system med kongruent smältande fast lösning (idealisk som en PCM) vid en minimumtemperatur, till skillnad från tidigare litteratur som föreslagt en maximumtemperatur, eller ett eutektiskt system. Teoretisk modellering av fasjämvikt har också genomförts för att komplettera det experimentella fasdiagrammet för systemet erytritol-xylitol. Efter granskning av de metoder som använts tidigare i PCM-litteraturen har här valts ett generiskt tillvägagångssätt (CALPHAD-metoden). Denna generiska metod kan bedöma vilken typ av material och fasändring som helst, till skillnad från en tidigare använda metoder som är specifika för materialtyper eller kemiska egenskaper. Denna teoretiska studie bekräftar termodynamiskt solvus, solidus, eutektisk punkt och erytritol-xylitol fasdiagrammet i sin helhet. Vad gäller hållbarhetsaspekter med PCM-baserad TES, lyfter denna avhandling fokus på förnybara och kostnadseffektiva material (t.ex. polyoler och fetter) som PCM. Som exempel har här undersökts erytritol och olivolja, med förnybart ursprung. Erytritol skulle kunna bli ett kostnadseffektivt PCM (163 USD/kWh), om det produceras av glycerol vilket är en biprodukt från biodiesel/bioetanolframställning. Olivolja är ännu ett kostnadseffektivt material (144 USD/kWh), och som här har påvisats innehålla potentiella PCM sammansättningar med lämpliga fasändringsegenskaper för kylatillämpningar. En övergripande slutsats från denna avhandling är att det finns ett behov av att standardisera tekniker, metoder och transparent resultatrapportering när det gäller undersökningar av fasjämvikt och fasdiagram i PCM-sammanhang. Internationella samarbetsplattformar för TES är en väg att koordinera arbetet. / <p>QC 20170830</p>

Le récepteur d’une centrale solaire à tour est l’élément clé de la conversion du rayonnement en chaleur. Dans le cadre de la thèse, il s’agit d’un récepteur métallique dans une centrale de type HSGT (Turbine hybride solaire gaz) refroidi par air pressurisé. En condition normale de fonctionnement, le récepteur chauffe l’air de 350 à 750°C. La température de l’air en sortie chute à 400°C en moins de 15 minutes si le soleil est masqué, par un nuage par exemple. L’objectif est de maintenir la température de l’air en sortie supérieure à 600°C durant 15 minutes sans ensoleillement. Pour parvenir à cet objectif, un stockage thermique intégré au récepteur est envisagé. Parallèlement le stockage de chaleur doit prolonger la durée de vie du récepteur en lui évitant de subir d’intenses chocs thermiques. L’étude porte sur la zone la plus chaude du récepteur, atteignant 800°C. Lorsque le soleil brille (le récepteur est insolé), une partie de la chaleur est stockée dans un matériau qui passe de l’état solide à liquide. Cette chaleur est restituée au récepteur lors de la transformation inverse (liquide à solide) si le soleil est masqué. Les variations de la température du récepteur sont ainsi plus douces et le récepteur est épargné des chocs thermiques. L’utilisation d’un matériau à changement de phase tel que le carbonate de lithium (fusion à 723°C) réduit le volume et la masse du stockage installé directement à l’arrière du récepteur. Ce matériau stocke une grande quantité de chaleur sur une gamme de température peu étendue. Cependant les matériaux à changement de phase ne permettent pas de transférer la chaleur rapidement à cause de leur faible conductivité thermique. C’est la raison pour laquelle l’intensification de ces transferts est étudiée. La mise en place d’ailettes en cuivre à l’intérieur du stockage améliore les transferts de chaleur, grâce à la conductivité thermique élevée du métal. Un modèle numérique représentatif du comportement thermique du stockage est développé. Le travail de conception du stockage aboutit à la fabrication d’un banc expérimental. Les résultats obtenus sont comparés au modèle afin de le critiquer. Les conclusions permettent d’envisager la conception d’un stockage thermique de protection à l’échelle du récepteur. / The thesis deals with the problem of thermal inertia and life time of the solar receiver of a Concentrated Solar Power tower plant. A specific attention is paid to the situation of HSGT (Hybridized Solar Gas Turbine) systems using pressurized air as HTF (Heat Transfer Fluid). The intermittence of solar radiation, mainly resulting from cloudy events, causes important temperature fluctuations that contribute to the premature aging. Therefore, a Thermal Energy Storage (TES) is developed for the protection of the receiver. The design focuses on the high temperature section of the receiver. As a consequence of the elevation of temperature in this stage, the expected temperature of the receiver ranges between 600°C and 800°C. Once the receiver is no longer irradiated, the temperature of the outlet air of the receiver, which is 750°C at designed point, decreases below 400°C in less than 15 minutes. The objective is to integrate the TES into the solar receiver to maintain this air temperature higher than 600°C after 15 minutes of discharge. A low capacity TES is targeted. Besides, the storage should enhance the lifetime of the receiver during the operation, by avoiding temperature drops. A test bench is designed based on a technology using both Phase Change Material (PCM) and metallic fins in order to enhance charge and discharge power of the storage unit. The selected metal is copper, because of its great thermal conductivity. The thermal storage medium must operate in the range 600°C – 800°C. The lithium carbonate has been selected mainly because of its phase change temperature, 723°C. A numerical model is developed in order to help the design of the test bench and compare experimental results. The conclusions lead to one-scale design of the thermal storage integrated to the solar receiver.