<p>Due to climatic change, increasing thermal loads inbuildings and rising living standards, comfort cooling inbuildings is becoming increasingly important and the demand forcomfort cooling is expanding very quickly around the world. Theincreased cooling demand results in a peak in electrical powerdemand during the hottest summer hours. This peak presents newchallenges and uncertainties to electricity utilities and theircustomers.</p><p>Cool thermal storage systems have not only the potential tobecome one of the primary solutions to the electrical powerimbalance between production and demand, but also shift coolingenergy use to off-peak periods and avoid peak demand charges.It increases the possibilities of utilizing renewable energysources and waste heat for cooling generation. In addition, acool storage can actually increase the efficiency of combinedheat and power (CHP) generation provided that heat drivencooling is coupled to CHP. Then, the cool storage may avoidpeaks in the heat demand for cooling generation, and this meansthat the CHP can operate at design conditions in most oftime.</p><p>Phase Change Materials (PCMs) used for cool storage hasobtained considerable attention, since they can be designed tomelt and freeze at a selected temperature and have shown apromising ability to reduce the size of storage systemscompared with a sensible heat storage system because they usethe latent heat of the storage medium for thermal energystorage.</p><p>The goal of this thesis is to define suitable PCM candidatesfor comfort cooling storage. The thesis work combines differentmethods to determine the thermophysical properties oftetradecane, hexadecane and their binary mixtures, anddemonstrates the potential of using these materials as PCM forcomfort cooling storage. The phase equilibrium of the binarysystem has been studied theoretically as well asexperimentally, resulting in the derivation of the phasediagram. With knowledge of the liquid-solid phase equilibriumcharacteristics and the phase diagram, an improvedunderstanding is provided for the interrelationships involvedin the phase change of the studied materials. It has beenindicated that except for the minimum-melting point mixture,all mixtures melt and freeze within a temperature range and notat a constant temperature, which is so far often assumed in PCMstorage design. In addition, the enthalpy change during thephase transition (heat of fusion) corresponds to the phasechange temperature range; thus, the storage density obtaineddepends on how large a part of the phase change temperaturerange is valid for a given application.</p><p>Differential Scanning Calorimetery (DSC) is one frequentlyused method in the development of PCMs. In this thesis, it hasbeen found that varying results are obtained depending on theDSC settings throughout the measurements. When the DSC runs ata high heating/cooling rate it will lead to erroneousinformation. Also, the correct phase transition temperaturerange cannot be obtained simply from DSC measurement. Combiningphase equilibrium considerations with DSC measurements gives areliable design method that incorporates both the heat offusion and the phase change temperature range.</p><p>The potential of PCM storage for peak shaving in differentcooling systems has been demonstrated. A Computer model hasbeen developed for rapid phase equilibrium calculation. The useof phase equilibrium data in the design of a cool storagesystem is presented as a general methodology.</p><p><b>Keywords:</b>Comfort cooling, peak shaving, PCM, coolthermal storage system, DSC, phase change temperature range,the heat of fusion, phase equilibrium, phase diagram. Language:English</p>

In this thesis, density functional theory (DFT) calculations and DFT based ab initio molecular dynamics simulations have been employed in order to gain insights into materials properties like diffusion, adsorption, catalysis, and structure. In transition metals, absorbed hydrogen atoms self-trap due to localization of metal d-electrons. The self-trapping state is shown to highly influence hydrogen diffusion in the classical over-barrier jump temperature region. Li diffusion in Li-N-H systems is investigated. The diffusion in Li3N is shown to be controlled by the concentration of vacancies. Exchanging one Li for H (Li2NH), gives a system where the diffusion no longer is dependent on the concentrations of vacancies, but instead on N-H rotations. Furthermore, exchanging another Li for H (LiNH2), results in a blockade of Li diffusion. For high-surface area hydrogen storage materials, metal organic frameworks and covalent organic frameworks, the hydrogen adsorption is studied. In metal organic frameworks, a Li-decoration is also suggested as a way to increase the hydrogen adsorption energy. In NaAlH4 doped with transition metals (TM), the hypothesis of TM-Al intermetallic alloys as the main catalytic species is supported. The source of the catalytic effect of carbon nanostructures on hydrogen desorption from NaAlH4 is shown to be the high electronegativity of the carbon nanostructures. A space-group optimized ab initio random structure search method is used to find a new ground state structure for BeC2 and MgC2. The fast change between the amorphous and the crystalline phase of GeSbTe phase-change materials is suggested to be due to the close resemblance between the local amorphous structure and the crystalline structure. Finally, we show that more than 80% of the voltage in the lead acid battery is due to relativistic effects. / Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 702

A model is proposed to predict the heat spreading behaviour experienced by laminate materials when heated over only a part of the domain, which is broken up into two regions, known as the heated and fin regions. The 2D, steady-state, two-region fin model is unique in its treatment of multilayer conduction heat transfer, giving the exact solution in the heat-spreading layer only, in both Cartesian and cylindrical coordinates. The experimentally and numerically validated two region fin model can help designers to assess improved heat transfer rates for laminate pouches for use to encapsulate supercooled salt hydrate phase change materials for long-term heat storage. Waste aseptic cartons (e.g. Tetra Brik) are a potentially useful resource for making laminate heat storage pouches since value-added end-uses are largely absent in Canada and in many other countries. The model is also useful for assessing improved temperature uniformity in heat spreading devices with applied heat fluxes.

Made available in DSpace on 2016-12-12T20:17:57Z (GMT). No. of bitstreams: 1 123626.pdf: 3763667 bytes, checksum: d445fd671e6acd5feacf4ec380ef5c9d (MD5) Previous issue date: 2015-07-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O presente estudo tem por objetivo investigar a existência de efeitos relacionados ao tipo de modelagem de camisetas fabricadas com tecidos que contenham fibras compostas por materiais de mudança de fase (PCM s) com a temperatura corporal, transpiração e percepção de conforto térmico. Para tal, foram combinados métodos quantitativos e qualitativos de coleta de dados e análise de imagens termográficas. Cinco voluntários aptos a realizar o procedimento experimental participaram do estudo, testando cada um três camisetas confeccionadas com tecido composto por 86% fio OLV ( 70% PES normal/30% Outlast® Viscose), 10% fio Outlast® PES filamento e 4% elastano, com gramatura de 140g/m2. As camisetas possuíam modelagens distintas: ajustada, tradicional ou ampla. O procedimento experimental consistiu em caminhada na esteira em velocidade moderada, de acordo com as aptidões de cada voluntário, por 20 minutos, seguido por 10 minutos de repouso, em ambiente climatizado. Avaliou-se durante o procedimento experimental: a) a percepção dos voluntários em relação à sensação térmica, de umidade e conforto geral durante o uso de cada uma das camisetas, utilizando a Escala Visual Analógica (VAS) em escala de 1 a 10; b) a percepção dos voluntários em relação à região superior do corpo em que sentiam maior desconforto em relação à sensação térmica e de umidade; c) a variação da temperatura durante o procedimento experimental mesurada através de termopares; d) a variação de transpiração; e e) a variação da radiação térmica das partes superiores do corpo através de imagens térmicas. As medidas foram coletadas durante o procedimento experimental. Os resultados indicam diferenças significativas entre a modelagem ajustada e a modelagem ampla nas regiões do peito e das costas, sendo que a modelagem ajustada possui uma maior variação entre as temperaturas iniciais e finais, porém constante entre as regiões do tórax. Durante o período de repouso, a modelagem ajustada mantém a temperatura estável até o final da avaliação, enquanto que as modelagens tradicional e ampla mantém a temperatura até aproximadamente o sétimo minuto, iniciando então a queda da temperatura. A avaliação subjetiva indica aumento de desconforto nos três itens analisados (sensação térmica, sensação de umidade e conforto geral), indicando maior desconforto durante o uso da modelagem ajustada.

The content of this thesis encompasses the fundamentals, modelling, chip design, nanofabrication process, measurement setup, and experimental results of devices exploiting the optical properties of phase-change chalcogenide materials. Special attention is paid to integrated Si₃N₄ nanophotonic circuits for optical switching and memory applications, as well as to multilayer stacks for colour modulation. Herein, the implementation of the first robust, non-volatile, phase-change photonic memory is presented. By utilising optical near-field effects for Read, Write and Erase operations, bit storage of up to eight transmission levels is demonstrated in a single device employing Ge₂Sb₂Te₅ as the active material. These on-chip memory cells feature single-shot read-out of the transmission state and switching energies as low as 13.4pJ at speeds approaching 1GHz. The capability to readily switch between intermediate states is also demonstrated, a feature that requires complex iteration-based algorithms in electronic phase-change memories. This photonic memory is not only the first truly non-volatile memory---a long-term elusive goal in integrated photonics---but could also potentially represent the first multi-level memory, including electronic counterparts, that requires no computational post-processing or drift correction. These findings provide a pathway towards solving the throughput limitations of current computer architectures by eliminating the so-called von-Neumann bottleneck and portend a new paradigm in all-photonic memory, non-conventional computing, and tunable photonic devices. Finally, novel capabilities in electro-optic colour modulation using phase-change materials are demonstrated. In particular, this thesis offers the first implementation of Ag₃In₄Sb₇₆Te₁₇-based optical cavities for colour modulation on low-dimensional multilayer stacks. Moreover, "gray-scale" image writing is demonstrated by establishing intermediate levels of crystallisation via voltage modulation. This finding, in turn, corresponds to the first demonstration of nonvolatile colour-depth modulation in the emerging phase-change materials nanodisplay technology, featuring resolutions down to 50nm. Furthermore, a comprehensive comparison is carried out for two types of materials: growth- (Ag₃In₄Sb₇₆Te₁₇) and nucleation-dominated (Ge₂Sb₂Te₅) alloys in terms of colour, energy efficiency, and resolution. These results provide new tools for the new generation of bistable and ultra-high-resolution displays and smart glasses while allowing for other potential applications in photonics and optoelectronics.

Les mémoires résistives PCRAM sont basées sur le passage rapide et réversible entre un état amorphe hautement résistif et un état cristallin faiblement résistif d’un matériau à changement de phase (PCM). Ces mémoires constituent un des candidats les plus prometteurs pour la nouvelle génération de mémoires non-volatiles grâce à un large éventail de propriétés uniques comme une vitesse de fonctionnement élevée, une capacité de stockage multi-niveaux sur plusieurs bits, une bonne endurance et une possibilité de miniaturisation poussée. Cependant, la nécessité d’utiliser des courants d’effacement (IRESET) importants pour l’étape d’amorphisation du PCM représente l’un des principaux freins à l’explosion de la technologie PCRAM sur le marché des mémoires non volatiles. Dans ce contexte, il a été démontré que le confinement du PCM dans des structures possédant des facteurs de forme élevés permet d’améliorer l’efficacité du chauffage nécessaire au changement de phase du PCM et donc de réduire les courants d’amorphisation. Afin d’incorporer des matériaux PCM dans de telles structures, il est alors nécessaire de développer un procédé de dépôt très conforme. C’est pourquoi un procédé de dépôt PE-MOCVD (Plasma Enhanced- Metal Organic Chemical Vapor deposition) à injection liquide pulsée a été développé dans ce travail. Dans un premier temps des films amorphes et homogènes du composé binaire GeTe ont été déposés à partir des précurseurs organométalliques TDMAGe et DIPTe. Les analyses XPS révèlent que les couches de GeTe déposées sont stoechiométriques mais présentent une forte contamination en carbone. Ainsi, un des objectifs de cette thèse a été de réduire le taux de carbone dans les couches afin d’optimiser leurs propriétés de changement de phase. Une étude de l’impact des paramètres de dépôt tel que la puissance, la pression, la nature et le débit des gaz utilisés est alors présentée. En étudiant et en optimisant les paramètres de dépôt, des couches de GeTe contenant seulement 2 % at. de carbone ont pu être obtenues. Dans un second temps, des films du composé ternaire GeSbTe ont été déposés en injectant simultanément les trois précurseurs TDMAGe, TDMASb et DIPTe dans le plasma de dépôt. Une large gamme de composition peut alors être obtenue en variant les paramètres d’injection et de dépôt. L’un des principaux avantages de ce procédé est la capacité de couvrir une large gamme de compositions permettant d’obtenir des films possédant des propriétés de changement de phase très variées. L’impact des paramètres plasma sur la conformité du dépôt a aussi été étudié. Il est montré que l’ajout d’une composante BF à la puissance RF du plasma permet d’améliorer le remplissage des structures possédant des facteurs de forme élevés. Enfin, l’intégration dans des dispositifs mémoires PCRAM tests de matériaux PCM obtenus par ce procédé PE-MOCVD a mis en évidence des propriétés électriques proches de celles obtenues avec des matériaux déposés par les procédés de dépôt conventionnels de type PVD. / Phase change random access memories PCRAM are based on the fast and reversible switch between the high resistive amorphous state and the low resistive crystalline state of a phase change material (PCM). These memories are considered to be one of the most promising candidates for the next generation of non volatile memories thanks to their unique set of features such as fast programming speed, multi-level storage capability, good endurance and high scalability. However, high power consumption during the RESET operation (IRESET) is the main challenge that PCRAM has to face in order to explode the non volatile memory market. In this context, it has been demonstrated that by integrating the phase change material (PCM) in high aspect ratio lithographic structures, the heating efficiency is improved leading to a reduced reset current. In order to fill such confined structures with the phase change material, a highly conformal deposition process is required. Therefore, a pulsed liquid injection Plasma Enhanced-Metal Organic Chemical Vapor Deposition process (PE-MOCVD) was developed in this work. First, amorphous and homogeneous GeTe films were deposited using the organometallic precursors TDMAGe and DIPTe as Ge and Te precursors. XPS measurements revealed a stoichiometric composition of GeTe but with high carbon contamination. Thus, one of the objectives of this work was to reduce the carbon contamination and to optimize the phase change properties of the deposited PCMs. The effect of deposition parameters such as plasma power, pressure and gas rate on the carbon contamination is then presented. By tuning and optimizing deposition parameters, GeTe films with carbon level as low at 2 at. % were obtained. Thereafter, homogeneous films of GeSbTe were deposited by injecting simultaneously the organometallic precursors TDMAGe, TDMASb and DiPTe in the plasma. A wide range of compositions was obtained by varying the injection and deposition operating parameters. Indeed, one of the main advantages of this process is the ability of varying films composition, which results in varying phase change characteristics of the deposited PCM. The impact of plasma parameters on the conformity of the process was also studied. It was shown that by adding a low frequency power component to the radio frequency power of the plasma, structures with high aspect ratio were successfully filled with the phase change material. Finally, electrical characterization of PCRAM test devices integrating phase change materials deposited by PE-MOCVD as active material have presented electrical properties similar to the ones obtained for materials deposited by conventional physical vapor deposition (PVD) process.

Ce travail concerne une étude numérique des performances thermiques d’un séchoir- serre équipé d’une unité de stockage de chaleur solaire dans des matériaux à changement de phase (MCPs). L'unité de stockage de chaleur solaire, placée sous le sol de la serre, est composée d’une couche de MCPs (paraffine) disposée entre une plaque en acier et une couche de béton. L'écoulement de l'air asséchant se déroule par convection forcée et le produit disposé sur les claies du séchoir est la banane (Bananas Musa ABB CV. Kluai "Namwa"). Les équations de transfert de chaleur dans la serre, basées sur la méthode nodale, sont déduites d'un bilan thermique établi pour les différents composants du séchoir-serre. Les transferts de chaleur dans les couches de MCPs et de béton sont décrits respectivement par le modèle enthalpique et l'équation de la conduction. Le modèle de cinétique de séchage de la banane est celui d’Oswin modifié. Les équations de transferts sont résolues par une méthode implicite aux différences finies et les algorithmes de Gauss et de Thomas. Nous analysons l'influence du débit d'air asséchant et de l’irradiation solaire sur les distributions spatio-temporelles des températures des composants de la serre et de l'unité de stockage, la durée de séchage, les efficacités thermiques du séchoir-serre et de l'unité de stockage d'énergie. Cette modélisation est complétée par des simulations du fonctionnement du séchoir serre-unité de stockage de chaleur en utilisant la notion de journée type et les données météorologiques de Nakorn Pathom (Thaïlande) et par une analyse de faisabilité technico-économique. Les résultats montrent notamment que l’unité de stockage de chaleur contribue à la réduction de la durée de séchage et augmente les performances thermiques du séchoir et l’unité de stockage. / This work is about a numerical study of the thermal behavior of a solar greenhouse dryer and a heat storage unit in phase change materials (PCMs). The heat storage unit containing of PCMs (paraffin) is disposed between a metal plate and a concrete layer and placed under the floor of the greenhouse. The air drying flows along the greenhouse by forced convection and the products placed on the dryer's rack is bananas (Bananas Musa ABB CV Kluai "Namwa"). The heat transfer equations in the greenhouse are based on the nodal method and deduced from a thermal balance on the different components of the solar greenhouse dryer. The heat transfers in the PCMs and the concrete slab are described by the enthalpy method and the conduction equation, respectively. The banana drying kinetic is described by the model modified of Oswin. Transfer equations are solved using an implicit finite difference method associated to Gauss and Thomas algorithms. We analyze the effects of the air drying volumetric flow rate and the solar irradiance on the temperature distribution of the greenhouse dryer and the heat storage unit, the drying time, the solar greenhouse dryer and heat storage unit efficiencies. This modeling is complemented by simulations of the solar greenhouse dryer with the heat storage unit using the day type and the meteorological data of Nakorn Pathom (Thailand) and by an economic analysis. The results show that the heat storage unit provides the reduction of the drying time and increases the thermal performances of the solar greenhouse dryer and the heat storage unit.

A présent, les bâtiments résidentiels et commerciaux sont en phase de devenir le secteur le plus consommateur d’énergie dans de nombreux pays, comme par exemple en France. Diverses recherches ont été menées de manière à réduire la consommation énergétiques des bâtiments et augmenter leur confort thermique. Parmi tous les différentes approches, la technologie du stockage de chaleur latent se distingue par une très bonne capacité à stocker la chaleur afin de réduire les écarts entre la disponibilité et la demande d’énergie. Dans le cadre de l’un de nos projets, nous avons l’intention d’intégrer au design des murs des bâtiments un type de brique transparente remplie de matériaux à changement de phase (MCP). Les MCP à l’intérieur de la brique sont soumis à des changements de phase liquide-solide. Cette thèse s’attaque à la problématique du processus de fusion au sein de la brique. Au cours de cette thèse, une méthode expérimentale non-intrusive a été développée afin d’améliorer les techniques expérimentales existantes. La vélocimétrie des images des particules (VIP) et la fluorescence induite par laser (FIL) ont été couplées pour étudier la convection naturelle et la distribution de la température. Puisqu’aucun thermocouple n’a été inséré au sein de la brique, le processus de la fusion a été considéré sans perturbation. Les résultats montrent que cette conception expérimentale a un avenir prometteur, même si elle reste à améliorer. Par la suite, nous présentons deux simulations numériques. Ces simulations se fondent sur la méthode de Boltzmann sur réseau à temps de relaxation multiple (LBM MRT), employée pour résoudre le champ de vitesse, et sur la méthode de différences finies, pour obtenir la distribution de la température. La méthode d’enthalpie a quant à elle été utilisée pour simuler le changement de phase. Les simulations en deux dimensions et trois dimensions ont toutes deux été réalisées avec succès. Point important, ces simulations numériques ont été développées en langage C pour tourner spécifiquement sur un processeur graphique (GPU), afin d’augmenter l’efficacité de la simulation en profitant de la capacité de calcul d’un GPU. Les résultats des simulations concordent bien avec les résultats de nos expériences et avec les résultats analytiques publiés. / The domestic and commercial buildings are currently becoming the major sector that consumes the biggest share of the energy in many countries, for example in France. Various researches have been carried out in order to reduce the energy consumption and increase the thermal comfort of builds. Among all the possible approaches, the latent heat storage technology distinguishes itself because of its excellent heat storage ability which can be used to efficiently reduce the discrepancy between the energy consumption and supply. In one of our project, we intend to integrate a type of transparent brick filled with phase change material (PCM) into the buildings' wall design. The PCM inside the brick undergoes the solid-liquid phase change. This dissertation addresses the important issues of the melting process inside the brick. In this dissertation, a non-intrusive experimental method was proposed to improve the existing experiment technique. The particle image velocimetry (PIV) and the laser-induced fluorescence (LIF) were coupled to investigate the natural convection and the temperature distribution. Because there was no thermocouple installed inside the brick, the melting process was thus considered to be less impacted. The results showed that this experimental design has a promising future, yet still needs to be improved. Two sets of efficient numerical simulations were also presented in this dissertation. The simulations were based on the thermal lattice Boltzmann method (TLBM), where the natural convection got solved by the LBM and the temperature equation was solved by the finite difference scheme. The enthalpy method was employed to simulate the phase change. Both the 2-dimensional and 3-dimensional configurations were successfully simulated. Moreover, the simulation programs were specifically developed - using the C language - to be run on the graphic processing unit (GPU), in order to increase the simulation efficiency. The simulation results demonstrated a good agreement with our experimental results and the published analytical results.

Modern buildings increasingly include the usage of innovative materials aimed at improving sustainability and reducing the carbon footprint of the built environment. Phase Change Materials (PCMs) are one such group of novel materials which reduce building energy consumption. These materials are typically flammable and contained within wall linings yet there has been no detailed assessment of their fire performance. Current standard fire test methods provide means to compare similar materials but do not deliver knowledge on how they would behave in the event of a real fire. Thus, the aim of this thesis is to develop a novel testing framework to assess the behaviour of these materials in realistic fire scenarios. For PCMs, a flammability study is conducted in the bench-scale cone calorimeter to evaluate the fire risk associated with these materials. Then, micro-scale Thermogravimetric Analysis (TGA) is used to identify the fundamental chemical reactions to be able to confidently interpret the flammability results. Finally, intermediate-scale standard fire tests are conducted to evaluate the applicability of the bench-scale results to realistic fire scenarios. These take the form of modified Lateral Ignition and Flame spread Test (LIFT) and Single Burning Item (SBI) tests to understand flame spread and compartment fires respectively. Finally, a simplified method to combine this knowledge for use in building design is proposed. This method allows the balancing of potential energy benefits with quantified fire performance to achieve the specified goals of the designer. Hemp-lime insulation is a material which has also becoming increasingly popular in the drive towards sustainability. The porous nature of the material means that smouldering combustions are the dominant reaction mode but there is currently no standardised test method for this type of behaviour. Thus, hemp-lime materials also represent an unquantified risk. The work in this thesis defines a simple, accessible and economically viable bench-scale method for quantifying the fire risk associated with rigid porous materials. This is applicable for both downward opposed flow and upward forward flow smoulder propagation conditions. The behaviour is then interpreted using micro-scale thermogravimetric analysis to understand the underlying pyrolysis and oxidation reactions. Designers can utilise this framework to quantify the smouldering risk associated with hemp-lime materials to enable their usage in the built environment. The holistic fire risk assessment performed in this thesis has quantified the behaviour of PCMs and hemp-lime insulation applicable to realistic fire scenarios. The simplified design method empowers designers to be able to realise innovative buildings through fundamental understanding of the fire behaviour of these materials. The outcomes of this thesis allow designers to mitigate the fire risk associated with these materials and achieve optimised engineering solutions. Furthermore, the novel fire testing frameworks provide the economically viable means to assess the fire performance of future PCMs and hemp-lime products which ensures lasting relevance of this research in the future.

The theoretical part of the diploma thesis deals with introduction to the issue of refrigeration systems with thermal energy storage. Possibilities of thermal energy storage with phase change are introduced. The thermodynamic principle of functioning of the particular refrigeration system type is explained here as well as its coefficient of performance and fundamental components. In addition, several examples of ice-making systems are discussed. In the practical part the design of a particular refrigeration system is calculated. The main part of the design is the cold evaporator with direct evaporation and the possibility of ice production and its usage for thermal energy storage. The calculation of the overall two-phase heat transfer is carried out.