The heat transfer behavior of phase change material fluid under laminar flow conditions in circular tubes and internally longitudinal finned tubes are presented in this study. Two types of boundary conditions, including uniform axial heat flux with constant peripheral temperature and uniform axial and peripheral temperature, were considered in the case of circular tubes. An effective specific heat technique was used to model the phase change process assuming a hydrodynamically fully-developed flow at the entrance of the tube. Results were also obtained for the phase change process under hydro dynamically and thermally fully developed conditions. In case of a smooth circular tube with phase change material (PCM) fluid, results of Nusselt number were obtained by varying the bulk Stefan number. The Nusselt number results were found to be strongly dependent on the Stefan number. In the case of a finned tube two types of boundary conditions were studied. The first boundary condition had a uniform axial heat flux along the axis of the tube with a variable temperature on the peripheral surface of the tube. The second boundary condition had a constant temperature on the outer surface of the tube. The effective specific heat technique was again implemented to analyze the phase change process under both the boundary conditions. The Nusselt number was determined for a tube with two fins with different fin height ratios and fin thermal conductivity values. It was determined that the Nusselt number was strongly dependent on the Stefan number, fin thermal conductivity value, and height of the fins. It was also observed that for a constant heat axial flux boundary condition with peripherally varying temperature, the phase change slurry with the internally finned tube performed better than the one without fins. A similar trend was observed during the phase change process with internal fins under the constant wall temperature boundary condition.

In this thesis, the possible usage of phase change materials in military shelters with the aim of decreasing the heating effect of the solar radiation is presented. In order to meet the rapidly growing demand for energy in military applications, a passive cooling technique, specifically, storing thermal energy with phase change materials is analyzed by using experimental approach. Not only different types of phase change materials but also different amounts of them are examined during the solar loading experiments. In order to simulate solar heat loading on prototype military shelters, solar radiation test or in other words sunshine test that is stated in military standard MIL

The heat transfer behavior of phase change material fluid under laminar flow conditions in circular tubes and internally longitudinal finned tubes are presented in this study. Two types of boundary conditions, including uniform axial heat flux with constant peripheral temperature and uniform axial and peripheral temperature, were considered in the case of circular tubes. An effective specific heat technique was used to model the phase change process assuming a hydrodynamically fully-developed flow at the entrance of the tube. Results were also obtained for the phase change process under hydro dynamically and thermally fully developed conditions. In case of a smooth circular tube with phase change material (PCM) fluid, results of Nusselt number were obtained by varying the bulk Stefan number. The Nusselt number results were found to be strongly dependent on the Stefan number. In the case of a finned tube two types of boundary conditions were studied. The first boundary condition had a uniform axial heat flux along the axis of the tube with a variable temperature on the peripheral surface of the tube. The second boundary condition had a constant temperature on the outer surface of the tube. The effective specific heat technique was again implemented to analyze the phase change process under both the boundary conditions. The Nusselt number was determined for a tube with two fins with different fin height ratios and fin thermal conductivity values. It was determined that the Nusselt number was strongly dependent on the Stefan number, fin thermal conductivity value, and height of the fins. It was also observed that for a constant heat axial flux boundary condition with peripherally varying temperature, the phase change slurry with the internally finned tube performed better than the one without fins. A similar trend was observed during the phase change process with internal fins under the constant wall temperature boundary condition.

The trends in virtualization as well as multi-core, multiprocessor environments have translated to a massive increase in the amount of main memory each individual system needs to be fitted with, so as to effectively utilize this growing compute capacity. The increasing demand on main memory implies that the main memory devices and their issues are as important a part of system design as the central processors. The primary issues of modern memory are power, energy, and scaling of capacity. Nearly a third of the system power and energy can be from the memory subsystem. At the same time, modern main memory devices are limited by technology in their future ability to scale and keep pace with the modern program demands thereby requiring exploration of alternatives to main memory storage technology. This dissertation exploits dynamic knowledge of memory state and memory data value to improve memory performance and reduce memory energy consumption. A cross-boundary approach to communicate information about dynamic memory management state (allocated and deallocated memory) between software and hardware viii memory subsystem through a combination of ISA support and hardware structures is proposed in this research. These mechanisms help identify memory operations to regions of memory that have no impact on the correct execution of the program because they were either freshly allocated or deallocated. This inference about the impact stems from the fact that, data in memory regions that have been deallocated are no longer useful to the actual program code and data present in freshly allocated memory is also not useful to the program because the dynamic memory has not been defined by the program. By being cognizant of this, such memory operations are avoided thereby saving energy and improving the usefulness of the main memory. Furthermore, when stores write zeros to memory, the number of stores to the memory is reduced in this research by capturing it as compressed information which is stored along with memory management state information. Using the methods outlined above, this dissertation harnesses memory management state and data value information to achieve significant savings in energy consumption while extending the endurance limit of memory technologies. / text

The demand for clean and environmentally benign energy resources has been a great concern in the last two decades. To alleviate the associated environmental problems, reduction of the use of fossil fuels by developing more cost-effective renewable energy technologies becomes more and more significant. Among various types of renewable energy sources, solar energy and bioenergy take a great proportion. This dissertation focuses on the heat transfer and flow in solar energy and bioenergy systems, specifically for Thermal Energy Storage (TES) systems in Concentrated Solar Power (CSP) plants and open-channel algal culture raceways for biofuel production. The first part of this dissertation is the discussion about mathematical modeling, numerical simulation and experimental investigation of solar TES system. First of all, in order to accurately and efficiently simulate the conjugate heat transfer between Heat Transfer Fluid (HTF) and filler material in four different solid-fluid TES configurations, formulas of an effective heat transfer coefficient were theoretically developed and presented by extending the validity of Lumped Capacitance Method (LCM) to large Biot number, as well as verifications/validations to this simplified model. Secondly, to provide design guidelines for TES system in CSP plant using Phase Change Materials (PCM), a general storage tank volume sizing strategy and an energy storage startup strategy were proposed using the enthalpy-based 1D transient model. Then experimental investigations were conducted to explore a novel thermal storage material. The thermal storage performances were also compared between this novel storage material and concrete at a temperature range from 400 °C to 500 °C. It is recommended to apply this novel thermal storage material to replace concrete at high operating temperatures in sensible heat TES systems. The second part of this dissertation mainly focuses on the numerical and experimental study of an open-channel algae culture raceway for biofuel production. According to the proposed flow field design of ARID-HV algal raceway, experiments and numerical simulation have been conducted to understand the enhancement of flow mixing in the flow field of ARID-HV raceway by cutting slots on top of the dam near the dead zones. A new method was proposed to quantitatively evaluate the flow mixing by using the statistics of temporal and spatial distribution of the massless fluid particles (centered in each cell at the inlet surface) in the raceway collecting the data of path-lines of fluid particles from CFD results. It is hoped that this method can be applied to assist the algal raceway flow field design as well as other engineering applications. The third part introduces the details about the construction work of a high temperature molten salt test loop. Because of the limited operating temperature of conventional synthetic oils, in order to obtain higher energy conversion efficiency, higher operating temperature is always desirable in a CSP plant which leads to the requirement of new generation of HTF. Currently, a halide salt eutectic mixture (NaCl-KCl-ZnCl₂) as a potential HTF for future CSP applications has been proposed by a multi-institute research team, led by University of Arizona. The thermophysical properties of the halide eutectic salt have been measured. However, this new developed halide eutectic salt has not been tested in a circulating loop at a high operating temperature for the measurement of heat transfer coefficient. It is a significant effort to build such a test system due to extremely high operating temperature. As a consequence, in the third part of this dissertation, details about the design of the lab-scale test system and all the equipment items will be introduced. The investigations included in this dissertation for the heat transfer and flow in solar energy and bioenergy systems are of particular interest to the renewable energy engineering community. It is expected that the proposed methods can provide useful information for engineers and researchers.

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.

This thesis presents the first-principles studies of materials properties within the framework of the density functional theory (DFT). The thesis constitutes three main parts, i. e., pressure-induced phase transitions in solids, data-storage and clean-energy materials. The first part focuses on the predictions of crystal structures and the determinations of electronic properties of Xe-H2, FeB4 and Co3O4. Pressurizing Xe-H2 compound yields the formation of H-rich Xe(H2)8, which can exhibit a metallic feature at comparatively lower pressure than pure hydrogen. Hard superconducting FeB4 gets transformed into a novel transparent phase under pressure owing to the enhanced overlap of atomic cores. Spinel Co3O4 undergoes the phase transition from a cubic to a monoclinic because of the charge transfer between cations via the increased 3d-3d interactions. The second part involves the study of structural and electronic properties of phase-change memory materials (PCMs), i. e., Ge2Sb2Te5 (GST) and Ga-doped In2O3. Van der Waals (vdW) interaction must be considered to obtain accurate crystal structure of layered GST. For Ga-doped In2O3 (GIO), the local structure of amorphous GIO is found to resemble that of amorphous In2O3, except the vicinity of doping atoms. The electronic property of a-GIO is metallic, which considerably differs from the semiconducting feature of the crystalline GIO. This emphasizes the contrast in the conductivity of the crystalline and amorphous upon phase switching of GIO. The third part associates with the search for clean-energy materials, viz., hydrogen production, hydrogen storage and green Mg-ion batteries. For hydrogen production, the role of intrinsic point defects to water adsorption on ZnO(10-10) surface is investigated. The findings show that the Zn and O defect-sites are energetically not favorable for the water adsorption and dissociation. For the purpose of storing hydrogen in a solid phase, silicene, doped by alkaline and alkaline earth metals, is investigated. We find that Li-doped and Na-doped silicene can attain the superior storage capacity. For cathode material of Mg-ion batteries, Mg2Mo6S8, the diffusivity of Mg ions occurs through an available channel in the bulk with the onset temperature of 200 K.

Αντικείμενο της διπλωματικής εργασίας αποτελεί η μελέτη και ανάλυση των μεθόδων διόρθωσης λαθών με χρήση κώδικα BCH που μπορούν να εφαρμοστούν σε συστήματα αποθήκευσης πληροφορίας τεχνολογίας PCM (Phase-Change Memory). Η τεχνολογία PCM αποτελεί μία νέα τεχνολογία που υπόσχεται υψηλές χωρητικότητες, χαμηλή κατανάλωση ισχύος και μπορεί να εφαρμοστεί είτε σε συσκευές αποθήκευσης σταθερής κατάστασης (Solid State Drives) είτε σε μνήμες τυχαίας προσπέλασης (Random-Access Memories), παρέχοντας μία εναλλακτική πρόταση έναντι μνημών τεχνολογίας flash και DRAM. Ένα από τα μειονεκτήματα της τεχνολογίας PCM είναι η ανθεκτικότητα εγγραφής (write endurance), η οποία μπορεί να βελτιωθεί με τη χρήση μεθόδων διόρθωσης λαθών που θα παρατείνουν τον χρόνο ζωής της συσκευής όταν, λόγω της φυσικής φθοράς του μέσου, αρχίσουν να υπάρχουν σφάλματα στα αποθηκευμένα δεδομένα. Για την εφαρμογή της διόρθωσης λαθών μπορούν να χρησιμοποιηθούν κώδικες BCH, οι οποίοι αποτελούν μια κλάση ισχυρών κυκλικών κωδίκων διόρθωσης τυχαίων λαθών, και κατασκευάζονται με χρήση της άλγεβρας πεπερασμένων πεδίων. Οι κώδικες BCH είναι ιδανικοί για διόρθωση λαθών σε συσκευές αποθήκευσης πληροφορίας όπου η κατανομή των λαθών είναι τυχαία. Αρκετοί αλγόριθμοι έχουν προταθεί για τις λειτουργίες αποδοτικής κωδικοποίησης και αποκωδικοποίησης κωδίκων BCH. Στην παρούσα εργασία μελετήθηκαν λύσεις που μπορούν να υλοποιηθούν με παράλληλες αρχιτεκτονικές, ενώ ειδικότερα για την λειτουργία αποκωδικοποίησης έγινε χρήση ενός παράλληλου αλγορίθμου που δεν χρειάζεται αντιστροφείς πεπερασμένου πεδίου για την επίλυση των εξισώσεων των συνδρόμων, επιτυγχάνοντας υψηλές συχνότητες λειτουργίας. Για την κατανόηση των λειτουργιών κωδικοποίησης και αποκωδικοποίησης απαιτείται η προσεκτική μελέτη της άλγεβρας πεπερασμένων πεδίων και της αριθμητικής της. Οι κώδικες BCH προσφέρουν πλεονεκτήματα όπως χαμηλή πολυπλοκότητα και ύπαρξη αποδοτικών μονάδων υλοποίησης σε υλικό. Στην παρούσα εργασία σχεδιάστηκαν ένας παράλληλος κωδικοποιητής και ένας παράλληλος αποκωδικοποιητής για τον κώδικα BCH(728,688). Τα δύο συστήματα υλοποιήθηκαν ως περιφερειακά σε ενσωματωμένο σύστημα βασισμένο σε επεξεργαστή MicroBlaze, με έμφαση σε μια καλή σχέση μεταξύ της συχνότητας λειτουργίας και των απαιτήσεων σε επιφάνεια υλικού και κατανάλωση ισχύος. Για την υλοποίηση χρησιμοποιήθηκε συσκευή FPGA σειράς Virtex-6. / The objective of this thesis is the study and analysis of BCH error-correction methods that can be applied on PCM (Phase-Change Memory) storage devices. PCM is a new technology that promises high capacities, low power consumption and can be applied either on Solid State Drives or on Random Access Memories, providing an alternative to flash and DRAM memories. However, PCM suffers from limited write endurance, which can be increased using error-correction schemes that will extend the lifetime of the device when, due to medium wear-out, errors start to appear in the written data. Thus, BCH codes (powerful cyclic random multiple error-correcting codes) can be employed. BCH codes are ideal for ECC (Error-Correction Coding) in storage devices, due to their fault model which is random noise. Several algorithms have been proposed for the efficient coding and decoding BCH codes. In the present thesis parallel implementations where studied. For the decoding process in particular, a parallel algorithm was used that does not require finite field inverter units to solve the syndrome equations, achieving high operation frequencies. For the understanding of BCH coding and decoding processes, basic knowledge of the finite field algebra and arithmetic is required. BCH codes offer advantages such as low complexity and efficient hardware implementations. In the present thesis a parallel BCH(728,688) encoder and a parallel BCH(728,688) decoder were designed. The above systems were implemented as peripherals on an MicroBlaze-based embedded system, with emphasis on an optimal tradeoff between area and power consumption. A Virtex-6 FPGA device was used for the final stages of the implementation.

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.