Dissertations / Theses on the topic 'Heat storage devices Testing'

Thesis (MEng) -- Stellenbosch University, 2014.<br>ENGLISH ABSTRACT: Solar energy is a time dependent, high-temperature radiant energy resource. The utility of a solar thermal energy system increases if the hot temperature source is available when it is needed most. This is realized by the thermal storage of the solar energy. Thermal storage gives greater versatility to a solar energy system by decoupling the heat source from the heat sink. A large quantity of energy may be stored during the melting process in a phase change material (PCM) within a small temperature range. This molten PCM can then deliver its absorbed heat at a constant temperature in a heating application. In this study a phase change storage system (PCS) is developed and proposed for a solar water heating application. This PCS system stores more heat per unit mass than would be possible with water across the same temperature range. The heat transfer rate in and out of many PCMs is slow because of the low thermal conductivity of the PCM. However, heat transfer enhancers (HTE), such as heat pipes and fins may be added to enhance heat absorption and heat removal rates. Heat pipes have the inherent capability to transfer heat at high rates across large distances, even where the temperature difference is small. In this thesis a description is given of a PCS system consisting of paraffin wax as the PCM and which uses rectangular heat pipes in conjunction with aluminium fins to enhance heat transfer. The storage design is modular and each module has the characteristic that enhanced heat transfer in and out of the PCM is possible when the module is heated or cooled. It also has the capability to quickly absorb or alternatively to supply heat at a nearly constant temperature during the phase change of the module. A rectangular module was designed and built. The module was then analysed under controlled heat absorption and heat removal cycles. The heat up experiment involved an electrical kettle as the hot temperature source. The heat sink was a mains water heat exchanger. The experimental results were compared to those of a transient numerical model, which calculates theoretically how the module will perform thermally under the given test conditions. The numerical model of the experimental set-up was validated when it was found that the numerical model results resemble the experimental results. The numerical model was then adapted to simulate a novel solar water heater (SWH) with an additional PCS container. The improvement over previous designs is that the additional storage container can be heated to a higher temperature than the allowable geyser temperature. The system also heats up and cools down at a faster rate than would be possible without the HTEs. From the numerical simulation the size and performance of such a system is determined. This numerical analysis indicated that a phase change storage system in a SWH application will increase the hot water delivered by a given solar collector and geyser by increasing the storage capacity and by heating up the geyser overnight for early morning hot water use.<br>AFRIKKANSE OPSOMMING: Son energie is ‘n tyd afhanklike, hoë temperatuur radiasie energiebron. Die bruikbaarheid van ‘n sontermiese energie sisteem verhoog indien die hoë temperatuur bron beskikbaar is wanneer dit die meeste benodig word. Dit kan verwesenlik word deur die sonenergie termies te stoor. Termiese storing bied groter veelsydigheid aan ‘n sontermiese stelsel deur effektief die hittebron te ontkoppel van die hitte sink. ‘n Groot hoeveelheid energie kan, gedurende die smeltingsproses in ‘n faseveranderingsmateriaal binne ‘n nou temperatuurband gestoor word. Hierdie gesmelte materiaal kan weer op sy beurt in die waterverhittingstoepassing, die geabsorbeerde hitte teen ‘n konstante temperatuur oordra. In hierdie studie word ‘n sonwaterverwarmer stelsel wat aangepas is deur ‘n addisionele latente hittestoor daaraan te heg, voorgestel. Hierdie faseverandering hittestoor kan meer hitte stoor as wat water in dieselfde temperatuur band sou kon. Die hitteoordrag tempo na en van baie van die faseveranderingsmateriale (FVM) is egter as gevolg van die lae termiese geleidingskoëfisient, stadig. Hierdie eienskap kan gelukkig verbeter word deur hittepype en hitteoordrag verhogings materiaal soos vinne by te voeg. Hittepype het die inherente eienskap om hitte teen ‘n hoë tempo oor groot afstande, oor te dra, selfs oor ‘n klein temperatuurverskil. In hierdie tesis word ‘n ondersoek rakende ‘n faseverandering storingsisteem wat bestaan uit paraffien was as die FVM en reghoekige hittepype wat te same met met aluminium finne gebruik word om die hitteoordragtempo te verhoog, beskryf. Die stoorontwerp is modulêr en elke module het die kenmerk van hoë hitteoordrag na en van die FVM. Die module het verder ook die eienskap om vining hitte te absorbeer of hitte af te gee. Dit gebeur teen ‘n konstante temperatuur gedurende die faseverandering van die FVM. Presies so ‘n reghoekige module is ontwerp en gebou en onder beheerde hitte absorbering- en hitte verwyderingsiklusse analiseer. Tydens die verhittings eksperiment is ‘n elektriese ketel van gebruik gemaak wat gedien het as die hoë temperatuur bron. Die hitte sink was ‘n hitteruiler wat kraanwater van ‘n konstante hoogte tenk ontvang het. Die resultate van die volledige toets is met die resultate van tydafhanklike numeriese model vergelyk. Hierdie numeriese model bereken teoreties wat die module se storing verrigting onder gegewe toets omstandighede sal wees. Die numeriese model se resultate het goed vergelyk met die resultate van die eksperimente. Die numeriese model van die module is toe aangepas om ‘n sonwaterverwarmer met addisionele stoortenk wat fase verandering materiaal gebruik, te simuleer. Hierdie ontwerp is anders as vorige ontwerpe in die sin dat hoër temperature as wat die warmwatertoestel kan hanteer, in die faseverandering storingstenk, bereik kan word. Die sisteem kan ook as gevolg van die hitteoordrag verhoging materiaal, vinniger verhit of afkoel en teen ‘n vinniger tempo. Die simulasie van die sonwaterverwarmer met FVM word gebruik om die grootte en verrigting van die sisteem te bepaal. Hierdie numeriese model toon aan dat wanneer ‘n addisionele faseverandering storingstelsel in ‘n sonwaterverwarmer toepassing gebruik word, die warm water wat die verbruiker uit die sisteem kan verkry, kan verhoog. Die rede hiervoor is dat meer hitte gestoor kan word, wat beskikbaar gemaak word aan die warm water tenk.

As the worldwide energy demand continues to increase, scientists and engineers are faced with the increasingly difficult task of meeting these needs. Currently, the major energy sources, consisting of oil, coal, and natural gas, are non-renewable, contribute to climate change, and are rapidly depleting. Renewable technology research has become a major focus to provide energy alternatives which are environmentally-friendly and economically competitive to sustain the future worldwide needs. Thermal energy storage using adsorption is a promising technology which can provide energy for heating and cooling applications using solar and waste heat sources. The current work aims to improve adsorption systems to provide higher energy outputs and therefore, more economical systems. New adsorbents and operating conditions were tested with the goal of storing the available energy more efficiently. A model was also developed to gain a better understanding of the adsorption system to improve this developing technology.

One of the fundamental components for the full scientific exploitation of future fusion experiments is the Neutral Beam Injectors (NBI). Such devices shall operate in ITER and DEMO experiments at particle energy levels, heating power and steady state working conditions that have never been simultaneously reached before in other experimental facilities. In addition to the challenging technological and manufacturing aspects, NBIs coupled with future fusion reactors should be characterized by much demanding efficiency, availability and reliability factors, composing and additional set of critical issues that claim for an accurate and robust design. The research activity of this PhD thesis focuses on particular components of the negative ion beam source, the accelerating electrostatic grids, which are characterized by high heating power and highly focused power densities, and hence require a continuous active cooling in order guarantee proper heat removal and temperature control. Present research aims to verify the present solution applied inside the NBI accelerator grids realized in PRIMA facility (i.e. MITICA experiment) and to perform further improvements in the heat transfer process with an acceptable pressure drop and reliable manufacturing process. The main advantages rely on the possibility to extend the fatigue life-cycle of different high thermal stress components and to investigate the possibility to employ alternative dielectric fluids instead of water. Such design solutions would in fact allow the exploitation of less performing fluids in terms of cooling capability. This is particularly relevant in view of DEMO and future power plants characterized by higher efficiency and reliability. The research activity is not only limited to numerical analyses but includes the manufacturing of the prototypes of the accelerator grid cooling channels where the novel channel design solutions have been implemented. In order to characterize the experimental thermo-fluid dynamic behaviour of the samples the hydraulic performances and the cooling efficiency in transient operations have been tested in a specific plant for thermo-hydraulic measurements, called Insulation and Cooling Experiment (ICE). In order to support further optimization design activity and the implementation of the cooling solutions inside full-scale models of the electrostatic accelerating grid in future injector beam source the experimental results have been obtained and compared both with Computational Fluid-Dynamic models in order to validate the numerical realized predictions. The thesis is organized in five chapters. The first one is an introduction to nuclear fusion and magnetic confinement. The second chapter gives a description of the NBI devices, both from the conceptual point of view and technology of its components. The third chapter tackles the development of the novel cooling solution designs on a single channel and single beamlet group sub-modelling of the electrostatic grid system. The fourth chapter confronts the numerical obtained results to the experimental ones performed in the specific test-bed facility. In the fifth chapter the different developed designs have been upgraded to the electrostatic grid full scale model and a general scheme for further design improvement is introduced. Final general conclusions are drawn in the last dedicated section of the work. An outline of dealt topics is placed at the beginning of each of the different five chapters.<br>Uno dei componenti fondamentali per la completa fruibilità scientifica dei futuri esperimenti sulla fusion nucleare è il sistema di iniezione dei neutri (NBI). Tali dispositivi dovranno operare negli esperimenti ITER e DEMO a livelli energetici delle particelle accelerate, carichi termici e condizioni di lavoro in regime stazionario che non sono mai state simultaneamente raggiunte in alcun impianto sperimentale. In aggiunta ai severi aspetti tecnologici e dal punto di vista della realizzazione, i sistemi di iniezione dei neutri accoppiati a futuri reattori a fusion dovranno essere caratterizzati da fattori di efficienza, disponibilità e affidabilità molto severi, contribuendo a comporre un ulteriore insieme di aspetti critici richiedenti un accurate e robusto lavoro di progettazione. L’attività di ricerca illustrata nella presente tesi di Dottorato si focalizza su particolari componenti della sorgente di fasci di ioni negative, le griglie di accelerazione, caratterizzate da elevate carichi termici e densità di potenze altamente localizzate, i quali richiedono un continuo ed attivo sistema di raffreddamento al fine di garantire un’appropriata rimozione del calore ed un adeguato controllo in temperatura. Scopo del presente lavoro di ricerca è la verifica dell’attuale soluzione progettuale inserita nelle griglie di accelerazione del Sistema di iniezione dei neutri che verrà realizzato nel complesso sperimentale PRIMA (ovvero in MITICA) nonché la realizzazione di ulteriori migliorie nei meccanismi di scambio termico con cadute di pressione accettabili e processi di lavorazione affidabili. Il maggiore vantaggio associate a tali risultati risiede nella possibilità di estendere il ciclo di vita a fatica dei diversi component soggetti ad elevati sforzi di natura termomeccanica e nell’ avvio di un’indagine volta alla possibilità di impiego di fluidi dielettrici alternativi all’acqua. Tali soluzioni progettuali permetterebbero di fatto l’impiego di fluidi meno prestanti dal punto di vista delle proprietà termo-fluidodinamiche caratterizzanti i meccanismi di scambio termico. Tale considerazione risulta particolarmente rilevante in vista di DEMO e di futuri impianti per la produzione di energia caratterizzati da alte efficienze termodinamiche ed elevati fattori di affidabilità. L’attività di ricerca non risulta limitata alle sole analisi numeriche ma include la realizzazione dei prototipi dei canali di raffreddamento delle griglie di accelerazione in cui sono state ricavate le innovative soluzioni progettuali. Al fine di caratterizzare in ambito sperimentale il comportamento termo-fluidodinamico dei provini, le prestazioni idrauliche e l’efficienza di raffreddamento in regimi transitori sono state testate in un apposito impianto per l’esecuzione di prove termoidrauliche, denominato Insulating and Cooling Experiment (ICE). Al fine di supportare ulteriori attività di ottimizzazione e l’implementazione delle soluzioni di raffreddamento in modelli in scala reale delle griglie di accelerazione elettrostatica in future sorgenti di iniezione di fasci, i risultati sperimentali così ottenuti sono stati confrontati con modelli fluido-dinamici al fine di validarne le previsioni realizzate numericamente. La tesi è suddivisa in cinque capitoli. Il primo capitolo effettua un’introduzione alla fusione nucleare ed al confinamento magnetico. Il secondo fornisce una descrizione dei dispositivi di iniezione dei neutri, sia da un punto di vista concettuale che tecnologico dei suoi componenti e sottosistemi. Il terzo capitolo affronta lo sviluppo delle soluzioni innovative di raffreddamento su sotto modelli a singolo canale e singolo gruppo di aperture delle griglie elettrostatiche. Il quarto capitolo confronta i risultati ottenuti numericamente con quelli sperimentali. Nel quinto capitolo le diverse geometrie sviluppate sono state riscalate alle dimensioni reali della griglia , esso inoltre introduce uno schema generale per ulteriori migliorie nella progettazione dei canali di raffreddamento. Le conclusioni sono tratte nell’ultima apposita sezione. Un sommario con gli argomenti trattati è riportato all’inizio di ogni capitolo.

The high energy density and stable temperature fields of latent heat thermal storage devices (LHTSD) make them promising in a range of applications, including solar energy storage, solar cooking, home heating and cooling, and thermal buffering. The chief engineering challenge in building an effective LHTSD is to find a way to complement the storage capabilities provided by the low-conductivity phase-change material with a suitable enhanced heat transfer mechanism. The principal aim of this project is to develop a tool to improve the design of a small-scale LHTSD, such as one that might be used in solar cooking for a family. An effective small-scale storage device would need to absorb solar energy quickly, release the energy at a high temperature, be affordable, and be manageable within a small household. An LHTSD using solar salts fulfills the latter two requirements: solar salts, a near-eutectic mixture of NaNO3 and KNO3 (60/40% by mass) commonly used in thermal storage applications, are inexpensive and widely available, and the use of latent heat storage means a relatively small chamber can hold enough energy to cook a family meal. The challenge, however, is to design a device that absorbs and releases energy from the solar salts, which have a very low thermal conductivity. The most practical tool to improve the spread of heat through the salts is a finned metal core within the LHTSD. This project uses numerical simulation to determine the most effective design of this finned core. A Cartesian grid solver is developed that is capable of simulating the convection-dominated melting processes within the storage device. The phase boundary is tracked using the enthalpy method, and conjugate heat transfer is calculated with a strongly coupled implicit scheme. A number of techniques are then used to with this solver in order to better understand the factors that affect the performance of a LHTSD and to improve the design of such devices. The thesis is organized as an introductory section followed by three case studies. In the first section, the project is introduced, and the governing equations and core numerical methods are described. In addition, a set of test simulations demonstrate that results using the developed numerical scheme match those of a range of experimental and numerical benchmarks. Each of the case studies aims to adapt the numerical scheme to a more specific problem concerning LHTSDs. In the first, the performance of four fin designs are compared over long-term (48 hour) simulations; the aim is to test the potential performance of the four LHTSDs given realistic solar conditions in New Delhi, India. In the second case study, a set of physical experiments are performed in an empty and a finned LHTSD, and matched 3-dimensional numerical simulations are used to explore the thermal, melt, and flow behavior of the solar salts with the chambers. The final study uses the computational scheme to optimize the design of the finned core of an LHTSD over a large parameter space. To optimize the best design, the key parameters are first prescreened to find which three parameters have the largest effect on the objective equation. A machine-learning optimization code using the dynamic Kriging method (DKG) is then used to build a response surface from which the optimized design can be determined. These three cases demonstrate the potential of the numerical scheme to explore the performance of finned LHTSD designs in a range of ways: the scheme can be used to predict behavior of devices in realistic conditions, to explore the behavior of solar salts during the melting and solidification process, and to determine an optimal design within a large parameter space. In doing so, they show the potential of this tool to help improve the performance and practicality of small-scale LHTSDs.

Thesis (Ph. D.)--University of California, Riverside, 2008.<br>Includes abstract. Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed March 10, 2010). Includes bibliographical references (p. 126-135). Also issued in print.

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on February 12, 2010). Thesis advisor: Dr. Galen J. Suppes. Includes bibliographical references.

Thesis (PhD) -- Stellenbosch University, 2014.<br>ENGLISH ABSTRACT: Currently the reduction of the levelised cost of electricity (LCOE) is the main goal of concentrating solar power (CSP) research. Central to a cost reduction strategy proposed by the American Department of Energy is the use of advanced power cycles like supercritical steam Rankine cycles to increase the efficiency of the CSP plant. A supercritical steam cycle requires source temperatures in excess of 620°C, which is above the maximum storage temperature of the current two-tank molten nitrate salt storage, which stores thermal energy at 565°C. Metallic phase change materials (PCM) can store thermal energy at higher temperatures, and do not have the drawbacks of salt based PCMs. A thermal energy storage (TES) concept is developed that uses both metallic PCMs and liquid metal heat transfer fluids (HTF). The concept was proposed in two iterations, one where steam is generated directly from the PCM – direct steam generation (DSG), and another where a separate liquid metal/water heat exchanger is used – indirect steam generation, (ISG). Eutectic aluminium-silicon alloy (AlSi12) was selected as the ideal metallic PCM for research, and eutectic sodium-potassium alloy (NaK) as the most suitable heat transfer fluid. Thermal energy storage in PCMs results in moving boundary heat transfer problems, which has design implications. The heat transfer analysis of the heat transfer surfaces is significantly simplified if quasi-steady state heat transfer analysis can be assumed, and this is true if the Stefan condition is met. To validate the simplifying assumptions and to prove the concept, a prototype heat storage unit was built. During testing, it was shown that the simplifying assumptions are valid, and that the prototype worked, validating the concept. Unfortunately unexpected corrosion issues limited the experimental work, but highlighted an important aspect of metallic PCM TES. Liquid aluminium based alloys are highly corrosive to most materials and this is a topic for future investigation. To demonstrate the practicality of the concept and to come to terms with the control strategy of both proposed concepts, a storage unit was designed for a 100 MW power plant with 15 hours of thermal storage. Only AlSi12 was used in the design, limiting the power cycle to a subcritical power block. This demonstrated some practicalities about the concept and shed some light on control issues regarding the DSG concept. A techno-economic evaluation of metallic PCM storage concluded that metallic PCMs can be used in conjunction with liquid metal heat transfer fluids to achieve high temperature storage and it should be economically viable if the corrosion issues of aluminium alloys can be resolved. The use of advanced power cycles, metallic PCM storage and liquid metal heat transfer is only merited if significant reduction in LCOE in the whole plant is achieved and only forms part of the solution. Cascading of multiple PCMs across a range of temperatures is required to minimize entropy generation. Two-tank molten salt storage can also be used in conjunction with cascaded metallic PCM storage to minimize cost, but this also needs further investigation.<br>AFRIKAANSE OPSOMMING: Tans is die minimering van die gemiddelde leeftydkoste van elektrisiteit (GLVE) die hoofdoel van gekonsentreerde son-energie navorsing. In die kosteverminderingsplan wat voorgestel is deur die Amerikaanse Departement van Energie, word die gebruik van gevorderde kragsiklusse aanbeveel. 'n Superkritiese stoom-siklus vereis bron temperature hoër as 620 °C, wat bo die 565 °C maksimum stoor temperatuur van die huidige twee-tenk gesmelte nitraatsout termiese energiestoor (TES) is. Metaal fase veranderingsmateriale (FVMe) kan termiese energie stoor by hoër temperature, en het nie die nadele van soutgebaseerde FVMe nie. ʼn TES konsep word ontwikkel wat gebruik maak van metaal FVM en vloeibare metaal warmteoordrag vloeistof. Die konsep is voorgestel in twee iterasies; een waar stoom direk gegenereer word uit die FVM (direkte stoomopwekking (DSO)), en 'n ander waar 'n afsonderlike vloeibare metaal/water warmteruiler gebruik word (indirekte stoomopwekking (ISO)). Eutektiese aluminium-silikon allooi (AlSi12) is gekies as die mees geskikte metaal FVM vir navorsingsdoeleindes, en eutektiese natrium – kalium allooi (NaK) as die mees geskikte warmteoordrag vloeistof. Termiese energie stoor in FVMe lei tot bewegende grens warmteoordrag berekeninge, wat ontwerps-implikasies het. Die warmteoordrag ontleding van die warmteruilers word aansienlik vereenvoudig indien kwasi-bestendige toestand warmteoordrag ontledings gebruik kan word en dit is geldig indien daar aan die Stefan toestand voldoen word. Om vereenvoudigende aannames te bevestig en om die konsep te bewys is 'n prototipe warmte stoor eenheid gebou. Gedurende toetse is daar bewys dat die vereenvoudigende aannames geldig is, dat die prototipe werk en dien as ʼn bevestiging van die konsep. Ongelukkig het onverwagte korrosie die eksperimentele werk kortgeknip, maar dit het klem op 'n belangrike aspek van metaal FVM TES geplaas. Vloeibare aluminium allooie is hoogs korrosief en dit is 'n onderwerp vir toekomstige navorsing. Om die praktiese uitvoerbaarheid van die konsep te demonstreer en om die beheerstrategie van beide voorgestelde konsepte te bevestig is 'n stoor-eenheid ontwerp vir 'n 100 MW kragstasie met 15 uur van 'n TES. Slegs AlSi12 is gebruik in die ontwerp, wat die kragsiklus beperk het tot 'n subkritiese stoomsiklus. Dit het praktiese aspekte van die konsep onderteken, en beheerkwessies rakende die DSO konsep in die kollig geplaas. In 'n tegno-ekonomiese analise van metaal FVM TES word die gevolgtrekking gemaak dat metaal FVMe gebruik kan word in samewerking met 'n vloeibare metaal warmteoordrag vloeistof om hoë temperatuur stoor moontlik te maak en dat dit ekonomies lewensvatbaar is indien die korrosie kwessies van aluminium allooi opgelos kan word. Die gebruik van gevorderde kragsiklusse, metaal FVM stoor en vloeibare metaal warmteoordrag word net geregverdig indien beduidende vermindering in GLVE van die hele kragsentrale bereik is, en dit vorm slegs 'n deel van die oplossing. ʼn Kaskade van verskeie FVMe oor 'n reeks van temperature word vereis om entropie generasie te minimeer. Twee-tenk gesmelte soutstoor kan ook gebruik word in samewerking met kaskade metaal FVM stoor om koste te verminder, maar dit moet ook verder ondersoek word.

Mobile computing devices are capable of changing how healthcare is delivered in the future, since they aim to merge and integrate all services into one device that is versatile, customisable, and portable. The aim of this study was to explore and describe the experiences of professional nurses with regard to accessing information at the point-of-care of the patient, in order to develop guidelines that could assist other professional nurses with implementing the mobile computing device for accessing information at the point-of-care of patients. To achieve the purpose of the study, a qualitative, explorative, descriptive, and contextual design was used to conduct this research – to gain an understanding of how the professional nurses experienced accessing information at the point-of-care via mobile computing devices. The study was conducted among the professional nurses employed at the public hospital, who were trained and provided with the mobile computing device for accessing information at the point-of-care for more than two years. In-depth interviewing was conducted to obtain the data. Data analysis was done using Tesch‘s method to make sense out of text and data. Four themes were identified, namely, the professional nurses‘ expression of various experiences regarding the training received; the need for support in implementing the mobile computing device; the accessing of information at the point-of-care as beneficial for educational purposes; and the accessing of information at the point-of-care as beneficial to patient care. Two main guidelines were developed. The study concludes with recommendations made with regard to the areas of nursing practice, education and research. Throughout the study, the researcher abided by the ethical considerations. The aspects of trustworthiness implemented in this study, included dependability, credibility, transferability and confirmability (Holloway & Wheeler, 2010:298).

Thesis (MScEng)--Stellenbosch University, 2013.<br>ENGLISH ABSTRACT: The increased necessity to obtain power from other sources than conventional fossil fuels has led to the growing interest in solar power. The problem with the proposed technology is that it can only provide power during the day and therefore requires some sort of storage system, if power is to be supplied throughout the day and night. A number of storage systems exist, but the one of particular interest for this research, is packed rock beds. Rock beds have the advantage that if designed right, they have the potential to be one of the most cost effective means of storing thermal energy for solar power plants. Discrete Element Models (DEM) of rock beds were therefore developed through both experimental and numerical procedures, by conducting a series of sensitivity, calibration and verification studies. The developed models were then used to study various aspects associated with rock beds, which were either too impractical, impossible or too expensive to conduct through actual experimental work. This research focused specifically on the potential of constructing self-supporting tunnels within the rock beds in order to improve the air flow uniformity through the bed, while minimizing the pressure drop. It was observed that if the appropriate steps were followed, stable self-supporting tunnels could be formed. Valuable information such as the rock orientations resulting from different packing directions could also be derived from the models and finally, a method to convert the DEM models into the appropriate format such that it could be imported into a CFD preprocessor for future CFD studies, was developed.<br>AFRIKAANSE OPSOMMING: Die verhoogde noodsaaklikheid om energie te verkry uit ander bronne as konvensionele fossielbrandstowwe, het gelei tot die groeiende belangstelling in sonkrag energie. Die probleem met die voorgestelde tegnologie is dat dit net energie gedurende die dag kan voorsien en dus word daar ’n stoorstelsel benodig indien energie deur beide die dag en nag voorsien moet word. Tans bestaan daar wel ’n aantal van hierdie stoorstelsels, maar die een wat van besondere belang is in hierdie navorsing, is verpakte klip beddens. Klip beddens het die voordeel dat, indien dit reg ontwerp is, dit oor die potensiaal beskik om een van die mees koste-doeltreffende middels te wees vir die stoor van termiese energie vir sonkragstasies. Diskreet Element Modelle (DEM) van die klip beddens is ontwikkel deur gebruik te maak van beide experimentele en numeriese metodes waartydens ’n reeks sensitiwiteits-, kalibrasie- en verifiëring studies uitgevoer is. Die ontwikkelde modelle is gebruik om verskeie aspekte van klip beddens te ondersoek, wat of te onprakties, onmoontlik of te duur is vanuit ’n eksperimentele oogpunt. Hierdie navorsing het spesifiek gefokus op die potensiaal om self-ondersteunende tonnels binne in die klip beddens te vorm, ten einde die egaligheid van die lugvloei deur die bed te verbeter, terwyl die drukval geminimeer word. Daar is waargeneem dat stabiele self-ondersteunende tonnels wel gevorm kon word indien die toepaslike stappe gevolg is. Waardevolle inligting soos die klip oriëntasies wat as gevolg van die verskillende verpakkings rigtings onstaan kon ook vanuit die model verkry word. Ten slotte is ’n metode ontwikkel om die DEM modelle na die toepaslike formaat te omskep sodat dit ten einde gebruik kan word in numeriese vloeidinamika studies.

This study describes a simulation-based approach for informing the incorporation of Phase Change Materials (PCMs) in buildings designed to the "Passive House" standard. PCMs provide a minimally invasive method of adding thermal mass to a building, thus mitigating overheating events. Phase change transition temperature, quantity, and location of PCM were all considered while incrementally adding PCM to Passive House simulation models in multiple climate zones across the United States. Whole building energy simulations were performed using EnergyPlus from the US Department of Energy. A prototypical Passive House with a 1500 Watt electric heater and no mechanical cooling was modeled. The effectiveness of the PCM was determined by comparing the zone-hours and zone-degree-hours outside the ASHRAE defined comfort zone for all PCM cases against a control simulation without PCM. Results show that adding PCM to Passive Houses can significantly increase thermal comfort so long as the house is in a dry or marine climate. The addition of PCM in moist climates will not significantly increase occupant comfort because the majority of discomfort in these climates arises due to latent load. For dry or marine climates, PCM has the most significant impact in climates with lower cooling degree-days, reducing by 93% the number of zone-hours outside of thermal comfort and by 98% the number of zone-degree-hours uncomfortable in Portland, Oregon. However, the application of PCM is not as well suited for very hot climates because the PCM becomes overcharged. Only single digit reductions in discomfort were realized when modeling PCM in a Passive House in Phoenix, Arizona. It was found that regardless of the climate PCM should be placed in the top floor, focusing on zones with large southern glazing areas. Also, selecting PCM with a melt temperature of 25°C resulted in the most significant increases in thermal comfort for the majority of climates studied.

The majority of UK’s intermediate level radioactive waste is currently stored in 316L and 304L austenitic stainless steel containers in interim storage facilities for permanent disposal until a geological disposal facility has become available. The structural integrity of stainless steel canisters is required to persevere against environmental degradation for up to 500 years to assure a safe storage and disposal scheme. Hitherto existing severe localised corrosion observances on real waste storage containers after 10 years of exposure to an ambient atmosphere in an in-land warehouse in Culham at Oxfordshire, however, questioned the likelihood occurrence of stress corrosion cracking that may harm the canister’s functionality during long-term storage. The more corrosion resistant duplex stainless steel grade 2205, therefore, has been started to be manufactured as a replacement for the austenitic grades. Over decades, the threshold stress corrosion cracking temperature of austenitic stainless steels has been believed to be 50-60°C, but lab- and field-based research has shown that 304L and 316L may suffer from atmospheric stress corrosion cracking at ambient temperatures. Such an issue has not been reported to occur for the 2205 duplex steel, and its atmospheric stress corrosion cracking behaviour at low temperatures (40-50°C) has been sparsely studied which requires detailed investigations in this respect. Low temperature atmospheric stress corrosion cracking investigations on 2205 duplex stainless steel formed the framework of this PhD thesis with respect to the waste storage context. Long-term surface magnesium chloride deposition exposures at 50°C and 30% relative humidity for up to 15 months exhibited the occurrence of stress corrosion cracks, showing stress corrosion susceptibility of 2205 duplex stainless steel at 50°C.The amount of cold work increased the cracking susceptibility, with bending deformation being the most critical type of deformation mode among tensile and rolling type of cold work. The orientation of the microstructure deformation direction, i.e. whether the deformation occurred in transverse or rolling direction, played vital role in corrosion and cracking behaviour, as such that bending in transverse direction showed almost 3-times larger corrosion and stress corrosion cracking propensity. Welding simulation treatments by ageing processes at 750°C and 475°C exhibited substantial influences on the corrosion properties. It was shown that sensitisation ageing at 750°C can render the material enhanced susceptible to stress corrosion cracking at even low chloride deposition densities of ≤145 µm/cm². However, it could be shown that short-term heat treatments at 475°C can decrease corrosion and stress corrosion cracking susceptibility which may be used to improve the materials performance. Mechanistic understanding of stress corrosion cracking phenomena in light of a comprehensive microstructure characterisation was the main focus of this thesis.

Scuola di dottorato"Archimede" in Scienze, Comunicazione e Tecnologie. Scienze e Tecnologie dei Sistemi Complessi, Ciclo XXVII, a.a. 2015-2016<br>Nowadays electronic applications involve a high density of power Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) which represent the major percentage of energy flow to be controlled. Moreover, new technologies, such as Silicon Carbide (SiC), have been well involved in the existing power applications. Therefore, the reliability of power devices is highly demanded. Since decades, a widely used accelerated test to evaluate the reliability of MOSFETs is the so-called High Temperature Reverse Bias (HTRB). In this stress test, the Devices Under Test (DUTs) are reverse polarized at a certain percentage of the rated breakdown voltage and maintained in this condition at high temperature for a determined long time. A typical HTRB test also incorporates Electrical Characterization Tests (ECTs) of DUTs before and after each stress period, seeking for failed devices. However, time elapsed between ECTs are long and degradation and failure information of DUTs might not be registered. In this context, an advanced methodology for HTRB test is proposed. The latter consists of applying more stress cycles of short duration together with more frequent ECTs at a relatively high temperature that can be directly compared to that of normal operation in power applications (i. e. 125 °C). With this methodology, more detailed information about degradation trends in electrical parameters, time of failures and stopping of stress test on degrading devices before full breakdown can be performed. The latter can be very useful in R&D stages, where the post-failure analysis of well-degraded devices, but not broken, is important. An automatized instrumentation, aimed to apply this methodology, has been implemented. The latter utilizes individual Thermal Control Modules (TCMs) to control the test temperature per single DUT. The temperature control is performed through an opposite mini-heater and firmware running on an 8-bit microcontroller. TCMs can be set remotely to apply test temperatures in the range [30-200 °C]. In addition, Switch Matrix Modules (SSMs) are implemented to configure the electrical connections required for HTRB or ECT tests remotely. A PC application controls all the modules through a Master Communication Module (MCM) also implemented. A commercial Source and Measure Unit (SMU) is used for the electrical stress. Full customization of HTRB and ECTs test parameters can be performed to optimize the stress and degradation data acquisition. Combining the advanced methodology and instrumentation above mentioned, more stressful conditions can be applied to shorten the overall test time without losing the electrical degradation trends of failing devices. In fact, features of the implemented instrumentation allow for controlling unbeneficial thermal runaway process on the single device, isolating thermal and electric of degraded devices, acquiring frequently electrical parameters data, performing ECTs at a relatively high temperature between shorter stress cycles, managing real-time control of HTRB test. These features are useful to get reliability data in a shorter time than a typical application of HTRB tests while preserving DUTs for post-failure analysis. The advanced methodology and automatized instrumentation have been applied to Si and SiC power MOSFETs with interesting results, demonstrating to be suitable for both shorter and more accelerated HTRB tests to acquire critical information necessary for the study of degradation processes and reliability in power devices. Moreover, results have demonstrated that degradation trends are not affected when more frequent ECTs at slightly different temperature are performed in the DUTs. In addition, accurate test results have shown that drawbacks of typical HTRB implementation have been solved through the advanced methodology and instrumentation reported. Complementing the work presented, Low-Frequency Noise Measurements (LFNMs) were also applied as valuable tool to investigate the degradation process in power MOSFETs after stressing them through HTRB test. A correlation between the results from advanced HTRB test and LFNM in power MOSFETs demonstrates that the electrical degradation is represented by a noise spectrum different to that for intrinsic 1/f noise.<br>Università della Calabria

M.Ing.<br>Ice storage systems are used to store thermal energy in the form of ice build-up inside storage tanks. During off peak hours, the chiller is used to charge up the storage tank until it is full. During on peak hours, the storage is discharged to meet a certain fraction of the building cooling load. The control strategy employed determines the extent to which the storage compensates the chiller and visa versa. Given the way in which electricity rates are structured, ice storage systems become an effective energy management strategy. The objective of the study is to compare energy savings derived by using conventional control strategies versus optimal control. Conventional control strategies can be classified as chiller priority control, constant proportion control and storage priority control. In chiller priority control, the chiller meets the cooling load subject to a pre-set limit not being exceeded. Should the limit be exceeded, the remaining cooling load (at each time horizon) is compensated for by the storage. In constant proportion control, both the storage and chiller meets a constant proportion of the cooling load. Storage priority control attempts to discharge as much of the storage as possible, such that at the end of the planning horizon, the ice build up in the storage tank is just depleted. Optimal control employs dynamic programming to ensure that the integrated cost of energy, during the entire planning horizon, is minimal. A steady state ice storage plant model for analysing the performance of the control strategies is presented. The model computes the inlet and outlet temperatures into the various components of the air-conditioning plant, being the air-handling units, heat exchanger, ice storage tanks and chiller. The maximal possible discharge and charging rate at each time period (for the different control strategies) is determined using the model. Given the state of charge of the ice storage tank at each time period, it is then possible to calculate chiller power consumption. The power consumed by fans, fan coil units and pumps (in the air-conditioning plant) has not been calculated in the present analysis, however, the model can easily be extended to include such calculations. The ice storage plant model, enabled simulations of the different control strategies to be carried out over building cooling load profiles for summer and winter. Based on a 24-hour planning horizon, optimal control is found to be optimal and the only consistently performing strategy for all seasons. For the 5000 kWh ice storage plant investigated, optimal control yielded 25% energy savings in June and 12% in January, amounting to a potential of R 11 000 per month. Chiller priority control was near optimal in January but consumed 25% more energy than the base case (without storage) in June. Constant proportion control was optimal in January but poorer in June. Storage priority control is found to be optimal in June but the lowest performer in January. The drawback of optimal control and storage priority control, however, is that they require prediction of future cooling loads. The variance when using auto-regressive neural network to predict the load is expected to be in the region of 2% and thus considered acceptable. Chiller priority control and constant proportion control are instantaneous and simple to implement hence their popularity.

碩士<br>國立臺北科技大學<br>能源與冷凍空調工程系碩士班<br>100<br>The study proposes to develop a compound freezing system, through which the study evaluates its performance after being attached with freezing, ice storage and heat recovery devices, and then applied to hypermarkets. Experiments are made to analyze cost-saving effect of the system during peak and off-peak hours. During the night, the freezing system with low load stores ice to supply for the need of refrigeration in the office in the daytime. As a result, the existing equipment is able to be applied more efficiently, and the office area can save the electricity expenses for the use of air-conditioning equipment, thus achieving the effect of saving electricity expenses. As to heat recovery, at the inlet of the condenser, a heat exchanger is additionally installed, letting the high-pressure and high-temperature refrigerant at the outlet of compressor undertake heat exchange with water. In this process, continuous circulation is performed by hot water pump. The acquired heat energy is stored at a heat storage tank. On the one hand, the operation effect of the system can be enhanced; on the other, warm water can be supplied to the toilet for use. Experimental results show that ice-stored air-conditioning equipment with indoor load 100% (300W) can save electricity expenses by around 72%, indoor load 75% (225W) can save electricity expenses by around 66%, and indoor load 50% (150W) can save electricity expenses by around 64%. The time for occurrence of various air-conditioning load values in a year is mostly during the time with partial load. Therefore, at least half of electricity expenses can be saved.

Large percentages of the South African population have no access to grid power and are located at distances that make provision for such facility uneconomical. Also traditional fuels are under pressure. Most areas in South Africa receive 300 days of sunshine per year. The proposed solar system addresses the needs of such communities. A solar thermal energy storage system utilizing phase change material has been proposed that can overcome the time mismatch between solar availability and demand. The system consists of two types of thermal heat storage. The latent heat storage used Phase Change Materials (PCM) which melts at a sufficiently high temperature for cooking a variety of food types. By choosing a suitable PCM to take advantage of the latent heat absorbed during phase changes. Heat losses from both the latent heat storage and condenser are captured in the surrounding sensible heat store. The objective of this project to develop a prototype modules which together as a system could provide the essential domestic power requirements of the target groups. This includes power for cooking, hot water and in addition a limited electrical power supply for the system itself as well as for other minor loads.<br>Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2008.

The main objective of this thesis is the development of prototypes of thermal energy storages suitable for coupling with low-grade waste heat (e.g. non-concentrating solar, industrial process heat) and their experimental testing. Benefits of thermal energy storages are several, but the experience in non-sensible heat storage is still limited, especially in the design of prototypes. High temperature heat storage (T >150°C) has been the subject of a quite extensive research, but low-grade heat sources are still not fully exploited, due to the competition with water, that is available at a risible cost. In the present thesis, two different technologies were investigated, latent heat and adsorption heat, by design and experimental testing of lab-scale storages. In particular, data from experimental testing on Phase Change Materials carried out at CNR-ITAE were used for the development of thermal energy storages using latent heat technology (with phase change materials). Since only limited data on PCM-based devices in the investigated temperature range were available, two approaches were followed: a custom fin-and-tube heat exchanger and a commercial plate heat exchanger were tested with the same PCM (a paraffin) and the results used for a design analysis. In order to complete the analysis, a simplified numerical model was developed through the commercial software COMSOL Multiphysics and validated against experimental results. The model was able to describe the behaviour of the fin-and-tube system with low computational effort, showing good possibility for a future design optimization and easy adaptability to different configurations. Measurement on adsorption equilibrium curves available for adsorbent materials, instead, were used as the input for the development of a thermal energy storage making use of adsorption technology. While the storage was designed to use the same heat sources as the latent thermal ones, different operating conditions on the user-side were considered, taking into account both cold or hot storage possibilities. The experimental measurements on both the technologies highlighted the good potential of the investigated systems and therefore that further research in the specific temperature range analysed is feasible and will allow overcoming the limitations that still exist. However, the intense research activity that is on-going in the field of thermal energy storage cannot preclude from a standardization, both in the definition of relevant indicators and the assessment of the systems. To this aim, an attempt has been made at comparing the developed storages (2 latent heat storages and 1 adsorption storage), by defining common performance indicators and evaluating whether they can be applied to such different cases, in terms of characteristics, sizes and application. Results obtained have shown that both technologies allow reaching a higher energy storage density than water, under all the examined conditions (i.e. charging temperature of 75°C to 90°C), with values up to 900 kJ/kg in the case of the adsorption heat storage. The operating parameters affecting storage operation were analysed as well: indeed, it was found that the performance of the storages is strongly dependent not only on the heat sources and external ambient conditions, but also on the control of the system (i.e. the flow rate imposed, the part load operation) and the construction features, such as the material used for the shells or the insulation. Finally, the methodology suggested for the evaluation of the storage could be successfully applied to all the systems, allowing a qualitative and quantitative comparison. The main outcomes of the work here reported can then lead the path towards the optimization of the heat storage systems, from lab-scale to pre-commercial ones, thus increasing the technology readiness level and making a step forward towards practical application.

Indiana University-Purdue University Indianapolis (IUPUI)<br>Since 1990s, rechargeable Li-ion batteries have been widely used in consumer electronics such as cell phones, global positioning systems (GPS), personnel digital assistants (PDA), digital cameras, and laptop computers. Recently Li-ion batteries received considerable attention as a major power source for electric vehicles. However, significant technical challenges still exist for widely deploying Li-ion batteries in electric vehicles. For instance, the energy density of Li-ion batteries is not high enough to support a long-distance commute. The Li-ion batteries used for the Nissan Leaf and Chevy Volt only can support 50 – 100 miles per charge. The cost of Li-ion battery packs in electric vehicles is still high. The battery pack for the Chevy Volt costs about $8,000, and the larger one in the Nissan Leaf costs about $12,000. To address these problems, new Li-ion battery electrode materials with high energy density and low cost should be developed. Among Li-ion battery cathode materials, vanadium pentoxide, V2O5, is one of the earliest oxides studied as a cathode for Li-ion batteries because of its low cost, abundance, easy synthesis, and high energy density. However, its practical reversible capacity has been limited due to its irreversible structural change when Li insertion is more than x = 1. Tremendous efforts have been made over the last twenty years to improve the phase reversibility of LixV2O5 (e.g., 0 ≤ x ≤ 2) because of vanadium pentoxides’ potential use as high capacity cathodes in Li-ion batteries. In this thesis, a new strategy was studied to develop vanadium pentoxide cathode materials with improved phase reversibility. The first study is to synthesize vanadium oxide cathodes via a new chemical route – creating a phase transformation from the vanadium sulfide to oxide. The β-Na0.33V2O5 was prepared via a new method of chemical synthesis, involving the chemical transformation of NaVS2 via heat-treatment at 600 °C in atmospheric air. The β-Na0.33V2O5 particles were well crystalized and rod-shaped, measuring 7–15 μm long and 1–3 μm wide with the formation of the crystal defects on the surface of the particles. In contrast to previous reports contained in the literature, Na ions were extracted, without any structural collapse, from the β -Na0.33V2O5 structure and replaced with Li ions during cycling of the cell in the voltage range, 1.5 V to 4.5 V. This eventually resulted in a fully reversible Li intercalation into the LixV2O5 structure when 0.0 ≤ x ≤ 2.0. The second study is to apply the synthesis method to LiVS2 for the synthesis of β׳-LixV2O5 for use as a high performance cathode. The synthesis method is based on the heat treatment of the pure LiVS2 in atmospheric air. By employing this method of synthesis, well-crystalized, rod-shaped β׳-LixV2O5 particles 20 – 30 μm in length and 3 – 6 μm in width were obtained. Moreover, the surface of β׳-LixV2O5 particles was found to be coated by an amorphous vanadium oxysulfide film (~20 nm in thickness). In contrast to a low temperature vanadium pentoxide phase (LixV2O5), the electrochemical intercalation of lithium into the β׳-LixV2O5 was fully reversible where 0.0 < x < 2.0, and it delivered a capacity of 310 mAh/g at a current rate of 0.07 C between 1.5 V and 4 V. Good capacity retention of more than 88% was also observed after 50 cycles even at a higher current rate of 2 C. The third study is the investigation of NaVS2 as a cathode intercalation material for sodium ion batteries. We have shown that reversible electrochemical deintercalation of x ~ 1.0 Na per formula unit of NaxVS2, corresponding to a capacity of ~200 mAh/g, is possible. And a stable capacity of ~120 mAh/g after 30 cycles was observed. These studies show that the new chemical synthesis route for creating a phase transformation from the vanadium sulfide to oxide by heat treatment in air is a promising method for preparing vanadium oxide cathode material with high reversibility. Although this sample shows a relatively low voltage range compared with other cathodes such as LiCoO2 (3.8 V) and LiFePO4 (3.4 V), the large capacity of this sample is quite attractive in terms of increasing energy density in Li-ion batteries. Also, NaVS2 could be a promising cathode material for sodium ion batteries.