Дисертації з теми "PCM cooling"

May 25, 2011, Reuters’ headline read: "New York State is prepared for summerelectricity demand". The NY operator forecasts for next summer a peak of 33GW, close to therecord ever reached. With soaring cooling demands, the electricity peak load represents a substantialconcern to the energy system. In the goal of peak shaving, research on alternative solutions based onThermal Energy Storage (TES), for both cooling and heating applications, has been largely performed.This thesis addresses thermal comfort applications with use of active free cooling through implementationof latent heat based TES. Active free cooling is based on the use of the freshness of a source, the outsideair for example, to cool down buildings. This work conceptualizes the implementation of TES basedcooling system with use of Phase Change Material in an in-house-built model. The principle of PhaseChange Material, or Latent Heat TES (LHTES), lies on latent energy which is the energy required for thematerial to change phase. In order to properly size this cooling system, a multi-objective optimization isadopted. This optimization, based on minimization of multi-objective functions, led to optimal designconfigurations. In parallel, the electrical consumption of the system and the volume uptake of the systemwere also considered. Through the obtained optimization studies, we identified non-linearinterdependency between the two objective functions: the cost of the system and the acceptable remainingcooling needs. By remaining cooling needs, we mean the cooling needs that the system cannot meet. As amatter of fact, sizing the system according to these cooling needs would imply a very high cost. It wasfound that for a certain amount of remaining cooling needs, the PCM-based cooling system reveals to bean interesting solution compared to conventional air conditioning in terms of electrical consumption andoverall system cost.
Best Master Thesis Award, granted by French Academic Institute
Cold Thermal Energy Storage

The demand for energy increases around Australia because of the massive growth in population and industrial sector, which lead to Increase energy supply. A result of this growth, Increase in the consumption of fossil fuel and that produce more CO2 emission. Many scientist and engineers claimed. Phase change material (PCM) considered a great option in the residential building to save energy and thermal comfort. From this concept, the thesis purposes are to analyse and investigate PCM performance in passive cooling in the residential ceiling by modelling, and experiment methods whether PCM will save cost and reduce CO2 emission. The method was divided into two parts the first one in modelling and the second part is experimenting. The first part was by modelling the PCM with other types of insulations in the ceiling with the consideration of weather data history around Murdoch University location and the measurement of the whole ceiling design. OPAQUE 3.0 beta software has been used to calculate all of heat gain, heat loss, and an energy reduction of the system in summer and winter. The second part was the experiment and analysed the effect of PCM in the small-scale build that symbolises house with the ceiling. Three-way valve and 5v fans used to control airflow within the ceiling in three different operation conditions Ventilation, Recycling, and Shutdown. Lab View and Arduino software were used to control the airflow and operation conditions by setting the upper limit temperature and the lower limit temperature of the human comfort zone. The outcome from modelling and simulation of the PCM shows an annual energy reduction between (13% - 21%) and CO2 equivalent emission reduced from 70 Kg to (60.9 Kg to 55.3 Kg). Furthermore, the experiment results indicate a temperature increase inside the build of 3 degrees Celsius as an effect known as greenhouse effect. Both results from simulation, experiment are close, and there was a minor difference in result. Weather was the main factor of not to cover the full potential of the PCM because the experiment done in June. PCM shows promising future in energy reduction and decrees CO2 emission.

The use of Phase Change Material, PCM, to change the thermal inertia of lightweight buildings is investigated in the CRAFT project C-TIDE. It is a joint project with Italian and Swedish partners, representing both industry and research. PCMs are materials where the phase change enthalpy can be used for thermal storage. The Swedish application is a night ventilation system where cold night air is used to solidify the PCM. The PCM is melted in the day with warm indoor air and thereby the indoor air is cooled. The system is intended for light weight buildings with an overproduction of heat during daytime. In the thesis, the results of experiments and numerical simulations of the application are presented. The theoretical background in order design the heat exchanger and applying the installation in thermal simulation software is presented. An extensive program is set up, in order to develop test methods and carry tests to evaluate the performance over time of the PCM. Testing procedures are set up according to ISO standards concerning service life testing. The tests are focused on the change over time of the Thermal Storage Capacity (TSC) in different temperature spans. Measurements are carried out on large samples with a water bath calorimeter. The service life estimation of a material is based on the performance of one or more critical properties over time. When the performances of these properties are below the performance requirements, the material has reached its service life. The critical properties of the PCM are evaluated by simulation of the application. The performance requirements of the material are set up according to general requirements of PCM and requirements according to building legislation. The critical properties of a PCM are the transition temperature, the melting temperature range and the TSC in the operative temperature interval. The critical property of the application is its energy efficiency.

The results of the study show that the night cooling system will lower the indoor air temperature during daytime. It also shows that the tested PCM does not have a clear phase change, but an increased specific heat in the operative temperature interval. Increasing the amount of material, used in the application, can compensate this. Finally, the tested PCM is thermally stable and the service life of the product is within the range of the design lives of the building services. It is essential to for all designers to know the performance over time of the properties of PCMs. Therefore it is desirable that standardized testing methods of PCM are established and standardized classification systems of PCMs are developed.

La reducció del consum energètic dels sistemes de calefacció i refrigeració dels edificis és un repte fonamental per assolir els objectius marcats per l’Horitzó 2020. Noves aplicacions d'emmagatzematge d'energia tèrmica en edificis es mostren prometedores per reduir aquest elevat consum energètic. Un dels objectius d'aquesta tesi doctoral és revisar les aplicacions passives i actives d'emmagatzematge d'energia que es troben en la literatura, especialment aquelles que utilitzen materials de canvi de fase (PCM). En aplicacions passives els requeriments de confort i les condicions climàtiques són els principals paràmetres que s’han tingut en compte fins ara. Per això s'estudia la influència de càrregues internes en el aplicacions passives de PCM. D'altra banda, es presenta un sistema innovador que actua com una unitat d'emmagatzematge tèrmic i alhora com un sistema de calefacció i refrigeració. El rendiment tèrmic d'aquest sistema es testeja sota condicions reals i s'avalua el seu potencial de reducció del consum d'energia.
La reducción del consumo energético de calefacción y refrigeración de los edificios es un reto para lograr los objetivos marcados por el Horizonte 2020. Nuevas aplicaciones de almacenamiento de energía térmica en edificios se muestran prometedoras para reducir este elevado consumo energético. Uno de los objetivos de esta tesis doctoral es revisar aplicaciones pasivas y activas de almacenamiento de energía que se encuentran en la literatura, especialmente aquellas con materiales de cambio de fase (PCM). En aplicaciones pasivas los requerimientos de confort y las condiciones climáticas son los principales parámetros que se han tenido en cuenta hasta ahora. Se estudia la influencia de cargas internas en aplicaciones pasivas de PCM. También, se presenta un sistema innovador que actúa como una unidad de almacenamiento térmico y como calefacción y refrigeración. El rendimiento térmico de este sistema se testea bajo condiciones reales y evalúa su potencial de reducción del consumo energético.
Reducing the energy consumption of heating and cooling systems of buildings is a key challenge to achieve the targets set for the Horizon 2020. New applications of thermal energy storage in buildings are promising to reduce the high energy consumption. One of the objectives of this PhD is to review passive and active applications of thermal energy storage in buildings found in the literature, especially those that use phase change materials (PCM). In passive applications comfort requirements and climatic conditions are the main parameters that have been considered so far. For this study, the influence of internal loads has been taken into account in passive PCM applications. Moreover, an innovative system which acts as a storage unit and a heating and cooling supply is presented. The thermal performance of this system is studied and the potential in reducing the energy consumption of heating and cooling is evaluated.

Solar chimney is an important passive design strategy to maximize solar gain to enhance buoyancy effect for achieving adequate air flow rate and a desired level of thermal comfort inside a building. Therefore, solar chimney has the potential advantages over mechanical ventilation systems in terms of energy requirement, economic and environmental benefits. The main aim of this project is to study the technical feasibility of a solar chimney incorporating latent heat storage (LHS) system for domestic heating and cooling applications. The research work carried out and reported in this thesis includes: the development of a detailed theoretical model to calculate the phase change material (PCM) mass for solar chimney under specific climatic condition, the development of a CFD model to optimise the channel depth and the inlet and outlet sizes for the solar chimney geometry, experimental and numerical investigations of the thermal performance of the proposed system using a prototype set-up, a parametric study on the proposed system to identify significant parameters that affect the system performance was carried out by using the verified numerical model. The numerical and experimental study showed that the numerical model has the ability to calculate the PCM mass for the proposed system for the given weather conditions. The optimum PCM should be selected on the basis of its melting temperature, rather than its other properties such as latent heat. The experimental work on the thermal performance of the proposed system has been carried out. The results indicated that the LHS based solar chimney is technically viable. The outlet air temperature and the air flow rate varied within a small range during phase change transition period which are important for a solar air heating system. A numerical model was developed to reproduce the experimental conditions in terms of closed mode and open mode. The model results were in a close agreement with the experimental results particularly the simulated results for the discharging process. With the verified model, a comprehensive parametric analysis intended to optimise the thermal performance of proposed the system was performed. The results analysed are quantified in terms of charging/discharging time of the PCM, temperature difference between outlet air and inlet air of the solar chimney, and mass flow rate of the chimney, which are the most important quantities of the proposed system.

Space cooling energy demand is projected to increase due to climate changes. For example, the South African climate change model projected warming to reach around 3 to 4°C along the coast, and 6 to 7°C in the interior. Such temperature increases will significantly increase the energy demand by building cooling applications. Thus, there is an urgent need to improve the energy efficiency in buildings and to reduce the peak cooling loads. Various studies for building free cooling using phase change materials have shown to reduce or avoid the need for mechanical space cooling. Very few of these studies covered Southern African climatic conditions and no research was found reporting a comparison of free cooling thermal performance of different PCM types for an individual climate scenario. The purpose of this study was to experimentally evaluate and compare the cooling performance of three PCM materials in plate-air heat exchanger modules subjected to Southern African climatic conditions and to use the data to deduce empirical correlations that can be used by thermal designers to determine the number of modules required to maintain an objective cooling load within the range of operating conditions. In this experimental investigation the cooling (discharging) performance of plate encapsulated Phase Change Materials (PCMs) for passive cooling applications were evaluated as measured by its average effectiveness, cooling power, energy absorption and phase transformation duration. A test facility that mimics a PCM-air heat exchanger module installed in a ventilation duct was used to consider the impact of varying air flow rate and inlet air temperature. PCM plate encapsulations with a thickness of 10 mm orientated vertically and spaced at a pitch of 15 mm were investigated. The thermal storage characteristics of three commercial PCMs were considered. Two paraffin type PCMs with melting temperature ranges of 25 °C to 28 °C and 22 °C to 26 °C and one type salt hydrate with a phase change temperature range 24 °C to 25 °C were used in air flows ranging in temperature from 30 °C to 35 °C and duct air velocities ranging from 0.4 m/s to 0.9 m/s. The results indicated that average effectiveness of the PCM modules decreased with increasing convective air mass flow rate. Increasing air mass flow rate (at constant inlet air temperature) or increasing the inlet air temperature (at constant air mass flow rate) increased the average cooling power. The phase transformation durations of the PCMs decreased as both the air flow rate and inlet air temperature increased. The salt hydrate (SP24E) module had the highest energy absorption capacity for all experimental conditions. The rate of energy absorption increased with inlet air temperature. From a design standpoint the desirable thermal performance of PCM is to have a high instantaneous heat absorption capacity and also extended over a longer period. Paraffinic PCMs met the first condition of high instantaneous heat absorption but did not meet the second condition of extended heat absorption duration. SP24E met the condition for extended heat absorption duration but had a lower instantaneous heat absorption capacity than the paraffin. Empirically-based correlations for determining the number of modules to maintain an objective cooling load were developed using a multiple regression analysis technique. From this, air conditioning system designers can determine the number of modules (installed in parallel) required to maintain an objective cooling load within the range of operating conditions tested.
Dissertation (MSc)--University of Pretoria, 2017.
Mechanical and Aeronautical Engineering
MSc
Unrestricted

The present thesis project has been developed at the Department of Energy and Building Services Engineering of the Munich University of Applied Sciences. The thesis intends to present an overview of the use of phase change materials (PCM) for building insulation applications. In light of the high energy consumption in the building sector, the latent heat storage capacity of PCMs could be effectively used to provide passive thermal regulation of the indoor temperature as well as reduce energy consumption due to thermal regulation in buildings, which is often caused by high energy consuming solutions, such as air conditioning systems. The first chapter is an introduction on conventional approaches and traditional materials used for building insulation, with an overview of the environmental impact of thermal regulation of buildings. The second chapter is a detailed analysis of the state of the art of phase change materials; this chapter also describes the thermodynamic process of latent heat storage in PCMs, along with the operating principles of the materials, the most effective installation procedures available, the advantages of PCMs compared to other conventional solutions, as well as several examples of PCM applications from the literature. The third chapter describes the Life-Cycle Cost Analysis (LCCA) as a tool to calculate the optimum thickness of conventional insulation materials and the limits of this approach when applied to PCM insulation sizing. The fourth chapter shows the different options available on the market for PCM insulation, with a detailed description of a real application of PCM integrated into a cooling ceiling system at the Energy Efficiency Center in Wurzburg (Germany). The fifth chapter presents the financial approaches to promote refurbishment and energy-improvement in buildings. The sixth and final chapter presents the conclusions of the research and future potential studies on the topic of PCMs.

In this master thesis, several cooling systems for PV-systems have been looked into by doing a smaller literature review and then a cooling module for a BIPV-panel was built out from the knowledge gathered. The cooling module used a PCM material separated into 12 bags and then placed in a 3x4 shaped pattern fastened to an aluminium plate that in turn was placed on the back of a PV-panel. This was tested in first a pilot test and then tested outdoors on panels with insulation on its back to simulate BIPV-panels. Temperature data from behind the panel was gathered with and without the cooling module and then compared with each other with added ambient temperature. It was found that the PCM cooled down the panels during similar weather conditions where the outside temperature and the amount of clouds where approximately the same, and it was also found that PCM technologies needs to be more optimised in terms of its material use, the amount of material, and its arrangement for it to be used in PV-panels. An economical calculation was made and it was found that it wasn't economically viable as it takes 14 years for the PV-panel with cooling to pay for itself while it takes 13 years for the PV-panel with cooling to pay for itself. These results are then discussed in comparison to other systems and earlier work done.
I denna exjobbsrapport så har ett antal olika kylningssystem till PV-paneler setts igenom genom en mindre litteraturstudie. Därefter byggdes en kylningsmodul för en BIPV utifrån den kunskapen som samlats in. Kylningsmodulen använde sig utav ett PCM material som var uppdelat mellan 12 påsar som placerades i ett 3x4 mönster som fästs på baksidan av en aluminiumplåt som i sin tur placerades på baksidan utav PV-panelen. Denna testades först i ett pilottest och sedan utomhus på paneler som isoleras baktill för att simulera BIPV-paneler. Temperaturdata samlades in från panelens baksida, med och utan kylnings modul, som sedan jämfördes med varandra samt omgivningens temperatur. Slutsatsen är att PCM kyler panelen under liknande väderförhållanden där ute temperaturen och molnigheten var ungefär densamma, men att PCM behöver optimeras mer i form av användningen av materialet, mängden av material, och hur det sätts upp som kylning på PV-paneler. En ekonomisk kalkyl genomfördes som visar att det inte är ekonomiskt gångbart eftersom det tar 14 för PV-panelen med kylning att betala av sig själv medan det tar 13 år för PV-panelen utan kylning att göra det. Dessa resultat diskuteras sedan i jämförelse med andra system och tidigare arbeten som gjorts inom området.

Les conditions actuelles de réchauffement de la planète ont mené aux pays du monde à s'engager dans la durabilité et l’efficacité énergétique et la réduction des émissions de gaz à effet de serre. En tant que troisième consommateur d'énergie, le bâtiment représente un élément clé envers l'efficacité énergétique et de la stabilisation de la température globale. Plusieurs solutions existent pour la réalisation de ces objectifs, et les travaux présentés tout au long de cette thèse concernent un composant solaire particulier à la construction externe du bâtiment, appelé cheminée solaire. Cette thèse de doctorat porte sur l'analyse expérimentale et numérique des dispositifs de stockage d'énergie, sous forme de matériaux à changement de phase (PCM), afin d'optimiser les performances de cette technologie solaire. Le but de cette étude est de caractériser l’impact des panneaux Rubitherm RT44 PCM sur une cheminée solaire en laboratoire et in situ afin de permettre une comparaison avec la version classique. De plus, un modèle numérique a été développé et testé dans le but d'obtenir un outil numérique capable de représenter le comportement d'une cheminée solaire. Enfin, une optimisation à deux objectifs du modèle numérique de cheminée solaire intégrée PCM a été réalisée afin de déterminer certains des paramètres optimaux de ce type de technologie afin d’obtenir le flux d’air sortant le plus élevé possible, tout en maintenant une température suffisamment élevée dans la cheminée atteindre la gamme de fusion des PCM
The current global warming conditions have led nations across the world to commit into energetic sustainability and greenhouse gas emission reduction. Being the third greatest energetic consumer, the building represents a major key towards energy efficiency and global temperature stabilization. Several solutions exist for the accomplishment of these goals, and the works presented throughout this dissertation concerns a particular external building solar-driven component known as solar chimney. This PhD thesis focuses on the experimental and numerical analysis of energy storage devices, in the form of Phase Changing Materials (PCMs), for the optimisation of the performance of this solar technology. The aim of this study is to characterize the impact of Rubitherm RT44 PCM panels on a solar chimney under laboratory and in-situ conditions to carry out a comparison against the classic version. Additionally, a numerical model was developed and tested in the interest of obtaining a numerical tool capable of representing the behaviour of a solar chimney. Finally a bi-objective optimization of the PCM integrated solar chimney numerical model was carried out in order to determine some of the optimal parameters of this type of technology to obtain the highest exiting air flow, all while maintaining a high enough temperature across the chimney to reach the fusion range of the PCMs

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.

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.

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.

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.

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.

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.

Keywords:Comfort cooling, peak shaving, PCM, coolthermal storage system, DSC, phase change temperature range,the heat of fusion, phase equilibrium, phase diagram. Language:English

The topic of this doctoral thesis is to study the thermal properties of PCM materials and discussion of their use for cooling of photovoltaic systems. The aim of the study is to measure and characterize the thermal properties of commercial PCM materials (Micronal®), their practical use is related to the phase transitions. The behavior of bulk materials at different temperatures is well described theoretically and experimentally verified. For the application use it is necessary to examine and determine the thermal properties of PCM materials depending on the phase transitions during heating and cooling. To study the thermal properties of materials the known transient methods of measuring are used which give full information about the behavior of the materials investigated in dependence on the temperature and thus allow the determination of the thermo-physical parameters of the system. For the transient measurements there are used especially pulse transient and step wise method. Newly is used also combination of linear temperature rise (the ramp wise) and the step wise method. The principle is based on the generation of a small amount of heat inside the studied sample and it is measured the thermal response of the system from which it may be then determined the necessary thermo-physical parameters. The theoretical part of this thesis focuses on characterization of methods for the determination of thermo-physical parameters of the investigated material. In the experimental part of the approached process of experiment, the results, the method of evaluation of the obtained data and also the discussion of results from the viewpoint of potential applications are presented.

Thermal energy storage (TES) including phase change materials (PCMs), is an important technology to provide free cooling and ventilation in buildings. They have potential advantages over mechanical ventilation systems in terms of energy requirements, economic and environmental benefits. The main aim of this research is to study an air-multiple PCMs unit for the free cooling and ventilation applications relying on the daytime and night-time temperature difference during the summer. The research work carried out and reported in this thesis includes an extensive literature review on TES, incorporating PCMs, experimental investigation of the parameters influencing the charging and discharging time and the air outlet temperature of an air-PCM unit. It has been observed that the heating/cooling rate of PCM is important factor in studying charging/discharging behaviour of a PCM. For this, the determination of the thermophysical properties of the selected PCMs by Differential Scanning Calorimetry (DSC) is carried out. Similar heating rate, as per experimental testing, established better validation results when used in CFD model. The CFD model aims to predict the outlet air temperatures and the PCM temperatures for validation of the experimental data. Further on, parametric study will use the verified CFD model of an air-multiple PCM unit to identify significant parameters affecting the air outlet temperature, the cooling time and the PCM charging time. Finally, this thesis will investigate the potential of an air-multiple PCM unit for free cooling and ventilation of an office building under Portuguese climatic conditions through a CFD model. The experimental study has shown that the air inlet temperature and velocity play a major role on the PCM charging/discharging time and on the air outlet temperature. The numerical and experimental studies show that the developed CFD model has the ability to give good agreement for the prediction of the PCM charging and discharging times and the air outlet temperature with experimental results. Based on the experimental work and numerical analysis, an air-multiple PCM unit is proposed with a cooling load of 1.02 kW for office building. This allowed the reduction of the initial capital cost, the maintenance cost and the environmental benefits when compared to a traditional air conditioning unit.

This work investigates three-dimensional power loop layout for application to a SiC based matrix converter, providing a symmetric, low-inductance solution. The thesis presents various layout types to achieve this design target, and details the implementation of a hybrid layout to the matrix converter phase-leg. This layout is more easily achievable with a surface-mount device package, which also offers benefits such as ease in manufacturing, and a compact package. In order to implement a surface-mount device, a PCB thermal management strategy should be utilized. An evaluation of these methods is also presented in the work. The final power loop solution that implements an aluminum nitride inlay is evaluated through simulated parasitic extraction and experimental double pulse tests. The layout achieves small, symmetric loop inductances. Finally, the full power, three-phase matrix converter demonstrates the successful implementation of this power loop layout.
Master of Science
In the United States, 40% primary energy consumption comes from electricity generation, which is the fastest growing form of end-use energy. Industries such as commercial airlines are increasing their use of electric energy, while phasing out the mechanical and pneumatic aircraft components, as they offer better performance and lower cost. Thus, implementation of high efficiency, electrical system can reduce energy consumption, fuel consumption and carbon emissions [1]. As more systems rely on this electric power, the conversion from one level of power (voltage and current) to another, is critical. In the quest to develop high efficiency power converters, wide bandgap semiconductor devices are being turned to. These devices, specifically Silicon Carbide (SiC) devices, offer high temperature and high voltage operation that a traditional Silicon (Si) device cannot. Coupled with fast switching transients, these metal oxide semiconductors field effect transistors (MOSFETs), could provide higher levels of efficiency and power density. This work investigates the benefits of a three-dimensional (3D) printed circuit board (PCB) layout. With this type of layout, a critical parasitic – inductance – can be minimized. As the SiC device can operate at high switching speeds, they incur higher di/dt, and dv/dt slew rates. If trace inductance is not minimal, overshoots and ringing will occur. This can be addressed by stacking PCB traces on top of one another, the induced magnetic field can be reduced. In turn, the system inductance is lowered as well. The reduction of this parameter in the system, reduces the overshoot and ringing. This particular work applies this technique to a 15kW matrix converter. This converter poses a particular design challenge as there are a large number of devices, which can lead to longer, higher inductance PCB traces. The goal of this work is to minimize the parasitic inductance in this converter for high efficiency, high power density operation.

En struktur analys på Ericssons MINILINK-6352 har utförts för att undersöka spänningar och deformationer på enheten, främst med fokus på de termiska gränskiktsmaterialen och buktningar av kretskortet. Dessa är viktiga aspekter när man överväger om enheten är termiska lämpad ur en mekanisk synvinkel, där god ytkontakt mellan de olika kropparna är avgörande för ordentlig kylning genom värmeledning. Analysen kräver tillräcklig materialdata till gränskiktsmaterialen och kretskortet för att kunna skapa lämpliga matematiska modeller. Enaxliga kompressionstester har genomförts för att karakterisera de hyperelastiska och viskoelastiska lagar för fyllda silikongummimaterial som används som termiska gränskiktsmaterial, som ibland kallas för gappad. Böjning av ett kretskort simulerades och jämfördes med ett tre--punkts böjtest för att verifiera om befintlig materialdata i beräkningsprogrammen var tillräcklig, jämförelsen visade god överensstämmelse. Kretskortet med dess komponenter, som modellerades som styva block, med gappads ovanpå som komprimeras av en platta simulerades och ett svagt område hittades. Detta område var sedan tidigare känt och har i ett senare skede eliminerats genom att tillsätta ytterligare en stödpelare. Därav visar denna studie en metod för att hitta intressanta regioner tidigt i konstruktionsfasen som lätt kan ändras för att uppfylla nödvändiga krav och undvika brister i konstruktionen. Arbetet har visat sig användbart genom att hitta detta svaga område i exempel produkten, arbetet ger även tillräckligt med information och exempeldata för att ytterligare utreda liknande produkter. Kombinationen av erfarenhet och simulering möjliggör smartare designval.
A structural analysis on Ericssons MINILINK-6352 has been performed in order to investigate stresses and deformations of the unit, mainly focusing on the thermal interface materials and warpage of the printed circuit boards. These are important aspects when considering if the unit is thermally adequate from a mechanical point of view, where good surface contact between various bodies are critical for proper cooling through heat conductivity. The analysis requires sufficient materal data for the interface material and the circuit board in order to create suitable mathematical models. Uniaxial compression tests have been conducted to characterise the hyperelastic and viscoelastic constitutive laws of a filled silicone rubber material used as a thermal interface material, commonly referred to as a thermal pad. Bending of a printed circuit board was simulated and compared to a three-point bend test on the circuit board in order to verify material data already available in the computational software, which showed good agreement. The entire radio unit was mechanically analysed during its sealing process. The circuit board with attached components modelled as stiff blocks with thermal pads on top compressed by plates was simulated and a weak area was found. This area in question was already known and has in a later stage been eliminated by adding an additional supporting pillar. Hence this study shows a methodology to find regions of interest at an early design phase which can easily be altered to fulfil necessary requirements and eliminate design flaws. This work has proven useful in finding weak regions in the example product, it also provides enough information and example data to further investigate similar products. The combination of experience and simulation allows for smarter design choices.

Dissertação de mestrado integrado em Engenharia Civil
Tanto a nível europeu como nacional os edifícios destinados à habitação e serviços consomem uma grande parte de toda a energia consumida, apresentando uma tendência crescente, no sentido em que neste momento se caminha para um crescimento acentuado do consumo energético, aumentando desta forma a emissão de gases de efeito de estufa. É atribuída grande importância à redução dos consumos energéticos nos edifícios e consequentes emissões de dióxido de carbono, tendo-se verificado, nos últimos anos, que esta é cada vez mais uma preocupação nacional e internacional, devendo-se criar medidas no sentido da conservação e armazenamento da energia. A incorporação de materiais de mudança de fase (PCM, do inglês Phase Change Materials) nos edifícios torna-se, por isso, numa medida essencial no combate aos elevados níveis de consumo energéticos verificados. Esta dissertação apresenta um estudo no sentido de incorporar PCM nas soluções construtivas mais usuais em Portugal, adequando-se o uso destes materiais ao clima nacional e o conseguindo-se prever a quais as poupanças energéticas daí inerentes. Para que então se consiga atingir estes objetivos, numa primeira fase recorreu-se à simulação dinâmica de várias soluções construtivas correntes com inclusão de alguns tipos de PCMs comercializados, concluindo-se qual a solução construtiva e o PCM que melhor se comporta perante o clima da cidade do Porto. Numa segunda fase de simulação usa-se então a solução construtiva em que se verificaram os melhores resultados e aplicando-a a um edifício unifamiliar com sistema de climatização com uma eficiência de 100%, retirandose daqui as necessidades energéticas para aquecimento (no inverno) e arrefecimento (no verão) do edifício com e sem PCM. Feita uma análise comparativa entre os dois casos conclui-se que o uso de PCM resulta numa poupança energética significativa no inverno e, nas condições testadas, a um acréscimo adicional de energia no verão.
Both at European and national levels, buildings destined to housing and services consume a great fraction of all the energy consumed, with that consumption presenting a tendency to grow, meaning that at this moment it’s going towards a sharp increase in the energetic consumption, leading to an increased emission of greenhouse gases. It is considered very important to reduce the energy consumption in buildings and its carbon dioxide emissions associated, having been observed in the last years that this is becoming more and more a national and international concern, showing that measures should be taken towards energy conservation and storage. In this sense, the incorporation of phase changing materials (PCM) in buildings turns out to be an essential measure, with a lot of potential regarding the reduction of the high energy consumption currently observed. This dissertation presents a study that aims to the incorporation of PCM in the construction elements most used in Portugal, adapting the use of these materials to the Portuguese climate, making it possible to predict the resulting savings in energy consumption. In order to accomplish these goals, in the first phase, a dynamic simulation was performed with the various types of construction elements currently used, with the inclusion of some kinds of commercialized PCMs, thus finding the construction solution with the best behavior when facing the climate found in Porto. In the second phase of simulation, it is used the construction solution with the best results applied to a single-family building with HVAC system with an efficiency of 100%, collecting this way the energy requirements for heating (during winter) and cooling (during summer) the building, with and without PCM. A comparative analysis between the two cases brings us to the conclusion that the use of PCM results in a significant energy saving during the winter, and under the tested conditions, it results in an additional increase of energy during the summer.

碩士
國立屏東科技大學
生物機電工程系所
99
Traditionally, the biochemical samples are cultured in Petri dishes. After completing the experiment, excessively used sample must be disposed. In order to save the cost and miniaturize the system, this research is to develop a micro-domain heating chip with waterwall cooling channel. The commercial software CFD-ACE+TM is utilized to simulate the thermal fields of the chip. There are two different constant temperature regions designed within the chip. Between these two isothermal areas, there is a waterwall cooling channel and the fluid in the channel can be used to control the temperature of the chip. The effects of various fluid flow velocities on the temperature distribution are examined. Simulation result shows that when the fluid flow rate in the channel becomes slow, it will be more easily heated by the isothermal areas with high temperatures. This makes the fluid temperature near the outlet getting higher and then the surface temperature of the chip is non-uniform. The optimal flow rate is found and it can be apply to the experiment. In our experiment, the chip system mainly consists of three parts. They include a PDMS-glass chip, two heating module and the fluid channel used to control the chip temperature. A PMMA channel for fluid flowing is fabricated under the chip. The heating module comprises two heaters that can be thermal controlled. When two different isothermal regions are created at the chip surface, we make use of the fluid which flows in the waterwall channel between the two heaters in order to cool the chip. Then three different isothermal zones can be created on the chip. The result shows that the fluid is easily heated by isothermal area, the effects of various flow rate in the channel on the surface temperature is noticeable. The obvious heat convective effect inside the cooling channel can be observed with the increasing of the fluid velocities. The large areas of the various isothermal regions are shown at the chip surface. Experiment results are compared with the simulated data, and it shows a similar trend. In the future we may establish several isothermal areas in the chip, and it could be applied in the fields of cell culture, drug screening or polymerase chain reaction in the chips.

碩士
輔仁大學
化學系
99
Morphology of P3HT and PCBM blend has been widely studied for organic photovoltaics because of its critical influence on power conversion efficiency (PCE) of polymer solar cells. Research shows that blend ratio and thermal treatment of the P3HT/PCBM layer have a profound effect on the morphology of this active layer. To investigate how PCBM affects the morphology of P3HT/PCBM, a freeze-dry method is applied to the wet P3HT/PCBM film. Minimum thermal energy is applied to the P3HT/PCBM film and morphology of the P3HT/PCBM film before thermal treatment is studied by using scanning electron microscope (SEM). Porous structure is observed in the freeze-dried P3HT/PCBM film. The pore size diminishes as the ratio of PCBM increases in the P3HT/PCBM film. Additionally, the freeze-dried P3HT/PCBM film is more resistant to the formation of PCBM crystals after thermal treatment than that prepared by a spin coating method. To minimize phase separation during the thermal treatment process that is required to enhance performance of polymer solar cells, a modified dynamic cooling process is applied to the fabrication of polymer solar cells. Formation of organized P3HT during the cooling process minimizes the required treatment time and enhances the performance of polymer solar cells. A polymer solar cell with 3.83 % PCE is prepared by using this technique.

碩士
輔仁大學
化學系
104
Low band gap copolymers have been widely used in the photoactive layer of high performance polymer solar cells. However, most low band gap copolymers are not crystallizable because of different monomers used in the polymer backbones. On the other hand, the thermal stability of low band gap copolymers with PCBM is relative poor which leads to phase separation between low band gap copolymers and PCBM. PCBM forms large size domains and reduces efficiency of exciton dissociation. A dynamic-cooling and freeze-drying process (DCFD) is applied to the fabrication of photoactive layer together with a functionalized compatibilizer to improve the compatibility issue and also molecular aggregation of photoactive layer. OM and SEM studies show that thermal stability of P3HT/PCBM film is enhanced through the H-bond formation between the compatibilizer (HOC-P3HT-COH) and PCBM. Absorption spectra and XRD experiments indicate that molecular aggregation of P3HT in the P3HT/PCBM film is also improved using the DCFD process. Crystal size of P3HT increases from 17.81 nm (spin-coating) to 24.7 nm (DCFD). It is found that similar results are acquired as applying the same techniques to a low band gap copolymer (pBCN)/PCBM system. Thermal stability of pBCN/PCBM film is enhanced after adding an end-functionalized compatibilizer – pBCN-OH. Crystal size of pBCN increases from 11.26 nm (spin-coating) to 19.63 nm.

碩士
輔仁大學
化學系
107
P3HT/PCBM blend films have been used in the photoactive layer of polymer solar cells. In the blend film, bulk-heterojuction (BHJ) structure can enhance contact area between materials and facilitate the exciton dissociation. In addition, controlling molecular aggregation of conjugating polymer has been a critical issue for polymer solar cells. Higher crystalline of P3HT is benificial to absorption spectra and carrier mobility. Thermal annealing has been used to improve crystalline of P3HT in many references. However, thermal annealing results in phase separation due to poor compatibility. Here, the new processes are applied to improve crystalline of polymer prior to coating process and decrease probability of phase separation so that minimum/or no post-treatment .With respect to materials, in high PCE polymer solar cells, low band-gap conjugated copolymer has been widely used to enhance absorption spectra recently, however, they are not often crystallizable because of different monomers used in the polymer backbones. Therefore, this study will apply the new processes to conjugated copolymer (pBCN). Part one, synergistic effect of dynamic cooling/freeze drying process is applied to pBCN/PCBM blend to enhance aggregation of pBCN and decrease agglomeration of PCBM. The dynamic-cooling process allows pBCN molecules to aggregate in solution into a more organized structure during the cooling process; the freeze-drying process prevents severe agglomeration of PCBM during the solvent removing process. To improve stability of blend films, we add additive (bis-PCBM) to decrease agglomeration of PCBM after thermal annealing. Part two, a shear–induced-crystallization (SIC) process is applied to the polymer solution prior to coating process. Experimental results indicate that after applying SIC process to a crystallizable polymer, pBCN, aggregation of pBCN is enhanced than that from spin-coating process. Additionally, film absorption study shows that aggregation of pBCN does not affected by addition of PCBM, which makes the SIC process feasible for the fabrication of polymer solar cells.

The trend in the electronic and electrical equipment industry towards denser and more powerful product requires a higher level of performance from cooling devices. In this context, passive cooling techniques such as latent heat storage systems have attracted considerable attention in recent years. Phase change materials (PCMs) have turned out to be extremely advantageous in this regard as they absorb high amount of latent heat without much rise of temperature. But unfortunately, nearly all phase change materials (PCMs) with high latent heat storage capacity have unacceptably low thermal conductivity, which makes heating and cooling processes slow during melting and solidification of PCMs. Augmentation of heat transfer in a PCM is achieved by inserting a high thermal conductivity material, known as thermal conductivity enhancer (TCE), into the PCM. The conglomeration of PCM and TCE is known as a thermal storage unit (TSU). In this thesis, detailed and systematic analyses are presented on the thermal performance of TSUs subjected to two types of thermal loading- (a) constant power loading in which a constant power level is supplied to the chip (heater) for a limited duration of time, and (b) cyclic loading. Eicosane is used as the PCM, while aluminium pin or plate fins are used as TCEs. First, a 1-D analytical model is developed to obtain a closed-form temperature distribution for a simple PCM domain (without TCE) heated uniformly from the bottom. The entire heating process is divided into three stages, viz. (a) sensible heating period before melting, during which heat is stored in the solid PCM in the form of specific heat, (b) melting period, during which a melt front progresses from the bottom to the top layer of the PCM and heat is stored in latent as well as in sensible forms, and (c) post melting period, during which energy is stored again in the form of sensible heat. For each stage, conduction energy equation is solved with a set of initial and boundary conditions. Subsequently, a resistance capacitance model of phase change process is developed for further analysis. For transient performance under constant thermal loading, experimental investigations are carried out for TSUs with different percentages of TCE. A numerical model is developed to interpret the experimental results. The thermal performance of a TSU is found to depend on a number of geometrical parameters and boundary conditions. Hence, a systematic approach is desirable for finding the best TSU design for which the chip can be operated for a longer period of time before it reaches a critical temperature (defined as the temperature above which the chip starts malfunctioning). As a first step of the approach, it is required to identify the parameters which can affect the transient process. It is found that the convective heat transfer coefficient, ‘h’ and the exposed area for heat transfer have little effect on the chip temperature during the constant power operation. A randomized search technique, Genetic Algorithm (GA), is coupled with the CFD code to find an optimum combination of geometrical parameters of TSUs based on the design criteria. First, the optimization is carried out without considering melt convection within the PCM. It is found that the optimum half-fin width remains fixed for a given heat flux and temperature difference. Assuming a quasi steady process, the results of optimization are then explained by constructing and analyzing a resistance network model. The resistance network model is then extended to include the effect of melt convection, and it is shown that the optimum pitch changes with the strength of convection. Accordingly, numerical analysis is carried out by considering the effect of melt convection, and a correlation for optimum pitch is developed. Having established the role of melt convection on the thermal performance of TSUs, rigorous computational and experimental studies are performed in order to develop correlations among different non-dimensional numbers, such as Nusselt number, Rayleigh number, Stefan number and Fourier number, based on a characteristic length scale for convection. The enclosures are classified into three types, depending on the aspect ratio of cavity, viz. shallow, rectangular and tall enclosures. For a shallow enclosure, the characteristic length is the height of cavity whereas for a tall enclosure, the characteristic length is the fin pitch. In case of rectangular enclosure, both pitch and height are the important characteristic lengths. For cyclic operation, it is required that the fraction of the PCM melting during the heating cycle should completely solidify back during the cooling period, in order that that TSU can be operated for an unlimited number of cycles. If solidification is not complete during the cooling period, the TSU temperature will tend to rise with every cycle, thus making it un-operational after some cycles. It is found that the solidification process during the cooling period depends strongly on the heat transfer coefficient and the cooling surface area. However, heat transfer coefficient does not play any significant role during the heating period; hence a TSU optimized for transient operation may not be ideal for cyclic loading. Accordingly, studies are carried out to find the parameters which could influence the behaviour of PCM under cyclic loading. A number of parameters are identified in the process, viz. cycle period and heat transfer coefficient. It is found that the required heat transfer coefficient for infinite cyclic operation is very high and unrealistic with air cooling from the surface of the TSU. Otherwise, the required cooling period for complete re-solidification will be very high, which may not be suitable for most applications. In an effort to bring down the cooling period to a duration that is comparable to the heating period, a new design is proposed where both ‘h’ and area exposed to heat transfer can be controlled. In this new design, the gaps between the fins in a plate-fin TSU are alternately filled with PCM, such that only one side of a fin is in contact with PCM and the other side is exposed to the coolant (air). In this arrangement, the same heat flow path through the fin which is used for heating the PCM (during the heating stage) can also be used for cooling and solidifying the PCM during the cooling part of the cycle. Natural or forced air cooling through the passages can be introduced to provide a wide range of heat transfer coefficient which can satisfy the cooling requirements. With this arrangement, the enhanced area provided for cooling keeps the ‘h’ requirement within a realistic limit. This cooling method developed is categorized as a combination of active and passive cooling techniques. Analytical and numerical investigations are carried out to evaluate the thermal performance of this modified PCM-based heat sink in comparison to the ones with conventional designs. It is found that, the performance of new PCM-based heat sink is superior to that of the conventional one. Experiments are performed on both the conventional and the new PCM-based heat sinks to validate the new findings.

The trend in the electronic and electrical equipment industry towards denser and more powerful product requires a higher level of performance from cooling devices. In this context, passive cooling techniques such as latent heat storage systems have attracted considerable attention in recent years. Phase change materials (PCMs) have turned out to be extremely advantageous in this regard as they absorb high amount of latent heat without much rise of temperature. But unfortunately, nearly all phase change materials (PCMs) with high latent heat storage capacity have unacceptably low thermal conductivity, which makes heating and cooling processes slow during melting and solidification of PCMs. Augmentation of heat transfer in a PCM is achieved by inserting a high thermal conductivity material, known as thermal conductivity enhancer (TCE), into the PCM. The conglomeration of PCM and TCE is known as a thermal storage unit (TSU). In this thesis, detailed and systematic analyses are presented on the thermal performance of TSUs subjected to two types of thermal loading- (a) constant power loading in which a constant power level is supplied to the chip (heater) for a limited duration of time, and (b) cyclic loading. Eicosane is used as the PCM, while aluminium pin or plate fins are used as TCEs. First, a 1-D analytical model is developed to obtain a closed-form temperature distribution for a simple PCM domain (without TCE) heated uniformly from the bottom. The entire heating process is divided into three stages, viz. (a) sensible heating period before melting, during which heat is stored in the solid PCM in the form of specific heat, (b) melting period, during which a melt front progresses from the bottom to the top layer of the PCM and heat is stored in latent as well as in sensible forms, and (c) post melting period, during which energy is stored again in the form of sensible heat. For each stage, conduction energy equation is solved with a set of initial and boundary conditions. Subsequently, a resistance capacitance model of phase change process is developed for further analysis. For transient performance under constant thermal loading, experimental investigations are carried out for TSUs with different percentages of TCE. A numerical model is developed to interpret the experimental results. The thermal performance of a TSU is found to depend on a number of geometrical parameters and boundary conditions. Hence, a systematic approach is desirable for finding the best TSU design for which the chip can be operated for a longer period of time before it reaches a critical temperature (defined as the temperature above which the chip starts malfunctioning). As a first step of the approach, it is required to identify the parameters which can affect the transient process. It is found that the convective heat transfer coefficient, ‘h’ and the exposed area for heat transfer have little effect on the chip temperature during the constant power operation. A randomized search technique, Genetic Algorithm (GA), is coupled with the CFD code to find an optimum combination of geometrical parameters of TSUs based on the design criteria. First, the optimization is carried out without considering melt convection within the PCM. It is found that the optimum half-fin width remains fixed for a given heat flux and temperature difference. Assuming a quasi steady process, the results of optimization are then explained by constructing and analyzing a resistance network model. The resistance network model is then extended to include the effect of melt convection, and it is shown that the optimum pitch changes with the strength of convection. Accordingly, numerical analysis is carried out by considering the effect of melt convection, and a correlation for optimum pitch is developed. Having established the role of melt convection on the thermal performance of TSUs, rigorous computational and experimental studies are performed in order to develop correlations among different non-dimensional numbers, such as Nusselt number, Rayleigh number, Stefan number and Fourier number, based on a characteristic length scale for convection. The enclosures are classified into three types, depending on the aspect ratio of cavity, viz. shallow, rectangular and tall enclosures. For a shallow enclosure, the characteristic length is the height of cavity whereas for a tall enclosure, the characteristic length is the fin pitch. In case of rectangular enclosure, both pitch and height are the important characteristic lengths. For cyclic operation, it is required that the fraction of the PCM melting during the heating cycle should completely solidify back during the cooling period, in order that that TSU can be operated for an unlimited number of cycles. If solidification is not complete during the cooling period, the TSU temperature will tend to rise with every cycle, thus making it un-operational after some cycles. It is found that the solidification process during the cooling period depends strongly on the heat transfer coefficient and the cooling surface area. However, heat transfer coefficient does not play any significant role during the heating period; hence a TSU optimized for transient operation may not be ideal for cyclic loading. Accordingly, studies are carried out to find the parameters which could influence the behaviour of PCM under cyclic loading. A number of parameters are identified in the process, viz. cycle period and heat transfer coefficient. It is found that the required heat transfer coefficient for infinite cyclic operation is very high and unrealistic with air cooling from the surface of the TSU. Otherwise, the required cooling period for complete re-solidification will be very high, which may not be suitable for most applications. In an effort to bring down the cooling period to a duration that is comparable to the heating period, a new design is proposed where both ‘h’ and area exposed to heat transfer can be controlled. In this new design, the gaps between the fins in a plate-fin TSU are alternately filled with PCM, such that only one side of a fin is in contact with PCM and the other side is exposed to the coolant (air). In this arrangement, the same heat flow path through the fin which is used for heating the PCM (during the heating stage) can also be used for cooling and solidifying the PCM during the cooling part of the cycle. Natural or forced air cooling through the passages can be introduced to provide a wide range of heat transfer coefficient which can satisfy the cooling requirements. With this arrangement, the enhanced area provided for cooling keeps the ‘h’ requirement within a realistic limit. This cooling method developed is categorized as a combination of active and passive cooling techniques. Analytical and numerical investigations are carried out to evaluate the thermal performance of this modified PCM-based heat sink in comparison to the ones with conventional designs. It is found that, the performance of new PCM-based heat sink is superior to that of the conventional one. Experiments are performed on both the conventional and the new PCM-based heat sinks to validate the new findings.

The nuclear industry has long relied upon bounding parametric analyses in predicting the safety margins of reactor designs undergoing design-basis accidents. These methods have been known to return highly-conservative results, limiting the operating conditions of the reactor. The Best-Estimate Plus Uncertainty (BEPU) method using a modernized version of the Code-Scaling, Applicability, and Uncertainty (CSAU) methodology has been applied to more accurately predict the safety margins of the Oregon State University Advanced Plant Experiment (APEX) facility experiencing a Loss-of-Feedwater Accident (LOFA). The statistical advantages of the Bayesian paradigm of probability was utilized to incorporate prior knowledge when determining the analysis required to justify the safety margins. RELAP5 Mod 3.3 was used to accurately predict the thermal-hydraulics of a primary Feed-and-Bleed response to the accident using assumptions to accompany the lumped-parameter calculation approach. A novel coupling of thermal-hydraulic and statistical software was accomplished using the Symbolic Nuclear Analysis Package (SNAP). Uncertainty in Peak Cladding Temperature (PCT) was calculated at the 95/95 probability/confidence levels under a series of four separate sensitivity studies.
Graduation date: 2013