In Photovoltaic/Thermal (PVT) technology, both PV and solar thermal technology are integrated in the same module for simultaneous electricity and heat production. Research has shown that there are multiple benefits from integrating PVT collectors with a ground source heat pump (GSHP) system, since it allows for seasonal storage of thermal energy over the year. Furthermore, it leads to reduced operating temperatures for the PVT collectors which can increase efficiency and lifetime. The aim of this study is to present the electric and thermal performance of a PVT collector developed by Solhybrid i Småland AB, for different environmental and fluid inlet conditions that can occur when PVT collectors are connected to a GSHP system. Furthermore, the performance of this PVT design is evaluated with ASHRAE (Standard 93-2003), to allow for comparison with other PVT collector designs, with values on the overall heat loss coefficient (UL) and heat removal factor (FR). The modelling tool used for the study is the software COMSOL Multiphysics, which uses the finite element method to solve the partial differential equations in heat transfer and fluid flow problems. Based on the performance curves, the thermal and electrical efficiency of the collector is approximately 48.0-53.4% and 19.0-19.2% respectively at a reduced temperature of zero and irradiance levels of 800-1000 W/m2 for the mass flow rate of 0.026 kg/sm2 which was determined as most suitable to increase thermal performance. Furthermore, these results resulted in a heat removal factor (FR) and overall heat loss coefficient (UL) of 0.56-0.62 and 53.4-53.5 W/m2 K respectively. The results on the performance of the PVT collector in different weather conditions shows that the inlet water temperature can significantly affect operating time and the amount of thermal energy that can be extracted during the year, especially if the collector operates in a colder climate like Sweden. To assess the accuracy of the created model, future work includes experimental testing of the studied PVT collector. / En panel med kombinerad teknik av både solceller och termisk solfångare (PVT) kan producera både elektricitet och värme samtidigt. Forskning har visat att det kan finnas flera fördelar med att integrera PVT-paneler med ett bergvärmesystem, eftersom det mjliggör lagring av termisk energi över året. Dessutom leder ett sådant system till lägre drifttemperaturer som kan öka PVT-panelens effektivitet och livslängd. Syftet med studien är att presentera den elektriska och termiska prestandan av en PVT-panel utvecklat av Solhybrid i Småland AB för olika driftförhållanden som kan uppstå på grund av olika väderförhållanden och inlopps-temperaturer när panelerna är kopplade till ett bergvärmesystem. Vidare utvärderas prestandan för denna panel med ASHRAEmetoden (standard 93-2003), för att möjliggöra jämförelse med andra PVT-paneler. Modelleringsverktyget som använts i studien är mjukvaran COMSOL Multiphysics, som använder finita elementmetoden för att lösa partiella differentialekvationer i värmeöverförings-och flödesproblem. Baserat på prestandakurvorna som presenteras i resultatet, är den termiska och elektriska verkningsgraden approximativt 48.0-53.4% respektive 19.0-19.2% för en reducerad temperatur med värdet noll, en solstrålning mellan 800-1000 W/m2, för en massflödeshastighet på 0.026 kg/sm2 som beslutades som den mest lämpliga för att öka den termiska prestandan. Resultaten resulterade i en värmeavledningsfaktor (FR) och total värmeförlustkoefficient (UL) på 0.56-0.62 respektive 53.4-53.5 W/m2 K. Resultaten på PVT-panelens prestanda under olika väderförhållanden visar att vattnets inloppstemperatur kan påverka drifttiden och mängden termisk energi som kan extraheras under året avsevärt, speciellt i nordiskt klimat. För att bedöma korrektheten i resultaten och den skapade modellen rekommenderas experimentell testning av den studerade PVT-panelen.

Bakterien Legionella pneumophila orsakar sjukdomen Legionella vilket har ökat i världen de senaste 20 åren och har troligtvis ett ännu större mörkertal. Den frodas i vattenrör mellan temperaturen 25–50 grader och vid installation av varmvattenrör i byggnader måste det tas hänsyn i riskzoner. Ett speciellt riskområde är varmvattenavstick som skapas för att kunna dra vidare vattenrör i framtiden. Där utsätts vattnet för större risk för stillastående och sjunkande temperaturprofil beroende på längd. Med hjälp av COMSOL Multiphysics® Modelling Software har ett teoretiskt ramverk för dimensionering av varmvattenavstick i byggnader skapats. Resultatet visar på hur stor strömningshastighet i vattenflödet, isoleringstjocklek och luftrörslängd har påverkan på hur långt avsticket kan vara utan att understiga kritisk temperatur. Resultatet kan användas som beslutsstöd givet att liknande avstickmodell och flödesprofil används samt om strömningshastighet i röret inte är längre än det i rapporten. / The bacterium Legionella pneumophila causes the disease Legionella which has seen an increase in the world over the last 20 years and likely has an even greater number of unrecorded cases. It thrives in water pipes between the temperature of 25-50 degrees and when installing hot water pipes in buildings certain factors must be taken into account. A special risk area is hot water branches that are created to be able to extend water pipes in the future. There, the water is at greater risk of stagnant and decreasing temperature profile depending on its length. With the help of COMSOL Multiphysics® Modelling Software, a theoretical framework for the dimensioning of hot water distances in buildings has been created. The result shows how the velocity in the water flow, the insulation thickness and the length of the air pipe have a great influence on how long the branch can be without falling below the critical temperature. The results can be used as decision support if one has a similar branch model and flow profile and also given a that a lower flow rate is not used.

Doctor of Philosophy / Department of Chemistry / Takashi Ito / Self-organized nanoporous materials have drawn a lot of attention because the uniform, highly dense, and ordered cylindrical nanopores in these materials provide a unique platform for chemical separations and chemical sensing applications. Here, we explore self-organized nanopores of PS-b-PMMA diblock copolymer thin films and anodic gallium oxide for chemical separations and sensing applications. In the first study, cyclic voltammograms of cytochrome c on recessed nanodisk-array electrodes (RNEs) based on nanoporous films (11, 14 or 24 nm in average pore diameter; 30 nm thick) derived from polystyrene-poly(methylmethacrylate) diblock copolymers were measured. The faradic current of cytochrome c was observed on RNEs, indicating the penetration of cytochrome c (hydrodynamic diameter ≈ 4 nm) through the nanopores to the underlying electrodes. Compared to the 24-nm pores, the diffusion of cytochrome c molecules through the 11- and 14-nm pores suffered significantly larger hindrance. The results reported in this study will provide guidance in designing RNEs for size-based chemical sensing and also for controlled immobilization of biomolecules within nanoporous media for biosensors and bioreactors. In another study, conditions for the formation of self-organized nanopores of a metal oxide film were investigated. Self-organized nanopores aligned perpendicular to the film surface were obtained upon anodization of gallium films in ice-cooled 4 and 6 M aqueous H2SO4 at 10 V and 15 V. The average pore diameter was in the range of 18 ~ 40 nm, and the anodic gallium oxide was ca. 2 µm thick. In addition, anodic formation of self-organized nanopores was demonstrated for a solid gallium monolith incorporated at the end of a glass capillary. Nanoporous anodic oxide monoliths formed from a fusible metal will lead to future development of unique devices for chemical sensing and catalysis. In the final study, surface chemical property of self-organized nanoporous anodic gallium oxide is explored through potentiometric measurements. The nanoporous anodic and barrier layer gallium oxide structures showed slow potentiometric response only at acidic pH (≤ 4), in contrast to metallic gallium substrates that exhibited a positive potentiometric response to H⁺ over the pH range examined (3-10). The potentiometric response at acidic pH probably reflects some chemical processes between gallium oxide and HCl.

Aluminium recycling requires 95% less energy than primary production with no loss of quality. The Black Dross (BD) produced during secondary aluminium production contains high amounts of water-soluble compounds, therefore it is considered as a toxic waste. In the present work, salt removal from BD by thermal treatment has been investigated in laboratory scale. The optimum conditions for treatment were established, i.e., temperature, gas flow rate, holding time, rotation rate, and sample size. The overall degree of chloride removal was established to increase as a function of time and temperature. Even Pretreated Black Dross (PBD) was evaluated as a possible raw material for the production of a calcium aluminate-based ladle-fluxing agent to be used in the steel industry. The effects of different process parameters on the properties of the produced flux were experimentally investigated, i.e. CaO/Al2O3 ratio, temperature, holding time, and cooling media. The utilization of PBD as the alumina source during the production of a calcium aluminate fluxing agent shows promising results. The iron/steel industry is responsible for 9% of anthropogenic energy and process CO2 emissions. It is believed that the only way to a long-term reduction of the CO2 emissions from the iron/steel industry is commercialization of alternative processes such as Direct Reduction (DR) of iron oxide. Detailed knowledge of the kinetics of the reduction reactions is, however, a prerequisite for the design and optimization of the DR process. To obtain a better understanding of the reduction kinetics, a model was developed step-by-step, from a single pellet to a fixed bed with many pellets. The equations were solved using the commercial software COMSOL Multiphysics®. The final model considers the reaction rate and mass transfer inside the pellet, as well as the mass transfers and heat transfer in the fixed bed. All the models were verified against experimental results, and where found to describe the results in a satisfying way. / <p>QC 20161128</p>

<div>Multiscale and multiphysics have been two major challenges in analyzing and designing new emerging engineering devices, materials, circuits, and systems. When simulating a multiscale problem, numerical methods have to overcome the challenges in both space and time to account for the scales spanning many orders of magnitude difference. In the finite-difference time-domain (FDTD) method, subgridding techniques have been developed to address the multiscale challenge. However, the accuracy and stability in existing subgridding algorithms have always been two competing factors. In terms of the analysis of a multiphysics problem, it involves the solution of multiple partial differential equations. Existing partial differential equation solvers require solving a system matrix when handling inhomogeneous materials and irregular geometries discretized into unstructured meshes. When the problem size, and hence the matrix size, is large, existing methods become highly inefficient.</div><div><br></div><div>In this work, a symmetric positive semi-definite FDTD subgridding algorithm in both space and time is developed for fast transient simulations of multiscale problems. This algorithm is stable and accurate by construction. Moreover, the method is further made unconditionally stable, by analytically finding unstable modes, and subsequently deducting them from the system matrix. To address the multiphysics simulation challenge, we develop a matrix-free time domain method for solving thermal diffusion equation, and the combined Maxwell-thermal equations, in arbitrary unstructured meshes. The counterpart of the method in frequency domain is also developed for fast frequency-domain analysis. In addition, a generic time marching scheme is proposed for simulating unsymmetrical systems to guarantee their stability in time domain. </div>

Modélisation et analyse d’un système de dégivrage en aéronautiqueRésuméCe manuscrit de thèse aborde les travaux de modélisation d’une nouvelle technologie électromécanique pour le dégivrage en aéronautique en mode vol.Le principe de fonctionnement de la technologie étudiée repose sur la déformation mécanique des surfaces à dégivrer à partir d’efforts électromagnétiques générés par une excitation en courant électrique de forte intensité. La solution imaginée par le partenaire industriel Zodiac Aerospace, a conduit à un démonstrateur dont les premiers essais ont été lancés préalablement à cette thèse. À partir des résultats obtenus, l’objectif de ces travaux de thèse a été d’obtenir un modèle adapté pour les futures démarches d’optimisation dans le but ultime d’aller vers une solution de dégivrage plus électrique que les solutions existantes, performante, et plus efficace en termes de rendement énergétique.Une modélisation multiphysique a été réalisée. Cette modélisation est constitué de plusieurs sous modèles analytiques qui ont été intégrés sur une plateforme de résolution numérique. La modélisation mécanique met en œuvre une approche de type plaque par éléments bande, qui a été résolu en fonction du temps par une méthode de différences finies. Le modèle mécanique résultant est dit semi-analytique. La modélisation électromagnétique repose sur une définition analytique et a présenté comme difficulté la complexité de la définition géométrique du démonstrateur. Un circuit électrique équivalent du dispositif complet a été identifié et les équations du modèle électrique ont été définies ; ceci a permis de réaliser une analyse énergétique pour comprendre la transformation des forces de nature différente et mettre en évidence la possibilité d’une future optimisation.Les résultats de simulation à partir du modèle final représentent assez bien la dynamique de la déformation mécanique observée expérimentalement mais présentent en revanche des limitations en termes de précision.Mots clé : Dégivrage électromécanique, aéronautique, modélisation multiphysique, déformation de plaques, force de Laplace. / Modeling and analysis of an electromechanical de-icing system in aeronauticsAbstractThis thesis report explains the modeling procedure of a new electromechanical de-icing technology in aeronautics for in-flight application.The operation principle of the technology resides in the mechanical deformation of the working surface caused by the effect of electromagnetic forces generated from a high-intensity current source.The industrial partner Zodiac Aerospace conceived this solution they carried out the construction of a demonstrator and a series of tests prior to this Ph.D. Based on the obtained results, the aim of this project was to achieve an adequate model of the de-icing system that should be suitable for further optimization of the device, such that a more electric de-icing solution will be proposed, with good performance and with higher energetic efficiency.A multiphysiscs model was developed, which comprises multiple analytical submodels that where integrated into a numerical resolution platform. The mechanical submodel implements a strip approach for plates solved via a finite differences method that permits time dependence evaluation, and can be defined as semi analytical. Another submodel is based on the mathematical definition of the electromagnetic behavior, the main complication of which was to consider the complex geometrical definition of the demonstrator. An equivalent electric circuit for the whole system was identified and the equations for an electrical submodel where then established. This allowed the study of the energy transformation and repartition, and reveals the possibility of future optimization.Simulation results from the final model properly reproduce the dynamics of the mechanical deformation response as were observed during the previous experiments, but also reveals some minor accuracy problems.Key words : Electromechanical de-icing, aeronautics, multiphysics modeling, deformation of plates, Laplace force.

Poor heat and mass transfer inside the adsorbent bed of thermal wave adsorption cooling cycles cause low system performance and is an important problem in the adsorbent bed design. In this thesis, a new adsorbent bed is designed, constructed and tested to increase the heat and mass transfer in the adsorbent bed. The adsorbent bed is constructed from a finned tube in order to enhance the heat transfer. Additionally, the finned bed geometry is theoretically modeled and the model is solved time dependently by using Comsol Multiphysics software program. The distributions of dependent variables, i.e. temperature, pressure and amount adsorbed, are simulated and plotted in Comsol Multiphysics. In the model, the dependent variables are computed by solving the energy, mass and momentum transfer equations in a coupled way and their variations are investigated two-dimensionally. The results are presented with multicolored plots in a 2-D domain. Furthermore, a parametric study is carried out for determining factors that enhance the heat and mass transfer inside the adsorbent bed. In this parametric study, the effects of several design and operational parameters on the dependent variables are investigated. In the experimental study, the finned tube is tested using natural zeolite-water and silica gel-water working pairs. Temperature, pressure and amount adsorbed variations inside the adsorbent bed at various operating conditions are investigated. After that, a second adsorbent bed with a larger size is constructed and tested. The effect of the particle diameter of the adsorbent is also investigated. The experimental and theoretical results are compared.

To simulate real world problems modeled by differential equations, it is often not sufficient to  consider and tackle a single equation. Rather, complex phenomena are modeled by several partial dierential equations that are coupled to each other. For example, a heart beat involve electric activity, mechanics of the movement of the walls and valves, as well as blood fow - a true multiphysics problem. There may also be ordinary differential equations modeling the reactions on a cellular level, and these may act on a much finer scale in both space and time. Determining efficient and accurate simulation tools for such multiscalar multiphysics problems is a challenge. The five scientific papers constituting this thesis investigate and present solutions to issues regarding accurate and efficient simulation using adaptive finite element methods. These include handling local accuracy through submodeling, analyzing error propagation in time-dependent  multiphysics problems, developing efficient algorithms for adaptivity in time and space, and deriving error analysis for coupled PDE-ODE systems. In all these examples, the error is analyzed and controlled using the framework of dual-weighted residuals, and the spatial meshes are handled using octree based data structures. However, few realistic geometries fit such grid and to address this issue a discontinuous Galerkin Nitsche method is presented and analyzed.

In der vorliegenden Arbeit wird eine Prozedur zur Ordnungsreduktion von Finite Elemente Modellen mikromechanischer Struktur mit elektrostatischem Wirkprinzip entwickelt und analysiert. Hintergrund der Ordnungsreduktion ist eine Koordinatentransformation von lokalen Finite Elemente Koordinaten in globale Koordinaten. Die globalen Koordinaten des reduzierten Modells werden durch einige wenige Formfunktionen beschrieben. Damit wird das Makromodell nicht mehr durch lokale Knotenverschiebungen beschrieben, sondern durch globale Formfunktionen, welche die gesamte Deformation der Struktur beeinflussen. Es wird gezeigt, dass Eigenvektoren der linearisierten mechanischen Struktur einfache und effiziente Formfunktionen darstellen. Weiterhin kann diese Methode für bestimmte Nichtlinearitäten und für verschiedene in Mikrosystemen auftretende Lasten angewendet werden. Das Ergebnis sind Makromodelle, die über Klemmen in Systemsimulatoren eingebunden werden können, die Genauigkeiten einer Finite Elemente Analyse erreichen und für Systemsimulationen typische Laufzeitverhalten besitzen.

Για την επίλυση προβλημάτων πολλαπλών πεδίων / πολλαπλών φυσικών έχουν προταθεί διάφορες τεχνικές στη βιβλιογραφία. Οι μέθοδοι χαλάρωσης στις διεπαφές είναι μια ενδιαφέρουσα προσέγγιση για την επίλυση αυτών των προβλημάτων. Υποθέτοντας κάποιες αρχικές τιμές στις διεπαφές του προβλήματος, οι μέθοδοι χαλάρωσης στις διεπαφές επιλύουν επαναληπτικά τα υποπροβλήματα και χαλαρώνουν τις τιμές στις διεπαφές έως ότου επιτευχθεί σύγκλιση. Τα κυριότερα πλεονεκτήματα των μεθόδων αυτών είναι ότι οι ρυθμοί σύγκλισής τους εξαρτώνται μόνο από τις παραμέτρους των ίδιων των προβλημάτων, τις παραμέτρους που σχετίζονται με την ανάλυση των προβλημάτων σε υποπροβλήματα και τις παραμέτρους που σχετίζονται με τον τελεστή που εφαρμόζεται στις διεπαφές. Στην παρούσα μεταπτυχιακή εργασία παρουσιάζεται μια νέα υλοποίηση μιας μεθόδου χαλάρωσης στις διεπαφές, της μεθόδου GEO. Η GEO βασίζεται σε έναν απλό μηχανισμό γεωμετρικής διόρθωσης και δρα επαναληπτικά, ώστε να χαλαρώσει τις τιμές στις διεπαφές. Πιο συγκεκριμένα, προσθέτει στις παλιές τιμές των διεπαφών έναν γεωμετρικά σταθμισμένο συνδυασμό των κανονικών παραγώγων των οριακών σημείων των γειτονικών πεδίων. Η υλοποίηση της μεθόδου GEO γίνεται στην πλατφόρμα FEniCS, η οποία είναι μια συλλογή ελεύθερου λογισμικού για την αυτοματοποιημένη, αποδοτική υλοποίηση διαφορικών εξισώσεων. Η υλοποίηση πραγματοποιείται με τρόπο τέτοιο που ο χρήστης να μπορεί εύκολα να ορίζει τις ιδιότητες των πεδίων του προβλήματος (όπως, γεωμετρία του προβλήματος, τελεστής μερικής διαφορικής εξίσωσης, οριακές συνθήκες, συνθήκες διεπαφών). Στο παρασκήνιο γίνεται η δημιουργία ή / και η βελτιστοποίηση των πλεγμάτων (τριγωνικά στοιχεία) για κάθε πεδίο του προβλήματος, η επίλυση των τοπικών προβλημάτων μερικών διαφορικών εξισώσεων και η εμφάνιση των υπολογισμένων τιμών για το πρόβλημα συνολικά και για τις διεπαφές. Η κυριότερη πρόκληση της υλοποίησης είναι η πρόσβαση στις τιμές των λύσεων στις διεπαφές και η εισαγωγή των χαλαρωμένων τιμών πίσω στα υποπροβλήματα για να αποτελέσουν τις οριακές συνθήκες των υποπροβλημάτων. Πραγματοποιούνται πειράματα σε προβλήματα-μοντέλα, ώστε να ελεγχθεί η εφαρμοσιμότητα και η σύγκλιση της μεθόδου. Στη συνέχεια, υλοποιείται μια παράλληλη έκδοση της μεθόδου και πραγματοποιούνται συγκριτικά πειράματα απόδοσης. Η παράλληλη υλοποίησή μας αποδεικνύεται πολύ χρήσιμη, ειδικά για μεγάλα προβλήματα. / Several approaches have been suggested in the literature for the solution of multiphysics / multidomain problems. Interface Relaxation (IR) methods are an interesting approach for the solution of these problems. Assuming initial guesses on the interfaces of the original problem, IR methods iteratively solve the subproblems and relax for new values on the interfaces until convergence is succeeded. Their main advantages are that their rates of convergence only depend on the parameters of the problem itself, the parameters related to its decomposition into subproblems and the parameters related to the operator imposed on the interfaces. In the present master thesis a new implementation of an IR method named GEO is presented. GEO is based on a simple geometric correction mechanism and acts iteratively so as to relax the values of the solution on the interfaces. In particular, it adds to the old interface values a geometrically weighted combination of the normal boundary derivatives of the adjacent subdomains. In this thesis GEO is implemented in FEniCS. The FEniCS project is a collection of free software for automated, efficient solution of differential equations. In order to evaluate the GEO implementation, it is applied on two different PDE problems with the same differential equation and boundary conditions and different domains. FEniCS methods are used to specify the problem's subdomains properties (i.e. geometry, PDE operator and boundary/interface conditions). They are also used to generate and/or refine meshes (triangular elements) for each subdomain, solve the local PDE problems and show the computed results in the global domain and on the interfaces. Getting values of the solutions on the interface (boundaries of the subproblems) and passing the new relaxed values back to the subproblems as updated values for the boundary conditions is the main challenge of the IR methodology implementation. Experiments are performed for 2-dimensional elliptic partial differential model problems with partitions in multiple subdomains and the results are examined in terms of the method's applicability and convergence. A parallel implementation of the GEO method using FEniCS is also presented, as well as its performance comparison to the serial implementation. The parallel implementation proves to be really useful, especially for large problems.