Dissertations / Theses on the topic 'COMSOL Multiphysics simulations'

In a world where money often is the main controlling factor, everything that can be tends to be more and more optimized. Regarding electrical machines, developers have always had the goal to make them better. The latest trend is to make machines as efficient as possible, which calls for accurate simulation models where different designs can be tested and evaluated. The finite element method is probably the most popular approach since it makes it possible to, in an easy and accurate way, get numerical solutions to a variety of physics problems with complex geometries and non-linear materials. This licentiate thesis includes two different projects in which finite element methods have had a central roll. In the first project, the goal was to develop a simulation model to be able to predict demagnetization of permanent magnets. It is of great importance to be able to predict if a permanent magnet will be demagnetized or not in a certain situation. In the worst case, the permanent magnets will be completely destroyed and the machine will be completely useless. However, it is more probable that the permanent magnets will not be completely destroyed and that the machine still will be functional but not as good as before. In a time where money is more important than ever, the utilization has to be as high as possible. In this study the demagnetization risk for different rotor geometries in a 12 kW direct driven permanent magnet synchronous generator was studied with a proprietary finite element method simulation model. The demagnetization study of the different rotor geometries and magnet grades showed that here is no risk for the permanent magnets in the rotor as it is designed today to be demagnetized. The project also included experimental verification of the simulation model. The simulation model was compared with experiments and the results showed good agreement. The second project treated the redesign of the rotor in the generator previously mentioned. The goal was to redesign the surface mounted NdFeB rotor to use a field concentrating design with ferrite permanent magnets instead. The motivation was that the price on NdFeB magnets has fluctuated a lot the last few years as well as to see if it was physically possible to fit a ferrite rotor in the same space as the NdFeB rotor. A new rotor design with ferrite permanent magnets was presented together with an electromagnetic and a mechanical design.

Many industries have entered a new global phase which takes the environment in mind. The gas turbine industry is no exception, where the utilization of green fuels is the future to spare the environment from carbon dioxide and NOx emissions. Hydrogen has been identified as a fuel which can fulfil the global requirements set by governments worldwide. Combustion instabilities are not inevitable during gas turbine operations, especially when using a highly reactive and diffusive fuel as hydrogen. These thermoacoustics instabilities can damage mechanical components and have economic consequences in terms of maintenance and reparation. Understanding these thermoacoustic instabilities in gas turbine burners is of great interest. COMSOL Multiphysics offers a robust acoustic module compared to other available acoustic simulation programs. In this thesis, an Acoustic finite element model was built representing an atmospheric combustion rig (ACR), used to test the burners performance and NOx emissions. Complementary computational fluid dynamics (CFD) simulations were performed for 100 % hydrogen as fuel by using the Reynolds average Navier-Stokes (RANS) lag EB k - epsilon turbulence model. Necessary data was successfully imported to the Acoustic finite element model. Different techniques of building the mesh were used in COMSOL Multiphysics and NX. Similar results were obtained, proving that both mesh tools work well in acoustic simulations. Two different ways of solving the eigenvalue problem in acoustics were implemented, the classic Helmholtz equation and Linearized Navier-Stokes equations, both in the frequency domain. The Helmholtz equation proved to be efficient and detected multiple modes in the frequency range of interest. Critical modes which lived in the burner and the combustion chamber were identified. Defining a hard and soft wall boundary condition at the inlets and outlet of the atmospheric combustion rig gave similar eigenfrequencies when comparing the two boundary conditions. The soft wall boundary condition was defined with a characteristic impedance, giving a high uncertainty whether the results were trustworthy or not. A boundary condition study revealed that the boundary condition at the outlet was valid for modes living in the burner and combustion chamber. Solving the eigenvalue problem with the Linearized Navier-Stokes equations proved to be computationally demanding compared to the Helmholtz equation. Similar modes shapes were found at higher frequencies, but pressure perturbations were observed in the region where the turbulence was dominant. A prestudy for a stability analysis was established, where the ACR and the flame was represented as a generic model. Implementing a Flame Transfer Function (FTF), more specifically a linear n - tau model, showed that the time delay tau is most sensible for a parametric change and hence needs to be chosen cautiously

L’apparition accidentelle d’un arc électrique dans le système de distribution électrique d’un aéronef peut compromettre la sécurité du vol. Il existe peu de travaux liés à cette problématique.Le but de ce travail est donc d’étudier le comportement d’un arc électrique, en conditions aéronautiques,par des approches théorique, numérique, et expérimentale. Dans ce travail, un modèle MHD de la colonne d’arc à l’ETL a été utilisé, et résolu à l’aide du logiciel commercial comsolMultiphysics. Afin de décrire l’interaction plasma-électrodes, le modèle a dû étendu pour inclure les écarts à l’équilibre près des électrodes. Ces zones ont été prises en compte en considérant la conservation du courant et de l’énergie dans la zone hors-équilibre. L’approche choisie et le développement du modèle ont été détaillés. La validation du modèle dans le cas d’un arc libre a montré un excellent accord avec les résultats numériques et expérimentaux de la littérature.Ce modèle d’arc libre a été étendu au cas de l’arc se propageant entre des électrodes en configuration rails et en géométrie 3D. Une description auto-cohérente du déplacement de l’arc entre les électrodes a été réalisée. La simulation numérique a été faite pour des arcs en régimes DC, pulsé et AC à des pressions atmosphériques et inférieures. Les principales caractéristiques de l’arc ont été analysées et discutées. Les résultats obtenus ont été comparés avec les résultats expérimentaux et ont montré un bon accord.Ce modèle d’arc électrique est capable de prédire le comportement d’un arc de défaut dans des conditions aéronautiques. Des améliorations du modèle sont discutées comme perspectives de ce travail
The ignition of an electric arc in the electric distribution system of an aircraft can be a serious problem for flight safety. The amount of information on this topic is limited, however. Therefore,the aim of this work is to investigate the electric arc behavior by means of experiment and numerical simulations.The MHD model of the LTE arc column was used and resolved numerically using the commercial software comsol Multiphysics. In order to describe plasma-electride interaction, the model had to be extended to include non-equilibrium effects near the electrodes. These zones were taken into account by means of current and energy conservation in the non-equilibrium layer. The correct matching conditions were developed and are described in the work. Validation of the model in the case of a free burning arc showed excellent agreement between comprehensive models and the experiment.This model was then extended to the case of the electric arc between rail electrodes in a 3D geometry. Due to electromagnetic forces the electric arc displaces along the electrodes. A self-consistent description of this phenomenon was established. The calculation was performed for DC, pulsed and AC current conditions at atmospheric and lower pressures. The main characteristics of the arc were analyzed and discussed. The results obtained were compared with the experimental measurements and showed good agreement.The model of electric arcs between busbar electrodes is able to predict the behavior of a fault arc in aeronautical conditions. Further improvements of the model are discussed as an outlook of the research

Throughout recent years, computer based programs has been applied to solve and analyze industrial problems. One of these developed programs is the Computational Fluid Dynamics (CFD) program. The purpose of implementing CFD analysis is to solve complex flow behavior which is not possible with ordinary calculus. The extensive application of CFD in the industry is a result of improved commercial CFD codes  in terms of more advance partial differential equations (PDE) describing various physical phenomena, CAD and mesh-grid generating tools and improved graphical user interfaces (GUI). Today, CFD usage has extended to fields such as aerodynamic, chemical process engineering, biomedical engineering and drying technology. As there is an on-going expansion of CFD usages in the industry, certain issues need to be addressed as they are frequently encountered. The general demand for simulation of larger control volumes and more advanced flow processes result in extensive requirement of computer resources. Numerous complex flow topics today require computer cluster networks which are not accessible for every company. The second issue is the implementation of commercial CFD codes in minor industrial companies is utilized as a black box based on the knowledge on fluid mechanic theory. A vital part of the simulation process is the evaluation of data through visual analysis of flow patterns, analysis on the sensitivity of the mesh grid, investigation of quantitative parameters such as pressure loss, velocity, turbulence intensity etc. Moreover, increased partnerships between industry and the academic world involving various CFD based design processes generally yields to a verbal communication interface which is a crucial step in the process given the fact of the level of dependency between both sides. The aim of this thesis is to present methods of CFD analysis based on these issues. In paper I, a heuristically determined design process of the geometry near the front trap door of an internal duct system was achieved by implementing the CFD code COMSOL MultiPhysics as a communication tool. The design process was established by two counterparts in the project in which CFD calculations and geometry modifications were conducted separately. Two design criteria presenting the pressure drop in duct and the outflow uniformity was used to assess geometry modifications conducted by a CAD-engineer. The geometry modifications were based on visual results of the flow patterns. The geometry modifications confirmed an improvement in the geometry as the pressure drop was reduced with 23% and the uniformity was increased with 3%. In paper II, volume-averaged equations were implemented in a tube-fin heat exchanger in order to simulate airflow. Focus was on achieving a correct volume flow rate and pressure drop (V-p) correlation. The volume averaged model (VAM) is regarded as a porous medium in which the arrangement of fins and tube bundles are replaced with volume-averaged equations. Hence, the computational time was reduced significantly for the VAM model. Moreover, experimental results of the (V-p) correlation showed good agreement with the VAM model.

This thesis describes methods for improving sensitivity in rapid singleplex and multiplex microarray assays. The assays utilize the optical characteristics of colloidal gold nanoparticles for the colorimetric detection of proteins. Multiplexed detection in sandwich immunoassays is limited by cross-reactivity between different detection antibodies. The cross-reactivity between antibodies can contribute to increased background noise - decreasing the Limit-of-Detection of the assay - or generate false positive signals. Paper I shows improved assay sensitivity in a multiplexed vertical flow assay by the application of ultrasonic energy to the gold nanoparticles functionalized with detection antibodies. The ultrasonication of the antibody conjugated gold nanoparticles resulted in a 10 000 fold increase in sensitivity in a 3-plex assay. COMSOL Multiphysics was used to simulate the acoustical energy of the probe used in Paper I for obtaining an indication of the size and direction of the forces acting upon the functionalized gold nanoparticles. In Paper II, it was studied if different gold nanoparticle conjugation methods and colorimetric signal enhancement of the gold nanoparticle conjugates could influence the sensitivity of a paper-based lateral flow microarray assay, targeting cardiac troponin T for the rapid diagnostics of acute myocardial infarction. Ultrasonication and signal enhancement of the detection gold nanoparticles has the potential of improving the sensitivity of paper based assays and expanding their potential future applications.

QC 20170911

This work is focused on computer simulations of fractal capacitors. The geometry of capacitors and its influence is investigated. Simulations are realized in programs Matlab, SolidWorks and Comsol Multiphysics. There are also several specific examples of different geometrics of capacitors their comparisons and assessment.

Les capteurs à ondes acoustiques de surfaces (SAW : Surface Acoustic Waves) présentent de nombreux avantages, dont une grande sensibilité, un paramètre clé dans diverses applications. Dans cette thèse, deux voies sont explorées pour améliorer la sensibilité des dispositifs SAWs : le passage en mode de Love, avec une couche guide d’onde en résine époxyde SU-8, et la montée en fréquence de 104 à 208 MHz. Avant de réaliser de tels dispositifs en salle blanche puis de les utiliser en tant que capteurs chimiques, des simulations numériques ont été entreprises, en utilisant tout d’abord le logiciel MATLAB, puis par la méthode des éléments finis, via le logiciel COMSOL Multiphysics. L’épaisseur optimale de la couche guide d’onde, permettant un gain important en sensibilité, a été estimée. Un écart entre l’expérience et la simulation a été trouvé soulignant la nécessité de poursuivre les phases d’optimisation dans cette voie. Une confrontation calculs/expériences a été menée avec succès pour les structures SH-SAW. Ces dispositifs ont été fonctionnalisés avec un dérivé d’anthracène pour détecter les ions zinc en milieu aqueux. Les résultats gravimétriques ont montré un gain en sensibilité d’un facteur 2.3, en augmentant la fréquence de travail de 104 MHz à 208 MHz
Surface Acoustic Wave (SAW) sensors have many advantages mainly a high sensitivity, which is a key parameter in various applications. Two strategies were explored, in this thesis, to enhance the sensitivity of SAW devices: switching to Love mode, with a waveguide layer in SU-8 epoxy resin, and frequency increase from 104 to 208 MHz. Prior to the realization of such devices in a clean room and their further use as chemical sensors, numerical simulations were done, first with MATLAB software, and then with the finite element method, via COMSOL Multiphysics software. The optimum thickness of the waveguide layer, allowing a significant gain in sensitivity, was estimated. A disagreement between experience and simulation was found highlighting the need to continue optimization steps. A confrontation between calculations / experiments was carried out for the SH-SAW structures. These devices were functionalized with an anthracene derivate for zinc ions detection in aqueous media. Gravimetric results indicate that increasing the operating frequency from 104 MHz to 208 MHz permits a gain in sensitivity by a factor of 2.3

The program COMSOL Multiphysics was used to simulate a flow of helium gas transporting ionized fission products out of an ion guide. Two important parameters to study from the simulation was the evacuation time and velocity of the ions. The mean evacuation time was shown to be 0.1173s, and the velocity of a single particle peaked at 2500m/s, 1000-1500m/s being more common.

Les Micro Systèmes Electro Mécaniques Radio-Fréquences (MEMS RF) bouleversent le paysage de la microélectronique, en laissant entrevoir des possibilités vertigineuses : exceptionnelles performances hyperfréquences, grande linéarité et faible consommation. Malgré ces avantages indéniables, la mise sur le marché de composants à base de MEMS RF est freinée par leurs manques de maturités au niveau du flot de conception, de la mise en boîtier (packaging) et de la fiabilité. Dans ce contexte, ces travaux de thèse ont porté sur l’étude théorique et expérimentale des techniques d’assemblage et de mise en boîtier pour l’intégration de micro-commutateurs RF opérant en bande X (10 GHz). Après une description des techniques de mise en boîtier suivie d’une analyse fonctionnelle, nous mettons en évidence une solution d’assemblage par report d’un capot avec un scellement en polymère. Afin de répondre aux enjeux de conception, nous avons identifié un besoin de modélisation à partir de logiciels de simulation éléments finis (EF) multi-physique, permettant de générer des macro-modèles comportementaux. Ainsi, nous discutons des possibilités offertes par deux logiciels EF réellement multi-physique : ANSYS et COMSOL. Finalement, nous proposons une solution (boîtier micro-usiné en Foturan et scellement en polymère BCB) compatible avec les possibilités technologiques, les contraintes dimensionnelles en terme d’encombrement, le respect des performances RF et la résistance mécanique. Cette solution a débouchée sur la réalisation et la caractérisation électrique d’un démonstrateur, montrant une très faible atténuation générée par le packaging, moins de 0. 05 dB de pertes à 10 GHz. De ce fait, nous avons pu valider une technique simple de packaging quasi-hermétique, adaptée au micro-commutateurs RF
Radio-Frequency Micro-Electro-Mechanical Systems (RF MEMS) are highly miniaturized devices intended to switch, modulate, filter or tune electrical signals from DC to microwave frequencies. RF Mems switches are characterized by their high isolation, low insertion loss, large bandwith and by their unparalleled signal linearity. Despite these benefits, RF Mems switches are not yet seen in commercial products because of reliability issues, limits in signal power handling and question in packaging. In this context, we put in evidence, a near hermetic packaging based on a micro-machined cap in Foturan sealed onto a photopatternable polymer Benzo-Cyclo-Butene (BCB) as a solution adapted to micro-switches RF. To answer the stakes in conception, we identified needs in multiphysics modelling able to generate behavioural macro-models. Finally, a demonstrator was characterised in terms of return and insertion losses measurements, which assures insignificant impact of the package on the RF losses

Corona discharge is one of the crucial problems related with high-voltage equipment. This paper focuses on the physical and numerical modelling of corona discharge in an Electrostatic precipitator (ESP). The model is based on Maxwells equations and the Finite element method (FEM) and is implemented with the COMSOL Multiphysics software.The simulation allows studying the electric charge distribution and the behaviour of the electric field inside the ESP. The work is focused primarily on time-dependent studies of the corona discharge.

Gaseous exhaust of different industries contains dust particles of different chemical precipitates that are harmful for the environment. Electrostatic Precipitators are very often used in industries to filter their gaseous exhaust and to prevent the atmosphere to being polluted. Electrostatic Precipitators are very efficient in their work. Electrostatic Precipitators use the force of the electric field to separate the dust particles from gaseous exhaust. Electrostatic Precipitators charge the dust particles and remove these particles by attracting these charged dust particles toward the collecting plates. The charging of dust particles requires a charging zone. When gas passes through that charging zone, the dust particles in the gas stream become charged and then these charged particles are attracted toward the collecting plates. The design of an Electrostatic Precipitators requires the knowledge of its working principle and the problems that often arise during its working. This thesis is the study of the working and the problems of the Electrostatic Precipitators. The main reason for problems in working of an Electrostatic Precipitator is the dust resistivity. This dust resistivity affects the collection performance of an Electrostatic Precipitator. This thesis also contains the simulation of an Electrostatic Precipitator. In the simulation part, the Electric Potential and the Electric Field of an ESP is modeled in an ideal condition, when no gas is flowing through the ESP. The industrial software Comsol Multiphysics is used for the simulation. A Comsol Multiphysics guide is given in appendix of this thesis report that provides information about using this software.

Berggren, O. (2014) COMSOL Multiphysics – Ett energitekniskt analysverktyg vid numerisk simulering av köldbryggor och analys av fukt i konstruktionsdetaljer. Examensuppsats i ämnet energiteknik. Institutionen för tillämpad elektronik och fysik vid Umeå Universitet. Konsultföretaget Tyréns har vid sitt kontor i Umeå önskat att utvärdera tillämpningen av programvaran COMSOL Multiphysics. Arbetet bestod av att på nytt simulera och analysera en energiteknisk problemställning, som sedan tidigare ska ha genomförts vid Tyréns. Det valda projektet kallas i detta arbete för referensprojektet och är en del av projekteringen av kulturhuset Väven i Umeå. I referensprojektet behandlas analyserna av köldbryggor och fuktkondensation för flertalet konstruktionsdetaljer, där en av analyserna valdes ut för vidare utvärdering i detta arbete. Målet med utvärderingen var att undersöka om resultaten från arbetet var jämförbara med referensprojektets resultat. I detta ingick det även en presentation av en översiktlig kostnadskalkyl för programvaran COMSOL Multiphysics. Resultaten från analysen av köldbryggan och kondensationen av fukt i konstruktionsdetaljen var i jämförelse med resultaten från referensprojektet något förhöjda, i snitt 20 %. Det genomförda arbetet påvisar att det är möjligt att återskapa de tidigare utförda simuleringarna från referensprojektet i enlighet med det krav och standarder som ställs. De erhållna resultaten är, trots en viss skillnad, jämförbara med de från referensprojektet och är giltiga för att användas vid en verklig projektering. Det slutsatser som kan dras utifrån de erhållna resultaten är att utfall av kondens kan undvikas och att den genomsnittliga värmegenomgångskoefficienten, , indikerar att entrétorgets energiprestanda ej kommer att nå upp till kraven i BBR. Detta trots att -värdet kan antas uppfylla kraven. Då simuleringarna har utförts utan problem i COMSOL Multiphysics och tillgodosett detta arbete med giltiga resultat, anses programvaran vara ett lämpligt simuleringsverktyg hos Tyréns. Kostnaden är dock för en flytande licens av Flixo, i jämförelse till COMSOL Multiphysics mycket lägre. COMSOL Multiphysics är vid utredningstillfället drygt fyra gånger så kostsamt. Fördelen med COMSOL Multiphysics är dock att det kan behandla flera olika typer av fysikaliska problemställningar i en-, två- och tredimensioner med endast grundprogrammet. För att användningen av COMSOL Multiphysics ska vara ekonomisk försvarbart, krävs det att programvaran också används vid tillämpningar utöver simuleringar kring köldbryggor och kondensation av fukt.
Berggren, O. (2014) COMSOL Multiphysics – An analysis tool for energy applications when conducting numerical simulations on thermal bridges and analysis of moisture in construction details. Master thesis in Energy Engineering. Department of Applied Physics and Electronics at Umeå University. The consultant company Tyréns has at its office in Umeå decided to evaluate the application of the software COMSOL Multiphysics.  The evaluation consisted of a simulation on an energy engineering problem with its origin from a project at Tyréns, performed in COMSOL Multiphysics. The chosen project for this task was a part of the design plans of the culture house Väven in Umeå. These design plans includes the analysis of a thermal bridge and moisture on a variety of construction details, where one of them was selected to be investigated further. The main purpose of the investigation was to analyze if the results obtained from the simulations performed in COMSOL Multiphysics were equivalent compared to the results from the design plans. The investigation also included the presentation of an overall cost estimation for the software COMSOL Multiphysics. The obtained results from the analysis of the thermal bridge and moisture in the construction were in both cases slightly raised compared to the results from the design plans, in average an increase of 20 %. The work undertaken concludes that there is fully possible to recreate the previously executed simulations extracted from the design plans in accordance to the requirements and standards that are set. The obtained results are equivalent, even though a minor difference, compared with the results from the design plans and are valid too be used in a real life scenario. The obtained conclusions are that it is possible to prevent moisture in the construction detail. However, the overall U-value, , indicates that the energy efficiency of the entrance square is not good enough to reach the requirements of the SNBBP (Swedish National Board of Housing, Building and Planning). Even though the U-value for the construction detail, , can be assumed to meet the criteria’s of the SNBBP. Due to the fact that the simulations were conducted with COMSOL Multiphysics without any major problems and provided valid results, it is considered that the software is an appropriate tool to perform simulations at Tyréns. However, the cost for a floating license of the software Flixo is much less then for COMSOL Multiphysics. COMSOL Multiphysics is at the time of this study four times as expensive as Flixo. COMSOL Multiphysics has though an advantage because it can treat problems with a multiphysical nature in one, two and three dimensions with the use of only its standard edition. To ensure that the use of COMSOL Multiphysics can be economical viable, it is necessary that the software is used in multiple applications besides performing simulations on thermal bridges and moisture in construction details.

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.

Due to changing anthropological activities, the consumption of resources is continuously increasing. As humans are spending more time indoors, the energy demand is also increasing. The building sector is a major consumer of energy. In buildings, space heating is important to maintain a comfortable space. For this, apart from increasing the thermal insulation and wellconstructed buildings, air-air heat recovery systems(among others) are being used to precondition the ambient air, so that the exhaust air from the conditioned space can pre-heat/ pre-cool the ambient air, depending on the season. In this thesis report, the run around coil heat recovery systems are discussed. A Multiphysics model on COMSOL® Multiphysics was created which was a scaled down version of an actual system. Real-life boundary conditions were provided as inputs to the model and its results were subsequently discussed. First, a literature review of the different air-air heat recovery systems was done, followed by discussing their various advantages and disadvantages. Next, an introduction to COMSOL® was made, followed by the construction of the model and the materials, mesh and physics conditions which were used along with the solver configuration. In the end the model showed success in pre-heating the ambient air in winter and pre-cooling it in summer seasons. Along with that other results were also discussed. In the end some options for future work on the project were also discussed.
Resursförbrukningen ökar kontinuerligt som ett resultat av förändrade antropologiska aktiviteter. Samtidigt ökar energibehovet i takt med att människor tillbringar allt mer tid inomhus. Byggsektorn är en stor energiförbrukare, inte minst genom byggnaders uppvärmning som är viktig för att upprätthålla goda komfortnivåer. För att uppnå detta används, förutom ökad värmeisolering och välkonstruerade byggnader, också bland annat så kallade luftluftvärmeåtervinningssystem för att förkonditionera den omgivande luften, så att frånluften från det konditionerade utrymmet kan förvärma eller -kyla den tillströmmande luften, beroende på säsong. I detta examensarbete diskuteras så kallade run around coil värmeåtervinningssystem. En Multiphysics-modell skapades med COMSOL® Multiphysics och utgjorde en nerskalad version av ett faktiskt system. Modellen simulerades med verklighetsbaserade randvillkor som insignaler varefter resultatet diskuterades. Inledningsvis gjordes en litteraturstudie av olika luft-luft värmeåtervinningssystem, följt av en diskussion om deras olika för- och nackdelar. Därefter konstruerades modellen i COMSOL® och inställningar för material, mesh och fysikförhållanden bestämdes och användes tillsammans med solver-konfigurationen. Simuleringen visade på att värmeåtervinningssystemet framgångsrikt förvärmer den tillströmmande luften på vintern och förkyler den under sommarhalvåret. Även andra resultat diskuterades liksom förslag på fortsatt arbete.

The thesis investigates the temperature distribution in the chip of an infrared camera caused by its read out integrated circuit. The heat from the read out circuits can cause distortions to the thermal image. Knowing the temperature gradient caused by internal heating, it will later be possible to correct the image by implementing algorithms subtracting temperature contribution from the read out integrated circuit. The simulated temperature distribution shows a temperature gradient along the edges of the matrix of active bolometers. There are also three hot spots at both the left and right edge of the matrix, caused by heat from the chip temperaturesensors and I/O pads. Heat from the chip temperature sensors also causes an uneven temperature profile in the column of reference pixels, possibly causing imperfections in the image at the levels of the sensors. Simulations of bolometer row biasing are carried out to get information about how biasing affects temperatures in neighbouring rows. The simulations show some row-to-row interference, but the thermal model suffers from having biasing heat inserted directly onto the top surface of the chip, as opposed to having heat originate from the bolometers. To get better simulation results describing the row biasing, a thermal model of the bolometers needs to be included. The results indicate a very small temperature increase in the active pixel array, with temperatures not exceeding ten millikelvin. Through comparisons with another similar simulation of the chip, there is reason to believe the simulated temperature increase is a bit low. The other simulation cannot be used to draw any conclusions about the distribution of temperature.
Examensarbetet undersöker den temperaturdistribution som uppkommer i ett chip till en IR-kamera till följd av värmeutvecklingen i dess egna utläsningskretsar. Genom att ha information om temperaturdistributionen är det möjligt att längre fram i utvecklingsprocessen skapa algoritmer som subtraherar bort chippets interna värmetillskott från den termiska bilden. Den simulerade temperaturdistributionen visar att de största temperaturgradienterna uppkommer längs den aktiva pixelmatrisens sidor. Det är även möjligt att se tre varmare områden vid både den vänstra och högra sidan av matrisen skapade av värme från chippets temperatursensorer och I/O-kretsar. Värme från temperatursensorerna påverkar även temperaturen i kolumnen med referenspixlar, vilket kan ge upphov till avvikelser i den termiska bilden i höjd med dessa temperatursensorer. Simuleringar av radvis basering av bolometrar utförs för att få information om hur bolometerbiaseringen påverkar temperaturen i angränsade rader. Simuleringarna visar att det finns störningar mellan rader, men simuleringsmodellen lider av avsaknaden av en termisk bolometermodell och tvingas applicera värme direkt på chipytan istället för att låta värme utvecklas i bolometrarna. För bättre simuleringsresultat innefattande bolometerbiasering bör en termisk bolometermodell inkluderas i simuleringen. Resultaten visar på en mycket liten temperaturökning inom den värmekänsliga aktiva pixelmatrisen, med temperaturökningar inom detta område som inte överstiger tio millikelvin. Genom jämförelser med en liknande simulering av samma chip är det inte omöjligt att dra slutsatsen att temperaturökningen är något låg. Det går inte att dra några slutsatser om temperaturens distribution genom denna jämförelse av simuleringar.

The objective of this report was to implement battery cycling and an intermittent current interruption (ICI) method for determining battery resistance into a simple lithium-ion battery model in the finite element methods (FEM) program COMSOL Multiphysics, andevaluate how accurately the model reflects the behaviour of voltage and internal resistance with respect to experimental results. The ICI technique consists of repeating the steps of first having a longer charging period and then having a short current interruption, where the internal resistance is calculated from the voltage drop that occurs when the current is turned off. The model was evaluated against measurements, made with the same technique (ICI), on assembled NMC-graphite batteries. Codes written in the statistical programming language “R” were used to process the data from both COMSOL and the experiments. Both the batteries and the model were constructed with a reference electrode, to enable measurement of each electrode by itself. The results as documented in this report show that it is possible to simulate the measurement technique in COMSOL, but that both the resistance and voltage profiles differed quite a lot from the behaviour of the tested batteries. The resistance of the positive electrode did however give good results and it was possible to improve the model by changing some parameters. The magnitude of the resistance, which was already quite close, could be improved by changing the porosity and particle size, and the voltage profiles were improved when using voltage-data achieved from the real measurements.

A dust layer, especially based on high-resistivity dust, at the collecting electrodes may cause a back corona discharge in electrostatic precipitators (ESP). It can significantly reduce the ESP efficiency and as a result cause ecological damages. To study the dust layer influence inside ESPs, it is necessary to derive an adequate model of the ESP precipitation process with a dust layer at the collecting electrode. The research of the present thesis is focused on stationary studies of the precipitation process with a dust layer at the collecting electrode in ESPs. Three mathematical models are proposed as a description of the precipitation process with a dust layer at the collecting electrode. The models are based on Maxwell’s equations and the finite element method (FEM). COMSOL Multiphysics software is used for their implementation. In all models the dust layer has constant conductivity and the air region has constant ion mobility. In the first model there are no coupling conditions, which is required in mathematics, are given between the two regions. The solution found by COMSOL Multiphysics does not provide physically acceptable coupling conditions. In the second model, a continuous transition zone is introduced between the two regions so that no coupling conditions are required. With the large derivatives in the transition zone, the nonlinear solver in COMSOL Multiphysics does not converge. Finally, in the third model, the dust layer and the grounded collecting electrode are replaced with a boundary condition for the air region. The properties of the third model are investigated, and these models can be used to study the influence of the dust layer. The results of these investigations are reported and discussed.

Due to the current public demand of faster, more powerful, and more reliable electronic devices, research is prolific these days in the area of high electron mobility transistor (HEMT) devices. This is because of their usefulness in RF (radio frequency) and microwave power amplifier applications including microwave vacuum tubes, cellular and personal communications services, and widespread broadband access. Although electrical transistor research has been ongoing since its inception in 1947, the transistor itself continues to evolve and improve much in part because of the many driven researchers and scientists throughout the world who are pushing the limits of what modern electronic devices can do. The purpose of the research outlined in this paper was to better understand the mechanical stresses and strains that are present in a hybrid AlGaN (Aluminum Gallium Nitride) / GaN (Gallium Nitride) HEMT, while under electrically-active conditions. One of the main issues currently being researched in these devices is their reliability, or their consistent ability to function properly, when subjected to high-power conditions. The researchers of this mechanical study have performed a static (i.e. frequency-independent) reliability analysis using powerful multiphysics computer modeling/simulation to get a better idea of what can cause failure in these devices. Because HEMT transistors are so small (micro/nano-sized), obtaining experimental measurements of stresses and strains during the active operation of these devices is extremely challenging. Physical mechanisms that cause stress/strain in these structures include thermo-structural phenomena due to mismatch in both coefficient of thermal expansion (CTE) and mechanical stiffness between different materials, as well as stress/strain caused by "piezoelectric" effects (i.e. mechanical deformation caused by an electric field, and conversely voltage induced by mechanical stress) in the AlGaN and GaN device portions (both piezoelectric materials). This piezoelectric effect can be triggered by voltage applied to the device's gate contact and the existence of an HEMT-unique "two-dimensional electron gas" (2DEG) at the GaN-AlGaN interface. COMSOL Multiphysics computer software has been utilized to create a finite element (i.e. piece-by-piece) simulation to visualize both temperature and stress/strain distributions that can occur in the device, by coupling together (i.e. solving simultaneously) the thermal, electrical, structural, and piezoelectric effects inherent in the device. The 2DEG has been modeled not with the typically-used self-consistent quantum physics analytical equations, rather as a combined localized heat source* (thermal) and surface charge density* (electrical) boundary condition. Critical values of stress/strain and their respective locations in the device have been identified. Failure locations have been estimated based on the critical values of stress and strain, and compared with reports in literature. The knowledge of the overall stress/strain distribution has assisted in determining the likely device failure mechanisms and possible mitigation approaches. The contribution and interaction of individual stress mechanisms including piezoelectric effects and thermal expansion caused by device self-heating (i.e. fast-moving electrons causing heat) have been quantified. * Values taken from results of experimental studies in literature

Cement hydration is the result of a series of simultaneous chemical reactions occurring during the production of concrete. An excessive amount of heat is generated, which consequently may give rise to thermal stresses and cause early age cracks in concrete that may affect its structural integrity, and load bearing capacity. Incorporating fly ash into the concrete mixture has shown to be an efficient method to reduce the temperatures developed during early age hydration, especially for massive concrete structures. Fly ash does additionally affect the concrete's development of compressive strength, tensile strength and Young's modulus. The MahanaKhon tower's mat foundation is divided into 14 layers, with fly ash incorporated in the concrete mix. A finite element model was developed of the mat foundation with COMSOL Multiphysics to simulate the developed temperatures and thermal stresses during curing. The simulations were carried out as parametric studies with different strain reference temperatures. The simulated temperatures were compared with existing temperature measurements that were conducted in three different elevations in each concrete layer. The result of the temperature analyses showed that the measured temperatures were generally larger than the simulated ones, which may have been the result of the numerical model's heat conductivity and convective heat transfer coeffcient not reflecting the actual case. Furthermore, the numerical model did not take into account the effects of solar radiation, which would most likely have increased the temperature of the concrete. The maximum simulated temperatures were mostly found in the center level of the concrete, followed by the lower level, and the lowest at the top. It was also observed that the maximum temperatures in some of the mat foundation layers could exceed 70 °C, which is generally considered high since the risk of delayed ettringite formation may arise. The large temperature is partially a result of not using cooling methods, such as cooling pipes, but also due to the high initial and ambient temperatures. The result of the thermal stress analyses showed that no tensile stresses arose when the strain reference temperature, Tref, was specified to 30 °C, corresponding to the mean ambient temperature. This is due to the concrete temperature not falling below Tref, and the concrete will therefore be in expansion and only be subject to compressive stresses. Increasing Tref to 50 °C, which was considered a reasonable estimation, resulted in developed tensile stresses in all mat foundation layers, where the majority of the mat foundation layers showed a risk of superficial surface cracks. The maximum tensile stresses were found at the final time of the simulations, which was expected, since the temperatures were at their lowest as a result of removing the curing insulation. Finally, setting Tref to 70 °C, corresponding to the maximum temperature during hardening, increased the induced tensile stresses considerably, due to the large temperature gradient between Tref and the concrete temperature. The maximum stresses were, as expected, located at the top level and caused by internal restraint. The second largest tensile stresses were found in the center level, also subject to internal restraint. The lowest tensile stresses were located in the lower level, subject to external restraint.
Cementhydratation är resultatet av en serie kemiska reaktioner som sker under tillverkningen av betong. Stora mängder värme genereras, vilket följaktligen kan ge upphov till termiska spänningar och orsaka tidig sprickbildning som påverkar betongens hållfasthet, och bärförmåga. Inkludering av flygaska i betongblandningen har visat sig vara en effektiv metod avsedd att minska temperaturerna som utvecklas under hydratationen i ung betong, särskilt i massiva betongkonstruktioner. Flygaska påverkar också betongens utveckling av tryckhållfasthet, draghållfasthet och elasticitetsmodul. MahanaKhon towers bottenplatta är uppdelad i 14 lager, där flygaska inkluderades i bottenplattans betong. En finit elementmodell av bottenplattan skapades i COMSOL Multiphysics, där de utvecklade temperaturerna och termiska spänningarna i den unga betongen simulerades under bottenplattans härdningsfas. Simuleringarna genomfördes som parameterstudier med olika referenstemperaturer. De simulerade temperaturerna jämfördes vidare med befintliga temperaturmätningar som utfördes i tre olika elevationer i varje gjutetapp. Resultaten av temperaturerna visade att de uppmätta temperaturerna var generellt högre än de simulerade, vilket bland annat kan bero på att betongens värmeledningsförmåga, samt konvektiva värmeöverföringskoefficient inte återspeglade det aktuella fallet. Den numeriska modellen tog inte heller hänsyn till effekten av solinstrålning, som sannolikt skulle ökat betongens temperatur. De maximala temperaturerna hittades mestadels i betongens mittnivå, följt av den lägre nivån och slutligen lägsta nivåerna vid toppen. Det observerades även att de maximala temperaturerna i bottenplattan kunde överstiga 70 °C, vilket generellt anses vara högt då risken för fördröjd ettringitbildning kan uppstå. De höga temperaturerna beror delvis på avsaknad av kylmetoder, såsom kylrör, men även på den höga initialtemperaturen och omgivningstemperaturen. Resultaten av spänningsanalysen påvisade att inga dragspänningar uppstod när referenstemperaturen Tref denierades till 30 °C, som motsvarar den genomsnittliga omgivningstemperaturen. Detta förklaras av att betongen kommer att vara i expansion och följaktligen endast utsättas för tryckspänningar. Efter att Tref ökats till 50 °C, vilken ansågs vara en rimlig estimering i denna studie, uppstod dragspänningar i alla lager i bottenplattan, där vissa utsattes för risk för ytsprickor. De maximala dragspänningarna uppstod vid simuleringarnas slut, vilket var förväntat då temperaturerna var som lägst vid den tidpunkten till följd av att isoleringen avlägsnades. Slutligen höjdes Tref till 70 °C, vilket motsvarar den maximala temperaturen i bottenplattan under härdning. De inducerade dragspänningarna ökade avsevärt på grund av den stora temperaturgradienten mellan Tref och betongtemperaturen. Samtliga lager utsattes i detta fall för risk för genomgående sprickor. De maximala dragspänningarna påträffades på toppnivån och orsakades av inre tvång. De näst största dragspänningarna fanns i mitten av plattan och var också resultatet av inre tvång. De lägsta dragspänningarna påträffades vid plattans lägre nivå, som utsattes för yttre tvång.

Spintronics is a spin-electronic field where the electron spinangular momentum, in conjunction with charge, is used to read andwrite information in magnetic sensors and logic circuits, e.g. hard disk drive (HDD), magnetic random access memory (MRAM) and broadband TeraHertz (THz) emitters. To realize the THz operations of the spin logic circuits THz manipulation of the magnetic state is pivotal. This THz manipulation of the magnetic state in anti-ferromagnetic magnetic materials can be realized by coupling the materials with THz antennas. On the other hand, these antennas enhance the THz amplitude of spin-electronic THz emitters when coupled with its output. Therefore, these THz antennas can not only be coupled with the input of magnetic logics to improve the efficiency of magnetic sate manipulation in logic devices but also with the output of the spintronic THz emitters to enhance the generated THz signal amplitude. In this project, we have examined four types of antennas: h-dipole, spiral, bow-tie, and a sub-THz antenna. All the antennas are placed on top of a MgO substrate material for simplicity. However, a bow-tie antenna is also fabricated on an antiferromagnetic substrate of TmFeO3 to check this antenna’s reliability to manipulate its magnetic state. We have studied the impact of antenna geometries on the generated electric field amplitude. We have optimized each antenna for maximum electric field norm profile, with an increase of 30% for the h-dipole and spiral antennas, and an increase of 100% for the bow-tie antenna. However, in this project we were not able to find any general conclusions about what geometrical parameters can further amplify the generated electric field. None of the antennas generated a large enough peak-to-peak electric field amplitude to manipulate the magnetic state of anti-ferromagnetic materials. However, they did successfully amplify the spintronic THz emitter output and could certainly be useful in that regard.

Electric and hybrid cars is one of the technologies to reduce the uses of fossil fuel. What is common with an electric car and a hybrid car is the use of battery to store electrical energy. To sustain high performance, long lifetime and to keep high safety in an electric vehicle it’s very important to control the temperature of the battery cells. Therefore it’s important to have a sufficient and well-designed cooling system that can keep the battery cells within recommended temperature range when the car is driving. In this thesis, battery cooling and battery heat generation in the KTH formula student car “EV12e” are simulated and analyzed. The first part is to modulate the heat production that can occur when driving the car at the formula student competition. The second part is analyzing predesigned air-cooling. The “Thévenin Equivalent circuit” was used as battery model with a fixed value of cells internal resistance, the heat was approximated with Joule heating and the internal chemical heating was neglected. By using logged data from last year’s car “EV11e” on Silverstone 2015, a drive cycle could be estimated for EV12e with driving time and by using a parametric study of driving behavior. To simulate the airflow and heat transfer in cooling channels the software “COMSOL Multiphysics®”. Simplified geometric structure of the battery and cooling channels were imported to the software together with parameters specified from the car “EV12e”. This data was then used to simulate the temperature changes in the battery. The result showed that the battery generates 0.8-1.4MJ heating at 500-900W, for driving time of 25 minutes and a specific driving behavior. When driving at 500W output power under outdoor temperature of 30 o C, the maximum temperature of the battery reaches 49 o C at the end of the race. If the driver uses the maximum theoretical power output, the internal heating can come up to 950W after 25 min driving and reaches temperature of 64 o C with the initial and outdoor temperature of 25 o C. The pre-designed air cooling can manage to keep the battery temperature under the maximum allowable battery cell temperature with the outdoor temperature at 25 o C or lower. If the outdoor temperature is higher than 25 o C the driver will have to consider the battery temperature when driving and should avoid quick accelerations.
Eldrivna bilar och elhybridbilar är en av de tekniska lösningarna för att minska användandet av fossila bränslen. Gemensamt för el och hybridbilar är att båda använder sig av batterier för att lagra elektrisk energi. För att erhålla bra prestanda, livslängd och säkerhet i ett eldrivet fordon är batteriernas temperatur en mycket avgörande faktor. För att undvika att temperaturen blir allt för hög i battericellerna behövs ett väldesignat kylsystem för att ta hand om värmeutvecklingen som uppstår inuti cellerna när bilen körs. I den här rapporten analyseras luftkylningen och värmeutvecklingen av högspänningsbatteriet i KTH Formulastudent bilen ”EV12e”. Arbetet är uppdelat i två delar: Första delen handlar om att göra en modell för värmeutvecklingen som uppstår i battericellerna vid tävling, andra delen utgörs av CFD med värmeöverföring och analysera om den redan designade luftkylningen är tillräcklig för att undvika överhettning under körning. I modell uppställningen för spillvärme användes Thévenin Equivalent ciruct som batterimodell och majoriteten av spillvärmen antogs komma från Ohm:isk uppvärmning. Genom att utgå från kör data med KTH Formula student bil ”EV11e” som tävlade 2015 på Silverstone kunde en modifierad körcykel för EV12e tas fram utifrån antagande om körtid och förarbeteende. För att simulera luftflöde i kylkanaler, värmeöverföring och batteriets temperatur användes simuleringar med FEM i programmet COMSOL Multiphysics®. I programmet importerades en geometrisk förenklad modell av batteriet till ”EV12e” samt in parametrar med bland annat den beräknade värmeutvecklingen. Resultatet var att batteriet genererar 0,8-1,4M Joule resistiv värme, vilket ger en genomsnittlig uppvärmning av 500-900W om körtiden antas vara 25minuter. Vid en körstill där batteriet genererar 500W spillvärme och en utomhus temperatur av 30o C blir den högsta uppmäta temperaturen 49o C efter körning. Om föraren istället använder maximala kapaciteten av batteriet kan den interna uppvärmningen bli som mest 950W vilket ger en högsta temperatur på 64o C om utomhus temperaturen är 25o C. Slutsatsen är att batteriets kylsystem klarar av att hantera värmeutveckling i batteriet för en utomhus temperaturen är som mest 25o C, om utomhustemperaturen är högre behöver förare anpassa sin körstill för att inte riskera att batterierna blir varmare än den maximala temperaturen på 65o C.

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.

Work is focused on computer modeling of PN junction and MOSFET transistor in the program COMSOL Multiphysics and in program TiberCAD. The text is discussed on the drift and diffusion in semiconductors. Also shown is a method of modeling the PN junction and MOSFET transistor in the programs and compare models.

Solid Oxide Fuel Cells are fuel cells that operate at high temperatures usually in the range of 600oC to 1000oC and employ solid ceramics as the electrolyte. In Solid Oxide Fuel Cells oxygen ions (O2-) are the ionic charge carriers. Solid Oxide Fuel Cells are known for their higher electrical efficiency of about 50-60% [1] compared to other types of fuel cells and are considered very suitable in stationary power generation applications. It is very important to study the effects of different parameters on the performance of Solid Oxide Fuel Cells and for this purpose the experimental or numerical simulation method can be adopted as the research method of choice. Numerical simulation involves constructing a mathematical model of the Solid Oxide Fuel Cell and use of specifically designed software programs that allows the user to manipulate the model to evaluate the system performance under various configurations and in real time. A model is only usable when it is validated with experimental results. Once it is validated, numerical simulation can give accurate, consistent and efficient results. Modeling allows testing and development of new materials, fuels, geometries, operating conditions without disrupting the existing system configuration. In addition, it is possible to measure internal variables which are experimentally difficult or impossible to measure and study the effects of different operating parameters on power generated, efficiency, current density, maximum temperatures reached, stresses caused by temperature gradients and effects of thermal expansion for electrolytes, electrodes and interconnects. Since Solid Oxide Fuel Cell simulation involves a large number of parameters and complicated equations, mostly Partial Differential Equations, the situation calls for a sophisticated simulation technique and hence a Finite Element Method (FEM) multiphysics approach will be employed. This can provide three-dimensional localized information inside the fuel cell. For this thesis, COMSOL Multiphysics version 4.2a will be used for simulation purposes because it has a Batteries & Fuel Cells module, the ability to incorporate custom Partial Differential Equations and the ability to integrate with and utilize the capabilities of other tools like MATLAB, Pro/Engineer, SolidWorks. Fuel Cells can be modeled at the system or stack or cell or the electrode level. This thesis will study Solid Oxide Fuel Cell modeling at the cell level. Once the model can be validated against experimental data for the cell level, then modeling at higher levels can be accomplished in the future. Here the research focus is on Solid Oxide Fuel Cells that use hydrogen as the fuel. The study focuses on solid oxide fuel cells that use 3-layered, 4-layered and 6-layered electrolytes using pure YSZ or pure SCSZ or a combination of layers of YSZ and SCSZ. A major part of this research will be to compare SOFC performance of the different configurations of these electrolytes. The cathode and anode material used are (La0.6Sr0.4)0.95-0.99Co0.2Fe0.8O3 and Ni-YSZ respectively.
ID: 031001387; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Adviser: .; Title from PDF title page (viewed May 22, 2013).; Thesis (M.S.M.E.)--University of Central Florida, 2012.; Includes bibliographical references (p. 101-107).
M.S.M.E.
Masters
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering; Thermofluids

This thesis investigates the possibility of using an unglazed flat-plate solar collector as a cooling radiator. The solar collector will be connected to the condenser of a heat pump and used as cooler during nighttime. Daytime the solar collector will be connected to the evaporator of the heat pump and used as heat source. The two widely differing fields of application make special demands on the solar collector. The task is given by the heat pump manufacturer Thermia and the main objective is to find out whether a solar collector should be used as a cooler or not. The performance of the solar collector under varying environmental conditions is investigated using COMSOL Multiphysics 3.3. Only the cooling properties are investigated here. The performance of the solar collector as a heat exchanger is estimated using the effectiveness-NTU method, and the solar collector is found to be a good heat exchanger at low wind speeds. The heat transfer coefficients of the convection and radiation are determined for varying temperature and wind speeds. The convective heat transfer coefficient is lowered by tubes above the absorber plate and for a high convective heat transfer rate the solar collector surface should be smooth. For a high radiative heat transfer rate the surface needs to have a high emissivity. The cooling rate is higher from a warm surface than from a cold and since no temperature change of the heat carrier is necessary the solar collector should be kept at a high temperature. To increase the cooling rate alterations need to be made to the solar collector that makes its heating performance deteriorate. A solar collector that can be used for cooling is not an efficient solar collector.

The aim of the work is to create a coherent overview of the silicon monocrystaline solar cell in terms of the physical principle of the structure and sequence of technological operations necessary for its production. The effect of individual manufacturing steps is discussed in relation to the requirement of decreasing recombination, optical and ohmic losses of the monocrystalline solar cell. Due to a theoretical assumption, one-dimensional model of solar cell was created in a PC1D software that was later optimized to achieve the highest possible efficiency. Using the available technologies, final model of the solar cell is manufactured in Solartec company and in the end of the work compared with the output of simulation.

Technological evolution and mass production is impacting the Earth daily due to global warming caused by greenhouse gas emissions, where the biggest factor is the emission of carbon dioxide mostly caused by the burning of fossil fuel and industrial processes. Therefore, alternatives for substituting the use of fossil fuel in industries are extremely important. This thesis project investigates the method of using plasma technology using a plasma burner  which is electrically generated and could be an ideal solution for industrial metallurgical, chemical and mechanical processes due to its unique characteristics such as high energy densities, extremely high temperatures, rapid heating of surfaces and melting materials with a small installation size. Using the software COMSOL Multiphysics, a 2D model geometry is set up to simulate and investigate the behavior of the plasma burner by varying different parameters to improve the performance of the plasma burner. The results are based on simulations and no experiments were performed. However, we visited RISE ETC to observe and learn about the plasma burner model. At last, a geometry investigation was done by calculating the thermal efficiency to designate the most efficient geometry.

Microelectromechanical systems (MEMS) depend on mechanical deformation to sense their environment, enhance electrical circuitry, or store data. Nonlinear forces arising from multiphysics phenomena at the micro- and nanoscale -- van der Waals forces, electrostatic fields, dielectric charging, capillary forces, surface roughness, asperity interactions -- lead to challenging problems for analysis, simulation, and measurement of the deforming device elements. Herein, a foundation for the study of mechanical deformation is provided through computational and experimental studies of MEMS microcantilever capacitive switches. Numerical techniques are built to capture deformation equilibria expediently. A compact analytical model is developed from principle multiphysics governing operation. Experimental measurements support the phenomena predicted by the analytical model, and finite element method (FEM) simulations confirm device-specific performance. Altogether, the static multistability and quasistatic performance of the electrostatically-actuated switches are confirmed across analysis, simulation, and experimentation.

The nonlinear multiphysics forces present in the devices are critical to the switching behavior exploited for novel applications, but are also a culprit in a common failure mode when the attractive forces overcome the restorative and repulsive forces to result in two elements sticking together. Quasistatic operation is functional for switching between multistable states during normal conditions, but is insufficient under such stiction-failure. Exploration of dynamic methods for stiction release is often the only option for many system configurations. But how and when is release achieved? To investigate the fundamental mechanism of dynamic release, an atomic force microscopy (AFM) system -- a microcantilever with a motion-controlled base and a single-asperity probe tip, measured and actuated via lasers -- is configured to replicate elements of a stiction-failed MEMS device. Through this surrogate, observable dynamic signatures of microcantilever deflection indicate the onset of detachment between the probe and a sample.

碩士
國立中央大學
環境工程研究所
102
In the literatures many exposure systems were proposed to study inhalation toxicology, however, the particle deposition flux or the exposed dose had not been well defined in these exposure systems. Moreover, Particle trajectory and deposition were highly depending on operation conditions. Therefore, in this study, we developed a new ESP type air-liquid interface (ALI) cell exposure system and numerically characterized its performance. The commercial CFD software, COMSOL Multiphysics, was coupling the fluid field and the electric field to simulate dynamic trajectory of charged particles in the system and to determine the particle deposition flux. The aim of this study was to establish a numerical simulation scheme to design and to develop an ESP type ALI system. Based on the numerical simulation it was found decreasing expanded degree of the upper exposure chamber would reduce reflux and mitigate unwanted particle loss. Therefore, the new configuration of the exposure chamber was re-designed by considering smoother streamline and particle trajectory to reduce unnecessary spaces and particle loss. The original design, Model A, needs 6 kV to achieve 100% collection of 100 nm particles, but the revised design, Model B, only requires 1 kV. In other words, Model B is more effective than Model A on particle collection. To further systematically evaluate the performance of the system, three indicators, including total penetration (P), region deposition ratio (f) and relative deposition density in region 2, were introduced. Higher flow rate would case lower total penetration because of more significant re-circulated flow. Although in 0 kV the region deposition ratio was not obviously changing with particle size, the size effect was not negligible when applying voltage. In addition, the applied electric field would increase particle deposition in region 2 and result in more uniform particle depositasion pattern.

This diploma thesis is concerned with a problem of the line heat simulation by different kinds of materials with computer - aided COMSOL Multiphysics. The thesis is composed of three thematic units. In the first part there is a line heat principle shortly described and his basic physical quantities which are necessary for correct defining of the simulation. The second part is concerned with the software, its function, auxiliary modulus and a description of single actions, which are essential for making of the model. In the last part there is the whole process of the multiphysical task creation that enables to simulate line heat in a specific material in reliance on time.

碩士
東海大學
環境科學與工程學系
100
The purpose of this study is to develop the design and simulation of photocatalytic reactors for the treatment of methyl blue (MB) wastewater by a homogeneous phase advanced oxidation process (AOPs). The model was built with the transient mass balance equation and the steady-state momentum equation, and was verified with both batch and continuous flow experiments under different operating conditions such as ultraviolet ( UV ) light intensity, aeration and feed concentration of methyl blue, A computational fluid dynamics ( CFD ) software in COMSOL MULITIPHYSICSTM was used to simulate and to assess the feasibility and rationality of the reactor design involving different hypothetical reactor configurations. In the UV/TiO2 photocatalysis study, batch experiments were performed using various initial MB concentrations and light intensities to determine the reaction kinetics. With a fixed aeration rate of 150 mL/min and alight intensity of 1.8 mW/cm2, the first-order MB reaction rate for initial concentrations of 1.6 mg/L and 32 mg/L were 5.6×10-2 and 1.01×10-2 min-1, respectively, indicating that the reaction rate decreased with initial concentration., Also, the MB first-order reaction rates under the light intensities of 0.6 mW/cm2, 1.2 mW/cm2, and 1.8 mW/cm2 were 1.01×10-2 min-1, 8.9×10-3 min-1 and 7.9×10-3 min-1, respectively, showing that light intensity was a critical factor. COMSOL verification study for the batch condition showed a close match between the experimental and simulated concentration profiles when the initial concentrations were low. Deviations were progressively larger when the initial concentration was increased, presumably due to the adversely effects such of light-shading and competitive adsorption, which were not considered in the simulation. The simulation results demonstrated that the square column reactor had more uniform flow distribution as compared to cylinder reactor having similar cross-section area. In addition, design with wide cylinder resulted in concentration accumulation near the base of the reactor due to inefficient dispersion. In contrast, narrow cylinder had an improved MB removal efficiency over the standard and wide cylinders, though accumulation near the reactor wall occurred when the flow velocity increased. Keywords : methyl blue, photocatalysis, immobilized, COMOSL MULTIPHYSICS, mass equation, momentum equation

Renal failure or kidney failure is a medical condition when the kidneys fail to filter toxins and waste products from the blood. Most of the time, problems encountered in kidney malfunction include abnormal fluid levels in the body, increased acid levels and abnormal levels of Urea, Glucose, Endothelin, β2-Microglobulin, Complement Factor D. In medicine, dialysis is a method that is used to remove waste products from blood when the kidneys are in a state of renal failure. Parameters characterizing the structure of dialyzers are very important because they decide overall clearance of toxin molecules and at the same time should allow retaining useful molecules in the blood. It is however not clear how the changes of dialyzer parameters will affect the clearance. This can be found out by doing simulation of a dialysis process. In this thesis, a numerical model was developed to simulate the process that goes on inside a dialyzer to determine which parameters are important for getting better clearance of toxin molecules and how the changes of those parameters can improve the performance of dialysis. In order to do that, a model of dialyzer membrane with details of the porosity is necessary. The dialyzer membrane that was considered in this research was Polyflux 210H. Here the cross sectional images of Polyflux 210H dialyzer membrane were taken by FESEM (Field Emission Scanning Electron Microscope) to obtain the porosity values of different layers. Using these porosity values, a multilayered membrane model was developed in Finite Element Software- COMSOL Multiphysics 4.3. Then a blood flow containing - Urea, Glucose, Endothelin, β2-Microglobulin, Complement Factor D and Albumin was introduced. For a certain blood flow rate the toxins diffuse through the membrane and on the other side of the membrane a dialysate flow was introduced to remove the toxins. Two different definitions of effective diffusivity were considered for the phenomenon of the diffusion of the molecules in the membrane. Between the two, the better definition was found out by comparing the results with experimental data of the manufacturer of Polyflux 210H. Then for the chosen definition, further analysis was done and the results were compared with another set of experimental data to validate the model. Then different parameters - magnitude and direction of both blood and dialysate flow, length and diameter of the fiber, pore sizes were changed to simulate how these changes affect toxin clearance and the removal of useful molecules. The results suggest some very interesting points to achieve better dialysis performance. First of all, the clearance rate of both Urea and Glucose increase rapidly with the increasing blood flow rate. When a maximum allowable blood flow rate is attained, increasing the dialysate flow rate can ensure better clearance rate for Urea and Glucose. In both the cases of increasing radius or length of the dialyzer fiber, the clearance rate of Glucose increases more rapidly than the clearance rate of Urea. For Endothelin and β2-Microglobulin the clearance rate increases twice compared to the initial condition. Meanwhile, the clearance rate of Albumin does not change that much. Also increasing the pore diameter up to 20 nm (but not more than that) can ensure higher clearance rate of Urea and Glucose, moderate clearance rate of middle molecules and minimum loss of Albumin.

M. Tech. Hydrogen storage modeling.
In this dissertation, a 2D dynamic simulation for a portion of metal hydride based hydrogen storage tank was performed using computational software COMSOL 4.0a Multiphysics. The software is used to simulate the diffusion and heating of hydrogen in both radial and axial directions. The model consists of a system of partial differential equations (PDE) describing two dimensional heat and mass transfer of hydrogen in a porous matrix. This work provides an important insight to the fundamental understanding of multi-physics coupling phenomena during hydrogen absorption/ desorption process. The simulation results could be applied to the on-board hydrogen storage technology, in particular for the hydrogen supply of a fuel cell for powering of a hydrogen fuel cell vehicle.

Dissertação de Mestrado em Engenharia Informática apresentada à Faculdade de Ciências e Tecnologia
This report will detail the work done for the course of Internship/Dissertation at the University of Coimbra, within the Intelligent Systems specialization of the Master’s in Informatics Engineering.With growing concerns regarding global warming and the unsustainability of fossil fuels, research regarding cheaper and more efficient use of renewable energy has been intensifying. However, performing physical experiments is expensive, due to the need to acquire proper material and equipment, making computer simulations especially important. Not only do they allow researchers to quickly test and compare different parameters, obtaining detailed results every time; they are also able to perform automatic parameter fitting.Currently, researchers rely on generic computing software like Wolfram Mathematica and Matlab. While these programs are very powerful, demand for more specialized software that offers a deeper focus on a smaller number of features is growing.One of these specializations is the production of hydrogen using solar energy. The application developed during this internship is aimed at filling the demand for that type of simulation, specifically one that uses multi-layer Photoelectrochemical (PEC) solar cells. The objective was to create a powerful desktop application that could fulfil the needs of any researcher in the area, without requiring any programming knowledge.During this internship, the Comsol Multiphysics software was used. This is a physics simulation program developed by Comsol Inc. in Sweden during 1986 that has been frequently updated since. Application Builder, a feature of Comsol Multiphysics, was the framework used. It allows for a quick implementation of standard Comsol Multiphysics features, while also facilitating the creation of new features using the JAVA programming language.This project was developed at the University of Žilina, at the satellite location Inštitút Aurela Stodolu in Liptovsky Mikulas, Slovakia. It was done as part of the Erasmus+ Internship Program.It comes in the sequence of research regarding PEC solar cells done by Dr. Peter Cendula, who served as the client for this project, at Zurich University of Applied Sciences; and work done on Comsol by Matúš Vaňko, at the University of Žilina. The former research focused on the more theoretical aspects of the use of PEC solar cells for hydrogen production. The latter work is more practical, exploring the creation of a GUI that allows users to simulate this situation.Current software used for simulating solar cells often requires a thorough understanding of the application itself, on top of the necessary knowledge about solar cells. The purpose of this project was to eliminate that barrier, making researcher’s jobs easier while still providing a very powerful specialized simulation tool.This internship was very valuable as an Informatics Engineering internship. Although learning about aspects of Scientific Simulation was important, the most relevant part of this project was the knowledge that could be gained related to Software Development. The necessity of writing good code, with proper documentation and testing, allowed for the opportunity to apply knowledge gained through the Informatics Engineering course, while also learning new things about Software Development such as, for example, good UI design.This report details every aspect of the creation of this app that is considered relevant. The Related Work section shows the research done about previous projects within the field and other related simulation apps.In Methodology and Planning, information about how the development process was organized is laid out, with the schedules for both the complete work and the development phase; along with the chosen software development methodology and the reasons for that choice. The Requirements and Architecture sections offer information used during the development and testing phases of the project.The following sections offer a more concrete look at the ideas behind the design of the application. Interaction Design and Final Interface explain the choices made regarding how the user is able to interact with the application, and how the application looks. Finally, some space is reserved for final remarks.
Este relatório irá detalhar o trabalho realizado no âmbito da Dissertação/Estágio na Universidade de Coimbra, dentro da especialização em Sistemas Inteligentes do Mestrado em Engenharia Informática.Com a preocupação crescente com o aquecimento global e com a falta de sustentabilidade dos combustíveis fósseis, tem-se vindo a intensificar a investigação na procura por usos mais baratos e eficientes de energias renováveis. No entanto, o preço de efetuar experiências físicas é elevado, devido à necessidade de adquirir materiais e equipamentos adequados, tornando simulações por computador especialmente importantes. Não só permitem aos investigadores testar e comparar diferentes parâmetros rapidamente, obtendo resultados detalhados; também permitem efetuar ajuste automático de parâmetros.Neste momentos, investigadores dependem de software computacional genérico como o Wolfram Mathematica e o Matlab. Enquanto estes programas são muito poderosos, a procura por software mais especializado com um foco mais aprofundado num número menor de funções.Uma destas especializações é a produção de hidrogénio usando energia solar. A aplicação desenvolvida durante este estágio tem como objetivo corresponder à procura por esse tipo de simulação, especificamente uma que usa células solares multi-camada fotoeletroquímicas (PEC). O objetivo foi criar uma aplicação de computador que conseguisse satisfazer as necessidades de qualquer investigador na área, sem requerer quaisquer conhecimentos de programação.Durante este estágio, o software Comsol Multiphysics foi usado. Trata-se de um programa do simulação de física desenvolvido pela Comsol Inc., na Suécia, em 1986, que tem sido frequentemente atualizado deste então. O Application Builder, uma funcionalidade do Comsol Multiphysics, foi a estrutura usada para realização deste projeto. Permite uma implementação rápida de funcionalidades do Comsol Multiphysics, ao mesmo tempo que facilita a criação de novas funcionalidades usado a linguagem de programação JAVA.Este projeto foi desenvolvido na Universidade de Žilina, na localização satélite Inštitút Aurela Stodolu em Liptovsky Mikulas, na Eslováquia. Foi feito como parte do Programa de Estágios Erasmus+. Vem na sequência de investigação relacionada com células solares PEC feito por Dr. Peter Cendula, que serviu como cliente deste projeto, na Universidade de Ciências Aplicadas de Zurique; e trabalho feito no Comsol por Matúš Vaňko, na Universidade de Žilina. O primeiro trabalho foca-se nos aspetos teóricos do uso de células solares PEC para produção de hidrogénio. O último trabalho e mais prático, explorando a criação de uma interface de utilizador que permite aos utilizadores simular esta situação. O software atualmente utilizado para simular células solares requer frequentemente uma compreensão profunda da aplicação em si, para além do conhecimento necessário sobre células solares. O propósito deste projeto foi eliminar essa barreira, tornando o trabalho dos investigadores mais fácil ao mesmo tempo que disponibiliza uma ferramenta de simulação especializada altamente poderosa.Este estágio foi muito valioso como um estágio de Engenharia Informática. Embora aprender sobre aspetos de Simulação Científica tenha sido importante, a parte mais relevante foi o conhecimento ganho relacionado com Desenvolvimento de Software. A necessidade de escrever bom código, com documentação e testes apropriados, perimitiu a oportunidade de aplicar conhecimentos ganhos ao longo do curso de Engenharia Informática, aprendendo ao mesmo tempo novas coisas sobre Desenvolvimento de Software como, por exemplo, bom desenvolvimento de Interfaces de Utilizador.Este relatório detalha todos os aspetos da criação desta aplicação que são considerados relevantes. A secção de Trabalho Relacionado mostra investigação feita em projetos prévios dentro da área e outras aplicações de simulação relacionadas.Em Metodologia e Planeamento, informação sobre como o processo de desenvolvimento foi organizado é disposta, com o plano para o trabalho completo e a fase de desenvolvimento; juntamente com a metodologia de desenvolvimento de software escolhida e as razões para essa escolha. A secção de Requisitos e Arquitetura oferece informação usada durante as fases de desenvolvimento e teste do projeto.As seguintes secções oferecem um olhar concreto às ideias por trás do desenho da aplicação. Desenho de Interação e Interface Final explicam as escolhas feitas sobre como o utilizador pode interagir com a aplicação, junto com o visual da aplicação. Finalmente, algum espaço foi reservado para comentários finais.
Outro - Parte do Programa Eramus+

The focus of the research is on the problem of ventilation on lead-melting production. The main sources of lead emissions in the refining shop are determined. The primary conditions for convective jet saving for its further removal and cleaning are defined. With COMSOL Multiphysics simulation platform the shop model is created for fluid flow analysis. The results of numerical calculation of air exchange scheme and its comparing with experimental data are shown. An own scheme of air distribution in refining shop is offered. The scheme takes into account all the requirements for saving of convective circulation, initiated by convective jets from melting pots.
Диссертация посвящена проблеме вентиляции свинцово-плавильного производства. Определены основные источники выделения аэрозолей свинца в рафинировочном цехе. Определены основные условия, и параметры сохранения конвективной струи для её дальнейшего удаления и очищения. В программе COMSOL Multiphysics® построена модель цеха для моделирования процессов течения воздуха. Представлены результаты численного моделирования организации схемы воздухообмена и их сравнение с физическим опытом. Предложена собственная схема распределения воздуха в рафинировочном цехе, в которой учитываются все требования, для сохранения естественной циркуляции, инициированной конвективными струями от котлов.