Proton exchange membrane fuel cells (PEMFCs) have attracted great attention due to their high power density, low-temperature operation and high energy conversion efficiency. However, the high cost of Pt catalysts and durability problems hinder their commercialization. So their cost must be lowered drastically and their durability must be extended. In an effort to overcome these problems, there have been intensive efforts to enhance the activity, durability and to lower the price of catalysts by alloying with other less expensive metals. In particular, the sluggish kinetics of ORR caused by Pt oxide at cathode and Pt catalyst degradation by electrochemical surface area (ECSA) loss have been a huge research area where a lot of researchers have paid lots of attention to solve. In this regard, the objective of this dissertation is to evaluate a series of Pt catalyst electrode surface electrochemical reactions on PEMFC electrode in order to help searching new catalysts and enhancing system design, assist in the search for new catalysts and improved system design by suggesting the developed mechanism of electrocatalyst activity and stability (durability). We have been focused on understanding the oxide-mediated dissolution of Pt by using electrochemical experiment methods such as RRDE, EQCN, SECM with a combination of ICP-MS and computational simulation with COMSOL Multiphysics. Firstly, in chapter 3, we showed the oxide-mediated Pt dissolution rate and the influence of hydrogen and cation underpotential deposition on Pt dissolution. In chapter 4, we revealed oxygen reduction reaction (ORR) plays a significant role in Pt oxide formation and reduction that influences the Pt catalyst dissolution, resulting in accelerated Pt dissolution rate at specific potential range. Finally, we found out the nature of mobile species generated during PtO₂ reduction process which have been disputed as Pt ion or other mobile species and fulfilled computational simulation for evaluation of SECM experiment in chapter 5. Based on these experiments and simulation, we were able to explain some mechanism of literature results that already were reported but have not been clearly explained so far. In terms of the purpose of this dissertation, the mechanism of oxide-mediated Pt dissolution, influence of ORR to Pt oxide formation/reduction and Pt dissolution, the nature of mobile species generated during PtO₂ reduction process, are sure to be very helpful in developing new catalysts and enhancing system design and suggested operating conditions. / text

I developed a thermal model of the Gravity Recovery and Climate Experiment satellite for the Center for Space Research to use in verifying their thermal models and for developing the next generation of satellites for their experiments. I chose COMSOL to model the satellite and used ProEngineer and 3Ds Max to generate the mesh from a .STEP file provided by DaimlerChrysler. I adjusted the model based on previous computer models and actual telemetry data from the GRACE satellite provided from 2002 through 2008. Using the model, I developed a sensitivity analysis of the satellites key thermal environment components and used that to recommend design changed for the next generation of satellites. Special attention should be given to redesigning the Star Camera Arrays and the heat transfer between the Main Equipment Platform and the Radiator. / text

Predictive models for diffusion-controlled particle dissolution are important for designing advanced and efficient solid products for controlled release applications. A computer-aided modeling framework was developed to derive the effective dissolution rates of multiple particles as the solid surface material eroded gradually into the surrounding liquid phase. The mathematical models were solved with numerical methods using the computational software MATLAB. Results from the models were imported into COMSOL Script to create three-dimensional plots of the particle size data as a function of time. The release model found for the monodispersed particles was manipulated to incorporate polydisperse solids, as these are found more frequently in chemical processes. The program was further developed to calculate the particle size as a function of time for particles encapsulated for use in controlled release. The parameters, such as radius size, coating material and encapsulation thickness, can be altered in the computer models to aid in the design of particles for different desired applications. Simulations produced conversion profiles and three-dimensional visualizations for the dissolution processes. Experiments for the dissolution of citric acid in water were performed using a reaction microcalorimeter to verify results found from the computer models.

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.

With the continuous improvement in knowledge and health risks associated with heavy metal expulsion, government environmental agencies are continuously reducing the legal disposal limits. However, the demand for items like IPods or energy-efficient appliances containing heavy metal like copper is on the rise. Whether from commercial or residential areas, heavy metals are known to have toxic effects on humans, animals, and/or ecosystems; hence, their removal is necessary part of preserving our environment. With the rising cost of natural resources, biological species have proven to be viable alternatives in the jet fuel and biodiesel industries. Algal biomass is widely considered economical because of its renewable, biodegradable, noncompetitive, and nontoxic properties. Currently, algae are being grown on waste water for the lipid; this research involves taking the left over or lipid-extracted algae (LEA) for utilization as a biosorbant to remove heavy metals from wastewater. Down selection via batch processes showed that Chlorella sorokianna and its associated lipid-extracted algae (LEA) demonstrated similar adsorption capacities of copper (II) as three current-in-use ion exchange resins. A feasibility study proved that the LEA was an economically realistic means to remove copper (II) from effluent. The LEA biomass is capable of a maximum adsorption of 14.36 ± 0.27 mg of copper (II) per gram of dry biomass for six regeneration, sorption-desorption, cycles with nitric acid. Using SEM and FTIR, the LEA is capable of ion exchange electrostatic interaction with various surface sites of carboxyl, hydroxyl, and metal groups. Next, the batch process was used to fabricate a lab-scale continuous column process much like ion exchange or activated carbon columns in a waste water treatment plant. Using the continuous systems' kinetics and cycle life, a cost analysis was performed on a plant scale column to reduce copper (II) in wastewater for recovery at a later date, which would yield cost saving over the life of columns. To install three LEA columns prior to ion exchange in a waste water treatment plant, the total capital expense is $1.03 million for a one year time line. The bidirectional flow columns are meant as pretreatment prior to ion exchange columns. The LEA columns provide a waste water treatment plant a sustainable, greener and cheaper alternative to offset costs associated with purifying waste water.

The main goal of this thesis project is to identify interesting concepts related to cooling of electrical motors and generators which could be evaluated using suitable computer simulation tools. As the project proceeded it was decided to focus on investigating how the air from a fan flows along the finned frame of a general purpose low voltage electrical machine, how the heat is transferred between the frame and the cooling air and what the temperature distribution looks like. It was also investigated if it is possible to make improvements in the effectiveness of the cooling without adding additional coolers. This investigation focused on varying the fin design and evaluating the resulting temperature distribution. Due to the complex nature of the simulations a segment, and not the full frame, was considered. Simulation model validation was performed through comparing air speed measurements that were performed on two different machines with the corresponding simulated air speed. The validation showed that good agreement between simulated and measured air speeds are obtained. The conclusion from the simulations is that slight modifications to the current fin design could increase the cooling effect of the finned surface. The air velocity measurements also indicate that the cooling of the machines surface could potentially be improved by small changes in the exterior of the frame. / Målet med detta examensarbete var att identifiera intressanta koncept relaterade till kylning av elektriska maskiner och generatorer, som kunde utvärderas med lämplig programvara för datorsimuleringar. Under projektets gång så bestämdes det att fokusera på hur luften från en fläkt flödar längs med en generell lågspänningsmaskin, hur värmen överförs från ramen till den omgivande luften och hur temperaturfördelningen ser ut. Det undersöktes även om det var möjligt att förbättra effektiviteten av kylningen utan att ansluta extra kylanordningar. Undersökningarna fokuserades på olika fendesigner och dess påverkan på värmefördelningen. På grund av simuleringarnas komplexitet så har simuleringarna endast utförts på ett segment istället för hela maskinen. Validering av simuleringarna utfördes genom att jämföra de simulerade lufthastigheterna med verklig lufthastighet som mättes på två maskiner i testmiljö. Valideringen visade att simuleringarna överensstämmer väl med de mätningar som utfördes. Slutsatsen utifrån simuleringarna är att mindre förändringar av fenornas nuvarande design kan förbättra fenornas kylningsförmåga. Mätningarna av lufthastigheten ger även indikationer på att kylningen av maskinens utsida eventuellt kan förbättras genom små förändringar av ramens exteriör.

[pt] Os sistemas micro eletromecânicos são dispositivos na escala dos micras que combinam estruturas mecânicas com circuitos elétricos, e são usados como sensores ou atuadores. Dentro destes dispositivos, estão os de onda superficial acústica (SAW em inglês) que usam variações na velocidade ou percurso de propagação da onda para fazer a detecção da variável a medir. Uma aplicação importante em processos químicos, é no acondicionamento de ambientes, monitorando a umidade. Para isso um sensor SAW comprado, foi coberto em sua superfície com uma camada de um polímero absorvente de vapor de agua. No qual o aumento na massa do polímero na superfície diminui a velocidade da onda. Por tanto o PolyVinyl Álcool foi escolhido para absorver o vapor de agua e foi preparado com 5.6 wt por cento, para ser depositado por meio de spin coating. Então uma serie de experimentos foram feitos numa câmara climática variando tanto a umidade como a temperatura, com o fim de avaliar o comportamento do sensor medindo a sua variação da frequência. Estes resultados foram comparados com um modelo analítico e uma simulação por elementos finitos. O modelo analítico foi presentado por Sielman, o qual determina como muda a densidade e espessura no polímero com a umidade. Estes valores foram substituídos na equação de Wohltjen que dá a variação da frequência de um SAW devido a absorção de gases. Em quanto a simulação por elementos finitos foi feita em Comsol Multiphysics achando a frequência para a qual o SAW ressona, com o aumento da densidade na camada acima do SAW para as umidades inseridas. / [en] Micro electromechanical systems (MEMS) are devices that combine mechanical structures with electrical circuits at the micro scale, to function as sensors or actuators. One type of MEMS are the surface acoustic waves (SAW) devices, which uses the surface wave velocity or propagation path variations to measure the variable of interest. One important application in chemical processes is related to environment condition control, specifically humidity measurement. With that purpose, a commercial SAW was purchased and coated with a polymer layer in its surface. The PolyVynil Alcohol (PVA) was chosen to be the sensing layer in the SAW due to water vapor absorption properties, that increases the mass over the surface and decrease the wave velocity, leading to sense this humidity changes. 5.6wt per cent PVA solution was prepared and deposited through spin coating. Therefore, a series of tests were carried out in a climatic chamber, varying the humidity and temperature conditions, with the aim to analyze the sensor behavior by measuring its frequency shift. These results were compared with an analytical model and a finite element simulation. The analytical model presented by Sielman determines how the polymer density changes with humidity. These density values were inserted into the Wohltjen equation, which gives the frequency shift of the SAW due to gas absorption. Regarding the finite element simulation, it was carried out in the Comsol Multiphysics software, by solving the different resonating frequencies as a function of the increase in the polymer density due to the insets of humidity values.

The diploma thesis deals with problems of air flow in stables. The research part is devoted to ventilation requirements in livestock breeding, fluid flow problems and the possibility of prediction of this flow through computer modeling methods. The following chapter focuses on the COMSOL Multiphysics software in which theo bject model was created. In the practical part of the diploma thesis is described model of air flow in stable object, including all partial steps necessary for it ssuccessful numerical realization. The conclusion of the thesis is devoted to comparison of obtained results with value smeasured in real breeding.

abstract: This study explores the possibility of two matrices containing metallic particulates to act as smart materials by sensing of strain due to the presence of the conducting particles in the matrix. The first matrix is a regular Portland cement-based one while the second is a novel iron-based, carbonated binder developed at ASU. Four different iron replacement percentages by volume (10%, 20%, 30% and 40%) in a Portland cement matrix were selected, whereas the best performing iron carbonate matrix developed was used. Electrical impedance spectroscopy was used to obtain the characteristic Nyquist plot before and after application of flexural load. Electrical circuit models were used to extract the changes in electrical properties under application of load. Strain sensing behavior was evaluated with respect to application of different stress levels and varying replacement levels of the inclusion. A similar approach was used to study the strain sensing capabilities of novel iron carbonate binder. It was observed that the strain sensing efficiency increased with increasing iron percentage and the resistivity increased with increase in load (or applied stress) for both the matrices. It is also found that the iron carbonate binder is more efficient in strain sensing as it had a higher gage factor when compared to the OPC matrix containing metallic inclusions. Analytical equations (Maxwell) were used to extract frequency dependent electrical conductivity and permittivity of the cement paste (or the host matrix), interface, inclusion (iron) and voids to develop a generic electro-mechanical coupling model to for the strain sensing behavior. COMSOL Multiphysics 5.2a was used as finite element analysis software to develop the model. A MATLAB formulation was used to generate the microstructure with different volume fractions of inclusions. Material properties were assigned (the frequency dependent electrical parameters) and the coupled structural and electrical physics interface in COMSOL was used to model the strain sensing response. The experimental change in resistance matched well with the simulated values, indicating the applicability of the model to predict the strain sensing response of particulate composite systems. / Dissertation/Thesis / Masters Thesis Civil and Environmental Engineering 2017

Steel is a material commonly used in various constructions such as high-rise buildings, sport arenas, ships etc. Steel is a versatile building material due to its isotropic characteristics, e.g. both high tensile- and compressive strength. This allows steel to be formed into open section profiles which reduces material usage but simultaneously allows the tensile- and compressive stress resistance to be high in directions were loads are applied. Although steel has a high stress resistance its sensitivity to fire is larger than other building materials due to its high thermal conductivity. The strength of the material is reduced at higher temperatures and thereby makes the dimensioning of beams in fire cases vital in fire safety design of structural elements. An aspect to consider when dimensioning open section building elements in steel is the shadow effect. The shadow effect is the result of the open cross-section geometrical shape of beams and columns, e.g. H-profiles. The interior of the profile is screened from thermal radiation caused by fire which makes the characteristics of the thermal exposure different from closed cross-section profiles. A common way to estimate the temperatures of steel after a certain time of fire exposure is to use numerical calculations described in Eurocode. In these calculations the shadow effect is applied as a reduction of the total heat exchange, i.e. both convection and thermal radiation, from the fire exposure. A more realistic approach is to separate these boundary conditions and treat them as independent quantities. Wickström (2001) argues that a void is created within the flanges and that reduction factor thereby only should be applied to the radiative part of the total heat exchange, acting as a reduction of surface emissivity within the profile. This, since the convection is not affected by the shadow effect. Wickströms (2001) suggestion of application has been investigated in this thesis and has showed a better correlation than the approach suggested in Eurocode when compared to experimental tests. Shadow effects calculated on the premises of separated boundary conditions for the total heat exchange has of yet only been investigated in detail with TASEF+-simulations, but these simulations predicts steel temperatures with satisfactory results. It is possible to reproduce a similar setup in the program COMSOL Multiphysics in two-dimensional simulations, and further three-dimensional simulations. This possibility has been investigated in this thesis. COMSOL Multiphysics has proven to be an adequate tool when it comes to simulate fire exposure on slender steel beam with shadow effects considered. Both three- and two-dimensional models produced simulation results correlating well to simulations conducted in TASEF. Additionally, adequate correlations with experimental tests were obtained for COMSOL Multiphysics as well. Further work regarding fire simulations with the utilisation of COMSOL Multiphysics is thereby suggested.