Ventiler utgör en avgörande roll i det industriella samhället och används flitigt inom områden som säkerhet, filtrering och reglering av flöden. Säkerställandet av hållbarhet och drift av ventilen är därför ytters viktigt. Ventilen som undersöks har fyra packningsringar gjord av grafit. Grafitringarna leder till ett enklare underhåll, där tidsbesparingen vid isärplockningen av ventilen är 5 timmar jämfört med utan. Andra fördelar med grafitringarna är den starka motstånden mot höga temperaturer, rost och kemikalier. Nackdelen är dess svaga motstånd mot drag- och skjuvspänning. Syfte med studien är att få en ökad förståelse av värmebildningen över ventilen samt den medförande spänning som förekommer. En ökad förståelse av hur spänning bildas i ventilen kan leda till åtgärder som leder till minskad sprickbildning. Målen med studien är att med numeriska metoder och modeller bestämma spänningen vid tre driftfall, min, normal samt max. Spänningen vid grafitpackningen undersöks samt den maximala och minimala spänningen för hela ventilen. Ett kompletterande mål till studien är att undersöka värmeövergångstalen för simuleringar sedan jämföra dessa med empiriska ekvationer. Resultatet visade att den maximala spänningen över grafitområdet ligger på cirka 600 MPa, medan borttagningen av grafitringarna leder till en minskning på 9%. Den maximala spänningen för hela ventilen är lokaliserad på kopplingen mellan inloppet och skalet. Spänningen vid kopplingen är 6000 MPa, vilket är ett orimligt högt värde, då liknande studier visar värden på 200-600 MPa. Borttagning av grafitringarna leder inte till någon skillnad i maximalspänningen för hela ventilen. Från en spänningsaspekt kan ingen fördel med grafitringarna ses. Värmeöverföringstal från COMSOL-simuleringar, vilket använder sig av Navier-Stokes ekvationer, är markant högre vid höga tryck än värmeöverföringstal från empiriska ekvationer. Detta kan tyda på att empiriska ekvationer inte är tillämpbara för de höga tryck och temperaturer som studien undersöker. / Valves play an important role in the industrial society and are widely used in areas such as safety, filtration, and flow regulation. Ensuring the sustainability and operation of the valve is therefore of incredible importance. The studied valve contains four graphite packing rings. The use of graphite rings ensures easier maintenance, resulting in a time saving of 5 hours during disassembly compared to the removal of the graphite rings. Other advantages of graphite rings include their strong resistance to high temperatures, rust, and chemicals. However, their drawback lies in their weak resistance to tensile and shear stress. The purpose of the study is to gain a better understanding of the heat transport across the valve and the accompanying stress that occurs. Increased knowledge of stress formation in the valve can lead to ways to reduce crack formation in the future. The objectives of the study are to use numerical methods and models to determine the stress at three operating conditions, min, normal and max. The stress at the graphite gasket is investigated as well as the maximum and minimum stress for the entire valve. A complementary goal of the study is to investigate the heat transfer coefficients for simulations and compare these with empirical equations. The results show that the maximum stress over the graphite area is approximately 600 MPa, while the removal of graphite rings leads to a 9% reduction. The maximum stress for the entire valve is located at the connection between the inlet and the shell. The stress at the connection is 6000 MPa, which is unreasonably high compared to similar studies that report values of 200-600 MPa. The removal of graphite rings does not affect the maximum stress for the entire valve. From a stress perspective, no advantage of the graphite rings can be found. Heat transfer coefficients from COMSOL simulations, which use Navier-Stokes equations, are significantly higher at high pressures compared to those from empirical equations. This suggests that empirical equations are not applicable for the high pressures and temperatures investigated in the study.

Ett foster har inte samma blodflöde och resistans mot förändringar i sin miljö som en vuxen människa har och kan vid små temperaturförändringar orsakas skada i till exempel den utvecklande hjärnan. Vid ultraljudsundersökning finns bevisat en viss värmeökning, men det råder ovisshet kring hur stor denna skulle kunna bli under en längre tids exponering av ultraljud. Syftet med detta arbete var att undersöka värmeutvecklingen vid obstetriskt ultraljud genom att utforma en 3D-modell i mjukvarumiljön COMSOL Multiphysics version 6.0. En modell kan bidra med kunskap för att besluta kring om riskerna med temperaturökning hos foster till följd av ultraljud behöver studeras vidare. Resultaten av framtagen modellering visade på en mycket liten uppvärmningseffekt. Slutsatsen drogs att om modellen i 3D ska kunna göra trovärdiga beräkningar i programmet krävs en mer avancerad dator än vanligt, med betydligt större minneskapacitet. Vidare utveckling av modell i COMSOL bör göras i 2D, alternativt med en mer avancerad dator, för att få tillförlitliga resultat. / A fetus does not have the same blood perfusion and resistance to changes in its environment as an adult and small changes in temperature can cause irreversible damage for example to the fetal brain. Ultrasound examinations are proven to cause some heat gain but there are uncertainties regarding the amount of heat gain during a longer time of ultrasound exposure. The purpose of this study was to analyse the heat development during obstetric ultrasound by designing a 3D-model in the software environment COMSOL Multiphysics version 6.0. A model could contribute to knowledge in making an informed decision whether the risks of heating in a fetus because of ultrasound are necessary to study further. The results of the developed model showed a very small heating effect. The conclusion was made that if the model in 3D is to be able to make correct calculations in the programme it is required to use a more advanced computer than usual, with significantly greater memory capacity. Further development of a model in COMSOL should be made in 2D, or with a more advanced computer, to get reliable results.

Some protein gels are products of the dairy industry and some are used as pH-sensitive gels for the controlled delivery of biologically active substances. To understand the dynamics of drug delivery it is very important to establish a mathematical model of protein gel swelling. This required the identification and integration of theory and equations from a wide range of topics. The aim of this research was to develop a mathematical model of transport in polyelectrolyte gels (using the example of β-lactoglobulin protein gels). A complete mathematical model of protein gel swelling was established. The swelling process of protein gels in this thesis involved multicomponent diffusion, chemical ionisation and mechanical deformation. Diffusion of electrolyte solutions through protein gels was modelled using the generalised Maxwell-Stefan (GMS) equation. The swelling pressure as a driving force in the GMS equation was described by rubber elasticity theory. Thermodynamic factors including the charged protein effect were considered in the GMS equation. The model included pH as a variable so it could be applied to both acidic and alkaline cases. The model yielded a set of partial differential equations with algebraic equations for which COMSOL was selected as the simulation software. Although it was found that COMSOL could not always solve the model equations, numerical solutions were obtained for several cases. The model predicted that the equilibrium swelling degree of the gel decreased with high concentration of salts in the bulk solution. The model also predicted that the non-ideal effects were not always small and they depended on the activity coefficients of the species. Satisfactory solutions could not be obtained for all cases using commercial software such as COMSOL Multiphysics. It was shown that COMSOL did not conserve mass but conservativeness was critical in this application because pH and hence the net protein charge is very sensitive to the mass of hydrogen present. In the future, research should be carried out to improve the pressure model in the GMS equation. Theoretical research on Manning condensation theory should be done to modify Manning’s model for more robust prediction of activities of water and ions with protein, and experiments should be done to validate the performance of the modified Manning model. Efforts should be made to write the programming code for a finite volume method to solve the system in three dimensions.

Ocular diseases such as glaucoma, age-related macular degeneration (AMD), diabetic retinopathy, and retinitis pigmentosa require drug management in order to prevent blindness and affecting millions of adults in US and worldwide. There is an increasing need to develop devices for drug delivery to address ocular diseases. This research focused on an implantable ocular drug delivery device design, simulation and experiments with design requirements including constant diffusion rate, extended period of time operation, the smallest possible volume of device and reservoir. The drug delivery device concept uses micro-/nano-channels module embedded between top and bottom covers with a drug reservoir. Several microchannel design configurations were developed and simulated using commercial finite element software (ANSYS and COMSOL), with a goal to investigate how the microchannel dimensions affect the diffusion characteristics. In addition to design simulations, various microchannel configurations were fabricated on silicon wafer using photolithography techniques as well as 3D printing. Also, the top and bottom covers of the device were fabricated from PDMS through replica molding techniques. These fabricated microchannel design configurations along with top and bottom covers were all integrated into the device. Both single straight microchannels (nine different sizes of width and depth) as well as four micro-channel configurations were tested using citric acid (pH changes) and Brimonidine drug (concentration changes using the Ultra-Violet Visible Spectrophotometer) for their diffusion characteristics. Experiments were conducted to obtain the diffusion rates through various single micro-channels as well as micro-channel configurations using the change in pH neutral solution to verify the functionality and normalized diffusion rate of microchannels and configurations. The results of experimental data of diffusion rate were compared with those obtained from simulations, and a good agreement was found. The results showed the diffusion rate and the optimum size of microchannel in conjunction with the required drug release time. The results obtained also indicate that even though specific diffusion rates can be obtained but delivering the drug with constant amount needs a mechanism at the device outlet with some control mechanism. For future studies, this result may be used as a baseline for developing a microfabricated device that allows for accurate drug diffusion in many drug delivery applications.

The ability to convert electrical energy into mechanical motion is of significant interest in many energy conversion technologies. For more than a decade Ionic polymer-metal composite (IPMC) as an electroactive smart polymer material has been extensively studied and has shown great potential as soft robotic actuators, artificial muscles and dynamic sensors in the micro-to-macro size range. IPMC consists of an ion exchange polymer membrane sandwiched between two noble metal electrodes on either side of the membrane. Under applied potential, the IPMC actuator results in bending deformation because of ion migration and redistribution across its surface due to the imposed voltage. Nafion are highly porous polymer materials which have been extensively studied as the ion exchange membrane in IPMC. Nafion has also been mixed with carbon nanotubes, graphene, and metallic nanoparticles to improve actuation and bending characteristics of electro-mechanical actuators. For the first time, liquid phase exfoliated Transition Metal Dichalcogenides (TMDs)-Nafion nanocomposite based electro-mechanical actuators has been studied and demonstrate the improvement in the electromechanical actuation performance. In this thesis, we create a 2D model of the TMD-Nafion based electromechanical actuator in COMSOL Multi-physics software. The behavior of the model is examined at different electric potentials, frequencies, and actuation lengths. The simulation results were compared with the experimental data for validation of the model. The data showed improvement in the actuation for TMD-Nafion actuator when compared with pure Nafion actuator. The improvement in the actuation was due to the increase in diffusivity of the TMD-Nafion actuator in comparison with pure Nafion actuator. This increase in the diffusivity as seen in the model is because of the new proton conducting pathways being established with the addition of TMDs. The model also shows an increase in the stress and strain values with the incorporation of TMDs. With the same length of the actuator we were able to obtain more stress and strain with the addition of TMDs. This helps in improving the performance of the actuator as it would be able to handle more stress cycles which also increases the life of the actuator.

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.

The American Society of Civil Engineers’ (ASCE’s) “2013 Report Card for America’s Infrastructure” estimated that “32% of America’s major roads are in poor or mediocre condition.” An estimated $100 billion dollars are needed to maintain that condition, and an additional $79 billion is needed to improve the quality of American roadways to an acceptable level. In many regions around the US, the service lives of concrete pavements are limited by the damage caused by freezing and thawing of pore solution inside the pavements. Alkali-activated slags (AAS) are produced from ground granulated blast furnace slag (GGBFS), a byproduct of iron production, and exhibit cementitious properties. AAS concretes have been shown to have improved corrosion and freeze/thaw resistance compared to traditional cementbased concretes. A Guarded Longitudinal Comparative Calorimeter (GLCC) was used to determine when the freezing and thawing of internal water occurs in three AAS mortars using solutions of NaOH, Na2CO3, or waterglass compared to a control Ordinary Portland Cement (OPC) mortar. AAS mortars using NaOH and Na2CO3 showed comparable thermal properties to the OPC mortar using the GLCC, and the AAS mortar using waterglass was shown to have higher heat capacity compared to the other AAS mixes. The compressive strengths varied by the alkaline solution used, with AAS with Na2CO3 showing inferior compressive strength to OPC, AAS with NaOH showing similar compressive strength to OPC, and AAS with waterglass showing superior compressive strength to OPC, but poor workability. A computer model of the GLCC testing procedure was created and showed good agreement with the experimental data. The GLCC model can be modified to approximate the results of the GLCC using a wider range of materials and internal solutions, like PCMs.

Tese de mestrado integrado. Engenharia Eletrotécnia e de Computadores. Faculdade de Engenharia. Universidade do Porto. 2013

A microfluidic device was created for single-cell capture and analysis using polydimethylsiloxane (PDMS) channels and a glass substrate to develop a microfluidic single-cell impedance sensor for cell diagnostics. The device was fabricated using photolithography to create a master mold which in turn will use soft lithography to create the PDMS components for constant device production. The commercial software, COMSOLTM Multiphysics, was used to quantify the fluid dynamics in shallow micro-channels. The device will be able to capture a cell and sequester it long enough to enable measurement of the impedance spectra that can characterize cell. The proposed device will be designed to capture a single cell and permit back-flow to flush out excess cells in the chamber. The device will be designed to use syringe pumps and the syringe-controlled channel will also be used to capture and release the cell to ensure cell control and device reusability. We hypothesize that these characteristics along with other proposed design factors will result in a unique microfluidic cell-capture device that will enable single-cell impedance sensing and characterization.

The computational ability to accurately predict the dynamic behavior of a nuclear reactor core in response to reactivity-induced perturbations is an important subject in the field of reactor physics. Space-time and point kinetics methodologies were developed for the purpose of studying the transient-induced behavior of the Oak Ridge National Laboratory (ORNL) High Flux Isotope Reactor’s (HFIR) compact core. The space-time simulations employed the three-group neutron diffusion equations, which were solved via the COMSOL partial differential equation coefficient application mode. The point kinetics equations were solved with the PARET code and the COMSOL ordinary differential equation application mode. The basic nuclear data were generated by the NEWT and MCNP5 codes and transients initiated by control cylinder and hydraulic tube rabbit ejections were studied. The space-time models developed in this research only consider the neutronics aspect of reactor kinetics, and therefore, do not include fluid flow, heat transfer, or reactivity feedback. The research presented in this dissertation is the first step towards creating a comprehensive multiphysics methodology for studying the dynamic behavior of the HFIR core during reactivity-induced perturbations. The results of this study show that point kinetics is adequate for small perturbations in which the power distribution is assumed to be time-independent, but space-time methods must be utilized to determine localized effects. En route to developing the kinetics methodologies, validation studies and methodology updates were performed to verify the exercise of major neutronic analysis tools at the HFIR. A complex MCNP5 model of HFIR was validated against critical experiment power distribution and effective multiplication factor data. The ALEPH and VESTA depletion tools were validated against post-irradiation uranium isotopic mass spectrographic data for three unique full power cycles. A TRITON model was developed and used to calculate the buildup and reactivity worth of helium-3 in the beryllium reflector, determine whether discharged beryllium reflectors are at transuranic waste limits for disposal purposes, determine whether discharged beryllium reflectors can be reclassified from hazard category 1 waste to category 2 or 3 for transportation and storage purposes, and to calculate the curium target rod nuclide inventory following irradiation in the flux trap.