Utvecklad för att bibehålla termisk komfort och minska exergianvändningen, Free Heat Exchange Window [FHEW] är en fönsterdesign som är tänkt att ersätta konventionella värmesystem i bostäder och kontorsbyggnader. Baserat på dubbelspaltkonceptet kommer fönstret utgöra en värmekälla under kalla vinterdagar och en värmesänka under varmare sommardagar. För att värdera huruvida teknologin kan bibehålla tillräcklig termisk komfort och avgöra dess optimala parameterkonfiguration utifrån byggnadens effektbehov skapas två olika modeller. En grundar sig på en datorsimulering av en lägenhet i COMSOL Multiphysics och den andra är en analytisk metod för beräkning av energibalanser i MATLAB. Resultaten från båda modellerna påvisade att hög inströmningstemperatur och låg inströmningshastighet är att föredra för minimering av effektbehovet. Å andra sidan ger en låg inströmnings temperatur och hög strömningshastighet en upphov till högre termisk komfort. Valet av den isolerande gasen som används i mittersta gas-spalten bedöms ha låg inverkan på prestandan, särskilt för höga strömningshastigheter. En alternativ modell med den isolerande gas-spalten omplacerad närmast utomhuset skulle kunna framföra bättre användning av den isolerande gas-spaltens funktion. Datorsimuleringen jämförs avslutningsvis med en ekvivalent lägenhetsmodell med enkelspaltiga fönster och element som värmekälla. Denna modell kräver lägre effekt, men är samtidigt mindre flexibel och inducerar en lägre termisk komfort. Datorsimuleringen rekommenderas på grund av dess antaganden och i vissa fall orimliga resultat endast som jämförelse med andra liknande modellen, snarare än verkliga data. / Developed to maintain thermal comfort and reduce exergy usage, Free Heat Exchange Window [FHEW] is a modern window design aimed to replace current heat systems in homes and office buildings. Based on the double slot concept, the window can be used as a heat source during cold winter days and heat sink during warmer summer days. To evaluate if the technology is viable to maintain thermal comfort and determine its optimal parameters with respect to energy efficiency, two different models will be made. One is based on computer simulations in COMSOL Multiphysics and one is based on analytical equations in MATLAB. The results from both models proved that a higher inflow temperature and a lower flow rate was prefered to minimize power demand. On the contrary, a lower inflow temperature and a higher flow rate is preferred to achieve the best thermal comfort. The differences between the choice of insulation gas gave unnoticeable deviation for indoor heat exchange for high flow rates. An alternative window model could reposition the insulation gas-gap to be between the whole system and the outdoors environment, instead of having it installed between the flowing air-gaps, for better use of the low thermal conductivity. The computer simulation is finally compared with an equivalent model using regular single slot windows and radiators as heaters. This model requires less energy but is less flexible and induces a less desirable thermal comfort. The computer simulation is due to its assumptions and in some instances implausible results only recommended to be compared to similar models, rather than real data.

Geothermal energy has become a focal point of the renewable energy revolution. Both shallow and deep types of geothermal energy have the potential to offset carbon emissions, reduce energy costs, and stimulate the economy. Before widespread geothermal exploration and exploitation can occur, both shallow and deep technologies require improvement by theoretical and experimental investigations. This thesis investigated one aspect of both shallow and deep geothermal energy technologies. First, a group of shallow geothermal energy piles was modeled numerically. The model was constructed, calibrated, and validated using available data collected from full-scale in-situ experimental energy piles. Following calibration, the model was parameterized to demonstrate the impact of construction specifications on energy pile performance and cross-sectional thermal stress distribution. The model confirmed the role of evenly spaced heat exchangers in optimal pile performance. Second, experimental methods were used to demonstrate the evolution of a fractured granite permeability as a function of mineral dissolution. Steady-state flow-through experiments were performed on artificially fractured granite cores constrained by 5 MPa pore pressure, 30 MPa confining pressure, and a 120°C temperature. Upstream pore pressures, effluent mineral concentrations, and X-Ray tomography confirmed the hypothesis that fracture asperities dissolve during the flow through experiment, resulting in fracture closure.

Buildings both commercial and residential are the largest consumers of electricity. Integrating Photovoltaic technology in building architecture or Building Integrated Photovoltaics (BIPV) provides an effective means for meeting this huge energy demands and provides an energy hub at the place of its immediate requirement. However, this technology is challenged with problems like low efficiency and high cost. An effective way of improving the solar cell efficiency and reducing the cost of photovoltaic systems is either by reducing solar cell manufacturing cost or illuminating the solar cells with a higher light intensity than is naturally available by the use of optical concentrators which is also known as Concentrating Photovoltaic (CPV) technology. Integrating this technology in the architecture is referred as Building integrated Concentrating Photovoltaics (BICPV). This thesis presents a detailed performance analysis of different designs used as BICPV systems and proposes further advancements necessary for improving the system design and minimizing losses. The systems under study include a Dielectric Asymmetric Compound Parabolic Concentrator (DiACPC) designed for 2.8×, a three-dimensional Cross compound parabolic concentrator (3DCCPC) designed for 3.6× and a Square Elliptical Hyperbolic (SEH) concentrator designed for 6×. A detailed analysis procedure is presented showcasing the optical, electrical, thermal and overall analysis of these systems. A particular issue for CPV technology is the non-uniformity of the incident flux which tends to cause hot spots, current mismatch and reduce the overall efficiency of the system. Emphasis is placed on modelling the effects of non-uniformity while evaluating the performance of these systems. The optical analysis of the concentrators is carried out using ray tracing and finite element methods are employed to determine electrical and thermal performance of the system. Based on the optical analysis, the outgoing flux from the concentrators is predicted for different incident angles for each of the concentrators. A finite element model for the solar cell was developed to evaluate its electrical performance using the outputs obtained from the optical analysis. The model can also be applied for the optimization of the front grid pattern of Si Solar cells. The model is further coupled within the thermal analysis of the system, where the temperature of the solar cell is predicted under operating conditions and used to evaluate the overall performance under steady state conditions. During the analysis of the DiACPC it was found that the maximum cell temperature reached was 349.5 K under an incident solar radiation of 1000 W/m2. Results from the study carried on the 3DCCPC showed that a maximum cell temperature of 332 K is reached under normal incidence, this tends to bring down the overall power production by 14.6%. In the case of the SEH based system a maximum temperature of 319 K was observed on the solar cell surface under normal incidence. An average drop of 11.7% was found making the effective power ratio of the system 3.4. The non-uniformity introduced due to the concentrator profile causes hotspots in the BICPV system. The non-uniformity was found to reduce the efficiency of the solar cell in the range of 0.5-1 % in all the three studies. The overall performance can be improved by addressing losses occurring within different components of the system. It was found that optical losses occurred at the interface region formed due to the encapsulant spillage along the edges of the concentrator. Using a reflective film along the edge of the concentrating element was found to improve the optical efficiency of the system. Case studies highlighting the improvement are presented. A reflective film was attached along the interface region of the concentrator and the encapsulant. In the case of a DiACPC, an increase of 6% could be seen in the overall power production. Similar case study was performed for a 3DCCPC and a maximum of 6.7% was seen in the power output. To further improve the system performance a new design incorporating conjugate reflective-refractive device was evaluated. The device benefits from high optical efficiency due to the reflection and greater acceptance angle due to refraction. Finally, recommendations are made for development of a new generation of designs to be used in BiCPV applications. Efforts are made towards improving the overall performance and reducing the non-uniformity of the concentrated illumination.

The hot box technique is an experimental method to achieve the U-value of elements in stationary conditions; however, it is not always possible to work in stationary conditions in real world. This thesis consisted of evaluating the heat transfer of a window of a historical building with a unique hot box set-up. The window had a low emissivity plastic film to improve thermal efficiency, and the hot box was unique because the outside temperature could not be controlled. The applicability of the hot box technique to dynamic conditions was assessed using COMSOL Multiphysics 5.3. COMSOL Multiphysics is a finite element method solver software with a heat transfer module. Two heat transfer simulations were conducted in 2D based on the indoor and outdoor temperature when the hot box was in operation. First, a stationary study was carried when the outdoor temperature remained stable for 1 day. Then, the study was extended to a transient study to analyze in detail the effect of the external temperature fluctuations for 5 days. The results indicate that a cautious approach should be taken when applying the hot box technique under transient conditions, but that stationary conditions could not be achieved during one day. Nevertheless, the reliability of the simulation solution could have improved more.

The presented project explores the optical properties of magnetoplasmonic Au/Ni core-shell structures. The work aims at controlling dimensions and parameters in order to influence and analyze the optical properties of the nanostructures. The softwares utilized for the simulations were COMSOL Multiphysics 5.1 and MATLAB. Experimental results were acquired from labs done at Ångströms laboratory. From the research based study where the gold to nickel ratio was influenced, it was observed that the transmissions for the nanostructures at the differing wavelengths produced transmissions of similar bearings. Modes for certain wavelengths were found in correspondence with the transmissions and could potentially render explanations for influence on the optical properties of the nanostructures. Conclusively, it can be stated that the optical properties of the nanostructures could be influenced and controlled by varying the dimensions and properties of the said structure. Differing dimensions corresponded to noteworthy changes in the cross sections, the transmissions as well as the mode formations.

Syftet med detta arbete är att simulera ett värmesystem i COMSOL Multiphysics, Pipe Flow Module, Non-Isothermal Pipe Flow som innehåller ekvationer och randvillkor för att modellera inkompressibel strömning och värmeöverföring i rör. Data om processen och dess komponenter har samlats in från industrin där arbetet är utfört och i vissa fall modifierats för att bättre beskrivas i programmet. Utifrån insamlad data har en modell byggts upp och två simuleringar har gjorts. En stationär för starten av systemet, den har sedan legat till grund för en dynamisk som simulerar förloppet från start till normaldrift. Tiden det tar för det aktuella fallet att nå drifttemperatur är 16 timmar. En felströmning upptäcktes samt att en av pumparna inte kommer att klara en start från 20 °C.

This thesis aims to develop an understanding about swelling and disintegration of multi-component polymeric structures such as pharmaceutical tablets. The thesis presents a model for the diffusion-driven water uptake, swelling deformation and subsequent disintegration of polymer matrix drug-delivery devices. Hygroscopic swelling occurs when a dry tablet enters a humid environment and absorbs water molecules. The modification of tablet structures changes the release profile of the drug in the desired manner. The previous research mostly focused on transport problems related to drug release. This study contributes an understanding of the mechanical behaviour of hydrophilic polymer release matrix materials which are treated as continuum. Modelling of the swelling problem involves concurrent large deformation of the polymer network and diffusion of the solvent through the network. A coupled diffusion-deformation model was created to study the relation between both physics. The coupled diffusion-deformation model was utilised to consider disintegration of polymer matrix through the inclusion of swelling agents. Two cases were presented to illustrate the application of the model: swelling-controlled and immediate-release drug delivery systems. This study used COMSOL Multiphysics®, a finite element commercial software to perform the analysis. Various physical modules: structural mechanics, chemical transport and mathematics were combined for solving coupled diffusion-deformation-damage boundary value problems. The numerical results were validated using existing experimental data from the literature. The model parameters were varied to investigate their sensitivity to the solution. Higher solvent concentration gradient in the matrix produced higher swelling strain, thus increased local stress. Disintegrability was measured by the time taken for the maximum principal stress to reach a given failure. Higher coefficient of water diffusion allows higher amount of water ingression into the matrix. Higher coefficient of hygroscopic swelling generates higher local swelling strain. This study facilitates in understanding the complex phenomena in the application of drug release formulation.

<p>Complex surface structures in nature often have remarkable optical properties. By understanding the origin of these properties, such structures may be utilized in metamaterials, giving possibilities to create materials with new specific optical properties. To simplify the optical analysis of these naturally developed surface structures there is a need to assist data analysis and analytical calculations with numerical calculations.</p><p>In this work an application tool for numerical calculations of optical properties of surface structures, such as reflectances and ellipsometric angles, has been developed based on finite element methods (FEM). The data obtained from the application tool has been verified by comparison to analytical expressions in a thorough way, starting with reflection from the simplest of interfaces stepwise increasing the complexity of the surfaces.</p><p>The application tool were developed within the electromagnetic module of Comsol Multiphysics and used the script language to perform post-process calculations on the obtained electromagnetic fields. The data obtained from this application tool are given in such way that easily allows for comparison with data received from spectroscopic ellipsometry measurements.</p>

All power electronics consist of solid state devices that generate heat. Managing the temperature of these devices is critical to their performance and reliability. Traditional methods involving liquid-cooling systems are expensive and require additional equipment for operation. Air-cooling systems are less expensive but are typically less effective at cooling the electronic devices. The cooling system that is used depends on the specific application. Until recently, silicon based devices have been used for the solid-state devices in power electronics. Newly developed silicon-carbide based wide band gap devices operate at maximum temperatures higher than traditional silicon devices. Due to the permissible increase in operating temperatures, it has been proposed to develop an air-cooling system for an inverter consisting of silicon carbide devices. This thesis presents recent research efforts to develop the proposed air-cooling system. The thermal performance of the each design iteration was determined by numerical simulations via the finite element method in both steady state and transient mode using COMSOL Multi-physics software version 3.5a. For all simulations presented in this thesis, the heat dissipated in the MOSFETS and diodes are specified as functions of current, voltage, switching frequency, and junction temperature. For both the steady state and transient simulations, the junction temperature was determined iteratively. Additionally in the transient simulations, the current distribution is a function of time and was deduced from the EPA US06 drive cycle. After several design iterations, a thermally feasible design has been reached. This design is presented in detail in this thesis. Under transient simulations of the final design, the maximum junction temperatures were determined to be below 146 ºC for air flow rates of 30 and 60 CFM, which is substantially lower than the 250 ºC maximum allowable junction temperature of Si-C devices. However for steady state simulations, junction temperatures were found to be much higher than the transient simulations. It was determined that a minimum flow rate of 50 CFM is required to meet the temperature requirements of the Si-C devices under steady state operating conditions. The power density of this air-cooled final design is 11.75 kW/L, and it is competitive with liquid-cooled systems.

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