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The thermal design constraint of power electronic converters under the specific power loss and heat sink is mainly determined by the maximum permissible junction temperature of the power devices. As the power density and switching frequency increase, transient electro-thermal models become more and more important for the thermal management system design of the power electronic converters. In traction inverters, the junction temperature has huge variation because the fundamental frequency and phase currents vary significantly during the load cycles. Thus, the junction temperature estimation becomes extremely important for the reliability of traction inverters. In this thesis, the transient electro-thermal analysis of a traction inverter considering the inter-dependency of the power losses and junction temperature in an iterative process is implemented. Considering the impact of circuit stray parameters on the switching loss, the temperature dependent power loss model is built based on the datasheet values and the measured switching losses. A state-of-the-art thermal model of the entire inverter including the power modules and the heat sink is developed considering the thermal coupling effects of multiple power devices. By using transient thermal simulation, the linearity of the heat transfer process of the entire traction inverter is verified. The impact of the material thermal properties on the thermal impedance is also presented. In addition, the accuracy of the combination of the thermal subsystem models is verified with simulation. The developed transient electro-thermal model is then used to simulate the junction temperature profiles of the inverter under different operating conditions. Finally, the developed model is experimentally verified. By considering the thermal impedance of the thermal grease layer, the simulation results match with the experimental results very well. The proposed electro-thermal model can provide important information for the thermal management system design, package optimization, long-term reliability analysis, and maximum rating characterization of the traction inverters. / Thesis / Master of Applied Science (MASc)

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Propulsive capabilities on a CubeSat are the next step in advancement in the Aerospace Industry. This is no longer a quest that is being sought by just university programs, but a challenge that is being taken on by all of the industry due to the low-cost missions that can be accomplished. At this time, all of the proposed micro-thruster systems still require some form of development or testing before being flight-ready. Stellar Exploration, Inc. is developing a monopropellant micropropulsion system designed specifically for CubeSat application. The addition of a thruster to a CubeSat would expand the possibilities of what CubeSat missions are capable of achieving. The development of these miniature systems comes with many challenges. One of the largest challenges that a hot thruster faces is the ability to complete burns for the specified mission without transferring excessive heat into the propulsion tank. Due to the close proximity of the thruster to the tank, thermal standoff options are necessary to help alleviate the heat going through the system, especially while in a thermally extreme environment. This thesis examines the heat transfer that occurs within a CubeSat with an operating hydrazine monopropellant thruster. Thermal analysis of the system revealed that having a solid stainless steel barrier between the thruster and tank led to increasing temperatures greater than 400K in the propellant tank while in an environment exposed to the sun. This creates a large amount of risk for the CubeSat and its mission. The use of a thermal insulating material or a hollow barrier for the standoff decreased the risk of using this system. This creates a standoff where the heat of the propellant reaction does not reach the propellant in the tank. Therefore, the maximum temperature that the tank reaches is equivalent to the temperature of the external environment while in extreme conditions. These results create the confidence that the thermal standoffs will function as intended to protect the spacecraft and its payload during flight.

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Standard methods for fire resistance testing require large-scale assemblies and are typically conducted on specialized furnaces at considerable cost. This research focused on developing a scaling methodology for a reduced-scale fire resistance test that reduces the size of the test article while maintaining the same thermal and structural response exhibited in the large-scale test. The developed scaling methodology incorporates uniform geometric scaling, Fourier number time scaling, and furnace boundary condition matching. The scaling laws were experimentally validated with fire exposure tests on gypsum wallboard samples at three scales (full-scale, 1/2-scale, and 1/6-scale). Next, these scaling laws were demonstrated for wood with combined thermo-structural loading. Dimensional lumber boards at ½-scale and ¼-scale were subjected to combined bending and thermal loading. Samples were placed in static three-point bending with the loading scaled to have structural similitude, while simultaneously, the bottom surface was exposed to a scaled fire exposure. Analytical modeling of wood pyrolysis demonstrated that, due to char kinetics as the heating rate is increased in the tests, equivalently less char is formed in the reduced-scale tests. Therefore, we developed a char timescale correction factor, calculated from both model predictions and measured charring rates, which modified the previous Fourier number time scaling laws. Finally, we investigated the effect of multi-orientation materials with a similar set of combined thermo-structural three-point bending tests on plywood samples. The stacking sequence of laminated wood significantly impacts the composite mechanical behavior of the material, especially when scaling down thermo-mechanical tests on plywood. A consequence of the different stacking sequences is that the data from the reduced-scale test cannot be directly scaled to predict the behavior of the larger-scale tests. Thus, modeling becomes essential to extrapolating the data from the reduced-scale test to predict the behavior of the larger-scale test. Reduced cross-sectional area models incorporating classical lamination theory were used to predict the mechanical response of the composite samples as the char front increased. / Doctor of Philosophy / How do we know that a structure will be safe during a fire? The response of structures to fire is typically evaluated using large-scale tests with combined thermo-structural loading: one side of the test sample is exposed to a furnace at standard gas temperatures, while at the same time the sample is loaded with a structural load. Fire resistance testing is essential to evaluating if building components can maintain structural integrity and allow people to egress a building safely during a fire. Standard methods for fire resistance testing require large-scale test samples and are typically conducted on specialized furnaces at national testing facilities at considerable cost. In order to support research and development efforts to design new fire-resistant structures, reduced-scale tests are more desirable because they are cost-effective. However, no reduced-scale test exists to evaluate fire resistance. This research focused on developing a methodology for reducing the size of a test with combined thermo-structural loading. The goal is to have a reduced-scale test that provides insight into the thermal and structural behavior of a similar sample in the large-scale test. The test scaling laws were demonstrated with both experiments and modeling. We developed a small-scale furnace setup to conduct combined thermo-structural tests on samples of different scales. To investigate material type, we tested samples made from gypsum wallboard, dimensional lumber, and plywood. This work will ultimately allow manufacturers to replace costly standard fire resistance tests with reduced-scale versions of these tests during the material screening phase.

This dissertation explores the properties of sulfonated poly(arylene ether sulfone)s for desalination membrane applications. A multi-scale approach is used to understand the relationships between the chemical structure of the polymer, the equilibrium water content, and the bulk properties. The polysulfones investigated here are aromatic polymers with relatively high ion contenremain in the glassy state at room temperature even when fully hydrated. In order to better understand the effects of water on these ionic polysulfones molecular dynamics (MD) simulation is used to investigate ion aggregation and hydration at the atomic scale. MD simulations show that the sulfonate and sodium ions are not simply paired. Instead, they form an ionic network. The molecular nature of melting water within sulfonated polysulfones is also examined by combining differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and MD simulation. Experimental evidence shows that at high ion contents, the spacing between the ionic groups impacts the amount of melting water present in the polymer. We conclude that the amount of melting water in the polymer is more closely related to geometric clustering effects than electrostatic effects. Finally, molecular-scale insight is used to understand the trends in hydrated tensile modulus and hydrated glass transition (Tg) temperatures in sulfonated polysulfones. Polymers with a more rigid backbone show different trends compared to those with a more flexible backbone. The modulus and Tg trends for the more flexible backbone are qualitatively consistent with the increase in intra-chain ionic associations (loops) predicted by the sticky Rouse model. / Doctor of Philosophy / This dissertation investigates new materials that could be used to make better membranes that can remove ions (salt) from water. Existing materials are too soft or too brittle when they are fully immersed in water. Consequently, they must be combined with more durable materials in order to make useful membranes. We would like to design durable ionic polymers (large chain-like molecules with ions attached) that interact with water and other ions in a very specific way in order to make membranes that can remove salt efficiently. The goal of this research is to create tools that can describe how changes to the chemical structure of the polymer impact how the polymer, water, and ions interact with each other so that we can improve membrane properties. We find that the ions on the polymer chain interact with each other to form threads, which can form a network inside of the polymer under the right conditions. When the ions are located far apart on the polymer chain, the ion threads link one polymer chain to another polymer chain. These ionic links strengthen the polymer network. However, when the ions are located closer together on the polymer chain, the chain starts to form loops between neighboring ions. As the number of loops increases, the polymer quickly becomes softer and more gel-like. We also find that water molecules are distributed within the polymer and are not always located next to the ions. When there is more water inside the polymer, the water molecules begin to group together to form clusters. At low temperatures, water molecules that have fewer than four neighboring molecules cannot freeze. However, water in a cluster of five molecules or more can freeze into an ice crystal. The insights gained from this research will help the community to design better polymers for desalination membrane applications.

The heats of immersion in n-alcohols of zeolites NaY, 5A and ZSM-5 and the kinetics of the immersion process have been determined using a Calvet MS-70 microcalorimeter. The specific heat of immersion decreased non-linearly as a function of chain length of alcohol for NaY and 5A. In contrast, the specific heat of immersion passed through a maximum at n-pentanol for ZSM-S. The specific immersion time as a function of chain length of alcohol showed an apparent linear increase in the order 5A > ZSM-S > NaY. NaY showed almost no increase. The effects of sample evacuation temperature and butyl alcohol isomer bulk on the heats of immersion were also investigated. These results were interpreted in terms of molecular accessibility of the wetting liquid into the pores of the zeolites and in terms of the Si/Al ratio of the zeolites. The overall kinetics of immersion appears to be first order. / Master of Science

Yes / Hydrochlorothiazide (HCT) is a diuretic BCS class IV drug with poor aqueous solubility and low permeability leading to poor oral absorption. The present work explores the cocrystallization technique to enhance the aqueous solubility of HCT. Three new cocrystals of HCT with water soluble coformers phenazine (PHEN), 4-dimethylaminopyridine (DMAP) and picolinamide (PICA) were prepared successfully by solution crystallization method and characterized by single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), fourier transform –infraredspectroscopy (FT-IR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Structural characterization revealed that the cocrystals with PHEN, DMAP and PICA exists in P21/n, P21/c and P21/n space groups, respectively. The improved solubility of HCT-DMAP (4 fold) and HCT-PHEN (1.4 fold) cocrystals whereas decreased solubility of HCT-PICA (0.5 fold) as compared to the free drug were determined after 4 h in phosphate buffer, pH 7.4, at 25 °C by using shaking flask method. HCT-DMAP showed a significant increase in solubility than all previously reported cocrystals of HCT suggest the role of a coformer. The study demonstrates that the selection of coformer could have pronounced impact on the physicochemical properties of HCT and cocrystallization can be a promising approach to improve aqueous solubility of drugs.

This dissertation aims to advance the current state of use of silicon atomic force microscope (AFM) cantilevers with integrated heaters. To this end, the research consists of two primary thrusts - demonstrating new applications for the cantilevers, and advancing the current state of understanding of their thermal and mechanical behavior to enable further applications. Among new applications, two are described. In the first application, the cantilevers are used for nanoscale material deposition, using heat to modulate the delivery of material from the nanoscale tip. In the second application, the cantilever performs thermal analysis with nanoscale spatial resolution, enabling thermal characterization of near surface and composite interphase regions that cannot be measured with bulk analysis techniques. The second thrust of the research seeks to address fundamental questions concerning the precision use of heated cantilevers. Efforts to this end include characterizing the mechanical, electrical, and thermal behavior of the cantilevers, and optimizing calibration methodology. A technique is developed for calibrating the cantilever spring constant while operating at elevated temperature. Finally, an analytical model is developed for the heat flow in the cantilever tip and relevant dimensionless numbers that govern the relative importance of the various components of the thermal environment are identified. The dimensionless numbers permit exploration of the sensitivity of the tip-substrate interface temperature to the environmental conditions.