Indiana University-Purdue University Indianapolis (IUPUI) / Proton exchange membrane fuel cells (PEMFC’s) offer an attractive alternative energy resource over traditional fossil fuels. The advantages such as high power density, relatively quick start-up, rapid response to varying loads and low operating temperatures make it a preferred technology option compared to other alternative energy sources. Nafion® by DuPont plays an integral role in the success of PEM fuel cells due to its high proton conductivity and high chemical and thermal stability. This research project aims to study the effect of mechanical and hygro-thermal stresses on the mechanical performance and proton conductivity of the membrane by subjecting it to realistic operating conditions such as those encountered in an automobile. In this thesis, the time-dependent behavior of the membrane has been modeled using a Prony series and the change in the conductivity due to mechanical loading was experimentally measured. The modeling of both electrochemical and mechanical properties can further be used in studying the degradation properties of the membrane and should guide the development of better membrane materials. Visco-elastic stress relaxation theory has been used in modeling the time-dependent behavior of the specimen. The EIS spectrum has been analyzed using a non-linear least squares method and an equivalent circuit method was also used to fit the spectra. This project was conducted in three phases. In the first phase a novel test facility was built to perform the experiments. A conductivity measurement test cell that measured the proton conductivity of a membrane was modeled and manufactured. The second phase included the design of different experiments that helped in modeling the interdependence of electrochemical and mechanical properties of the membrane. In this process, three series of experiments that tested the electrochemical and mechanical properties of the specimen were conducted. The membrane was held at constant strain and the through plane impedance was measured at different times during the test, specifically before and after stretching at ambient and varying environmental conditions. The membrane was also subjected to both mechanical and hygro-thermal loading conditions during the test. In the third phase, time-dependant mathematical model for the changes in the material properties were developed. The experimental apparatus thus tested the mechanical and electrochemical properties of the membrane simultaneously while the specimen was being subjected to constant mechanical and varying hygro-thermal conditions. Since the testing method is a novel procedure, the reliability and repeatability of the experimental facility has been verified before conducting the experiments. The experimental apparatus can further be used to test the membrane at varying strain rates and different hygro-thermal loading conditions in a consistent manner. The model developed can be used to analyze the degradation behavior of membrane and also to build better fabrication methods and membrane materials in future.

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京都大学 / 新制・課程博士 / 博士(工学) / 甲第24587号 / 工博第5093号 / 新制||工||1975(附属図書館) / 京都大学大学院工学研究科合成・生物化学専攻 / (主査)教授 古川 修平, 教授 生越 友樹, 准教授 堀毛 悟史, 教授 松田 建児 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

The aim in this project is to find a design space for a condenser type bushing given by HitachiEnergy. The design space shows which combinations of air and silicon-rubber (SiR) conductivity remain under a specified electric field strength value. This range of value represents how humidity affects air and SiR conductivity. Hitachi energy provided two different models, one with foils and one without foils. The design space for these models consists of how humidity affects the conductivity of both air and SiR. The values of air conductivity are gathered from different studies with different air humidity and external effects that affect the conductivity such as high aerosol concentration and high radon concentration. The values used for simulation will be approximated because of the different external effects and will range from 10^(−12)–10^(−13) S/m for humid conditions, 10^(−14) S/m for average humidity conditions and 10^(−15)–10^(−16) S/m for dry conditions. The range of SiR conductivity and the correlated weather conditions was given by Hitachi Energy and range from 10^(−11)–10^(−15) S/m where 10^(−11) S/m is for humid conditions, 10^(−12)–10^(−14) S/m for average humidity conditions and 10^(−15) S/m for dry conditions. For each of these combinations of conductivity the maximum electric field strength is calculated using COMSOL Multiphysics and compared to the threshold value of 2 kV/mm. Using these parameters the maximum electric field strength on the sheds of the bushing was calculated using COMSOL Multiphysics for all combinations of SiR and air conductivity. The results shows a pattern for both models. SiR conductivity must be higher or equal to the air conductivity to be below the threshold of 2 kV/mm.

In this study, the thermal properties of low dimensional materials such as graphene and boron nitride nanotube were investigated. As one of important heat transfer characteristics, interfacial thermal resistance (ITR) between graphene and Cu film was estimated by both experiment and simulation. In order to characterize ITR, the micropipette sensing technique was utilized to measure the temperature profile of suspended and supported graphene on Cu substrate that is subjected to continuous wave laser as a point source heating. By measuring the temperature of suspended graphene, the intrinsic thermal conductivity of suspended graphene was measured and it was used for estimating interfacial thermal resistance between graphene and Cu film. For simulation, a finite element method and a multiparameter fitting technique were employed to find the best fitting parameters. A temperature profile on a supported graphene on Cu was extracted by a finite element method using COMSOL Multiphysics. Then, a multiparameter fitting method using MATLAB software was used to find the best fitting parameters and ITR by comparing experimentally measured temperature profile with simulation one. In order to understand thermal transport between graphene and Cu substrate with different interface distances, the phonon density of states at the interface between graphene and Cu substrate was calculated by MD simulation.As another low dimensional material for thermal management applications, the thermal conductivity of BNNT was measured by nanoscale thermometry. For this work, a noble technique combining a focused ion beam (FIB) and nanomanipulator was employed to pick and to place a single BNNT on the desired location. The FIB technology was used to make nanoheater patterns (so called nanothermometer) on a prefabricated microelectrode device by conventional photolithography processes. With this noble technique and the nanoheater thermometry, the thermal conductivity of BNNT was successfully characterized by temperature gradient and heat flow measurements through BNNT.

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Grain size distribution, porosity, and hydraulic conductivity from over 400 unlithified sediment samples were analized. The measured hydraulic conductivity values were then compared to values calculated using 20 different empirical equations commonly used to estimate hydraulic conductivity from grain size analyses. It was found that most of the hydraulic conductivity values estimated from the empirical equations correlated very poorly to the measured hydraulic conductivity values. Modifications of the empirical equations, including changes to special coefficients and statistical off sets, were made to produce modified equations that considerably improve the hydraulic conductivity estimates from grain size data for beach, dune, off shore marine, and wadi sediments. Expected hydraulic conductivity estimation errors were reduced. Correction factors were proposed for wadi sediments, taking mud percentage and the standard deviation (in phi units) into account.

Construction projects involving the installation or repair of subsurface structures or utilities often require dewatering to induce a temporary lowering of the local groundwater elevation to facilitate construction. In the event that a known contaminant plume is present in an adjacent area, this dewatering may inadvertently draw the contaminant into the previously uncontaminated work area. Uretek Holdings, Inc. has developed its Injectable BarrierSM to be installed prior to dewatering exercises to provide a groundwater cut-off by reducing the potential movement of groundwater due to the hydraulic gradient induced by dewatering. A benefit of Injectable BarrierSM as compared to conventional methods of hydraulic control is that excavation is not required prior to its installation and no excess soils are generated through its installation. Injectable BarrierSM is a proprietary process registered with the United States Patent and Trademark Office by Uretek Holdings, Inc. Since methodical in-situ testing of the effectiveness of the Injectable BarrierSM has not been performed to date, it was the focus of this research to test the performance of the barrier under in-situ conditions utilizing a subsurface environment indicative of a West-Central Florida location. A testing plot to perform this research was selected on Hillsborough County property in Tampa, Florida which provided both a relatively shallow groundwater elevation in addition to a clay confining layer at a relatively shallow depth, making this an ideal location for testing the performance of the Injectable BarrierSM. After establishing the native conditions through baseline pump testing and repeating the testing procedure following the installation of the Injectable BarrierSM, a quantification of the reduction in hydraulic conductivity was achieved. Pumping tests were performed on the Injectable BarrierSM at its standard spacing as well as modified versions of the barrier with variation in the lateral spacing to include 6 foot, 4 foot, 3 foot, and 2 foot injection patterns to determine if a modified injection process could improve its performance. The 3 foot lateral spacing corresponding to the standard Injectable BarrierSM process indicated a 20% reduction in the hydraulic conductivity following its installation. By performing a small scale excavation following the completion of all pumping tests, it was discovered that the dispersion of the material in the subsurface appeared insufficient to provide the coverage needed to establish a barrier capable of further reducing the local hydraulic conductivity, especially at the shallowest injection depth of 3 feet below land surface (ft bls). It is concluded that modified amounts of injected material, closer lateral injection spacing, and potentially modified injection temperatures and component ratios could increase the effectiveness of the Injectable BarrierSM.

Sand transport in hilly terrain geometry is different and complex to understand compared to horizontal pipeline, due to the influence of the geometry that greatly affect multiphase flow and sand behaviour at the dip. The overall aim of this research work is to use experimental method to investigate the effects of multiphase flow behaviour on sand transport in a dip configuration. Experimental work was carried out to understand the complex dynamic mechanisms that exist during sand multiphase flow using 2” inch dip test facility with different inclination angles of ±24° and ±12° configurations. In order determine the multiphase flow parameters and sand flow regimes, extensive data were collected and analysed from continuous local measurement of instantaneous liquid hold up and sand hold up using conductivity rings. Significant observations were made during this study from which several conclusions were made. In the air–water test, three slug behaviours were observed at the dip: complete stratified flow downhill with slug initiation at dip; stratified flow (with energetic ripple) downhill with slug initiation and slug growth upward dip; and aerated slug downhill and slug growth at the dip. These behaviours are different from published work on this subject with low angle of inclination. The data analysis revealed that the two types of slug initiation mechanisms (wave growth and wave coalescence) observed are geometry specifics. The slug translational velocities (at the dip and uphill section) were used as criterion to determine the flow condition for each slug initiation mechanism at the dip. Significant observations were made during this study from which several conclusions were made. In the air–water test, three slug behaviours were observed at the dip: complete stratified flow downhill with slug initiation at dip; stratified flow (with energetic ripple) downhill with slug initiation and slug growth upward dip; and aerated slug downhill and slug growth at the dip. These behaviours are different from published work on this subject with low angle of inclination. The data analysis revealed that the two types of slug initiation mechanisms (wave growth and wave coalescence) observed are geometry specifics. The slug translational velocities (at the dip and uphill section) were used as criterion to determine the flow condition for each slug initiation mechanism at the dip. Five sand-water flow regimes (full suspension, streak, saltation, sand dune, and sand bed) were established by physical observation and data analysis. It was also observed that sand streaks were denser towards the central line of pipe bottom in the downhill pipe than that in uphill pipe. At downhill pipe section, there were sand gathering toward the central line of the pipe bottom. The characteristics of sand transportation at the dip section were found slightly different from downhill and uphill pipe for higher sand concentrations. When dense streak occurred at the downhill, the sand particles become dispersed at the dip. The minimum transport conditions (MTC) were determined at different sand concentration. The sand minimum transport condition in the dip section was found to be slightly lower than those in the downhill and uphill section. The minimum transport condition for a single phase water flow for the 24˚ dip. test section was slightly higher (with difference of about 0.1m/s) than that of the 12˚ at the downward and upward of the dip section at low sand concentration. In addition, local sand measurements using conductivity time series results at the downhill and uphill section showed the influence of sand concentration and flow condition on sand flow patterns. The air-water-sand results showed that sand deposits occurred in uphill section after sand transport at the downhill and dip sections. This was due to different flow regimes exhibited at the different pipe sections. The stratified (wavy) flow was the dominant flow in downhill pipe; therefore sand was observed transporting within the liquid film as thin streak for most of test conditions. The slug initiation at the dip section was observed to be a major factor that influences the sand behaviour. Sand particles in the slug unit (at the dip and uphill of the pipe) were observed to be entrained in the slug body once slug is initiated, thereby changing the force vector generating turbulence flow at the front of slug body. Once the sand particles entered the film zone of the slug unit, they immediately stopped moving forward due to the film velocity significantly lower than the slug body coupled with gravity effect. . Sand particles were found to be falling back while travelling with the water film at some conditions, until they were picked up by the next slug body. The results of this work provide a better understanding to the study of multiphase flow for pipeline design and most especially sand behaviour at the dip. The sand dune regime is identified distinctively using conductivity ring technique which would assist in determining the operating conditions that allow sand dune formation. The knowledge of flow condition at full suspension of sand is an important parameter to determine the erosion rate over the life span of the pipeline. Also, the quantity of sand bed and flow condition of sand settling at the dip is useful information for production chemist in order to determine the effectiveness of corrosion inhibitor at the bottom of the pipe. In conclusion, sand transport characteristics and MTC were strongly dependent on the gas-liquid flow regime and pipe geometry; and cannot be generalised on the superficial liquid and gas velocities of the transport fluid.