Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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Item Analysis of water transport phenomena in thin porous media of a polymer electrolyte membrane fuel cell(Montana State University - Bozeman, College of Engineering, 2018) Battrell, Logan Robb; Chairperson, Graduate Committee: Ryan Anderson; Aubree Trunkle, Erica Eggleton, Lifeng Zhang and Ryan Anderson were co-authors of the article, 'Quantifying cathode water transport via anode humidity measurements in a polymer electrolyte membrane fuel cell' in the journal 'Energies' which is contained within this thesis.; Ning Zhu, Lifeng Zhang and Ryan Anderson were co-authors of the article, 'Transient, spatially resolved desaturation of gas diffusion layers measured via synchrotron visualization' in the journal 'International journal of hydrogen energy' which is contained within this thesis.; Virat Patel, Ning Zhu, Lifeng Zhang and Ryan Anderson were co-authors of the article, '4-D imaging of the desaturation of gas diffusion layers by synchrotron radiography' submitted to the journal 'Journal of power sources' which is contained within this thesis.This thesis explores and quantifies water transport related to the desaturation of the thin porous layer known as the Gas Diffusion Layer (GDL) associated with Polymer Electrolyte Membrane (PEM) fuel cells. The proper management of water within this layer is critical to optimal fuel cell performance. If there is not enough water, the membrane can become dehydrated, which leads to poor cell performance, but if too much water accumulates or becomes flooded, gas transport is restricted, which also lowers performance and can potentially lead to total cell failure. Understanding the desaturation of this layer is thus key to obtaining and maintaining optimal fuel cell performance. This behavior is explored both at the macroscale, through the quantification of the removal of excess water from an active fuel cell, as well as at the micro-scale, through the use of synchrotron X-ray computed tomography (X-ray CT) to visualize and quantify the desaturation of an initially flooded GDL. The macro-scale investigation extends the previously developed qualitative Anode Water Removal (AWR) test, which functions to identify when poor PEM fuel cell performance is due to excess water, to a diagnostic protocol that quantifies the amount of water being removed by the test through an analysis of the anode pressure drop. Results show that the protocol can be applied to a variety of fuel cell setups and can be used to quickly quantify water management capabilities of novel GDL materials. The microscale investigations show that while both convection and evaporation play a role in the desaturation, evaporation is required to fully desaturate the GDL. Additionally, the microscale investigation allows for the spatial segmentation of the GDL to identify local desaturation rates and temporal saturation profiles, which show that the overall desaturation of the GDL is a heterogeneous process that depends on initial conditions, flow field geometry and the natural anisotropy of the material. Results show that future control strategies and modeling studies will need to expand their investigated domains in order to accurately capture the fully heterogeneous nature of this process.Item Numerical methods for simulating droplet dynamics in microfluidic devices(Montana State University - Bozeman, College of Engineering, 2016) Cauble, Eric Charles; Chairperson, Graduate Committee: Mark OwkesProton exchange membrane (PEM) fuel cells are of beneficial interest due to their capability of producing clean energy with zero emissions. An important design challenge hindering the performance of fuel cells is controlling water removal to maintain a hydrated membrane while avoiding excess water that may lead to channel blockage. Fuel cell water management requires a detailed knowledge of multiphase flow dynamics within microchannels. Direct observation of these gas-liquid flows is difficult due to the small scale and viewing obstructions of the channels within the fuel cell. Instead, this work uses a computational fluid dynamics (CFD) approach to compute the dynamics and formation of droplets in fuel cell channels by imposing contact angles and computing the curvature at the interface along the wall boundary. This thesis focuses on developing and implementing two methods to assist in computing the dynamical behavior of droplets in PEM fuel cells. The contact angle method leverages a conservative volume-of-fluid (VOF) formulation coupled with novel methodologies to impose and track dynamic contact angles. In particular, it is shown that variation of the contact hysteresis angle influences the wetting properties of the droplet and significantly impacts water transport throughout a fuel cell channel. The proposed curvature scheme employs the method of least squares to fit an implicit polynomial function to a cloud of points created at the interface. The points are constructed from the volume of fluid (VOF) representation of the phase interface and the curvature is computed explicitly from this best fit polynomial function. It is shown that the new curvature method is second-order accurate and can be used to compute the curvature of a droplet along a boundary with prescribed contact angles. This thesis presents details of the numerical approaches used to implement contact angles and to compute the curvature based on novel methods. The developed numerical methods are then used to simulate a droplet contained in a channel with an incoming gas flow and discuss the results relevant to water management in PEM fuel cells.Item The electrochemical oxidation of lithium-ammonia solutions(Montana State University - Bozeman, College of Engineering, 1968) Bennett, John EdwinItem Hall effect and electrical conductivity studies of some MHD and fuel cell related materials(Montana State University - Bozeman, College of Letters & Science, 1978) Snyder, Stuart CodyItem Fuel cell studies in acid liquid ammonia solutions(Montana State University - Bozeman, College of Engineering, 1969) Strah, David AlanItem Electrical conductivity and hydrogen diffusion properties of lanthanum chromite based ceramics(Montana State University - Bozeman, College of Letters & Science, 1981) Shifflett, Peter ScottItem The electrochemical reduction of basic liquid ammonia solutions(Montana State University - Bozeman, College of Engineering, 1970) Wang, Shoou-IItem Simulation, design and validation of a solid oxide fuel cell powered propulsion system for an unmanned aerial vehicle(Montana State University - Bozeman, College of Engineering, 2009) Lindahl, Peter Allan; Chairperson, Graduate Committee: Steven R. ShawThis thesis presents a physically-based model for design and optimization of a fuel cell powered electric propulsion system for an Unmanned Aerial Vehicle (UAV). Components of the system include a Solid Oxide Fuel Cell (SOFC) providing power, motor controller, Brushless DC (BLDC) motor, and a propeller. Steady-state models for these components are integrated into a simulation program and solved numerically. This allows an operator to select constraints and explore design trade-offs between components, including fuel cell, controller, motor and propeller options. We also presents a graphical procedure using the model that allows rapid assessment and selection of design choices, including fuel cell characteristics and hybridization with multiple sources. To validate this simulation program, a series of experiments conducted on an instrumented propulsion system in a low-speed wind tunnel is provided for comparison. These experimental results are consistent with model predictions.Item Extended cluster weighted modeling methods for transient recognition control(Montana State University - Bozeman, College of Engineering, 2006) Zhu, Tao; Chairperson, Graduate Committee: Steven R. ShawThis dissertation considers cluster weighted modeling (CWM), a novel non-linear modeling technique for the electric load transient recognition problem. The original version of CWM is extended with a new training algorithm and a real-time CWM prediction method. In the training process, a new training algorithm is derived that is a mixture of expectation maximization (EM) - least mean squares (LMS). The algorithm addresses the singular matrix inversion problem in EM. A recursive EM-LMS algorithm is developed that allows the CWM to adapt to time varying systems. In the prediction process, a sequential version of CWM prediction based on the novel idea of tail prediction is proposed to improve the real-time performance of load transient recognition. This idea also gives rise to a real-time transient overlapping resolution method that is critical for robust online operation. Other aspects of real-time transient processing methods, such as transient scaling, detection under conditions of transient overlap, and off-training set transient indication are also developed and combined into the sequential CWM model. The sequential CWM technique is applied to an electric load transient recognition model for hybrid fuel cell system control. The model provides real-time information about the steady-state behavior of incoming load transients to control and allocate power between the fast sources and the fuel cell. An implementation of this system in a Xilinx FPGA is discussed.Item In-situ electrical terminal characterization of fuel cell stacks(Montana State University - Bozeman, College of Engineering, 2010) Seger, Eric Matthew; Chairperson, Graduate Committee: Steven R. ShawThis thesis demonstrates in-situ characterization of a 5kW solid oxide fuel cell (SOFC) stack and a 165W proton exchange membrane fuel cell (PEMFC) stack at the electrical terminals, using impedance spectroscopy and time-domain modeling. The SOFC experiments are performed using excitation from the power electronic ripple current and exogenous excitation generated from several different sources including a hybrid system which uses a secondary power source for the generation of the small-signal currents. The PEMFC experiments are performed using exogenous excitation from a boost converter. In contrast to typical off-line analysis using specialized instrumentation, the measurements are made as the stacks deliver power to their respective loads. The power electronic switching waveform is used as a source of excitation. This technique could be implemented on-line for continuous condition assessment of the stack. The results show typical data from the stack, comparison of model predictions and measured data, and whole-stack impedance spectroscopy results.
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