Browsing by Subject "Fuel cell"
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Item Advanced controls and modeling of a hybrid vehicle(2008-12) Harrison, Matthew; Gale, Richard O.; Maxwell, Timothy T.The Texas Tech University Advanced Vehicle Engineering Team has been working in vehicle competitions for 20 years. From that experience the team designed a hybrid vehicle to compete in the Challenge X Competition and the EcoCAR Competition. The Challenge X competition was designed around General Motors' Equinox, which was donated by General Motors. From that platform the team went into the design, implementation, testing and calibration of the vehicle in order to design a low-emission, fuel-efficient vehicle of the future. The vehicle was a mild hybrid 2007 Saturn Geenline Vue. In this way, Texas Tech and its sponsors can give back to the community and help the environment and global economy. After the completion of the Challenge X Competition, the EcoCAR Competition began in 2008, which followed in the Challenge X Competition's footsteps. The EcoCAR design team is currently in the designing phase of the project; it is during this stage of the project that the design team will decide with what vehicle architecture the team will submit for competition. This thesis discusses the steps taken in the implementation of the Challenge X vehicle for years 3 and 4 of the competition. Also, it has the initial design architectures for the EcoCAR competition and the team structure that will enable the team to function to the best of its ability.Item Compression/injection molding of bipolar plates for proton exchange membrane fuel cells(2009-12) Devaraj, Vikram; Beaman, Joseph J.; Koo, JosephFuel cells are electrochemical energy conversion devices that convert chemical energy to electrical energy efficiently. Bipolar plates form an integral part of a fuel cell and their high manufacturing cost and low production rate have hindered the commercialization of fuel cells. Bipolar plates require high electrical conductivity, strength, chemical resistance and thermal conductivity. This thesis presents efforts to manufacture bipolar plates which meet these requirements using compression or injection molding. Compression or injection molding processes allow cost-effective, large-scale manufacturing of bipolar plates. A variety of material systems for the fabrication of bipolar plates are processed, molded and characterized.Item Continuous manufacturing of direct methanol fuel cell membrane electrode assemblies(2010-12) Koraishy, Babar Masood; Wood, Kristin L.; Meyers, Jeremy P.; Manthiram, Arumugam; Bourell, David L.; Jensen, DanielDirect Methanol Fuel Cells (DMFC) provide an exciting alternative to current energy storage technologies for powering small portable electronic devices. For applications with sufficiently long durations of continuous operation, DMFC’s offer higher energy density, the ability to be refueled instead of recharged, and easier fuel handling and storage than devices that operate with hydrogen. At present, materials and manufacturing challenges impede performance and have prevented the entry of these devices to the marketplace. Higher-performing, cost-effective materials and efficient manufacturing processes are needed to enable the commercialization of DMFC. In a DMFC, the methanol-rich fuel stream and the oxidant are isolated from one another by a proton-conducting and electrically insulating membrane. Catalysts in the electrodes on either side of the Membrane Electrode Assembly (MEA) promote the two simultaneous half-reactions which allow the chemical energy carried in the fuel and oxidant to be converted directly into electricity. The goal of this research effort is to develop a continuous manufacturing process for the fabrication of effective DMFC MEAs. Based on the geometry of the electrode and materials used in the MEA, we propose a roll-to-roll process in which electrodes are coated onto a suitable substrate and subsequently assembled to form a MEA. Appropriate coating methods for electrode fabrication were identified by evaluating the requirements of continuous manufacturing processes; an appropriate set of these processes was then reduced to practice on a custom-designed flexible test bed designed explicitly for this project. After establishing baseline capabilities for several candidate methods, a spraying process was selected and a continuous manufacturing process concept was proposed. Finally, key control parameters of the spraying process were identified and their influence tested on actual MEAs to define optimal operating conditions.Item Control-oriented modeling of dynamic thermal behavior and two‒phase fluid flow in porous media for PEM fuel cells(2013-12) Hadisujoto, Budi Sutanto; Moon, T. J. (Tess J.); Chen, Dongmei, Ph. D.The driving force behind research in alternative clean and renewable energy has been the desire to reduce emissions and dependence on fossil fuels. In the United States, ground vehicles account for 30% of total carbon emission, and significantly contribute to other harmful emissions. This issue causes environmental concerns and threat to human health. On the other hand, the demand on fossil fuel grows with the increasing energy consumption worldwide. Particularly in the United States of America, transportation absorbs 75% of this energy source. There is an urgent need to reduce the transportation dependence on fossil fuel for the purpose of national security. Polymer electrolyte membrane (PEM) fuel cells are strong potential candidates to replace the traditional combustion engines. Even though research effort has transferred the fuel cell technology into real‒world vehicle applications, there are still several challenges hindering the fuel cell technology commercialization, such as hydrogen supply infrastructure, cost of the fuel cell vehicles, on‒board hydrogen storage, public acceptance, and more importantly the performance, durability, and reliability of the PEM fuel cell vehicles themselves. One of the key factors that affect the fuel cell performance and life is the run‒time thermal and water management. The temperature directly affects the humidification of the fuel cell stack and plays a critical role in avoiding liquid water flooding as well as membrane dehydration which affect the performance and long term reliability. There are many models exists in the literature. However, there are still lacks of control‒oriented modeling techniques that describe the coupled heat and mass transfer dynamics, and experimental validation is rarely performed for these models. In order to establish an in‒depth understanding and enable control design to achieve optimal performance in real‒time, this research has explored modeling techniques to describe the coupled heat and mass transfer dynamics inside a PEM fuel cell. This dissertation is to report our findings on modeling the temperature dynamics of the gas and liquid flow in the porous media for the purpose of control development. The developed thermal model captures the temperature dynamics without using much computation power commonly found in CFD models. The model results agree very well with the experimental validation of a 1.5 kW fuel cell stack after calibrations. Relative gain array (RGA) was performed to investigate the coupling between inputs and outputs and to explore the possibility of using a single‒input single‒output (SISO) control scheme for this multi‒input multi‒output (MIMO) system. The RGA analyses showed that SISO control design would be effective for controlling the fuel cell stack alone. Adding auxiliary components to the fuel cell stack, such as compressor to supply the pressurized air, requires a MIMO control framework. The developed model of describing water transport in porous media improves the modeling accuracy by adding catalyst layers and utilizing an empirically derived capillary pressure model. Comparing with other control‒oriented models in the literature, the developed model improves accuracy and provides more insights of the liquid water transport during transient response.Item Dynamic modeling of membrane swelling in fuel cell manufacturing(2010-12) Silverman, Timothy J.; Beaman, Joseph J.; Meyers, Jeremy P.; Chen, Dongmei; Edgar, Thomas F.; Fahrenthold, Eric P.Fuel cells are promising energy conversion devices, but they have not been widely adopted because of their very high cost. The most expensive component of a fuel cell is the membrane electrode assembly, a polymer film coated with catalyst material. The catalyst layer is fabricated by depositing and drying a liquid ink on the membrane. The membrane can rapidly absorb water from the ink, causing swelling strain sufficient for wrinkling, which can cause defects in the finished product. These challenges limit most catalyst layer fabrication to individual preparation by hand. We seek to understand the swelling phenomenon in a way that enables the control of defects during mass production. Membrane swelling is a transient, three-dimensional, coupled mass transfer, heat transfer and solid mechanics problem. Existing models describe the membrane in fuel cell operating conditions, making use of simplifying assumptions that are not valid for predicting manufacturing defects. We present a new model incorporating effects that are missing from other models. We present simulation results for scenarios relevant to the control of defects. Simple spatial variations in water content can cause curl and wrinkling; we establish criteria for the formation of these defects by simulating the membrane's response when subjected to the full pre-swollen coating and drying process. We investigate the sensitivity of wrinkling to nonuniformity in the coating and to processing conditions in the coating line. We propose a rationale for controlling wrinkling caused by these effects and for diagnosing coating defects using the membrane's wrinkling response. We show how the membrane behaves differently depending on whether the coating is applied to one side or to both sides simultaneously. We have designed and constructed a machine to pre-swell the membrane, apply a coating and then dry the coating under controlled tension, speed, temperature and humidity. We present the design and discuss how the machine may be used, together with the membrane model, to predict and control defects in catalyst-coated membranes.Item Dynamic subdivided relative humidity model of a polymer electrolyte membrane fuel cell(2013-05) Headley, Alexander John; Chen, Dongmei, Ph. D.The development of a control-oriented dynamic relative humidity model for a polymer electrolyte membrane (PEM) fuel cell stack is presented. This model is integrated with a first law based thermal model, which tracks energy flow within four defined control volumes in the fuel cell; the cathode channel, anode channel, coolant channel, and fuel cell stack body. Energy and mass conservation equations are developed for each control volume. On top of mass conservation, electro-drag and osmosis models were also implemented within the model to account for the major modes of vapor transfer through the membrane between the anode and cathode. Requisite alterations to the thermal model as well as mass flow rate calculations are also discussed. Initially, the model utilized a single lumped control volume for the calculation of all values each channel (anode and cathode). This lumped value method is computationally inexpensive, and makes the model optimal for control design. However, investigation of the mass-based Biot number showed the need for greater granularity along the length of the channels to properly capture the relative humidity dynamics. In order to improve the resolution of the model, while still minimizing the computation expense, the model was subdivided into a series of lumped value models. The cathode channel was the point of focus as it is the major concern from a controls perspective. This method captures the proper trends found in far more complex CFD models, while still maintaining a quick calculation time. Different levels are subdivision (3 and 6 submodels) are investigated, and the differences discussed. Particularly, temperature range, relative humidity range, the effect on the modeled voltage, and calculation time are compared. This control-oriented model is low order and based on lumped parameters, which makes the computational expense low. Formulation of this model enables the development of control algorithms to achieve optimal thermal and water management.Item Dynamical simulation of molecular scale systems : methods and applications(2010-12) Lu, Chun-Yaung; Henkelman, Graeme; Rossky, Peter J.; Makarov, Dmitrii E.; Vanden Bout, David A.; Truskett, Thomas M.Rare-event phenomena are ubiquitous in nature. We propose a new strategy, kappa-dynamics, to model rare event dynamics. In this methodology we only assume that the important rare-event dynamics obey first-order kinetics. Exact rates are not required in the calculation and the reaction path is determined on the fly. kappa-dynamics is highly parallelizable and can be implemented on computer clusters and distributed machines. Theoretical derivations and several examples of atomic scale dynamics are presented. With single-molecule (SM) techniques, the individual molecular process can be resolved without being averaged over the ensemble. However, factors such as apparatus stability, background level, and data quality will limit the amount of information being collected. We found that the correlation function calculated from the finite-size SM rotational diffusion trajectory will deviate from its true value. Therefore, care must be taken not to interpret the difference as the evidence of new dynamics occurred in the system. We also proposed an algorithm of single fluorophore orientation reconstruction which converts three measured intensities {I₀,I₄₅,I₉₀} to the dipole orientation. Fluctuations in the detected signals caused by the shot noise result in a different prediction from the true orientation. This difference should not be interpreted as the evidence of the nonisotropic rotational motion. Catalytic reactions are also governed by the rare-events. Studying the dynamics of catalytic processes is an important subject since the more we learn, the more we can improve current catalysts. Fuel cells have become a promising energy source in the past decade. The key to make a high performance cell while keeping the price low is the choice of a suitable catalyst at the electrodes. Density functional theory calculations are carried out to study the role of geometric relaxation in the oxygen-reduction reaction for nanoparticle of various transition metals. Our calculations of Pt nanoparticles show that the structural deformation induced by atomic oxygen binding can energetically stabilize the oxidized states and thus reduces the catalytic activity. The catalytic performance can be improved by making alloys with less deformable metals.Item Fuel cell based battery-less ups system(Texas A&M University, 2008-10-10) Venkatagiri Chellappan, MirunaliniWith the increased usage of electrical equipment for various applications, the demand for quality power apart from continuous power availability has increased and hence requires the development of appropriate power conditioning system. A major factor during development of these systems is the requirement that they remain environment-friendly. This cannot be realized using the conventional systems as they use batteries and/or engine generators. Among various viable technologies, fuel cells have emerged as one of the most promising sources for both portable and stationary applications. In this thesis, a new battery less UPS system configuration powered by fuel cell is discussed. The proposed topology utilizes a standard offline UPS module and the battery is replaced by a supercapacitor. The system operation is such that the supercapacitor bank is sized to support startup and load transients and steady state power is supplied by the fuel cell. Further, the fuel cell runs continuously to supply 10% power in steady state. In case of power outage, it is shown that the startup time for fuel cell is reduced and the supercapacitor bank supplies power till the fuel cell ramps up from supplying 10% load to 100% load. A detailed design example is presented for a 200W/350VA 1- phase UPS system to meet the requirements of a critical load. The equivalent circuit and hence the terminal behavior of the fuel cell and the supercapacitor are considered in the analysis and design of the system for a stable operation over a wide range. The steady state and transient state analysis were used for stability verification. Hence, from the tests such as step load changes and response time measurements, the non-linear model of supercapacitor was verified. Temperature rise and fuel consumption data were measured and the advantages of having a hybrid source (supercapacitor in parallel with fuel cell) over just a standalone fuel cell source were shown. Finally, the transfer times for the proposed UPS system and the battery based UPS system were measured and were found to be satisfactory. Overall, the proposed system was found to satisfy the required performance specifications.Item Fuel cells as a backup energy source for high availability network servers(Texas A&M University, 2008-10-10) Humphrey, Daniel AlanThis thesis proposes an uninterruptible power supply, UPS for high availability servers with fuel cells as its back up energy source. The system comprises a DC to DC converter designed to accommodate the fuel cell? s wide output voltage range. A server power supply is specified, designed and simulated for use with this UPS. The UPS interfaces internal to the server power supply, instead of providing standard AC power. This topology affords enhanced protection from faults and increases overall efficiency of the system by removing power conversions. The UPS is simulated with the designed power supply to demonstrate its effectiveness.Item Infrared spectroscopy of fluoroalkyl-phosphonic-acid-based proton conductors(2011-05) Liang, Chunchao; Korzeniewski, Carol; Thompson, Jonathan E.The structural properties of two fluoroalkyl phosphonic acid proton conductors were investigated as a function of hydration state in both proton and sodium ion exchanged forms with the use of transmission infrared spectroscopy. The mid-infrared spectral bands were recorded and assigned for the first time. Water condensation and transport in membrane pores and channels was probed through comparative parallel measurements performed on the structurally similar and well-studied ionomer, Nafion (perfluorosulfonic acid ionomer). For the phosphonic acid based conductors, vibrational modes associated with the phosphate moiety were observed near 1290cm-1 and between 1100-1000cm-1. Similar to Nafion, the strongest ionomer spectral bands appeared in the region between 1350-1100 cm-1 and likely contain dominant contributions from C-F stretching modes. A key finding was related to the appearance of a feature near 970 cm-1, which for Nafion has been associated with the vibrations of the two ether groups on the ionomer side chain. Similar to Nafion, which contains a sulfonate as the ionomer side chain end group, the 970 cm-1 feature is split in spectra of the phosphonate ionomer. The splitting is not apparent in spectra of the phosponyl ionomer studied in the present work, behavior which been reported for fluoroalkyl sulfonyl and fluoroalkyl bis-sulfonyl imide species. Possible explanations for the splitting in relation to ionomer structure are discussed.Item Modeling, design, development, and control of a pilot-scale continuous coating line for proton exchange membrane fuel cell electrode assembly(2012-08) Devaraj, Vikram; Beaman, Joseph J.; Prudhomme, Serge M; Fahrenthold, Eric P; Longoria, Raul G; Meyers, Jeremy PFuel cells are electrochemical energy devices that convert the chemical energy in a fuel into electrical energy. Although they are more efficient, clean, and reliable than fossil fuel combustion systems, they have not been widely adopted because of manufacturing challenges and high production cost. The most expensive component of a fuel cell is the membrane electrode assembly (MEA), which consists of an ionomer membrane coated with catalyst material. Best performing MEAs are currently fabricated by depositing and drying liquid catalyst ink on the membrane, however, this process is limited to individual preparation by hand due to the membrane’s rapid water absorption that leads to shape deformation and coating defects. This work models the swelling and drying phenomena of the membrane and coating during manufacturing, and then applies the results to develop and control a continuous coating line for the production of defect free fuel cell MEAs. A continuous coating line can reduce the costs and time needed to fabricate the MEA, incentivizing the commercialization and widespread adoption of fuel cells. Membrane swelling is a three-dimensional, transient, coupled mass transfer, heat transfer, and solid mechanics problem. Existing models describe the membrane’s behavior in operating conditions, but none predict the behavior during manufacturing. This work develops a novel physics-based model that describes the behavior of the membrane and coating in a continuous manufacturing scenario and incorporates effects that are missing from existing models. A model that can predict wrinkles, the most commonly observed defect during manufacturing, is presented. Simulation results from the above models are used to design and develop an improved continuous MEA coating process that includes pre-swelling and two-stage drying of the coated membrane. A prototype pilot-scale coating line to implement and test the improved coating process is designed and constructed. Finally, a Linear-Quadratic-Gaussian type controller is developed using the physics-based model of the manufacturing process to optimally control the temperature and humidity of the drying zones, and its effectiveness when implemented on the coating line is discussed.Item Numerical simulation of electrochemical adsorption process by kinetic Monte Carlo methods(2010-12) Li, Song; Korzeniewski, Carol; Pappas, Dimitri; Thompson, Jonathan E.Electrocatalytic reactions are of great interest for fuel cell technology. Oxidation reactions, such as the transformation of CO to CO2 and the dissociative chemisorption of small alcohols are influenced by the presence of anions. Thus, the incorporation of anion adsorption into kinetic models for these small molecule oxidation reactions is desired to develop mechanisms of experimentally practical systems. This dissertation focuses on models for anion adsorption that can be applied in more realistic kinetic descriptions of small molecule oxidation reactions. In this work, anion adsorption is modeled through the use of kinetic Monte Carlo (kMC) methods. An overview of the formulation, implementation, application and challenges is provided. Then, the adsorption of anions to form several overlayer structures, such as p(2x2) and (r3×r3)R30 on (100) and (111) electrode surfaces during linear scan voltammograms are modeled. Simple lateral interaction models were tested initially and formed a foundation for approaching more complicated adlayer structures that are representative of practical systems. The overall goal was to develop reaction schemes for anion adsorption on (111) and (100) planes that can be incorporated into models for small molecule oxidation reactions to improve the predictive capabilities of the simulations.Item The design and evaluation of a water delivery system for evaporative cooling of a proton exchange membrane fuel cell(2009-06-02) Al-Asad, Dawood Khaled AbdullahAn investigation was performed to demonstrate system design for the delivery of water required for evaporative cooling of a proton exchange membrane fuel cell (PEMFC). The water delivery system uses spray nozzles capable of injecting water directly and uniformly to the nickel metal foam flow-field (element for distributing the reactant gases over the surface of the electrodes) on the anode side from which water can migrate to the cathode side of the cell via electroosmotic drag. For an effective overall cooling, water distribution over the surface of the nickel foam has to be uniform to avoid creation of hotspots within the cell. A prototype PEMFC structure was constructed modeled after a 35 kW electrical output PEMFC stack. Water was sprayed on the nickel metal foam flow-field using two types of nozzle spray, giving conical fog type flow and flat fan type flow. A detailed investigation of the distribution pattern of water over the surface of the nickel metal flow field was conducted. The motive behind the investigation was to determine if design parameters such as type of water flow from nozzles, vertical location of the water nozzles above the flowfield, area of the nozzles, or operating variables such as reactant gas flow had any effect on water distribution over the surface of the Ni-metal foam flow field. It was found that the design parameters (types of flow, area and location of the nozzle) had a direct impact on the distribution of water in the nickel metal foam. However, the operating variable, reactant gas flow, showed no effect on the water distribution pattern in the Ni-foam.