bluuebunny/crossref_metadata_2025 huggingface dataset:
Control Design for a Bottoming Solid Oxide Fuel Cell Gas Turbine Hybrid System
Authors: Mueller Fabian , Jabbari Faryar , Brouwer Jacob , Roberts Rory , Junker Tobias , Ghezel-Ayagh Hossein
Published: September 2008

A bottoming 275 kilowatt planar solid oxide fuel cell (SOFC) gas turbine (GT) hybrid system control approach has been conceptualized and designed. Based on previously published modeling techniques, a dynamic model is developed that captures the physics sufficient for dynamic simulation of all processes that affect the system with time scales greater than ten milliseconds. The dynamic model was used to make system design improvements to enable the system to operate dynamically over a wide range of power output (15 to 100% power). The wide range of operation was possible by burning supplementary fuel in the combustor and operating the turbine at variable speed for improved thermal management. The dynamic model was employed to design a control strategy for the system. Analyses of the relative gain array (RGA) of the system at several operating points gave insight into input/output (I/O) pairing for decentralized control. Particularly, the analyses indicate that for SOFC/GT hybrid plants that use voltage as a controlled variable it is beneficial to control system power by manipulating fuel cell current and to control fuel cell voltage by manipulating the anode fuel flowrate. To control the stack temperature during transient load changes, a cascade control structure is employed in which a fast inner loop that maintains the GT shaft speed receives its setpoint from a slower outer loop that maintains the stack temperature. Fuel can be added to the combustor to maintain the turbine inlet temperature for the lower operating power conditions. To maintain fuel utilization and to prevent fuel starvation in the fuel cell, fuel is supplied to the fuel cell proportionally to the stack current. In addition, voltage is used as an indicator of varying fuel concentrations allowing the fuel flow to be adjusted accordingly. Using voltage as a sensor is shown to be a potential solution to making SOFC systems robust to varying fuel compositions. The simulation tool proved effective for fuel cell/GT hybrid system control system development. The resulting SOFC/GT system control approach is shown to have transient load-following capability over a wide range of power, ambient temperature, and fuel concentration variations.
Characterization of Scandia Stabilized Zirconia Doped With Various Bi2O3 Additions as an IT-SOFC Electrolyte
Authors: Bai Bing , Sammes Nigel M. , Smirnova Alevtina L. , Tompsett Geoff
Published: September 2008

Bi2O3 doped scandia stabilized zirconia systems have shown promise for use as electrolytes in IT-SOFCs. Sintering properties, crystal phase transformation, microstructure, as well as electrical conductivity of the Bi2O3 doped Sc2O3-ZrO2 systems were investigated. The effect of Bi2O3 doping from 0 to 2.0mol%, and different sintering temperatures, on the properties and performance of the electrolyte were examined. The presence of Bi2O3 aided the sintering process and better sintering for the doped system was achieved at lower temperatures. The rhombohedral phase in 10ScSZ was successfully stabilized to cubic phase at room temperature with a concentration of 1 mol% and 2 mol% Bi2O3 sintered at 1100°C–1400°C. The achievement of cubic structure depends upon both the Bi2O3 concentration and the sintering temperature. Higher electrical conductivity was achieved with Bi2O3 doped Sc2O3-ZrO2 systems than 10ScSZ below 600°C. A maximum conductivity of 1.68 × 10−2 S/cm at 700°C was obtained for 2 mol% Bi2O3 doped sample sintered at 1100°C.
Effect of Sub-Freezing Temperature on a PEM Fuel Cell
Authors: Yan Q. G. , Toghiani H.
Published: September 2008

The cold-start behavior and the effect of subzero temperatures on fuel cell performance were studied using a 25-cm2 PEMFC. The fuel cell system was housed in an environmental chamber that allowed the system to be subjected to temperatures ranging from sub-freezing to those encountered during normal operation. Fuel cell cold-start was investigated under a wide range of operating conditions. The cold-start measurements showed that the cell was capable of starting operation at −5 °C without irreversible performance loss when the cell was initially dry. The fuel cell was also able to operate at low environmental temperatures, down to −15 °C. However, irreversible performance losses were found if the cell cathode temperature fell below −5 °C during operation. Freezing of the water generated by fuel cell operation damaged fuel cell internal components. Several low temperature failure cases were investigated in PEM fuel cells that underwent sub-zero start and operation from −20 °C. Cell components were removed from the fuel cells and analyzed with scanning electron microscopy (SEM). Significant damage to the MEA and backing layer was observed in these components after operation below −5 °C. Catalyst layer delamination from both the membrane and the gas diffusion layer (GDL) was observed, as were cracks in the membrane, leading to hydrogen crossover. The membrane surface became rough and cracked and pinhole formation was observed in the membrane after operation at subzero temperatures. Some minor damage was observed to the backing layer coating Teflon and binder structure due to ice formation during operation.
Performance Evaluation of a Thermally Integrated Fuel Cell System in the Presence of Uncertainties
Authors: Tsourapas Vasilis , Sun Jing , Stefanopoulou Anna
Published: September 2008

In this work, we focus on robustness analysis of an integrated fuel cell and fuel reforming (FCFR) system, which relies on a feedback controller to mitigate hydrogen starvation and temperature overshoot during load transitions. The fuel reformer is used to process natural gas into a hydrogen rich flow to be utilized in a proton exchange membrane fuel cell (PEM-FC). The feedback controller uses the catalytic burner (CB) and the catalytic partial oxidizer (CPOX) temperatures as measurements and adjusts the air and fuel actuator commands to assure fast load following and high steady state efficiency. Several uncertainty sources which can potentially lead to closed loop performance deterioration are considered, including CPOX clogging, hydro-desulphurizer (HDS) clogging, fuel uncertainty and CB parameter uncertainty. Steady state and transient performance are analyzed for the different uncertainty scenarios, for both open and closed loop operation (i.e., with and without feedback control). The robustness of load following and CPOX temperature regulation of the closed loop system (feedforward and feedback controlled) is established, while the open loop system (feedforward controlled) is shown to be vulnerable to all sources of uncertainties considered.
Hydrogen Generation by Gasification of Rice Husk in an Integrated Fuel Cell Processor
Authors: Lin Kuen-Song , Ku Chi-Nan , Hsieh Chien-Te , Chan Shih-Hung , Su Ay
Published: September 2008

Fuel processing is defined as conversion of any biomass, hydrocarbons or organics to a fuel gas reformate suitable for fuel cell (FC) anode reaction system. Rice husk is one of the potential organic sources of hydrogen and heat energy that can be generated from rice husk gasification processes. The high-purity hydrogen fed to the FC stack for power generation makes waste rice husk utilization system economically and environmentally attractive. Thus, the main objectives of this work were to develop a rice husk gasification process and the potential applications of high-purity hydrogen from syngas (CO and H2) on stationary power generator of FC system. In the lab-scale fixed-bed and bench-scale downdraft experimental approaches, gasification of rice husk was accompanied by a substantial production of syngas at 760–900 K. It was found that in addition to over 90% of syngas generation, approximately 7.17 × 105 kcal/hr of thermal energy was recovered and the cold gas efficiency was 78–86% when the gasifier was operated at O/C atomic ratios between 1.1 and 1.3. The product syngas can be further separated by pressure swing adsorption and Pd membrane purification units, which effectively purified and generated 99.999% pure hydrogen in an integrated FC Processor. Finally, cost or benefit analysis of a rice husk gasifier of 10-TPD (tons per day) was also performed to confirm the economic potential for such a recycling practice and determine if further development of stationary FC system would be warranted.
Synthesis, Characterization, and Hydrogen-Storage Ability of Surface-Modified Multi-Wall Carbon Nanotubes
Authors: Lin Kuen-Song , Ku Chi-Nan , Hsieh Chien-Te , Chan Shih-Hung , Su Ay
Published: September 2008

Carbon nanotubes (CNTs) have attracted increasing attention because of their unique structural, mechanical, and electronic properties. Surface chemistry modifications are also useful and critical to manipulate the adsorptive properties of CNTs and develop their hydrogen storage potential. Therefore, the synthesis or identification of multi-wall carbon nanotubes (MWCNTs) and H2 storage capacity in MWCNTs were investigated. Experimentally, the MWCNTs were produced from the catalytic-assembly benzene-thermal routes by reduction of C6Cl6 with metallic K or Na in the presence of Co/Ni catalyst precursors at 503–623 K. The diameters of K-MWCNTs and Na-MWCNTs ranged from 30–100 and 20–60 nm, respectively. The H2 storage capacity of MWCNTs improved by Pd or NaAlH4 ranged from 2.5–3.5 wt%. Extended X-ray absorption fine structural (EXAFS) spectra showed that the Pd or PdCl2 possess a Pd-Pd or Pd-Cl bond distance of 2.76 or 2.25 Å with a coordination number of 6 or 2, respectively. Therefore, Pd nanoparticles are well dispersed on MWCNTs, which may improve the H2 storage capacity significantly.
Porous Current Collectors for Passive Direct Methanol Fuel Cells
Authors: Chen R. , Zhao T. S.
Published: September 2008

A passive direct methanol fuel cell (DMFC) with its cathode current collector made of porous metal foam was investigated experimentally. The measured polarization curves showed that the passive DMFC having the porous current collector yielded much higher voltages than did the cell having the conventional perforated-plate current collector under the high methanol concentration operation. It was further demonstrated that the improved performance for the porous current collector was attributed to (i) the enhanced oxygen transport on the cathode as a result of a larger specific transport area, (ii) the increased operating temperature as a result of the lower effective thermal conductivity of the porous structure, and (iii) the faster water removal as a result of the capillary action in the porous structure. In particular, the constant-current discharging tests showed that the passive DMFC with the porous current collector not only yielded much high voltages but also offered much more stable operation. It was also shown that the significant improvement on the operation stability was attributed to the fact that the capillary force in the porous current collector can reduce the liquid water accumulation on the cathode.
Fabrication of Composite Carbon Nanotubes With Different Oxidation Levels by a Self-Assembly Surface Modification
Authors: Hsieh Chien-Te , Lin Kuen-Song , Chan Shih Hung , Su Ay
Published: September 2008

An efficient technique to fabricate metal-oxide/carbon composite nanotubes has been developed through a self-assembly processing that includes implantation of acidic groups and interaction between surface oxides and metal ions or hydration molecules. To functionalize carbon nanotubes, gaseous oxidation at 300 °C was firstly employed to build functional oxygen groups including carboxyl, carbonyl and hydroxyl group, on the ends or sidewalls of the nanotubes. It revealed that the oxidized nanotubes express a slight improvement of surface hydrophilicity, which was demonstrated by contact angle measurement. X-ray photoelectron spectroscope investigation indicated that the ratio of attached metal-oxide onto the oxidized nanotubes gradually increases with oxidation level, i.e., surface O/C atomic ratio. This evidence reflected that the surface oxides act as an adsorption center that strongly interacts with metal ions or hydration molecules in aqueous phase. Applying this method, SnO2, RuO2, NiO and PtRu nanoparticles having an average size of 5 nm were assembled on the oxidized carbon nanotubes.
Parameterization of Fuel Cell Stack Voltage: Issues on Sensitivity, Cell-to Cell Variation, and Transient Response
Authors: Schilter Arlette L. , McKay Denise A. , Stefanopoulou Anna G.
Published: September 2008

We present here a calibrated and experimentally validated lumped parameter model of fuel cell polarization for a hydrogen fed multi-cell, low-pressure, proton exchange membrane (PEM) fuel cell stack. The experimental methodology devised for calibrating the model was completed on a 24 cell, 300 cm2 stack with GORE™ PRIMERA® Series 5620 membranes. The predicted cell voltage is a static function of current density, stack temperature, reactant partial pressures, and membrane water content. The maximum prediction error associated with the sensor resolutions used for the calibration is determined along with a discussion of the model sensitivity to physical variables. The expected standard deviation due to the cell-to-cell voltage variation is also modelled. In contrast to other voltage models that match the observed dynamic voltage behavior by adding unreasonably large double layer capacitor effects or by artificially adding dynamics to the voltage equation, we show that a static model can be used when combined with dynamically resolved variables. The developed static voltage model is then connected with a dynamic fuel cell system model that includes gas filling dynamics, diffusion and water dynamics and we demonstrate the ability of the static voltage equation to predict important transients such as reactant depletion and electrode flooding. It is shown that the model can qualitatively predict the observed stack voltage under various operating conditions including step changes in current, temperature variations, and anode purging.
Development of Segmented-in-Series SOFC Stacks Using Numerical Models and Parametric Study
Authors: Fujita Kenjiro , Matsuzaki Yoshio , Yakabe Hisataka , Yamashita Shoji , Ogasawara Kei , Sakurai Teruhiro
Published: September 2008

The voltage loss in a single cell of a segmented-in-series flat-tube-type solid oxide fuel cell (SOFC) stack was evaluated. The stack exhibits a particular configuration, and the current flows along an in-plane direction in the anode and cathode; this differs from conventional planar-type SOFCs. Distributions of the current in the cell were studied in detail for many parameters such as the length of electrodes and conductivities of the cell components. Gas diffusion in a porous substrate and anode and the fuel utilization affect the concentration polarization; thus, they were also considered. By using the simulation results, appropriate configurations for the cell and stack were designed, and the simulation was validated by performance tests for a practical fuel cell stack. The stack exhibited a high performance of 0.76 V at 0.2 A/cm2 at Uf = 81.6% with dry H2 fuel, yielding a DC energy conversion efficiency of 53.6% HHV. Moreover, a bundle comprising 34 stacks was also fabricated, and excellent values of output voltage (342.5 V), output power (338.3 W), and electrical efficiency (49.5% HHV) at a current density of 0.2 A/cm2 were obtained.
Modeling Balance of Plant Components for a PEM Fuel Cell
Authors: Rocheleau David N. , Sagona John F.
Published: September 2008

To integrate a fuel cell into a vehicle platform many subsystems must be engineered to support the electrical power production of the fuel cell plant. These subsystems include the control of fuel and air supply as well as managing thermal and water throughput in the fuel cell stack. For the fuel cell plant to operate at optimum performance, one must examine the individual components that make up the “balance of plant” of the fuel cell system. Specifically, the power used to run the system must be scrutinized with the power produced by the system. Knowing how individual balance of plant components perform is the first step in design and optimization studies, as well as automated control system development. To address these issues, this paper examines how balance of plant components and subsystems affect parasitic power consumption, fuel cell power production, membrane hydration, hydrogen usage, and water production.
Thermal Gradient Induced Current Recirculation on Load Change in Solid Oxide Fuel Cells
Authors: Gemmen Randall S. , Johnson Christopher D.
Published: September 2008

This paper considers recent model results examining the transient performance of three common solid oxide fuel cell (SOFC) geometries (cross-flow, co-flow, and counter-flow) during load reduction events. Of particular note for large load decrease (e.g., shutdown) is the occurrence of reverse current over significant portions of the cell, starting from the moment of load loss up to the point where equilibrated conditions again provide positive current. This behavior results from the temperature gradients that exist in an SOFC stack. Also reported are test results from an experiment employing two separate button cells coupled together electrically (anode-to-anode and cathode-to-cathode) which are used to confirm the model predictions. The test results confirm the predictions of the model in that temperature gradients are a driver for current circulation within a cell. Also reported are test results of a button cell operated under reverse current to help begin to identify what effects such operation may have on fuel cell performance and durability.
Development of Planar Type SOFC Stacks Operable Under Rapid Starting
Authors: Ukai Kenji , Nakamura Yasuhisa , Mizutani Yasunobu , Hisada Koji , Yokoyama Misuzu , Yasuhara Masato , Nagai Kohki , Hirakawa Masahiro , Kashima Shoichi , Orishima Hiroshi , Honda Sawao , Hashimoto Shinobu , Awaji Hideo
Published: September 2008

Toho Gas Co. Ltd. and Sumitomo Precision Products Co. Ltd. have been jointly developing a SOFC system using scandia-stabilized zirconia (ScSZ) electrolyte cells. Especially, we focused the scandia tetragonal zirconia polycrystalline (Sc-TZP) electrolyte, because the Sc-TZP electrolyte has good mechanical and electrical properties, therefore high reliability and power generation characteristics are expected. We have been developing the 1kW SOFC system using Sc-TZP electrolyte cells as proof of concept since 2002. The 1kW SOFC combined heat and power (CHP) system was installed in The 2005 World Exposition, Aichi, Japan (EXPO2005), and the system successfully operated during about six months. During the demonstration, some troubles caused by balance of plant (BOP) system and controlling system, and these experiences are useful to our system development. The target of our developing system is a small-scale commercial CHP application and target power range is below 10kW class. To apply such a small-scale commercial use, the rapid start up is very attractive for customers in Japanese market. In this study, we have been developing the rapid starting system. To shorten the start up time, reducing the volume of cell stack and strengthening the cell are developed in parallel. Because heating capacity is very affected factor to determine the start up time. To reduce the volume of cell stack, the improvement of cell performance is very attractive. For the electrolyte-supported type cell, the electrical conductivity of electrolyte material is very important factor on the cell performance. On the other hand, to realize the rapid start up system, the mechanical strength of electrolyte is also important factor, because in the rapid start up conditions, large temperature distribution may be easily occurred, and it leads the cell broken. The relation between electrical conductivity and mechanical strength is trade off in the electrolyte material, and then we focused the electrolyte in the range from 4mol% to 7mol%, and demonstrated that these materials have good combination of electrical and mechanical properties. To estimate the suitable composition, the mechanical strength of electrolyte from room temperature to 1073K that is the maximum operating temperature of our system were investigated. And piston on ring (POR) method was also investigated to estimate the strength of actual electrolyte sheets. Part of this work was performed as R & D program of New Energy and Industrial Technology Development Organization (NEDO).
Improved Electrocatalytic Activity of Oxygen Reduction on Platinum Using Nano-Cobalt in Direct Methanol Fuel Cell Cathode Electrodes
Authors: McGrath Kimberly , Carpenter Douglas
Published: September 2008

High surface area nanometal particles of nano-cobalt (n-Co) (approx 8 nm particles), produced at QuantumSphere Inc., were blended in various ratios with Pt and Nafion® ionomer, and investigated for their electrocatalytic activity in the oxygen reduction reaction (ORR). The ORR was evaluated by voltammetry using Pt/n-Co blended catalyst on glassy carbon to determine both kinetic activity and as an indicator of direct methanol fuel cell (DMFC) cathode performance. Kinetic enhancement was observed for Pt:n-Co where n-Co is 30–50% (by weight) of the catalyst mixture, including a minimum of 10 mV improvement in the open circuit voltage (OCV). By Tafel slope measurements, it is clear that the mechanism for ORR does not change, however the reaction rate is enhanced by addition of n-Co to Pt in the catalytic ink. For ink compositions similar to those used for standard DMFC cathodes, eliminating 50% of the Pt black resulting in 50% higher energy density while reducing total catalyst cost by roughly 44%.
A Two-Phase, Transient Model for the Cathode of a PEMFC Using Thin Film-Agglomerate Approach
Authors: Chu Hsin-Sen , Chang Shih-Ming
Published: September 2008

This study presents a transient, one-dimensional, and two phase model of the proton exchange membrane fuel cell cathode. A thin film-agglomerate approach is applied to the catalyst layer. The model includes the transport of gaseous species, liquid water, proton, and electrochemical kinetics. The effect of water flooding both in the gas diffusion layer and catalyst layer in the cathode are investigated. The effects of agglomerate radius and the catalyst layer thickness on the overall cell performance are also investigated. The results show that the time for fuel cells to reach the steady state is in the order of 10 sec due to the effect of water accumulated both in the porous layer and the membrane. However the time for proton transport is in the order of 0.1 sec. In addition, before the ionic potential reaches the steady state, it would get a critical value. The critical value would depend on the operating cell voltage. There seems to be an optimum in the catalyst layer thickness and agglomerate radius.
A kW-Class NaBH4/H2O2 Fuel Cell for Air Independent Propulsion
Authors: Luo Nie , Miley George H. , Mather Joe , Burton Rodney , Hawkins Glenn , Byrd Ethan , Holcomb Frank , Rusek John
Published: September 2008

A kilo-Watt-class direct sodium-borohydride/hydrogen-peroxide (NaBH4/H2O2) fuel cell is fabricated and characterized in this research. Aqueous solution of NaBH4 is directly utilized at the fuel cell anode in place of gaseous hydrogen. Similarly H2O2/water solution is directly reduced at the cathode without being first converted through molecular oxygen. The direct utilization of fuel/oxidant results in much higher (35% higher) efficiency in energy utilization. The potential for a very high efficiency (over 80%) was fully validated in the experiments, because the use of H2O2 overcomes the oxygen over-potential problem inherent to prior H2/O2 fuel cell designs. Initial results indicate: 1) conversion efficiency over 50% at a practical current density of 200 mA/cm2; 2) power density over 0.5 W/cm2, at 60 degree Celsius. The kilo-Watt-stack consists of 24 cells, generating an OCV (open circuit voltage) of ∼ 42 V. The design of the reactant manifold overcomes some issues unique to an all-liquid-reactant fuel cell. Such a technology is ideal for propulsion/power in air independent environment such as space and underwater.
Hydrogen Production for PEM Fuel Cells via Oxidative Steam Reforming of Methanol Using Cu-Al Catalysts Modified With Ce and Cr
Authors: Patel Sanjay , Pant K. K.
Published: September 2008

The performance of Cu-Ce-Al-oxide and Cu-Cr-Al-oxide catalysts of varying compositions prepared by co-precipitation method was evaluated for the PEM fuel cell grade hydrogen production via oxidative steam reforming of methanol (OSRM). The limitations of partial oxidation and steam reforming of methanol for the hydrogen production for PEM fuel cell could be overcome using OSRM and can be performed auto-thermally with idealized reaction stoichiomatry. Catalysts surface area and pore volume were determined using N2 adsorption-desorption method. The final elemental compositions were determined using atomic absorption spectroscopy. Crystalline phases of catalyst samples were determined by X-ray diffraction (XRD) technique. Temperature programmed reduction (TPR) demonstrated that the incorporation of Ce improved the copper reducibility significantly compared to Cr promoter. The OSRM was carried out in a fixed bed catalytic reactor. Reaction temperature, contact-time (W/F) and oxygen to methanol (O/M) molar ratio varied from 200–300°C, 3–21 kgcat s mol−1 and 0–0.5 respectively. The steam to methanol (S/M) molar ratio = 1.4 and pressure = 1 atm were kept constant. Catalyst Cu-Ce-Al:30-10-60 exhibited 100% methanol conversion and 152 mmol s−1 kgcat−1 hydrogen production rate at 300°C with carbon monoxide formation as low as 1300 ppm, which reduces the load on preferential oxidation of CO to CO2 (PROX) significantly before feeding the hydrogen rich stream to the PEM fuel cell as a feed. The higher catalytic performance of Ce containing catalysts was attributed to the improved Cu reducibility, higher surface area, and better copper dispersion. Reaction parameters were optimized in order to maximize the hydrogen production and to keep the CO formation as low as possible. The time-on-stream stability test showed that the Cu-Ce-Al-oxide catalysts subjected to a moderate deactivation compared to Cu-Cr-Al-oxide catalysts. The amount of carbon deposited onto the catalysts was determined using TG/DTA thermogravimetric analyzer. C1s spectra were obtained by surface analysis of post reaction catalysts using X-ray photoelectron spectroscopy (XPS) to investigate the nature of coke deposited.
Analysis and Control of Fuel Cell Hybrid Vehicle
Authors: Kim Sang-Kwon , Choi Seo-Ho
Published: September 2008

In order to increase efficiency of the fuel cell vehicle, it can be hybridized by using batteries or ultra-capacitors. A fuel cell vehicle model is developed and validated by comparing the simulation results with real vehicle operating results from the Hyundai Tucson fuel cell hybrid vehicle. And various types of hybridization structure are compared by simulation and the effect of component sizing is also studied. In the vehicle model, the component and controller models were developed to have modularity and integrated to have forward facing characteristics. Thus, the hybrid controller is designed and optimized by using the simulation. This paper also presents the fuel economy of the developed fuel cell hybrid vehicle when it is operated on the chassis dynamometer.
Effect of Channel Aspect Ratio on Planar SOFC Performance
Authors: Elizalde-Blancas Francisco , Yavuz Ibrahim , Pakalapati Suryanarayana , Celik Ismail
Published: September 2008

The optimization process is in general an important issue to show the viability of solid oxide fuel cells (SOFCs) compared to traditional power sources. This optimization process can be done in a faster and cheaper way by making use of numerical simulations. In this study, three-dimensional, non-isothermal, steady state numerical simulations of planar solid oxide fuel cells (SOFC) are performed using the commercial FLUENT software. First, a detailed analysis of grid and iteration-dependent simulations is performed. This analysis predicts a 20% difference between a coarse and fine grid in the velocity magnitude in both anode and cathode gas flow channels, and in the y-component of current density. Then, the performance of a planar SOFC with changing channel aspect ratio is analyzed comparing their V-I curves and critical parameters like temperature, concentration, and current density distributions. The predictions show a 12 degrees difference in temperature at the fuel exhaust between low and high aspect ratio channel simulations. These results suggest that the channel aspect ratio is a significant parameter, worthwhile to be investigated.
Three-Dimensional Based Model of a Planar SOFC Fuelled by Biomass Gas
Authors: Cordiner Stefano , Feola Massimo , Mulone Vincenzo , Romanelli Fabio
Published: September 2008

Efficient and low polluting production of electricity and heat is an issue which cannot be postponed. Fuel cells, which convert the chemical energy stored in a fuel into electrical and thermal energy, are an efficient solution for such a problem. These devices rely on the combination of hydrogen and oxygen into water: oxygen is extracted from the air while hydrogen can be obtained from either fossil fuels or renewable sources. The use of biomass as hydrogen source in connection with fuel cells is an argument of particular interest, since high temperature gasification processes are actually utilized. Solid Oxide Fuel Cells (SOFC), working at high temperatures, have become therefore an interesting candidate to realize the internal reforming of the feed gas from a gasifier. The reforming reaction occurs at the anode of the SOFC, upstream and separated from the fuel cell reaction. The section of the anode where reforming occurs is adjacent to the section where electrochemical reaction occurs. So, heat produced by the electrochemical reaction can be transferred internally with minimal losses. Simulation models of the performance of SOFC stacks and biomass gasifiers are useful to visualize temperature, current and concentration distributions, which are difficult to measure by experimental techniques, allowing the definition of optimal choices in terms of geometries and operating conditions. In this work, an analysis of a SOFC coupled with a biomass gasifier is performed. The objective of this study is the identification of the main effects of the operating conditions on the fuel cell performance in terms of efficiency, and the distribution of the main electro-thermal-fluid-dynamics variables, namely current and temperature. A gasifier model has been implemented to calculate the equilibrium compositions using the Gibbs free energy minimization method. The obtained results are directly used to estimate the inlet gas composition for the SOFC. The SOFC has been modelled by a 3D approach (FLUENT), which solves the energy and mass transport and the internal reforming, coupled with a 0D electrolyte model which, starting from the local information in terms of gas composition, temperature and pressure, is able to predict the fuel cell performance in terms of electrical response and mass-energy fluxes. The whole model has been applied to the analysis of an integrated SOFC-gasifier system to address a planar SOFC response by varying the gasifier operating conditions and the global system performance.
A Novel Method for Measuring the Temperature Distribution Within the Fuel Cell Using Array Micro Sensors
Authors: Lee Chi-Yuan , Lee Shuo-Jen , Hsieh Chi-Lieh , Wu Guan-Wei , Lee Yu-Ming , Chuan Chih-Wei
Published: September 2008

The fuel cell has the potential to become an important source of electric power. However, measuring the temperature inside the fuel cell is difficult. Hence, in this investigation, array of micro sensors are set up inside a fuel cell to measure the temperature distribution. The substrate of the bipolar plate in a fuel cell is made of stainless steel (SS-316) and the electroforming technique is implemented to fabricate channels in the stainless steel substrate. Then NEMS (Micro-Electro-Mechanical Systems) technologies are employed to fabricate the platinum temperature sensor on the rib of a channel of stainless steel. The major advantages of array micro platinum temperature sensors are their small volume, high accuracy, short response time, simplicity in their fabrication, their mass production and ability to measure the temperature precisely and more effectively than a traditional thermocouple. The stainless steel bipolar plate is a good conductor of electric and heat. It has high mechanical strength and is non-porous. The graphite bipolar plate does not have such extensive advantages. This work electroforms a channel on stainless steel and then fabricates an array of micro temperature sensors on the rib of the channel. It is used to measure the temperature distribution at all locations in a fuel cell with a metallic bipolar plate. In the experiment, the temperature- is measured from 31 to 80 degrees Celsius and its resistance range from 0.593 to 0.649 ohm. The experimental results demonstrate that the temperature was almost linearly related to the resistance and the accuracy and sensitivity are under 1 degrees Celsius and 1.85×10−3 over degrees Celsius, respectively.
Modeling of Micro-Water Gas Shift Reactor Using Integrated Heat Exchange and Reaction Approach
Authors: Kim Gap-Yong , Mayor J. Rhett , Ni Jun
Published: September 2008

Conventional reactors are large in size and thus have limitations on heat and mass transfer. To overcome these limitations, microreactors have been introduced. This study discusses the development of an integrated reaction and heat exchange approach to microreactor design that enhances reaction yields by allowing the reactant stream to follow optimal reactant temperature profiles. The study details the formulation of two-dimensional model for the integrated reaction and heat exchange reactor design, and applies these models to a parametric study of microreactor designs for the water gas shift (WGS) reaction. The parametric study investigates the sensitivities of design parameters for both the parallel-flow and counter-flow configurations and contributes to establishing general design guidelines for the micro-WGS reactor. The integrated approach achieved significantly higher catalyst utilization when compared to a conventional adiabatic reactor. The study also showed potentials of miniaturizing the reactor by reducing the wall thickness of the reactor without performance loss.
Validated Modeling and Synthesis of Medium-Scale Polymer Electrolyte Membrane Fuel Cell Aircraft
Authors: Bradley Thomas H. , Moffitt Blake A. , Mavris Dimitri , Parekh David E.
Published: September 2008

This paper describes a methodology for design and optimization of a polymer electrolyte membrane (PEM) fuel cell unmanned aerial vehicle (UAV). The focus of this paper is the optimization of the fuel cell propulsion system and hydrogen storage system for a baseline aircraft. Physics-based models, and experimentally-derived sub-system performance data are used to characterize the performance of each configuration within a design space. The results of aircraft synthesis and performance modeling routines are used to create response surface equations where tradeoffs among component specifications can be explored. Significant tradeoffs between fuel cell performance, hydrogen storage and aircraft aerodynamic and propulsion system design are presented. Validation and test results from a proof-of-concept fuel cell UAV propulsion system are presented. Validated models of the fuel cell and aircraft systems are used to predict the performance of fuel cell UAVs at the scale of the baseline aircraft.
CFD and Flow Network Analysis of Manifolding in a PEMFC
Authors: Mackie R. , Sui P. C. , Djilali N.
Published: September 2008

Near-uniform flow distribution in a fuel cell stack is essential to stack performance and overall system efficiency. The gradients induced by the non-uniformity of the flow within each of the unit cells also have a significant impact on stack durability. In typical configurations, the oxidant and fuel are fed into a stack through manifolds and then enter each unit cell through secondary inlet port. After flowing through the unit cells, the spent gases as well as possible liquid water then enter the outlet header to leave the stack. The objective of this paper is to develop a practical model to predict cell-to-cell flow distribution in a proton exchange membrane fuel cell (PEMFC) stack. The flow distribution is first simulated using a computational fluid dynamics (CFD) tool, CFD-ACE+, in a 3D computational domain for single-phase gas flows. The simulations use a domain encompassing the flow from the inlet header through an array of unit cells to the outlet header. The CFD simulations show that in the outlet header, the flow injected from the unit cells to the header changes the flow pattern considerably, which results in a reduced cross section area for the flow in the axial direction. A circulation zone is seen near the low velocity end of the header, which may potentially become a region where liquid water accumulates. Increasing static pressure along the flow direction is observed in the inlet header. The simulated results are validated and found to be in good agreement with experimentally measured pressures in a fuel cell stack. Based on the observations in the CFD simulations, a flow network model is developed to provide quick estimates of the flow distribution as a function of stack dimensions including header and unit cell geometry. In essence, the flow network model solves for the pressure at each junction of the unit cell and the header. Three fitting parameters are introduced to account for effects of surface roughness of the headers, reduced effective header area in the outlet header, and pressure drop in the unit cell. The flow network model is shown to capture the characteristics of pressure variation and flow distribution obtained in the CFD simulations. The flow network model can effectively match experimental data and be used as a fast tool for initial design of a PEMFC stack.
Dynamic Cell Level Modeling and Experimental Data From a Proton Exchange Membrane Fuel Cell
Authors: Kang Sang-Gyu , Kim Han-Sang , Ha Taehun , Min Kyoungdoug , Mueller Fabian , Brouwer Jack
Published: September 2008

A quasi three-dimensional dynamic model of a proton exchange membrane fuel cell (PEMFC) has been developed and evaluated by comparison to experimental data. A single PEMFC cell is discretized into 245 control volumes in three dimensions to resolves local voltage response, current generation, species mole fractions, temperature, and membrane hydration spatially in the PEMFC. The model can further simulate transients in electrical load, inlet flow conditions, ambient conditions, and/or other parameters to provide insight into the local dynamic performance of a PEMFC. The quasi three-dimensional model has been validated against an experimental single cell. To compare the model, polarization constants were tuned to match one experimental operating point of the fuel cell. With this tuning, the model is shown to predict well the voltage current (V-I) behavior for the full range of cell operating current. Further, model comparison to an instantaneous increase in current indicates that the model can predict the transient electrochemical response of the PEMFC. This suggests such a model can be utilized for PEMFC system development, transient analysis of a PEMFC in general, as well as transient control design.
Design of Hydrogen Fuel Cell Autorickshaw
Authors: Khattak Ikhlaq , Yousaf Mirza Jamil
Published: September 2008

In Asia there are less private cars, but there is a high proportion of 2-stroke engines in scooters, motorcycles, auto-rickshaws (Tuk-Tuks), all running on petrol-oil mixtures with levels of hydrocarbon emissions (from partially burnt fuel and oil) well in excess of levels permitted in the USA and Europe. Worldwide Rickshaw/scooter/motorcycle type engine production is estimated at 17 million per year. According to National Transport Research Center (NTRC), the total population of registered (all types) motor vehicles in Pakistan in year 2000 was 4.224 million, out of which more than half of the population is (2.206 million) two wheelers or three wheelers (motorcycle/scooter/auto rickshaw). Almost all auto rickshaws have two stroke power packs and also 60% of motorcycle/scooters are of the same category. Pakistan is a very densely populated developing country, with very loose environment protection rules, which are practically unregulated due to large financial implications. This scenario leads to adverse air quality conditions especially in large cities of the country where the main contributory factors are vehicular traffic, that too, two stroke vehicles Industry, diesel-powered vehicles, and the omnipresent three-wheeled, two-stroke rickshaws all contribute to the extremely dirty air. Taxi/car use is increasing, but rickshaws have the advantage of being able to swarm through the congested car traffic in cities. This explains the over .6 million motorcycles/scooters/rickshaws currently in Pakistan, of which approximately 20% are two stroke Auto-rickshaws of 175 cc. Pakistan’s vehicle fleet has a growth rate of 8.0% (1990–99). The purpose of this study is to examine a particular application of fuel cell technology “The Auto Rickshaws”. They are small three-wheeled vehicles that can carry three people. Due to their small size and low price, rickshaws have traditionally been powered by high power density two-stroke internal combustion engines. Two-stroke engines produce a great deal of pollution and are an object of concern in many Asian countries. Severe pollution from two-stroke engines is a significant driver for cleaner technology. Thus, the target of this study is the Asian urban commuter, since a rickshaw is largely used in many Asian cities and contributes directly to air pollution in major crowded cities of Pakistan also. Countries like China, India, Bangladesh, Taiwan and Pakistan [1] are facing dramatic growth rates in two-stroke vehicle population as bicycle rickshaws are being replaced, so, low-powered but clean rickshaws would be a major step in providing mobility without compromising urban air quality.
Estimation of Flooding in PEMFC Gas Diffusion Layer by Differential Pressure Measurement
Authors: Ito Kohei , Ashikaga Kensuke , Miyazaki Tomohiko , Ohshima Hiroki , Kakimoto Yasushi , Masuda Hiromitsu , Oie Yoshiyuki , Sasaki Kazunari
Published: September 2008

The flooding, especially in gas diffusion layer (GDL), is one of the critical issues to put PEMFC to practical use. However, the experimental data of the flooding in GDL is so insufficient that the optimization design to solve the flooding problem in GDL has not established until now. In this study we show a method to estimate the water saturation, namely the water droplet occupation for unit volume in GDL. We fabricated a simple interdigitated cell where the supply gas is enforced to flow under rib. This structure made it possible to capture the water droplet in GDL with the measurement of differential pressure through the cell. We operated the cell and measured the differential pressure, and estimated the water saturation with assuming that the flow in GDL is Darcy flow and that the GDL can be treated as sphere packed bed. In addition to deferential pressure measurement, we measured the ionic resistance in polymer electrolyte membrane by AC impedance method. We evaluated the effect of the water saturation on the decrease of cell voltage.
Analysis of Different Configurations of Hybrid Fuel Cells System With Supercapacitors and Battery for Small Stationary Applications
Authors: Cordiner Stefano , Pagliarini Francesco , Prencipe Michele , Romanelli Fabio
Published: September 2008

The overall characteristics of electric power grid in terms of continuity of the supply and energy quality are of outmost importance for both industrial and civil applications with special attention to the uninterruptible ones. Net congestion problems are becoming more and more frequent boosting the development of small energy generation systems with back-up function. In this field low temperature fuel cells are an interesting solution addressing both environmental and efficiency issues. In the present work the application of Polymer Electrolyte Fuel Cells (PEFC) for an Uninterruptible Power Supply (UPS) system (<1kWe) is analysed by examining different possible technical solutions. This system is composed by a PEFC 1kWe stack, assisted by a set of battery and a supercapacitors pack, and using hydrogen stored into a metal hydride tank. Critical aspects as system start-up, response rapidity and autonomy are addressed to obtain an optimal configuration. Both numerical and experimental analysis have been carried out to characterize component behaviour. Once realized and tested, the system has proved to be able to work as UPS with an autonomy of 6.5 hours, only determined by hydrogen storage capability.
A Study of Transport Geometry on Heat/Mass Transfer and Polarization of a Solid Oxide Fuel Cell
Authors: Ji Yan , Chung J. N. , Yuan Kun
Published: September 2008

The main objective of this paper is to examine the effects of transport geometry on the efficiency of an electrolyte-supported solid oxide fuel cell. A three-dimensional thermo-fluid-electrochemical model is developed to the influences of channel dimensions, rib width and electrolyte thickness on the temperature, mass transfer coefficients, species concentration, local current density and power density. Results demonstrate that decreasing the height of flow channels can significantly lower the average solid temperature and improve the cell efficiency due to higher heat/mass transfer coefficient between the channel wall and flow stream, and a shorter current path. However, this improvement is limited for the smallest channel. The cell with a thicker rib width and a thinner electrolyte layer has higher efficiency and lower average temperature. Numerical simulation will be expected to help optimize the design of a solid oxide fuel cell.
Development of an Automated Control System Verification Platform for a Solid Oxide Fuel Cell
Authors: Absmeier John , Das Tuhin , Gopalswamy Swaminathan , Paike Ravi S.
Published: September 2008

The fuel cell industry is currently undergoing rapid development, and applications of fuel cell based power sources are diversifying. The advent of new and more sophisticated application areas and the expanding market necessitates development of efficient and robust fuel cell based power supplies that are reliable in their performance. These demands are answered not only by improved plant designs and innovations, but also by developing high-quality control algorithms. Quality and reliability of the complete system are ensured through extensive and varied testing. To this end an automated Hardware-in-the-Loop based control code verification and validation platform for the Delphi Solid Oxide Fuel Cell plant and control system has been developed. Verification activities are managed using the System Verification Manager tool. This paper outlines the application of this platform for safety and diagnostics verification and validation for a Solid Oxide Fuel Cell system.