bluuebunny/crossref_metadata_2025 huggingface dataset:
Xenogeneic Murine Tyrosinase DNA Vaccine for Malignant Melanoma of the Digit of Dogs
Authors: Manley C.A. , Leibman N.F. , Wolchok J.D. , Rivière I.C. , Bartido S. , Craft D.M. , Bergman P.J.
Published: December 2010

Background: Malignant melanoma of dogs is a highly aggressive neoplasm and is the 2nd most common digit tumor. Metastatic disease is a common sequela for which few effective treatment options exist. Studies show that xenogeneic tyrosinase DNA vaccination yields immune responses and prolongation of survival in dogs with oral malignant melanoma.

Objectives/Hypothesis: Describe clinical findings and tumor characteristics of a cohort of dogs with digit malignant melanoma, and evaluate the prognostic utility of a proposed staging system. Determine if a novel xenogeneic DNA vaccine is safe and potentially effective for treatment of dogs with digit melanoma.

Animals: Fifty‐eight dogs with digit malignant melanoma treated at the Animal Medical Center between 2004 and 2007.

Methods: Retrospective, medical records review of dogs with digit melanoma treated with xenogeneic DNA vaccine.

Results: Overall median survival time (MST) for dogs treated with loco‐regional control and xenogeneic DNA vaccine was 476 days with a 1‐year survival rate of 63%. MST for dogs presenting with metastasis was 105 days versus 533 days for dogs presenting without metastasis (P < .0001). Forty‐eight percent of the dogs in the latter group were alive at 2 and 3 years. A proposed staging system proved prognostic with stages I–IV dogs surviving >952, >1,093, 321, and 76 days, respectively.

Conclusions and Clinical Importance: The xenogeneic murine tyrosinase DNA vaccine was safe and appears effective when used in conjunction with local and regional disease control. The proposed staging system was prognostic in this study and future studies might benefit from utilizing this staging system.
Clinical Assessment of Blood Glucose Homeostasis in Horses: Comparison of a Continuous Glucose Monitoring System with a Combined Intravenous Glucose and Insulin Test Protocol
Authors: Johnson P.J. , Wiedmeyer C.E. , LaCarrubba A. , Messer N.T. , Dingfelder H.A. , Cogswell A.M. , Amorim J.R.R. , Ganjam V.K.
Published: December 2010

Background: The combined glucose‐insulin test (CGIT) is helpful for evaluating insulin sensitivity. A continuous glucose monitoring system (CGMS) reports changes in interstitial glucose concentrations as they occur in the blood. Use of the CGMS minimizes animal contact and may be useful when performing a CGIT.

Hypothesis: Results obtained using a CGMS are useful for the evaluation of glucose responses during the evaluation of insulin sensitivity in equids.

Animals: Seven mature, obese ponies.

Methods: Ponies were equipped with CGMS for determination of interstitial glucose concentrations. Glucose (150 mg/kg, IV) and insulin (0.1 U/kg, IV) were administered and blood glucose concentrations determined at (minutes after time zero) 1, 5, 15, 25, 35, 45, 60, 75, 90, 105, and 120 with a hand‐held glucometer. Blood chemistry results were compared with simultaneously obtained results using CGMS.

Results: Concordance coefficients determined for comparison of blood glucose concentrations determined by a hand‐held glucometer and those determined by CGMS after the zero time point were 0.623, 0.764, 0.834, 0.854, and 0.818 (for delays of 0, 5, 10, 15, and 20 minutes, respectively).

Conclusions and Clinical Importance: Interstitial glucose concentrations obtained by the CGMS compared favorably to blood glucose concentrations. CGMS may be useful for assessment of glucose dynamics in the CGIT.
Biomarkers of Brain Injury in Foals with Hypoxic‐Ischemic Encephalopathy
Authors: Ringger N.C. , Giguère S. , Morresey P.R. , Yang C. , Shaw G.
Published: December 2010

Background:Neonatal hypoxic‐ischemic encephalopathy (NHIE) is a disease affecting newborn foals for which there is no antemortem diagnostic test.

Hypothesis:Ubiquitin C‐terminal hydrolase 1 (UCHL1) and the phosphorylated axonal forms of neurofilament H (pNF‐H) are markers of brain injury in foals with NHIE.

Animals:Thirty‐three foals with a clinical diagnosis consistent with NHIE and 17 healthy foals.

Methods:Retrospective study. Concentrations of UCHL1 and pNF‐H in plasma were measured by ELISA. The performance of the assays for the diagnosis of NHIE was assessed by receiver operating characteristic curve analysis. Concentrations of UCHL1 and pNF‐H were measured throughout the brains of 2 healthy foals.

Results:The diagnostic performance of UCHL1 (AUC = 0.86) was significantly higher (P= .001) than that of pNF‐H (0.52) for the diagnosis of NHIE. Median concentrations of UCHL1 (6.57 ng/mL; 2.35–11.90 ng/mL) in foals with a clinical diagnosis of NHIE were significantly (P< .001) higher than those of healthy controls (2.52 ng/mL; 1.4–4.01 ng/mL). The right sided reference interval for UCHL1 concentrations in healthy foals was 0–4.01 ng/mL. The sensitivity and specificity of UCHL1 (>4.01 ng/mL) for diagnosis of NHIE were 70% (51–84%) and 94% (72–99%), respectively. UCHL1 concentrations were higher in gray than white matter, while pNF‐H concentrations were higher in white than gray matter.

Conclusions and Clinical Importance:UCHL1 has potential as a marker of brain injury in foals with NHIE.
Laminar Leukocyte Accumulation in Horses with Carbohydrate Overload‐Induced Laminitis
Authors: Faleiros R.R. , Johnson P.J. , Nuovo G.J. , Messer N.T. , Black S.J. , Belknap J.K.
Published: December 2010

Background:While there is evidence of laminar leukocyte infiltration in black walnut extract (BWE)‐induced laminitis, there is no such evidence for carbohydrate overload (CHO) laminitis.

Objective:To assess presence of leukocytes and signs of epidermal stress/injury in the laminar tissue from horses with CHO‐induced laminitis.

Animals:Twenty‐four adult horses.

Methods:Immunohistochemistry for myeloid cell markers calprotectin (CP) and monocyte‐specific marker (CD163) was performed on laminar sections obtained from 2 groups of horses in the CHO model: the developmental time point (DTP) group (n = 6) and the onset of lameness (LAM) group (n = 6), and a control (CON) group (n = 8).

Results:DTP was characterized by an increase in CP+leukocytes (7.8‐fold increase versus CON,P< .001), and LAM time point was characterized by a more marked increase in laminar CP+(108.5‐fold,P< .001) and mild increase in CD163+(1.9‐fold,P= .007) cell counts. Increased CP epidermal signal (indicating epidermal stress or injury) occurred consistently at the LAM time point, although histological evidence of basement membrane (BM) detachment was minor, only being present in 3/6 horses.

Conclusions and Clinical Relevance:Maximal laminar leukocyte infiltration and epithelial stress occurred at the onset of lameness in the CHO model showing a different temporal pattern from the BWE model, where maximal leukocyte infiltration clearly precedes epithelial stress. Leukocyte infiltration before major histological changes in the CHO model indicates that leukocyte infiltration can be a cause of and not a reaction to BM degradation and structural failure.
Energy Harvesting From Impulsive Loads Using Intentional Essential Nonlinearities
Authors: Quinn D. Dane , Triplett Angela L. , Vakakis Alexander F. , Bergman Lawrence A.
Published: December 2010

Energy harvesting devices designed with intentional nonlinearities offer the possibility of increased performance under broadband excitations and realistic environmental conditions. This work considers an energy harvesting system based on the response of an attachment with strong nonlinear behavior. The electromechanical coupling is achieved with a piezoelectric element across a resistive load. When the system is subject to harmonic excitation, the harvested power from the nonlinear system exhibits a wider interval of frequencies over which the harvested power is significant, although an equivalent linear device offers greater efficiency at its design frequency. However, for impulsive excitation, the performance of the nonlinear harvesting system exceeds the corresponding linear system in terms of both magnitude of power harvested and the frequency interval over which significant power can be drawn from the mechanical vibrations.
One-Dimensional Computational Analysis of Proton Exchange Membrane Fuel Cell: A Parametric Study
Authors: Ghadiri Moghaddam Davood , Dashtaki Hamed , Kermani Mohammad Jafar
Published: December 2010

In this paper a one-dimensional, isothermal model of a PEM fuel cell has been developed to investigate the effect of some structural and operational parameters on the cell performance. Also a homogenous model used to modeling the cathode catalyst layer (CCL) which numerically solved. Overall, the model predictions agree qualitatively with the experiment results. The structural and operational parameters which considered in this paper are: (i) the volume fraction of the Nafion® ionomer phase within the CCL, Lm,c; (ii) the volume fraction of the gas diffusion layer (GDL) material buckled into the CCL, Lg,c; (iii) the catalyst layer saturation, s; (iv) the membrane thickness, δm; (v) membrane type (Nafion® or Dow); and (vi) operating cell pressure, P. The results show that with decreasing in saturation (decreasing the liquid water phase and increasing the gas water phase in the CL), the cell performance will improved. Also the result shows, the Lm,c and the membrane thickness are more effective parameters on CL performance than the others. The best performance are occurred at Lm,c = 0.4. The result indicates the linear increases in the cell performance for decreasing in the membrane thicknesses. Membrane thicknesses were calculated by assuming a 30% swelling of the dry membrane. The present model predicts some sensitivity to pressure variation and the cell performance will increase as pressure increases.
Design and Simulation of the Dynamic Behavior of a H-Infinity PEM Fuel Cell Pressure Control
Authors: Dashtaki Hamed , Ghadiri Moghaddam Davood , Kermani Mohammad Jafar , Hoseini Abardeh Reza , Menhaj Mohammad Bagher
Published: December 2010

In this paper, a simplified model partial pressure of Polymer Electrolyte Membrane Fuel Cell (PEMFC) is introduced. A Multi-Input–Multi-Output (MIMO) dynamic model with two inputs and two outputs is considered, where the inputs are control variable of anode and cathode, and the outputs are partial pressures of hydrogen and oxygen. Initially, the H∞ robust control strategies were applied to stabilize the system. The results show that the amplitude of alternative disturbances is decreased from 10 atm to 0.25 atm. Also, the pressure of each electrode tracks various input pressure profiles with negligible steady-state errors. On the other hand, the electrode pressure does not depend on the variations of constrained electrical current profiles by consumer in the PEM fuel cells. According to unsuitable percent overshoot (P.O.) and settling time of transient model response, system identification techniques are adopted to estimate the system’s transfer functions. After that a PID controller acting as a supervisory controller is properly developed to adjust the transient state behavior of the overall system. This makes the amplitude of alternative disturbances decrease from 10 atm to 0.003 atm. With this controller, the percent overshoot also decreases from 46% to 2% and the settling time (for 2% error) decreases from 0.26 to 0.03 seconds.
Modification of Results From Computational-Fluid-Dynamics Simulations of Single-Cell Solid-Oxide Fuel Cells to Estimate Multi-Cell Stack Performance
Authors: Sembler William J. , Kumar Sunil
Published: December 2010

A typical single-cell fuel cell is capable of producing less than one volt of direct current. Therefore, to produce the voltages required in most industrial applications, many individual fuel cells must typically be stacked together and connected electrically in series. Computational fluid dynamics (CFD) can be helpful to predict fuel-cell performance before a cell is actually built and tested. However, to perform a CFD simulation using a 3-dimensional model of an entire fuel-cell stack would require a considerable amount of time and multiprocessor computing capability that may not be available to the designer. To eliminate the need to model an entire multi-cell assembly, a study was conducted to determine the incremental effect on fuel-cell performance of adding individual solid-oxide fuel cells (SOFC) to a multi-fuel-cell stack. As part of this process, a series of simulations was conducted to establish a CFD-nodal density that would produce reasonably accurate results but that could also be used to create and analyze the relatively large models of the multi-cell stacks. Full 3-dimensional CFD models were then created of a single-cell SOFC and of SOFC stacks containing two, three, four, five and six cells. Values of the voltage produced when operating with various current densities, together with temperature distributions, were generated for each of these CFD models. By comparing the results from each of the simulations, adjustment factors were developed to permit single-cell CFD results to be modified to estimate the performance of stacks containing multiple fuel cells. The use of these factors could enable fuel-cell designers to predict multi-cell stack performance using a CFD model of only a single cell.
Electrochemical Performance of Ni-YSZ, Ni/Ru-GDC, LSM-YSZ, LSCF and LSF Electrodes for Solid Oxide Electrolysis Cells
Authors: Kim-Lohsoontorn P. , Yim H.-B. , Bae J.-M.
Published: December 2010

The electrochemical performance of solid oxide electrolysis cells (SOECs) having nickel – yttria stabilized zirconia (Ni-YSZ) hydrogen electrode and a composite lanthanum strontium manganite – YSZ (La0.8Sr0.2MnO3−δ – YSZ) oxygen electrodes has been studied over a range of operating conditions temperature (700 to 900°C). Increasing temperature significantly increased electrochemical performance and hydrogen generation efficiency. Durability studies of the cell in electrolysis mode were made over 200 h periods (0.1 A/cm2, 800°C, and H2O/H2 = 70/30). The cell significantly degraded over the time (2.5 mV/h). Overpotentials of various SOEC electrodes were evaluated. Ni-YSZ as a hydrogen electrode exhibited higher activity in SOFC mode than SOEC mode while Ni/Ru-GDC presented symmetrical behavior between fuel cell and electrolysis mode and gave lower losses when compared to the Ni-YSZ electrode. All the oxygen electrodes gave higher activity for the cathodic reaction than the anodic reaction. Among the oxygen electrodes in this study, LSM-YSZ exhibited nearest to symmetrical behavior between cathodic and anodic reaction. Durability studies of the electrodes in electrolysis mode were made over 20–70 h periods. Performance degradations of the oxygen electrodes were observed (3.4, 12.6 and 17.6 mV/h for LSM-YSZ, LSCF and LSF, respectively). The Ni-YSZ hydrogen electrode exhibited rather stable performance while the performance of Ni/Ru-GDC decreased (3.4 mV/h) over the time. This was likely a result of the reduction of ceria component at high operating voltage.
Modeling of Fluid Behavior and Calculation of the Permeability of the Gas Diffusion Layer in PEM Fuel Cell Using Lattice Boltzmann Method
Authors: Gao Y.
Published: December 2010

In the current work, a lattice Boltzmann method (LBM) is developed to study the fluid flow through digitally reconstructed 3D models of carbon paper GDLs generated by x-ray computed tomography, and the research on permeability calculation in the gas diffusion layer is also included. The methods involves the generation of a 3D digital model of a carbon paper GDL as manufactured using x-ray images acquired through x-ray micro-tomography at a resolution of 1.74 microns. The reconstructed 3D images then read into the LB model in order to predict three orthogonal permeability tensors when pressure is prescribed in the different flow direction. The Lattice Boltzmann method (LBM), an evolving pore-scale modeling approach, has received increasing attention in computational fluid dynamics. In the LBM, fluid is represented by a distribution of particles moving on a regular lattice. The LBM is extremely appealing in porous medium simulation, because the bounce-back boundary condition is efficient to treat solid boundary. It can deal with the boundary condition more easily than other tradition method. At the inlet/outlet boundaries, a pressure boundary condition is applied. This study characterizes the relationships between anisotropic permeability and porosity for gas diffusion layer, where hydrodynamics is analyzed in detail. The results indicate that the LBM is powerful and is able to provide excellent estimation on the permeability in a porous medium. The calculated permeability is in good agreement with existing measurements. The relationship between the permeability and the porosity is fitted well with the Kozeny-Carman equation and existing results.
2D CFD Modeling of Ammonia Fueled Solid Oxide Fuel Cells With Proton Conducting Electrolyte
Authors: Ni Meng
Published: December 2010

The use of ammonia as a fuel for solid oxide fuel cells (SOFCs) is a promising way for clean power generation. In this study, a 2D model is built to investigate the coupled transport and chemical/electrochemical reactions in a planar SOFC with proton conducting electrolyte (SOFC-H). The model consists of an electrochemical model relating the current density-voltage characteristics and a 2D computational fluid dynamics (CFD) model simulating the heat and mass transfer phenomena. The conservation laws for mass, momentum, energy and species are discretized and solved with the finite volume method (FVM). The coupling of pressure and velocity is treated with SIMPLEC algorithm. Simulations are conducted to study the distributions of current density, electrolyte Nernst potential, rate of ammonia thermal cracking and gas composition in the SOFC. The effects of operating potential and temperature on the rate of chemical/electrochemical reactions and the electric output of ammonia fueled SOFC-H are examined.
Proton Exchange Membranes Based on Blends of Poly(Benzimidazole) and Butylsulfonated Poly(Beznimidazole) for High Temperature PEMFC
Authors: Lin Hsiu-Li , Hu Chih-Ren , Su Po-Hao , Chou Yu-Cheng , Lin Che-Yu
Published: December 2010

Phosphoric acid doped poly(benzimidazole) (PBI) is one of excellent candidates of proton exchange membranes for high temperature (150–180°C) proton exchange membrane fuel cells (PEMFCs). However, the strong inter-polymer hydrogen bonds cause low elongation and brittleness of PBI membranes. In this work, we synthesize poly(benzimidazole) (PBI) and butylsulfonated poly(benzimidazole) (PBI-BS), in which around 22 mole% of imidazole –NH groups of PBI are grafted with sulfonated butyl groups. We show the elongation, phosphoric acid doping level, and proton conductivity of PBI can be improved by blending ∼ 20 wt% of PBI-BS in the PBI membrane, and the membrane electrode assembly prepared from PBI/PBI-BS (8/2 by wt) blend membrane has a better PEMFC performance at 140°C ∼ 180°C than that prepared from PBI membrane. It is believed that the crosslink interactions of imidazole -NH and -N=C-groups with side chain –C4H8−SO3H groups of PBI-BS reduces the inter-PBI hydrogen bonds and increases the free volume of polymers, which leads to the enhancements of the membrane toughness and phosphoric acid doping level and the PEMFC performance.
On the Measured PEMFC Anode and Cathode Reversible Heats
Authors: Burheim Odne S. , Kjelstrup Signe , Pharoah Jon G. , Vie Preben J. S. , Mo̸ller-Holst Steffen
Published: December 2010

A recently constructed 2D calorimeter was used to measure the work and the total heat production of a single PEM fuel cell that is operated on hydrogen and oxygen at 50 °C and 1 bar. The cells had different membranes and catalyst layers, but the same porous transport layer and micro-porous layer. In this paper the distribution of the reaction entropy between the anode and the cathode, also known as the Peltier heats, was determined. This was done by the use of the measured heat through the anode and the cathode polarisation plates, the measured cell resistance, the measured overpotential and a fuel cell thermal model. The results show that the reaction entropy is almost solely related to the cathode and that the Peltier heat of the anode is near zero.
Toward Developing a Computational Capability for PEM Fuel Cell Design and Optimization
Authors: Chen Ken S. , Carnes Brian , Jiang Fangming , Luo Gang , Wang Chao-Yang
Published: December 2010

In this paper, we report the progress made in our project recently funded by the US Department of Energy (DOE) toward developing a computational capability, which includes a two-phase, three-dimensional PEM (polymer electrolyte membrane) fuel cell model and its coupling with DAKOTA (a design and optimization toolkit developed and being enhanced by Sandia National Laboratories). We first present a brief literature survey in which the prominent/notable PEM fuel cell models developed by various researchers or groups are reviewed. Next, we describe the two-phase, three-dimensional PEM fuel cell model being developed, tested, and later validated by experimental data. Results from case studies are presented to illustrate the utility of our comprehensive, integrated cell model. The coupling between the PEM fuel cell model and DAKOTA is briefly discussed. Our efforts in this DOE-funded project are focused on developing a validated computational capability that can be employed for PEM fuel cell design and optimization.
In Situ Membrane Parameter Determination Using Simultaneously Locally Resolved Impedance Spectroscopy and Dynamic Water Partial Pressure Measurement in PEFCs
Authors: Bayer M. H. , Wokaun A. , Scherer G. G. , Schneider I. A.
Published: December 2010

Tunable diode laser absorption spectroscopy (TDLAS) is used to measure the local ac response of the water partial pressure to a sinusoidal current excitation during locally resolved impedance measurements in a sub-saturated polymer electrolyte fuel cell (PEFC). The experimental results, along with the locally resolved impedance data are compared to calculated data as obtained from a 1+1 dimensional ac impedance model. The detailed experimental data allows model validation and in situ parameter determination. The model results are in good agreement with the experimental results. This emphasizes the importance to consider the build-up of water partial pressure oscillations along the gas channels in ac impedance models for sub-saturated PEFCs. The results show that minor modifications of literature membrane parameters are needed for a good fit to the experimental data set.
CFD Modeling Considering Different Kinetic Models for Internal Reforming Reactions in an Anode-Supported SOFC
Authors: Paradis Hedvig , Andersson Martin , Yuan Jinliang , Sunde´n Bengt
Published: December 2010

Fuel cells are electrochemical devices that transform chemical energy into electricity. Solid oxide fuel cells (SOFCs) are particularly interesting because they can handle the reforming of hydrocarbon fuels directly within the cell. This is possible due to their high operating temperature. The purpose of this study is to develop an anode-supported SOFC model, to enhance the understanding of the internal reforming and effects on the transport processes. In this study, a CFD approach, based on the finite element method, was implemented for the analysis to unravel the interaction between internal reforming, momentum, heat and mass transport. COMSOL Multiphysics is used to analyze the effects of different global kinetic models available for the steam reforming reaction. The three different reaction rates applied in this study were developed and correlated through experimental studies found in the literature. An equilibrium equation is implemented for the reaction rate for the water-gas shift reaction. The partial pressures and the related reaction order of the pressure are found to affect the reaction rate.
Dynamic Modeling of a Solid Oxide Fuel Cell System in Modelica
Authors: Andersson Daniel , A˚berg Erik , Yuan Jinliang , Sunde´n Bengt , Eborn Jonas
Published: December 2010

In this study a dynamic model of a solid oxide fuel cell (SOFC) system has been developed. The work has been conducted in a cooperation between the Department of Energy Sciences, Lund University, and Modelon AB using the Modelica language and the Dymola modeling and simulation tool. Modelica is an equation based, object oriented modeling language, which promotes flexibility and reuse of code. The objective of the study is to investigate the suitability of the Modelica language for dynamic fuel cell system modeling. A cell electrolyte model including ohmic, activation and concentration irreversibilities is implemented and verified against simulations and experimental data presented in the open literature. A 1D solid oxide fuel cell model is created by integrating the electrolyte model and a 1D fuel flow model, which includes dynamic internal steam reforming of methane and water-gas shift reactions. Several cells are then placed with parallel flow paths and connected thermally and electrically in series. By introducing a manifold pressure drop, a stack model is created. The stack model is applied in a complete system including an autothermal reformer, a catalytic after-burner, a steam generator and heat exchangers. Four reactions are modeled in the autothermal reformer; two types of methane steam reforming, the water-gas shift reaction and total combustion of methane. The simulation results have been compared with those in the literature and it can be concluded that the models are accurate and that Dymola and Modelica are tools well suited for simulations of the transient fuel cell system behaviour.
Study of a Pseudo Bipolar Design for a Piezoelectric Proton Exchange Membrane Fuel Cell With Nozzle and Diffuser
Authors: Ma Hsiao-Kang , Wang Jyun-Sheng , Chang Ya-Ting
Published: December 2010

Previous studies of a piezoelectric proton exchange membrane fuel cell with nozzle and diffuser (PZT-PEMFC-ND) have shown that a PZT device could solve flooding problems and improve cell performance. The results also indicated that the rectification efficiency (γ) of the diffuser elements, the PZT vibrating frequency (f), and the displaced volume per stroke (ΔV) affected the flow rate of the PZT device. The rectification efficiency of the diffuser elements, which is an indicator of the preferential direction, depends on the geometrical parameters (AR and θ) and the Reynolds number. In this study, an innovative design for a PZT-PEMFC-ND bi-cell with pseudo bipolar electrodes was developed to achieve a higher power in the stack design to solve water flooding problems and improve cell performance. This new design, with a reaction area of 8 cm2, contains two cells with two outside anodes and two inside cathodes that share a common PZT vibrating device for pumping air flow. The influence of the varying aspect ratio (AR) of the diffuser elements on the unit cell flow rate were investigated using a three-dimensional transitional model. The results show that a proper AR value of 11.25 for the diffuser with a smaller θ of 5° could ensure a smoother intake of the air and thus better cell performance. A lower AR value of 5.63 resulted in smaller actuation pressure inside the chamber, and thus the produced water could not be pumped out. However, a larger AR of 16.88 induced a blocking phenomenon inside the diffuser element, and thus less air was sucked into the cathode chamber. The performance of the PZT-PEMFC-ND bi-cell could be 1.6 times greater than that of the single cell. This performance may be influenced by the phase difference of the operating modes.
Macroscopic Modeling of Two-Phase Flow Transport Inside Polymer Electrolyte Fuel Cells
Authors: Yoneda Masakazu , Takimoto Masato
Published: December 2010

It is very important to understand the transport phenomena under various operating and structural conditions to achieve the high performance of Polymer Electrolyte Fuel Cell (PEFC). In this study, the effect of liquid water removal inside flow channel on the performance of a large-sized cell was investigated. To calculate the performance of a cell or stack, we developed a simulation tool with macroscopic models of MEA characteristics such as electrochemical kinetics, catalyst utilization, limiting current density, and two-phase transport inside the gas diffusion layer (GDL) and the flow channel. At first, we investigated the effect of wall contact angle and cross-section of flow channel on the liquid water removal by the Moving Particle Semi-implicit method and calculated the velocity ratio (liquid water velocity for gas velocity) inside the flow channel including the effect of mesoscopic structure of GDL. Applying this correlation to the two-phase model of the macroscopic PEFC simulation, we confirmed that the performance in the case of hydrophilic and shallow-shaped channel is much better in other case under low utilization operation.
Theoretical Study of Transport Parameters Inside Catalyst Layer of Polymer Electrolyte Fuel Cell
Authors: Cheng Chin-Hsien , Su Ay
Published: December 2010

One of the key components inside fuel cell is the catalyst layer which has the most complex composition and transport phenomena. Physical parameters which often used in the simulation works regarding catalyst layer are mostly based on the empirical relations or derivation from experimental results. Transport parameters for species inside Nafion phase are critical for the catalyst layer modeling. This paper uses a nano-scale approach — classic molecular dynamic (CMD) simulation to evaluate the transport parameters inside Nafion phase of the catalyst layer. Two important transport parameters, oxygen diffusivity and water diffusivity, are evaluated at different conditions. The dependency of these two transport parameters on the various operation conditions such as different water content and temperature etc are also investigated. Simulation works at different scale (ex: CFD etc) can be easily improved by incorporating correlations obtained by the present work based on the CMD.
The Influence of Transient Variations on the Durability of PEM Fuel Cells
Authors: Chen Chang-Ching , Sung Chia-Chi , Liao Chun-Ting
Published: December 2010

Recently, a number of studies have shown that the ionic conductivity of a membrane electrode assembly (MEA) strongly depends on the water retention ability of the proton exchange membrane in the fuel cell. This suggests that water management in the cell is important in achieving high PEMFC performance. Therefore, membrane dehydration, water flooding, and cell durability have become major challenges in PEMFC applications. In this study, we investigated the effect of the transient phenomenon on PEMFC performance using an electrode with an area of 25 cm2. Parameters, including the cell temperature, stoichiometry of the fuel/oxidant, relative humidity of the reactive gas, were used for analyzing the performance of PEMFCs, along with fluid field imaging technologies. The results indicated that the ionic conductivity of the proton exchange membrane has a positive effect on PEMFC performance. PEMFC voltage will cause a sudden change in the current density overshoot phenomenon. This is because the decline in oxygen concentration and the oxygen concentration itself are also affected by the water concentration. This study revealed the relationship between the transient phenomenon and the performance of PEMFCs.
Electroless Ni-Fe-P Alloy on Ferritic Stainless Steel Solid Oxide Fuel Cell Interconnect
Authors: Geng Shujiang , Zhao Hui
Published: December 2010

In this study, Ni-Fe-P alloy layer was deposited on the ferritic stainless steel by means of a cost-effective technique of electroless method. After thermal exposure at 800°C in air corresponding to the environment of the SOFC cathode, the oxidation kinetics indicated that the mass gain of steel with Ni-Fe-P alloy layer was higher than that of the steel substrate on which a Cr2O3 layer was mainly grown. A double-layer oxide scale with a NiO/(Ni,Fe)3O4/(Ni,Cr)3O4 outer layer and a protective Cr2O3 inner layer was formed on the steel with Ni-Fe-P alloy. The formation of the oxide outer layer was highly desirable to prevent the evaporation of the chromia inner layer developed from the substrate steel, and reduced the scale area specific resistance (ASR).
Effect of PTFE Loading on the Performance of the GDL in Water Removal
Authors: Shahraeeni Mehdi , Hoorfar Mina
Published: December 2010

Pore network modeling is a relatively new approach for simulation of fluid flows in porous media of the fuel cells. The porous media is simulated with a network of pores connected to each other through throats. The radius of the pores and throats, the length of the throats and other geometric specifications of the network is extracted with respect to the tomography of the porous media under study. The flow of the fluid though the network is then studied using simplified Navier-Stokes equation (usually Darcy’s law). In this paper, a pore-network approach is adopted in order to study the motion of liquid water inside GDL of PEM fuel cells. The effect of wettability of the medium is examined on the movement of water droplets inside the GDL.
Novel Approaches for the Integration of High Temperature PEM Fuel Cells Into Aircrafts
Authors: Novillo Eva , Pardo Mo´nica , Garci´a-Luis Alberto
Published: December 2010

Reduced greenhouse gas emissions via improved energy efficiency represents the ultimate challenge for the energy economy of the future. In this context, fuel cells for power generation aboard aircrafts have a promising potential to effectively contribute to the greening of air transportation. They can simplify today’s aircraft comprising electric, pneumatic and hydraulic systems towards a more electric airplane. Although they are not considered in the short term as an alternative propulsion system for commercial aviation, many efforts are being devoted to their use as auxiliary power units and even aiming to build a distributed power network that might alleviate duties of the engine driven generators. In addition they allow new functions as zero emission during taxiing on ground and /or increase safety by replacing the emergency ram air turbine (RAT) by a fuel cell based emergency power generator. The present paper focuses on the effort that Compan˜i´a Espan˜ola de Sistemas Aerona´uticos (CESA) is putting into the development of an aeronautical fuel cell system based on a high temperature PEMFC covering all aspects from fundamental research in materials & processes to final integration concepts as a function of different architectures. A great deal of time and effort has been invested to overcome the challenges of PEM fuel cell operation at high temperatures. Among the advantages of these systems are the enhancement of electrochemical kinetics, simplification of water management and cooling, recovery of wasted heat and the possibility of utilizing reformed hydrogen thanks to higher tolerance to impurities. However, new problems arise with the high temperature concept that must be addressed like structural and chemical degradation of materials at elevated temperatures. One of the aeronautical applications where a fuel cell has an important role to play in the short term is the emergency power unit. Weight and mechanical complexity of traditional ram air turbines could be drastically reduced by the introduction of a hydrogen fueled system. In addition, the output of the fuel cell is aircraft’s speed independent. This means additional power supply in case of emergency allowing a safer landing of the aircraft. However, a RAT replacement must overcome the specific difficulties concerning the very short start-up times allowed and the heating/cooling strategies to quickly raise the temperature to elevated levels and accurately maintaining the optimum operating range once in service.
Development and Characterization of Conductive Materials for PEMFC Bipolar Plates
Authors: Mighri Frej , Nguyen Luc , Elkoun Said
Published: December 2010

The aim of this work was to develop and characterize electrically conductive bipolar plates (BPPs) used in proton exchange membrane fuel cells (PEMFCs). These BPPs were made from highly conductive blends of polyethylene terephthalate (PET) and polyvinylidene fluoride (PVDF), as matrix phase. The conductive materials were developed from carefully formulated blends composed of conductive carbon black powder (CB) mixed with pure PET, PVDF, or with PVDF/PET systems. They were first developed by twin screw extrusion (TSE) process then compression molded to give BPP final shape. Focus was made on the effect of crystallization of PVDF and PET polymers on the electrical through-plane resistivity of BPPs. It was observed that lower resistivity was obtained with PVDF/CB blends due to the higher interfacial energy between the PVDF matrix and CB and also the higher density and crystallinity of PVDF, compared to those of PET. For the different systems studied, slow cooling rates helped to attain the lowest values of through-plane resistivity since higher PET crystallinity led to smaller amorphous region in which CB was more concentrated. In addition, BPPs made from (PVDF/PET)/CB blends led to lower through-plane resistivity when the PVDF/PET phase had a co-continuous morphology. This is mainly due to the selective localization of the CB in the PET phase leading to a denser conductive carbon network. The lowest through-plane resistivity was around 0.3 Ohm.cm obtained with a (50/50 PVDF/PET)/CB filled with 30 wt% CB.
In-Plane Temperature Measurement and Water Droplet Detection of a Proton Exchange Membrane Fuel Cell Using Phosphor Thermometry: Initial Development
Authors: Inman Kristopher , Wang Xia , Sangeorzan Brian
Published: December 2010

Thermal behavior inside fuel cells plays a significant role in fuel cell performance and durability. Internal temperatures of a proton exchange membrane (PEM) fuel cell govern the ionic conductivities of the polymer electrolyte, influence the reaction rate at the electrodes, and control the water vapor pressure inside the cell. Temperature gradients also influence mass transport due to phase-change-induced flow and thermo-osmosis. Many techniques developed for studying in situ temperatures such as thermocouples sensors either disrupt fuel cell performance or carry unknown accuracy. The objectives of this research are to design and construct thermal sensors based on the principles of the lifetime-decay method of phosphor thermometry to measure temperatures of cathode gas diffusion layer inside a PEM fuel cell with minimal invasion. The sensors also demonstrate the possibility of detecting water droplet formation in the flow channels qualitatively making it possible to experimentally relate local temperature distribution with liquid water formation. Further development is required in order to increase the accuracy and utility of the sensors before conclusive testing can be performed.
First Principle Electrochemical Impedance Spectroscopy Simulation for SOFCs
Authors: Xie Yuanyuan , Xue Xingjian
Published: December 2010

Electrochemical impedance spectroscopy (EIS) is a widely utilized experimental method for fundamental mechanism understanding and diagnosis of solid oxide fuel cells (SOFCs). However, EIS experimental results are in general interpreted using equivalent circuit model method. When EIS response induced by very complicated multi-physics processes in SOFC is approximated with a simple equivalent circuit, it will inevitably lead to ambiguity. In this research, first principle EIS simulation method is developed to link multi-physics processes of a button cell to EIS response. The EIS modeling method is validated using experimental data from open literature. The validated EIS model is employed to investigate SOFC performance. Simulation results indicate that EIS response contains a plethora of SOFC behavior information that collectively contributed by intrinsic SOFC material property, porous microstructure, as well as operating conditions. The simulation method developed in this research can be potentially utilized for interpretation and de-convolution of experimental EIS results.
Pore Structure Modeling of Flow in Gas Diffusion Layers of Proton Exchange Membrane Fuel Cells
Authors: Shi Zhongying , Wang Xia
Published: December 2010

The gas diffusion layer (GDL) in a proton exchange membrane (PEM) fuel cell has a porous structure with anisotropic and non-homogenous properties. The objective of this research is to develop a PEM fuel cell model where transport phenomena in the GDL are simulated based on GDL’s pore structure. The GDL pore structure was obtained by using a scanning electron microscope (SEM). GDL’s cross-section view instead of surface view was scanned under the SEM. The SEM image was then processed using an image processing tool to obtain a two dimensional computational domain. This pore structure model was then coupled with an electrochemical model to predict the overall fuel cell performance. The transport phenomena in the GDL were simulated by solving the Navier-Stokes equation directly in the GDL pore structure. By comparing with the testing data, the fuel cell model predicted a reasonable fuel cell polarization curve. The pore structure model was further used to calculate the GDL permeability. The numerically predicted permeability was close to the value published in the literature. A future application of the current pore structure model is to predict GDL thermal and electric related properties.
Combination of a Nonlinear Static and a Linear Dynamic Model of the NETL HyPer System
Authors: Restrepo Bernardo , Banta Larry E. , Tsai Alex J. , Tucker David
Published: December 2010

A nonlinear steady-state thermodynamic model was coupled with linearized dynamic transfer functions to achieve a dynamic description of the NETL HyPer Fuel Cell Gas Turbine (FC/GT) power plant. Nonlinear dynamic models insure accuracy in modeling steady-state behavior over a wide range of operation, but such models are often complex and difficult to implement in real-time using conventional control systems equipment. Conversely, the linearized models provide the ability to predict transient behavior upon which dynamic control systems can be constructed, but are valid only about a narrow operating point. In systems with one or two state variables, it is relatively straightforward to construct controllers that use gain scheduling schemes. But the HyPer system contains many coupled state variables and high degrees of nonlinearity. A method called Real-Time Piecewise Linear Dynamic Modeling (RPLDM) has been implemented to provide both modeling accuracy and real-time performance for the HyPer system over a multi-dimensional hypersurface. Both the nonlinear and the linear constituent models were constructed based on experimental data collected in tests performed on the HyPer system. The models presently consider only the cathode circuit of the fuel cell and contain a recuperated gas turbine system equipped with an electric generator, a simulated fuel cell cathode and various bypass valves for thermal management and system control. The key variables of air temperature, air pressure and mass flow to the cathode of the fuel cell and the turbomachinery have been predicted to within 2% of measured values. This paper presents the modeling technique and comparisons of the model output with experimental data.
Nonlinear Analysis of Two-Phase Instabilities in PEMFC Parallel-Channel Cathodes
Authors: Siefert Nicholas , Ho Chi-Hsin , Litster Shawn
Published: December 2010

Liquid water management is a critical issue in the development of proton exchange membrane (PEM) fuel cells. Liquid water produced electrochemically can accumulate and flood the microchannels in the cathodes of PEM fuel cells. Since the liquid coverage of the cathode can fluctuate in time for two-phase flow, the rate of oxygen transport to the cathode catalyst layer can also fluctuate in time, and this can cause the fuel cell power output to fluctuate. This paper will report experimental data on the voltage loss and the voltage fluctuations of a PEM fuel cell due to flooding as a function of the number of parallel microchannels and the air flow rate stoichiometric ratio. The data was analyzed to identify general scaling relationships between voltage loss and fluctuations and the number of channels in parallel and the air stoichiometric ratio. The voltage loss was found to scale proportionally to the square root of the number of channels divided by the air stoichiometric ratio. The amplitude of the fluctuations was found to be linearly proportional to the number of microchannels and inversely proportional to the air stoichiometric ratio squared. The data was further analyzed by plotting power spectrums and by evaluating the non-linear statistics of the voltage time-series.
Design and Optimization of a Power Management Strategy for a Fuel Cell-Battery Hybrid Vehicle
Authors: Fadel Ahmad , Zhou Biao
Published: December 2010

The implementation of a fuel cell-battery hybrid vehicle requires a supervisory control strategy that will manage the power distribution between the fuel cell and the battery. Fuzzy logic is one of the most commonly used control methods for this application. However, the disadvantage with this type of control is that there are no clear methods to determining the training data for the fuzzy logic controller and thus, most controllers developed in literature rely on experience in designing the fuzzy logic parameters. This paper presents an alternative local optimization approach that does not require prior knowledge of the driving cycle. In order to validate the effectiveness of the optimization approach, standard performance measures that consider battery life, fuel consumption and system efficiency are developed in this paper. The mathematical system modeling in this paper is based on a small SAE Baja vehicle powertrain. The design process of two different power management strategies (one using fuzzy logic and another using optimization) are presented, the mathematical model is then used to simulate and compare the results obtained from each control method.
Cathode Temperature Management During Hybrid System Startup
Authors: Banta Larry E. , Restrepo Bernardo , Tsai Alex J. , Tucker David
Published: December 2010

Management of air flow through the cathode of a hybrid Solid Oxide Fuel Cell/Gas Turbine generation system is of critical importance for the survival of the fragile fuel cell. The cell must be protected from excessive thermal gradients within each cell/stack and from pressure differences between the anode and cathode. While significant modeling of hybrid system performance has been done for the steady state case, only modest attention has been given to startup and shutdown of a hybrid system. Various researchers have performed modeling studies on SOFC during startup, and have concluded that thermal ramp-up times can require anywhere from less than one hour to more than four hours to avoid thermal shock and potential destruction of the fuel cells. For hybrid systems employing single spool turbine/compressor systems, gradual ramping will be difficult because the rotating components must be brought up to full operating speed quickly to avoid stalling the compressor. This paper proposes a strategy for accommodation of the conflicting startup constraints using both experimental data from the NETL HyPer system and simulation approaches.
Experimental and Numerical Analysis of Subfreezing Operation in PEM Fuel Cells
Authors: Mishler Jeff , Wang Yun , Mukherjee Partha P. , Mukundan Rangachary , Borup Rodney L.
Published: December 2010

In this work, we present a neutron radiography and analysis, as well as modeling study on cold-start operation of polymer electrolyte membrane (PEM) fuel cells. Fuel cells with Gore™ or LANL MEAs and SGL or E-Tek ELAT GDLs are tested in varying subfreezing temperatures (−40 to 0°C) to determine the time scale of cold-start failure, amount of solid water formation, solid water formation location, and. A higher PTFE-loading in the MPL is found to decrease loss in electrocatalytic surface area in our case. Theoretical analysis is also conducted and model predictions are compared with the experimental data in terms of the cell voltage evolution.