scholarly journals Deconvolution of Gas Diffusion Polarization in Ni/Gadolinium-Doped Ceria Fuel Electrodes

2021 ◽  
Author(s):  
Cedric Grosselindemann ◽  
Niklas Russner ◽  
Sebastian Dierickx ◽  
Florian Wankmueller ◽  
Andre Weber
Keyword(s):  
Cell Model ◽  
Gas Diffusion ◽  
Transport Parameter ◽  
Inert Component ◽  
Fuel Gas ◽  
Current Voltage ◽  
Wide Range ◽  
Diffusion Polarization ◽  
Precise Quantification ◽  
Hydrogen Electrooxidation

Abstract The deconvolution of physicochemical processes in impedance spectra of SOCs with nickel/ceria fuel electrodes is challenging as gas diffusion strongly overlaps with the electrochemical processes at fuel and air electrode. To overcome this issue, symmetrical cells were applied and the gas diffusion process at the fuel electrode was quantified by altering the inert component (nitrogen / helium) in a ternary fuel gas mixture. An effective gas transport parameter considering microstructural and geometrical features was derived, enabling a precise quantification of polarization resistances related to gas diffusion and hydrogen electrooxidation. The obtained values were applied to parameterize a dc cell model. The model validation in fuel cell and electrolyzer mode showed an excellent agreement between measured and simulated current/voltage characteristics over a wide range of technically meaningful gas compositions and operating temperatures.

Experimental Correlation of a Thermal / Fluid Dynamic / Electrical Performance Model of a Multiple-Tube, Vapor-Anode AMTEC Cell

1999 ◽  
Author(s):  
Terry J. Hendricks ◽  
Chendong Huang ◽  
Joseph C. Giglio
Keyword(s):  
Test Data ◽  
Model Prediction ◽  
Cell Model ◽  
Performance Model ◽  
Cell Performance ◽  
High Current ◽  
Current Voltage ◽  
Wide Range ◽  
Model Predictions ◽  
Prediction Test

Abstract An AMTEC (Alkali-Metal Thermal-to-Electric Conversion) cell performance analysis model described by Hendricks et al. (1998) has been correlated with experimental data by comparing its predictions for Beta” alumina solid electrolyte (BASE) and evaporator temperatures, voltage, power output, and conversion efficiency with experimental measurements on two versions of a PX-6 AMTEC cell. The critical features of this AMTEC cell model, the PX-6 experimental set up and testing, and the model correlation PX-6 test data are discussed in this work. Model prediction/test data comparisons are presented across a wide range of current-voltage conditions and hot side temperatures for two significantly different cell lengths. Cell model predictions demonstrate good agreement with experimental PX-6 test data in simultaneously predicting BASE tube and evaporator temperatures, the onset of sodium (Na) condensation in the BASE tubes, current-voltage characteristics, and power output in high current ranges (i.e., > 1.5 A). The model also has demonstrated good capability to predict cell conversion efficiency at high currents when Na is not condensing in the BASE tubes. The good model prediction/test data comparisons have demonstrated the progress in developing this cell performance model and increased confidence in its technical foundations, algorithm implementation, and capability to predict AMTEC cell performance. The AMTEC cell model’s capability to simultaneously predict many critical cell performance parameters across a wide range of hot side temperatures, at high current conditions, and different cell lengths demonstrates the progress that has been made in its development. It has demonstrated good predictive capability, utility, and flexibility as a performance design and analysis tool for sophisticated AMTEC cell design. Testing limitations prevented testing at low current levels (i.e., < 1.5 A), so future experimental validation studies should focus on correlating model predictions at low currents.

CFD Analysis of a Constructal Flow Distributor as a Bipolar Plate for PEMFC’s

2009 ◽  
Author(s):  
Bladimir Ramos-Alvarado ◽  
Abel Hernandez-Guerrero ◽  
Daniel Juarez-Robles ◽  
Cuauhtemoc Rubio-Arana ◽  
Francisco Vital-Flores
Keyword(s):  
Fuel Cell ◽  
Gas Flow ◽  
Cell Model ◽  
Flow Analysis ◽  
Current Density Distribution ◽  
Gas Diffusion ◽  
Proton Exchange ◽  
Membrane Electrode ◽  
Wide Range ◽  
Flow Distributor

A plate-type constructal flow distributor is implemented as a gas distributor for a proton exchange membrane fuel cell. A 3D complete model is simulated using CFD techniques. The fuel cell model includes the gas flow channels, the gas diffusion layers and the membrane electrode assembly (MEA). The governing equations for the mass and momentum transfer are solved including the pertinent source terms due to the electrochemical reactions in the different zones of the fuel cell. Similar configurations have been already presented in previous studies but using the flow distributor as a heat remover; however, the similarity between heat transfer and mass transfer phenomena has lead to investigate the performance of such distributors in fuel cells. In terms of flow analysis, it was found that the constructal flow distributor presents a low pressure drop for a wide range of Reynolds number conditions at the inlet, as well as an excellent uniformity of flow distribution. Some of the advantages of the constructal model, over traditional flow patterns, are the uniformity of current density distribution, the adequate consumption of species and the possibility to increase the bifurcation levels to cover a larger reaction area.

scholarly journals Study and Assessment of Defect and Trap Effects on the Current Capabilities of a 4H-SiC-Based Power MOSFET

Electronics ◽  
2021 ◽  
Vol 10 (6) ◽  
pp. 735
Author(s):  
Fortunato Pezzimenti ◽  
Hichem Bencherif ◽  
Giuseppe De Martino ◽  
Lakhdar Dehimi ◽  
Riccardo Carotenuto ◽  
...  
Keyword(s):  
Drain Current ◽  
Oxide Semiconductor ◽  
Temperature Dependent ◽  
Channel Mobility ◽  
Blocking Voltage ◽  
Current Voltage ◽  
Wide Range ◽  
Temperature Ranges ◽  
Joint Contribution ◽  
State Resistance

A numerical simulation study accounting for trap and defect effects on the current-voltage characteristics of a 4H-SiC-based power metal-oxide-semiconductor field effect transistor (MOSFET) is performed in a wide range of temperatures and bias conditions. In particular, the most penalizing native defects in the starting substrate (i.e., EH6/7 and Z1/2) as well as the fixed oxide trap concentration and the density of states (DoS) at the 4H-SiC/SiO2 interface are carefully taken into account. The temperature-dependent physics of the interface traps are considered in detail. Scattering phenomena related to the joint contribution of defects and traps shift the MOSFET threshold voltage, reduce the channel mobility, and penalize the device current capabilities. However, while the MOSFET on-state resistance (RON) tends to increase with scattering centers, the sensitivity of the drain current to the temperature decreases especially when the device is operating at a high gate voltage (VGS). Assuming the temperature ranges from 300 K to 573 K, RON is about 2.5 MΩ·µm2 for VGS > 16 V with a percentage variation ΔRON lower than 20%. The device is rated to perform a blocking voltage of 650 V.

scholarly journals Gas Damping in Capacitive MEMS Transducers in the Free Molecular Flow Regime

Sensors ◽  
2021 ◽  
Vol 21 (7) ◽  
pp. 2566
Author(s):  
Boris A. Boom ◽  
Alessandro Bertolini ◽  
Eric Hennes ◽  
Johannes F. J. van den Brand
Keyword(s):  
Flow Regime ◽  
Gas Diffusion ◽  
Diffusion Time ◽  
Molecular Flow ◽  
Free Molecular Flow ◽  
Simple Analytical Model ◽  
Gas Damping ◽  
Wide Range ◽  
Capacitive Mems ◽  
Insight Into

We present a novel analysis of gas damping in capacitive MEMS transducers that is based on a simple analytical model, assisted by Monte-Carlo simulations performed in Molflow+ to obtain an estimate for the geometry dependent gas diffusion time. This combination provides results with minimal computational expense and through freely available software, as well as insight into how the gas damping depends on the transducer geometry in the molecular flow regime. The results can be used to predict damping for arbitrary gas mixtures. The analysis was verified by experimental results for both air and helium atmospheres and matches these data to within 15% over a wide range of pressures.

scholarly journals Transport Parameter Correlations for Digitally Created PEFC Gas Diffusion Layers by Using OpenPNM

Processes ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 1141
Author(s):  
Ángel Encalada-Dávila ◽  
Mayken Espinoza-Andaluz ◽  
Julio Barzola-Monteses ◽  
Shian Li ◽  
Martin Andersson
Keyword(s):  
Fuel Cell ◽  
Energy Conversion ◽  
Transport Phenomena ◽  
Electrical Energy ◽  
Gas Diffusion ◽  
Polymer Electrolyte Fuel Cell ◽  
Carbon Paper ◽  
Transport Parameter ◽  
Transport Parameters ◽  
Depth Analysis

A polymer electrolyte fuel cell (PEFC) is an electrochemical device that converts chemical energy into electrical energy and heat. The energy conversion is simple; however, the multiphysics phenomena involved in the energy conversion process must be analyzed in detail. The gas diffusion layer (GDL) provides a diffusion media for reactant gases and gives mechanical support to the fuel cell. It is a complex medium whose properties impact the fuel cell’s efficiency. Therefore, an in-depth analysis is required to improve its mechanical and physical properties. In the current study, several transport phenomena through three-dimensional digitally created GDLs have been analyzed. Once the porous microstructure is generated and the transport phenomena are mimicked, transport parameters related to the fluid flow and mass diffusion are computed. The GDLs are approximated to the carbon paper represented as a grouped package of carbon fibers. Several correlations, based on the fiber diameter, to predict their transport properties are proposed. The digitally created GDLs and the transport phenomena have been modeled using the open-source library named Open Pore Network Modeling (OpenPNM). The proposed correlations show a good fit with the obtained data with an R-square of approximately 0.98.

scholarly journals Holistic Approach to Design, Test, and Optimize Stand-Alone SOFC-Reformer Systems

Processes ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 348
Author(s):  
Michael Höber ◽  
Benjamin Königshofer ◽  
Philipp Wachter ◽  
Gjorgji Nusev ◽  
Pavle Boskoski ◽  
...  
Keyword(s):  
Rural Communities ◽  
High Efficiency ◽  
Diffusion Processes ◽  
Holistic Approach ◽  
Maximum Error ◽  
Gas Diffusion ◽  
Electrochemical Analysis ◽  
Internal Reforming ◽  
Operation Conditions ◽  
Wide Range

Reliable electrical and thermal energy supplies are basic requirements for modern societies and their food supply. Stand-alone stationary power generators based on solid oxide fuel cells (SOFC) represent an attractive solution to the problems of providing the energy required in both rural communities and in rurally-based industries such as those of the agricultural industry. The great advantages of SOFC-based systems are high efficiency and high fuel flexibility. A wide range of commercially available fuels can be used with no or low-effort pre-treatment. In this study, a design process for stand-alone system consisting of a reformer unit and an SOFC-based power generator is presented and tested. An adequate agreement between the measured and simulated values for the gas compositions after a reformer unit is observed with a maximum error of 3 vol% (volume percent). Theoretical degradation free operation conditions determined by employing equilibrium calculations are identified to be steam to carbon ratio (H2O/C) higher 0.6 for auto-thermal reformation and H2O/C higher 1 for internal reforming. The produced gas mixtures are used to fuel large planar electrolyte supported cells (ESC). Current densities up to 500 mA/cm2 at 0.75 V are reached under internal reforming conditions without degradation of the cells anode during the more than 500 h long-term test run. More detailed electrochemical analysis of SOFCs fed with different fuel mixtures showed that major losses are caused by gas diffusion processes.

scholarly journals "Creep currents" in single frog atrial cells may be generated by electrogenic Na/Ca exchange.

1986 ◽  
Vol 87 (6) ◽  
pp. 857-884 ◽  
Author(s):  
J R Hume ◽  
A Uehara
Keyword(s):  
Voltage Clamp ◽  
Time Course ◽  
Single Cells ◽  
Mechanical Activity ◽  
Common Mechanism ◽  
Mechanical Relaxation ◽  
Equilibrium Conditions ◽  
Atrial Cells ◽  
Current Voltage ◽  
Wide Range

The objective of these experiments was to test the hypothesis that the "creep currents" induced by Na loading of single frog atrial cells (Hume, J. R., and A. Uehara. 1986. Journal of General Physiology. 87:833) may be generated by an electrogenic Na/Ca exchanger. Creep currents induced by Na loading were examined over a wide range of membrane potentials. During depolarizing voltage-clamp pulses, outward creep currents were observed, followed by inward creep currents upon the return to the holding potential. During hyperpolarizing voltage-clamp pulses, creep currents of the opposite polarity were observed: inward creep currents were observed during the pulses, followed by outward creep currents upon the return to the holding potential. The current-voltage relations for inward and outward creep currents in response to depolarizing or hyperpolarizing voltage displacements away from the holding potential all intersect the voltage axis at a common potential, which indicates that inward and outward creep currents may have a common reversal potential under equilibrium conditions and may therefore be generated by a common mechanism. Measurements of inward creep currents confirm that voltage displacements away from the holding potential rapidly alter equilibrium conditions. Current-voltage relationships of inward creep currents after depolarizing voltage-clamp pulses are extremely labile and depend critically upon the amplitude and duration of outward creep currents elicited during preceding voltage-clamp pulses. An optical monitor of mechanical activity in single cells revealed (a) a similar voltage dependence for the outward creep currents induced by Na loading and tonic contraction, and (b) a close correlation between the time course of the decay of the inward creep current and the time course of mechanical relaxation. A mathematical model of electrogenic Na/Ca exchange (Mullins, L.J. 1979. Federation Proceedings. 35:2583; Noble, D. 1986. Cardiac Muscle. 171-200) can adequately account for many of the properties of creep currents. It is concluded that creep currents in single frog atrial cells may be attributed to the operation of an electrogenic Na/Ca exchange mechanism.

Ambient Condition Effects on NOx and CO Emissions From Process Heaters

2008 ◽  
Author(s):  
Wesley R. Bussman ◽  
Charles E. Baukal
Keyword(s):  
Atmospheric Pressure ◽  
Ambient Air ◽  
Operating Conditions ◽  
Nox Emissions ◽  
Ambient Conditions ◽  
Fuel Gas ◽  
Natural Draft ◽  
Actual Operating ◽  
Wide Range ◽  
Pollution Emissions

Because process heaters are typically located outside, their operation is subject to the weather. Heaters are typically tuned at a given set of conditions; however, the actual operating conditions may vary dramatically from season to season and sometimes even within a given day. Wind, ambient air temperature, ambient air humidity, and atmospheric pressure can all significantly impact the O2 level, which impacts both the thermal efficiency and the pollution emissions from a process heater. Unfortunately, most natural draft process burners are manually controlled on an infrequent basis. This paper shows how changing ambient conditions can considerably impact both CO and NOx emissions if proper adjustments are not made as the ambient conditions change. Data will be presented for a wide range of operating conditions to show how much the CO and NOx emissions can be affected by changes in the ambient conditions for fuel gas fired natural draft process heaters, which are the most common type used in the hydrocarbon and petrochemical industries. Some type of automated burner control, which is virtually non-existent today in this application, is recommended to adjust for the variations in ambient conditions.

Pore Structure Modeling of Flow in Gas Diffusion Layers of Proton Exchange Membrane Fuel Cells

2010 ◽  
Author(s):  
Zhongying Shi ◽  
Xia Wang
Keyword(s):  
Fuel Cell ◽  
Pore Structure ◽  
Proton Exchange Membrane ◽  
Cell Model ◽  
Transport Phenomena ◽  
Pem Fuel Cell ◽  
Gas Diffusion ◽  
Proton Exchange ◽  
Structure Model ◽  
Exchange Membrane

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.

Sign in / Sign up

Export Citation Format

Share Document