Oxygen Starvation Effects on PEMFC Durability

2010 ◽  
Author(s):  
Mathias Gerard ◽  
Jean-Philippe Poirot-Crouvezier ◽  
Daniel Hissel ◽  
Marie-Cecile Pe´ra
Keyword(s):  
Peak Power ◽  
Cathode Side ◽  
Local Conditions ◽  
Local Current ◽  
Oxygen Starvation ◽  
Long Time ◽  
A Cell ◽  
Starvation Effects ◽  
Semi Empirical ◽  
Stack Model

The problem of oxygen starvation on PEMFC is often observed (partially or totally in a cell). It is caused by water management problems (water droplet in the channels) or air management faults (delay during peak power). In our previous work, the current distribution has been measured along the cell during air starvation and calculated by modeling; the effects of the local temperature and the hygrometry in the MEA have been identified. However the mechanisms of degradation are still not completely understood. Several points have to be investigated like the short and long dated changes in performances and the degradation mechanisms in such a condition. In this paper, the study is completed by two sets of experiments. The first one is carried out with a bi-cell stack developed with specific design to compute the local current density by measuring the local induced magnetic field. Secondly, a long time ageing test is run with a 6 cells stack (220 cm2) during oxygen starvation cycling conditions. Both tests (with characterizations) coupled with the 2D serpentine meshing stack model (taking into account transport phenomena, heat transfer and semi-empirical electrochemical reactions) provide information on the MEA local conditions effects during oxygen starvation. Especially the different reaction mechanisms at the cathode side are explained likewise the consequences on ageing.

Distribution Study of Species and Current Density During Oxygen Starvation

2009 ◽  
Author(s):  
Mathias Gerard ◽  
Jean-Philippe Poirot-Crouvezier ◽  
Daniel Hissel ◽  
Marie-Cecile Pe´ra ◽  
Alain Memponteil ◽  
...  
Keyword(s):  
Oxygen Concentration ◽  
Current Distribution ◽  
Current Density ◽  
Cell System ◽  
Magnetic Sensors ◽  
Cathode Side ◽  
Transient Time ◽  
Local Conditions ◽  
Local Current ◽  
Oxygen Starvation

In a fuel cell system the stack is strongly coupled with the main system components, among which the compressor is one of the most important. Malfunction of this auxiliary device (delay during peak power, low stoichiometry operation, emergency stop, etc) is directly responsible for bad oxygen distribution in the cathode (substoichiometry reactants feeding). This phenomenon is usually called oxygen starvation. In this study we want to identify the consequences of oxygen starvation on performance and durability of PEMFC stacks and more particularly on the current distribution along the cell. The oxygen concentration decreases along the channel and induces a change of the local electrochemical response; it means that the local current density on the cell is redistributed on the surface. This bad distribution of reactive gas (in a transient time or long time) decreases performance but may also have an effect on cathode degradation like carbon corrosion and platinum dissolution/oxidation. The current distribution along the cell is studied by two approaches (modeling and experiments). The local current is computed by measuring the local induced magnetic field and using Maxwell equations. The experiments are performed with a bi-cell stack developed by CEA with specific design for the magnetic sensors. The 3D model using serpentine bipolar plate meshing is adapted to dynamically compute the catalyst layer local conditions (local current, temperature, gases partial pressure, water activity). It is able to reproduce the conditions of low or high oxygen concentration in the cathode side.

Distribution Study of Species and Current Density During Oxygen Starvation

2010 ◽  
Vol 7 (5) ◽  
Author(s):  
Mathias Gerard ◽  
Jean-Philippe Poirot-Crouvezier ◽  
Daniel Hissel ◽  
Marie-Cecile Pera
Keyword(s):  
Fuel Cell ◽  
Oxygen Concentration ◽  
Current Distribution ◽  
Current Density ◽  
Magnetic Sensors ◽  
Cathode Side ◽  
Transient Time ◽  
Local Conditions ◽  
Local Current ◽  
Oxygen Starvation

In a fuel cell system the stack is strongly coupled with the main system components, among which the compressor is one of the most important. Malfunction of this auxiliary device (delay during peak power, low stoichiometry operation, emergency stop, etc.) is directly responsible for bad oxygen distribution in the cathode (substoichiometry reactants feeding). This phenomenon is usually called oxygen starvation. In this study we want to identify the consequences of oxygen starvation on the performance and durability of polymer electrolyte membrane fuel cell stacks, and more particularly, on the current distribution along the cell. The oxygen concentration decreases along the channel and induces a change in the local electrochemical response; it means that the local current density on the cell is redistributed on the surface. This bad distribution of reactive gas (in a transient time or long time) decreases the performance but may also have an effect on cathode degradation such as carbon corrosion and platinum dissolution/oxidation. The current distribution along the cell is studied by two approaches (modeling and experiments). The 3D model using serpentine bipolar plate meshing is adapted to dynamically compute for the catalyst layer local conditions (local current, temperature, gases partial pressure, and water activity). It is able to reproduce the conditions of low or high oxygen concentration in the cathode side. The experiments are performed with a bi-cell stack developed by CEA with specific design for the magnetic sensors (the local current is computed by measuring the local induced magnetic field and using the Maxwell equations).

Direct Measurement of the Local Current Density Under Land-Channel Areas With Partially-Catalyzed MEAs

2012 ◽  
Author(s):  
Shan Jia ◽  
Hongtan Liu
Keyword(s):  
Fuel Cell ◽  
Current Density ◽  
Cell Voltage ◽  
Current Density Distribution ◽  
Cathode Side ◽  
High Cell ◽  
Land Area ◽  
Local Current Density ◽  
Local Current ◽  
Voltage Region

In a PEM fuel cell, local current density can vary drastically under the land and channel areas. The non-uniform current density distribution not only affects the overall performance of the fuel cell, but also leads to the local temperature and concentration differentiation on the MEA, which can cause problems such as membrane dehydration and catalyst degradations at certain locations. In order to investigate the local current performance, the objective of this work is to directly measure the local current density variations across the land and channel at the cathode in a PEM fuel cell with partially-catalyzed MEAs. First, the cathode flow plate is specially designed with a single-serpentine channel structure, and the gas diffusion electrode at cathode side is cut to fit this flow field size (5.0cm×1.3cm). Then five different partially-catalyzed MEAs with 1mm width corresponding to different locations from the middle of the gas channel to the middle of the land area are made. Fuel cells with each of the partially-catalyzed MEAs have been tested and the results provide the lateral current density distribution across the channel and the land areas. In the high cell voltage region, local current density is highest under the center of the land area and decreases toward the center of the channel area; while in the low cell voltage region local current density is highest under the middle of the channel area and decrease toward the center of the land area. Different flow rates are tested at the cathode side of the cell to study their effects on the local current density performance along the land-channel direction. And the results show that the flow rate barely has the effect on the current at the high cell voltage region, while it plays a significant role at the low voltage region due to the mass transport effect.

scholarly journals Design and interpretation of cell trajectory assays

2013 ◽  
Vol 10 (88) ◽  
pp. 20130630 ◽  
Author(s):  
Lucie G. Bowden ◽  
Matthew J. Simpson ◽  
Ruth E. Baker
Keyword(s):  
Cell Biology ◽  
Time Interval ◽  
Short Time Interval ◽  
Trajectory Data ◽  
Time Intervals ◽  
Different Types ◽  
Long Time ◽  
A Cell ◽  
Cell Trajectory ◽  
Short Time

Cell trajectory data are often reported in the experimental cell biology literature to distinguish between different types of cell migration. Unfortunately, there is no accepted protocol for designing or interpreting such experiments and this makes it difficult to quantitatively compare different published datasets and to understand how changes in experimental design influence our ability to interpret different experiments. Here, we use an individual-based mathematical model to simulate the key features of a cell trajectory experiment. This shows that our ability to correctly interpret trajectory data is extremely sensitive to the geometry and timing of the experiment, the degree of motility bias and the number of experimental replicates. We show that cell trajectory experiments produce data that are most reliable when the experiment is performed in a quasi-one-dimensional geometry with a large number of identically prepared experiments conducted over a relatively short time-interval rather than a few trajectories recorded over particularly long time-intervals.

scholarly journals Study on the selection of vegetation for ecological restoration of residual soil slopes in South China

2020 ◽  
Vol 198 ◽  
pp. 04039
Author(s):  
Wang De-yong ◽  
Hu Jun-long ◽  
Wang Jing ◽  
Zun Qingjun
Keyword(s):  
Ecological Restoration ◽  
South China ◽  
Field Tests ◽  
Growth Cycle ◽  
Ratio Test ◽  
Residual Soil ◽  
Soil Slope ◽  
Local Conditions ◽  
Long Time ◽  
Selection Of

Vegetation selection is one of the key contents of slope ecological restoration, based on the characteristics of climate and soil in South China and the principle of local conditions, this paper studies the selection of vegetation in the ecological restoration project of the residual soil slope. The typical herbs, shrubs and trees suitable for the area are determined by theoretical analysis. At the same time, through field tests, the growth and development of vegetation after the spraying are monitored for a long time, and the interaction relationship between vegetation community after multiple vegetation mix-ups is analyzed. The results show that plant selection should avoid the choice of a single plant, and should try to achieve complementary coordination between species. At the same time, when taking a variety of plant mixing spray, the configuration ratio of different plants should be determined according to the growth cycle of different plants and the results of indoor ratio test, so as to avoid mutual interference.

scholarly journals Prototipe Alat Kirim Pesan Singkat Tindak Kejahatan sebagai Solusi Peningkatan Keamanan Berbasis Lokasi

2019 ◽  
Vol 19 (1) ◽  
pp. 100-108
Author(s):  
Wire Bagye ◽  
Maulana Ashari ◽  
Mohammad Taufan Asri Zaen
Keyword(s):  
Cell Phone ◽  
Security Forces ◽  
Storage Location ◽  
Long Time ◽  
A Cell ◽  
Arduino Uno ◽  
Main Component ◽  
Short Time ◽  
Relief Efforts ◽  
Short Messages

Very rarely the crime can be done early help or handled by the security forces while the perpetrators are still at the scene of the crime. The effort to get help from crime by reporting to the police requires a relatively long time, which is between 30 minutes to 2 hours. To reduce the number of criminal acts and early relief efforts, a tool to send short messages of crime was developed. Development of tools implements the Arduino Uno R3 microcontroller as the main component for program storage. Location coordinates are obtained from the Ubox 160n GPS module. Short messages containing biodata and location coordinates will be sent by the GSM SIM900L module. The destination number will receive a message that can be used to trace the location of the crime through Googlemaps. This tool equipped with a battery that can be recharged with a cell phone charger making this tool portable, practical and efficient. Using this Alat kirim pesan singkat tindak kejahahatan is very time efficient. The sending of a crime message is done in a very short time. By tapping the message directly the Googlemaps application opens and displays the location of the crime.

scholarly journals On the differences between two semi-empirical sea-level models for the last two millennia

2012 ◽  
Vol 8 (4) ◽  
pp. 3551-3581 ◽  
Author(s):  
M. Vermeer ◽  
S. Rahmstorf ◽  
A. Kemp ◽  
B. Horton
Keyword(s):  
North Carolina ◽  
Sea Level Rise ◽  
Sea Level ◽  
Time Scales ◽  
Long Time ◽  
Global Mean Sea Level ◽  
Semi Empirical ◽  
The Last Two Millennia ◽  
Global Mean

Abstract. We compare hindcasts of global mean sea level over the past millennium obtained using two semi-empirical models linking temperature and sea-level rise. The models differ in that one of them includes a term for a very long-term sea-level rise component unfolding over many millennia. On short (century) time scales, both models give very similar results. Proxy sea-level reconstructions from the northern (North Carolina) and southern (New Zealand and Tasmania) hemispheres are used to test the ability of both models to reproduce the longer-term sea-level evolution. In both comparisons the model including the second term produces a markedly better fit from 1000 AD to the present. When both models are used for generating sea-level projections, they behave similarly out to 2100 AD. Further out, to 2300–2500 AD, the projections differ significantly, in no small part due to different values for the sea-level response time scale τ obtained. We conclude that careful model validation on long time scales is important before attempting multi-century projections.

scholarly journals Comparison and Analysis of kW-Class SOFC-CHP Systems with Different Fuels

2020 ◽  
Author(s):  
Jianzhong Zhu ◽  
Hao Meng ◽  
Minfang Han
Keyword(s):  
Natural Gas ◽  
Combined Heat And Power ◽  
Inlet Temperature ◽  
Electrical Efficiency ◽  
Air Inlet ◽  
Operational Costs ◽  
System Energy ◽  
Comparison And Analysis ◽  
Semi Empirical ◽  
Stack Model

Abstract SOFC is an ideal device for developing distributed combined heat and power (CHP) systems. In this paper, kW-class SOFC system models based on semi-empirical SOFC stack model were established to optimize the systems with the aim of maximizing the system electrical efficiency. Four types of SOFC-CHP systems using different fuel including natural gas (NG), hydrogen, methanol, syngas were compared, and the relationships between key parameters and system energy effciency were analyzed. Simlulation results show that decreasing the air inlet temperature (AIT) and increasing stack temperature will promote electrical effciency most significantly. In addition, the operational costs of four different systems were also compared, and among which the methanol-fueled system was the lowest.

scholarly journals Dynamics of dissolved oxygen inside salmon seacages with lice shielding skirts at two hydrographically different sites

2020 ◽  
Vol 12 ◽  
pp. 559-570
Author(s):  
KE Jónsdóttir ◽  
Z Volent ◽  
JA Alfredsen
Keyword(s):  
Dissolved Oxygen ◽  
Vertical Mixing ◽  
Preventive Measure ◽  
Lepeophtheirus Salmonis ◽  
Local Conditions ◽  
Non Invasive ◽  
Salmon Lice ◽  
Local Current ◽  
Low Levels ◽  
Temporal And Spatial

Shielding skirts are widely used as a non-invasive preventive measure against salmon lice Lepeophtheirus salmonis infestations on Atlantic salmon Salmo salar in sea-cages. Low levels of dissolved oxygen (DO) are reported from some sites, but not others. This disparity is usually explained by local variations in current flow and hydrography. The aim of the present study was to investigate these local variations through vertical mapping of DO and hydrography at 2 hydrographically different sites equipped with shielding skirts. The 2 sites chosen, Fornes and Soløya, are in northern Norway and are equipped with a permeable and a non-permeable skirt, respectively. Over a period of 3 d, current speed and direction were recorded outside the cage, while DO and hydrography were measured both inside and outside the cage, above and below the skirt. At Fornes, the DO inside the cage varied throughout the study period, while DO outside remained stable. The variation in DO inside the cage co-occurred with variations in strength and depth of a present pycnocline that broke down during the study period. At Soløya, DO levels were high throughout the study, and there was no gradient in salinity, temperature or density, indicating good vertical mixing. These data illustrate how the interaction between skirts and local conditions can influence the temporal and spatial variations of DO inside shielded cages and highlight the importance of studying local current conditions and hydrography when applying shielding skirts.

Penggabungan Fitur Bentuk dan Fitur Tekstur yang Invariant terhadap Rotasi untuk Klasifikasi Citra Pap Smear

2016 ◽  
Vol 7 (1) ◽  
Author(s):  
Yuwanda Purnamasari Pasrun ◽  
Chastine Fatichah ◽  
Nanik Suciati
Keyword(s):  
Local Binary Pattern ◽  
Pap Smear ◽  
Texture Feature ◽  
Pap Test ◽  
Rotation Invariant ◽  
Cell Classification ◽  
Result Show ◽  
Long Time ◽  
A Cell ◽  
Image Shape

Abstract. Pap test is a cervical cancer screening manually and requires a long time that it needs an exact cell classification system based computers. Features determination by observation in characteristic differences between the datasets visually betweenclass will help a cell classification results which has relevant characteristics between classes. In addition, the change in orientation of the cells at the time of the acquisition will affect the value of the generated feature so extraction method that is rotation invariant is needed to overcome that problem. This research proposes the combination of simple shapes feature and the texture feature from extraction Local Binary Pattern Histogram Fourier (LBP-HF) that invariant to rotation as additional features to classify pap smear images. The result show that the proposed feature combination yield good performance with accuracy 92.44% for two category cell and 70.06% for seven class cell.Keywords: classification, lbp-hf,  pap smear image, shape feature. Abstrak. Pap test adalah pemeriksaan kanker serviks secara manual yang membutuhkan waktu yang lama sehingga dibutuhkan sistem klasifikasi sel berbasis komputer yang tepat. Penentuan fitur melalui observasi pada perbedaan ciri antarkelas secara visual pada dataset akan membantu hasil klasifikasi sel untuk mendapatkan ciri yang relevan antarkelas. Selain itu, adanya perubahan orientasi sel pada saat akuisisi akan mempengaruhi nilai fitur yang dihasilkan sehingga dibutuhkan metode ekstraksi fitur yang invariant terhadap rotasi. Penelitian ini mengusulkan penggabungan fitur bentuk sederhana dan fitur tekstur dengan ekstraksi fitur Local Binary Pattern –Histogram Fourier yang invariant terhadap rotasi sebagai ciri tambahan dalam mengklasifikasikan citra pap smear. Hasilnya menunjukkan bahwa kombinasi fitur menghasilkan performa yang baik dengan akurai 92,44% untuk dua kategori sel dan 70,06% untuk tujuh kelas sel.Kata Kunci: klasifikasi, lbp-hf, citra pap smear, fitur bentuk.

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